BENTHOS OF A SEASONALLY-ASTATIC, SALINE, SODA LAKE IN MEXICO

Alkaline-saline lakes, or soda lakes, are inhabited by specialized biota that can tolerate high water temperature, high salinity, high pH, and low dissolved oxygen concentration. In addition, these parameters could also show wide temporal fluctuations (circadian, seasonal, yearly, etc.). Of special scientific interest are temporary soda lakes due to in addition to having to contend with the parameters previously mentioned, the biota of these lakes has to deal with water loss from their habitat. The effects of multiple stressors on the benthic macroinvertebrate community were monitored in Tecuitlapa Sur, a shallow (z_MAX = 0.5 m), seasonally-astatic, warm (24-27°C), mesosaline (K₂₅ = 10.5-62.6 mS cm^-1), poorly oxygenated (DO_SAT = 52-72%), soda-alkaline (pH = 9.7-10) lake in Mexico. The benthic macroinvertebrate community consisted of two species: Culicoides occidentalis sonorensis (Diptera: Ceratopogonidae) and Tanypus Apelopia sp. (Diptera: Chironomidae). C. occidentalis was the most important species numerically and in biomass (> 90%). Salinity and pH appears to be the most important environmental factors controlling the composition of the benthic organisms in Tecuitlapa Sur. However, shallowness, habitat homogeneity and the short inundation period (June-November) contributed to such low species richness. Seasonal abundance dynamics was associated with phases in their reproductive cycles: environmentally-triggered (i.e., temperature rise, water level descent) pupation and emergence periods. We concluded that whereas physical and chemical variables exerted the primary control on benthic macroinvertebrate community composition in Tecuitlapa Sur, another assembly of variables influenced species distribution and abundance.

Baltanás, Angel, Department of Ecology, Universidad Autónoma de Madrid, E-28049, Madrid, Spain

COMMUNITY STRUCTURE AND SIZE SPECTRA IN TWO SHALLOW SALINE LAKES IN LOS MONEGROS (NE SPAIN)

Community structure and functioning are frequently assessed by using macroscopic descriptors with a heavy taxonomic approach (species richness, diversity, distribution patterns, …). There is, however, an alternative, non-taxonomic approach which focuses on the relative abundance of body-size classes within communities. Body-size carries information at two different levels: first, it is a life-history trait influenced by both environmental and phylogenetic factors; and second, it affects the assembly and functioning of communities as far as what will you eat and who will eat you (not to mention the amount of energy involved in both activities) is heavily dependent on body size. Therefore, 'size-spectra' –the distribution of body size abundances– is able to summarize community structure and functioning in such a way that comparisons among different communities are readily available.

Here, we analyze size-spectra of two shallow temporary salt lakes which differ in kind and degree of primary production but share the metazoan communities occurring in them. Both lakes are located in a semi-arid district (Bujaraloz-Sástago, NE Spain) rich in Tertiary sedimentary deposits (mainly limestones, marls and gypsum) modeled during the Quaternary.

Thirty enclosures —plastic cylinders of 29 cm of diameter—placed on each lake at the beginning of the aquatic phase were used as sampling units and collected in triads on a fortnightly basis (from January 2 1996 to April 13 1996). Half of them (randomly selected) were treated with an additional input of phosphorus (enough to reach a final concentration of 100 micrograms per liter) in order to explore the effect of an increase in primary production.

Size-spectra were developed by counting and measuring algae and metazoans in the enclosures at each sampling date. A linear model was fitted to the size distribution data for each lake, date, and treatment; and the regression parameters compared among them. No differences were found between enriched and control enclosures; although, changes in size-spectra with time were detected. Slopes of the fitted models suggest that system functioning differs between lakes. Energy use in La Muerte is controlled by primary producers (bottom-up) whereas metazoan consumers are the main controllers in Piñol (top-down).

Carlos Montes, Department of Ecology, Universidad Autónoma de Madrid, E-28049, Madrid, Spain

THE DETERMINANTS OF FOOD-WEB STRUCTURE IN TWO SHALLOW SALINE LAKES IN LOS MONEGROS (NE SPAIN): LOCAL FACTORS VS. REGIONAL FACTORS

A likely explanation of food web structure is based on energetic constraints. In other words, food web length is limited by the availability of energy entering the food web: food webs are expected to be longer in more productive ecosystems. An alternative explanation suggests that food web structure should be explained by dynamic constraints — the average level of predictability in a given ecosystem. Thus, food-web length depends on the capability of a given community to recover after an environmental disturbance (resilience). Salt lakes are frequently highly fluctuating systems (and sometimes unpredictable too) with productivity values ranging from very low to very high values. So they are good model ecosystems for testing food-web theory.

We here explore food-web structure in two shallow temporary salt lakes (La Muerte & Piñol) located in a semi-arid region, NE Spain. As both lakes are quite close (less than 2 km apart), they share many features at the regional scale (climate, geology, lithology, ...) which determine dynamic constraints (duration of the aquatic phase, ionic composition, fluctuations in salinity, ...). On the other hand, both lakes greatly differ in their energetic constraints at the local scale. La Muerte Lake is more diverse in types of primary producers (phytoplankton, phytobenthos, microbial mats) and is much more productive than Piñol Lake. Then, longer (and more complex) food-webs are expected to occur in the former.

Food-web features were estimated by sampling artificial enclosures fortnightly during the aquatic phase. Half of the experimental units were enriched with phosphorous (to a final concentration of 100 micrograms per liter) to compensate for local differences in energetic constraints. Artificial nutrient enrichment produced no significant effect on food-web structure thus suggesting the lakes are buffered (regional scale) against such kinds of disturbances. When the consumer guild of the community is considered, some features —like species composition or food web length— seem to be independent of local factors (energetic constraints) but controlled by regional factors (dynamic constraints). However, other features —like community structure, biomass distribution and production— changes dramatically from one lake to the other pointing out the importance of the dynamics at the local scale.

Horne, A. J., U.C. Berkeley Civil and Environmental Engineering Department, Univ. of Calif., Berkeley, CA, 94710, USA, horne@ce.berkeley.edu

LIMNOLOGICAL EFFECTS OF THE ANTHROPOGENIC DESSICATION OF A LARGE SALINE LAKE, WALKER LAKE, NEVADA.

Walker Lake (A = 140 km², V = 2.6 km³, Zmax = 28 m) is a large terminal saline lake located in the desert region of west-central Nevada within the Great Basin of the Western United States. The lake is monomictic, strongly N limited, and supports summer blooms of the nitrogen-fixing blue-green algae Nodularia. Agricultural development in the Walker River Basin began at the turn of the century and freshwater diversion has dramatically effected the lake’s limnology. Lake elevation has dropped an average of 0.3 m per year, salinity has increased from 2,500 to over 10,000 mg L-1, and since the late 1950’s the lake has exhibited severe hypolimnetic anoxia. As a result biological diversity has decreased, internal loading of ammonia has increased, and the lake currently provides degraded habitat for stocked trout. We studied the lake’s limnology from 1992 through 1996. This period coincided with drought conditions in California which resulted in accelerated lake desiccation. Between 1991 and 1994, TDS increased from 11,600 to 13,700 mg L-1. We confirmed the temperature-oxygen squeeze first observed by Cooper and Koch (1984) in which lake trout are sandwiched between an upper layer of warm water and a deep layer of anoxic water during the summer. In addition, lake trout are likely exposes to chronically toxic levels of ammonia. The ammonia, which accumulates in the hypolimnion as a result of ammonia release from anoxic sediments, is mixed from the hypolimnion to the metalimnion during summer mixing events. Our study also documented a shift in zooplankton species as a result of increased salinity between the 1970’s and the 1990’s. Acanthocyclops vernalis became extinct while the rotifer Hexarthra fennica became dominant. Unlike nearby saline lakes (e.g., Mono, Pyramid) where management plans have been implemented, the anthropogenic desiccation of Walker Lake continues unabated. We propose a composite management strategy of augmented freshwater inflow to stabilize salinity and lake elevation at current levels combined with hypolimnetic oxygenation to provide lake trout with a cold, toxin-free, deep-water refuge during the summer.

Bailey, P.W., Department of Biological Sciences, Monash University, Clayton, Victoria, 3168, Australia. paul.bailey@sci.monash.edu.au

WATER QUALITY AND STREAM DIATOM COMMUNITIES IN WATERSHEDS WITH VARYING DEGREES OF SECONDARY SALINIZATION IN VICTORIA, AUTSTRALIA.

Secondary salinization poses one of the greatest threats to streams in arid regions of the world. Thirty-nine streams were examined for water quality and diatom assemblages in watersheds with varying degrees of secondary salinization in Victoria, Australia. Specific conductance averaged 0.043 mS in upland streams in watersheds with low salinization compared to greater than 2.4 mS in lowland streams with high salinization. Na⁺ and Cl^- were the dominant ions in most waters; CaCO₃ was relatively low. Experiments showed sediments to have limited buffering capacity when exposed to elevated salinity. pH averaged 6.2 in upland streams compared to 7.4 in lowland streams. Nutrients were low in upland streams. Two hundred and forty-five diatom taxa were identified from the 39 streams. Diatom diversity (H’) in drainages with low salinization ranged from 3.8 to 5.5 and 3.3 to 3.9, respectively. Principal components and canonical correspondence analyses showed Bacillaria paradoxa and Nitzschia frustrulum to have strong positive loadings for PO₄ concentrations, while Amphora coffeaeformis and Cymbella pusilla had strong positive loadings for CO3 and conductivity. Eunotia pectinalis and Tabellaria flocculosa showed a strong inverse association with pH and SO₄.

Camara, M. R., Dept. of Oceanography and Limnology, Univ. Federal do Rio Grande do Norte, Natal, Brazil, 59072-970, mrcamara@ufrnet.br

DISPERSAL OF ARTEMIA FRANCISCANA (CRUSTACEA: ANOSTRACA: ARTEMIIDAE) POPULATIONS IN THE COASTAL SALTWORKS OF RIO GRANDE DO NORTE, NORTHEASTERN BRAZIL.

The genus Artemia (Crustacea: Anostraca: Artemiidae) is a complex of sibling species and superspecies defined by the criterion of reproductive isolation. The bisexual Artemia franciscana superspecies is endemic to the Americas and the Caribbean, with various populations established in South American countries, either by deliberate inoculation or natural dispersal. In spite of the presence of Artemia franciscana in several saltworks in the State of Rio Grande do Norte (RN) (Northeastern Brazil) which were colonized from inoculations made in Macau (RN) in April 1977 with cysts from a San Francisco Bay (California, U. S. A.) stock, there is no recent data on the degree of regional dispersal of this anostracan. For twelve months (July 1996 to June 1997), fifty five saltworks located in the municipalities of Areia Branca, Grossos, Galinhos, Guamaré, and Macau in RN were visited and sampled for the presence of Artemia franciscana and the occurrence of its cysts. The results showed that populations of Artemia franciscana were found in all fifty five saltworks, although significant amounts of cysts were only found in six sites. The presence of Artemia franciscana in all sites visited brings further evidence to the ample dispersal of this anostracan throughout the saltwork region of RN as a consequence of the inoculation carried out in Macau (RN) in 1977. On the other hand, the relatively low incidence of predominantly oviparous populations (n=6) suggests that cyst production has been selected against in most of these populations.

Sorgeloos, P., Artemia Ref. Center, Univ. Ghent, B-9000, Ghent, Belgium, Patrick.Sorgeloos@rug.ac.be

HEAT RESISTANCE AND STRESS PROTEINS IN CYSTS OF ARTEMIA LIVING IN DIFFERENT THERMAL HABITATS

We compared cysts (encysted gastrulae) of Artemia franciscana produced in the salterns of south San Francisco Bay (SFB) with those produced from SFB adults in salt ponds in the Mekong delta of south Vietnam (SV) where water temperatures (about 40 C max.) are much higher than those in south SFB (rarely 20 C max.). Cysts from the SV ponds exhibited greater resistance to high temperatures than those from SFB, and that was achieved during a single growing season in SV, not increasing during subsequent years of culture in SV. However, the increase in thermal tolerance of SV cysts was not reflected in changes in the levels of stress (heat shock) proteins of the hsp70 family, or of p26, an important small hsp / molecular chaperone in these cysts. The levels of these proteins are similar in cysts from a variety of Artemia species from greatly different ecological settings, with one striking exception - the cysts of A. tibetiana which are much less heat-tolerant and also contain lower levels of stress proteins. Those results are not surprising since these cysts were produced in Lake Largkor in the mountains of Tibet, at an altitude of about 4500m where the maximum daily water temperature during the period of cyst production is only about 15 C, and well below zero at night. (Grants from the United States NSF and Flemish Science Council are acknowledged.)

Degermendzhy, A. G., Ecosystem Biophysics Laboratory, Institute of Biophysics (Siberian Branch of Russian Academy of Sciences), Academgorodok, Krasnoyarsk, 660036, Russia, ibp@ibp.krasnoyarsk.su

ECOLOGICAL AND MEDICATIVE SPECIFICS OF SIBERIAN SALT LAKES: BIOPHYSICAL EXPERIMENTAL APPROACH AND MATHEMATICAL MODELING

One of the impending ecological problems recognized by the world community at 1992 the UN Rio-de-Janeiro Summit is reducing biodiversity of the biosphere. Among the detrimental consequences of this reduction is impairment of the natural matter turnover. Ecosystems of salt lakes in the south of Siberia with extremely low species diversity are an ideal "natural laboratory" offering its potentialities to investigate the "low biodiversity limit - turnover stability" problem. Shira is a mineral lake (54N, 90E; 9x5 km, 24 m deep) with more than 100 investigation history and is an adequate object for investigation of the said problem. The report is of two parts: I and II. Part I presents physical-geographical conditions and hydrochemical composition of major salt lakes of Khaakasia. Part II gives detailed information about Shira lake, its ecological and medical-healing capacities.

The aims of scientific work are: 1) to assess present ecological condition of Shira lake, including evaluation of sanitary, hydrobiological, hydrochemical and hydrological condition of the lake and its medicative status; 2) to develop a system of monitoring the condition of the lake; 3) to develop a computer system for forecasting the condition of the lake on the basis of the structural-functional layout of the ecosystem; 4) to analyze and make recommendations on water management of the lake; 5) to develop legal and economic rules for the management of the spa area.

Degermendzhy, N. N., Department of Biology, Krasnoyarsk State Medical Academy, P. Zheleznyak Str., 1, Krasnoyarsk, 660022, Russia, ibp@ibp.krasnoyarsk.su

STRUCTURAL-FUNCTIONAL COMPONENTS OF THE BACTERIOPLANKTON COMMUNITY IN THE ECOSYSTEM OF UNIQUE SIBERIAN SALT LAKE - SHIRA (KHAKASIA,RUSSIA)

The work is to study plankton organisms of Shira Lake (salt medicative lake in the south of Siberia, Republic of Khakasia), to review the data of field observations and produce kinetic characteristics. Basic microbiological characteristics of bacterioplankton are estimated by seasons and by stations. Special experiments with isolated groups of microorganisms have been carried out to estimate growth rates and their dependence on limiting substrates. Studies of the recent decade have been generalized. During this period total bacterioplankton numbers ranged from 3.01 to 4.58 mil.cells/ml. Bacterioplankton numbers varied with seasons, the maximum was observed in winter, the minimum - in spring and summer. Productivity of the lake varied from 0.01 to 0.83 g/m3(day, the biomass 0.50-0.83 m3g/, generation time - 34.1- 261.6 hours. P/B coefficient is 0.12 and 0.54, K2 is between 0.02 and 0.96. Numbers and kinetic characteristics (bacterial reproduction rates and their dependence on limiting factors, oxygen consumption rate) of individual physiological bacterioplankton groups (total abundance of bacteria, sulphate-reducing microorganisms, heterotrophs, denitrifiers, aerobic cellulose-destroying bacteria, phosphoric bacteria) have been studied to be used in prognostication models.

Detwiler, P., Salton Sea Ecosystem Research Group, Center for Inland Waters and Department of Biology, San Diego State Univ., San Diego, CA, 92182, pdetwile@sunstroke.sdsu.edu

A SURVEY OF THE BENTHIC FAUNA OF THE SALTON SEA

Our group has quantitatively sampled the benthic macroinvertebrate community at the Salton Sea bimonthy between January and May 1999.

Sampling occurred in three main habitats: benthic sediments (2–12 m), shoreline rocky substrates, and shoreline barnacle shell sand. The benthic macroinvertebrate community of the Salton Sea is characterized by low species diversity (5 species) at high densities. The polychaete Neanthes succinea, a key food chain organism for fish and birds, is found in all habitats. Its abundance varied between habitats and seasons. Between January and May, average densities ranged from 421/m² in sandy silt habitat to 6,899/m² on algae-covered rocks. Starting in May, Neanthes gradually disappeared from depths greater than 4 meters, when the sediments became anoxic. Polychaete reproductive activity was greatest in March, when planktonic heteronereids were collected in abundance.

On shoreline rocky substrates, invertebrate densities were highest in May. The barnacle Balanus amphitrite reached a maximum density of 146,540/m². The gammarid amphipod Gammarus mucronatus was observed at densities up to 125,780/m² in association with two previously unreported chlorophtyes Chaetomorpha sp. and Enteromorpha sp. We also have documented the presence of two invertebrates species previously unknown in the Salton Sea: the polychaete Streblospio benedicti and the amphipod Corophium sp.

Scudder, Barbara C., U.S. Geological Survey, 8505 Research Way, Middleton, WI

SALTON SEA CALIFORNIA: ECOLOGICAL CHARACTERISITICS AND ENVIRONMENTAL MANAGEMENT PROBLEMS

The Salton Sea in southern California is situated 227 feet below sea level in an arid location known as the Salton Trough. Irrigation has turned this desert environment into a highly productive agricultural region. The Sea was formed less than 100 years ago by a levee break that allowed the entire flow of the Colorado River to pour into the Salton Basin for about 15 months. With an area of 380 square miles, the Salton Sea is the largest lake in California. The salinity of the Sea has gradually increased to its present level of 45 parts per thousand. In addition to its high salinity, the Sea is characterized by intense solar exposure, high surface-area to volume ratio (maximum depth is 51 feet), high nutrient loading, and lack of surface-water outflows. Although thermal stratification develops periodically, it is usually of short duration due to frequent mixing driven by high winds. Anoxic conditions are common, coupled with ammonia concentrations near 1 mg L-1, exceeding nitrate-nitrogen concentrations. All of these features constitute a unique limnological environment that requires adaptability of the resident biota. Certain species, including the fish Tilapia (Oreochromis spp.) and several species of ciliates and benthic invertebrates have adapted successfully and exist at high population levels. Unfortunately, the Sea is also an environment where catastrophic fish and bird kills due to a variety of causes are common. The situation presents difficult challenges for management of this unique inland sea.

Forester, Richard M., MS 980 U.S.Geological Survey, DFC, Denver CO, 80225, forester@usgs.gov

AN OSTRACODE'S VIEW OF SOLUTE EVOLUTION

The solute evolutionary process, whether driven by evaporative concentration or ground-water surface-water interactions, results in only a few solute types, and it must have always been so. The solute types are bounded by well-defined changes in solute composition, and they exist over mineral-solubility determined ranges of total dissolved solids (TDS), which define solute fields. Consequently, solute fields provide fundamental environmental categories to which aquatic organisms, such as ostracodes, have adapted.

"Freshwater" ostracodes typically live in waters where calcium-bicarbonate is the dominant or at least a common solute. The calcium-bicarbonate field has two common subfields; calcite saturation, around 300 mg/L, defines the upper TDS limit for some "freshwater" species, whereas other species range up to about 1,500 to 3,000 mg/L, where either calcium or bicarbonate is lost from solution to mineral precipitates at a solute triple field junction. Different halobiotic ostracode species occupy either the calcium or the bicarbonate enriched solute fields, while euryhaline species commonly occupy subfields of the three primary solute fields. Further, the halobiotic ostracode species do live in "freshwater," when such waters have a saline solute composition.

The occurrence patterns of continental ostracodes, therefore, indicate that their distributions are determined by major solute types rather than TDS. This is supported by examples of nearby lakes containing saline water, but having exclusive solute types and ostracode species. Similarly, lakes such as Great Salt Lake, Utah, whose solute composition changed from bicarbonate-enriched to calcium-enriched as a result of climate-driven changes in the relative amount of surface vs ground-water input, show a stratigraphic change in solute-dependent saline ostracodes. Thus, ostracode species occurrence patterns seem to imply a physiological adaption to particular solute fields, whose boundaries are defined by solute-evolutionary processes. Examination of the ostracode fossil record shows that the modern-day associations and mutual exclusion patterns extend to at least 5 Mya. Further, species from the Paleocene and Eocene Green River deposits, for example, show association or exclusion patterns that resemble those of today. Thus, just as the process of solute evolution has always existed, so too apparently have the physiological evolutionary adaption to its byproducts.

Lu, C.T., U.S. Geological Survey, Biological Resources Division, Western Ecological Research Center, San Francisco Bay Estuary Field Station, Vallejo, CA 94592, USA, corinna_lu@usgs.gov

OVERVIEW OF AN INTEGRATED ECOLOGICAL STUDY OF THE NAPA-SONOMA SALT PONDS, SAN FRANCISCO BAY

Prior to European settlement, San Francisco Bay was surrounded by extensive tidal and intertidal marshes, mudflats, salt pans, grasslands, and riparian forests. Abundant freshwater tributaries connected to the Bay via brackish intertidal sloughs and created one of the largest and biologically rich estuaries in North America. Alteration of the estuary began in the 18^th century and accelerated during the 1850’s when diking of tidal marsh and other bayland habitats was supported by state and federal legislation. More than 90% of the natural habitat was converted for commercial agriculture and salt ponds use.

Commercial salt ponds have existed in the San Francisco Bay estuary since the 1860’s. Although wildlife use has been documented for some salt ponds, extensive ecological studies have not been conducted. Current restoration goals include converting many of the Bay’s current salt ponds back to tidal marsh. Before such actions are taken, the current wildlife use and trophic interactions should be established in order to make informed management decisions. Previous studies have documented extensive waterbird use of salt ponds in both the north and south bay areas. Given the drastic loss of waterbird habitat in California, particularly the Central Valley region, these ponds probably provide critical habitat for an already drastically reduced waterfowl population that migrates along the Pacific Flyway each spring and autumn.

Therefore, we are conducting an ecological study to assess the significance of salt ponds in the Napa-Sonoma Marsh Complex, particulary for waterbirds. We will assess the trophic structure of salt pond communities and determine how they relate to physical and biological influences of the salt pond environment. Our project includes integrated studies of nutrient concentrations, algal primary productivity, zooplankton, macroinvertebrates, fishes, and plants. Supporting studies include hydrologic and physical conditions found within six study ponds of varying salinity. These studies will be combined to develop a conceptual model of salt pond communities and provide a foundation for future resource management decisions.

Saros, Jasmine E., Department of Biology, University of Wisconsin - LaCrosse, 1725 State Stree, La Crosse, WI 54601 USA

THE RECONSTRUCTION OF ENVIRONMENTAL CHANGE FROM DIATOM ASSEMBLAGES IN SALINE LAKES

Diatom assemblages are commonly used to reconstruct long-term climatic and hydrologic change in lakes in arid regions, because of the responsiveness of diatoms to water-chemistry variables affected by changes in precipitation relative to evaporation (P-E). Reconstructions of shifts in P-E are based on modern data sets that relate diatom distribution to environmental variables, particularly salinity and anion composition. The use of these modern data sets to reconstruct paleoclimate from fossil diatoms assumes that fossil species are well represented in the modern data set, that salinity is the primary driver of species shifts, and that salinity/ionic changes are a result of shifts in P-E. We show examples of problems associated with these assumptions based on our experience working in the northern Great Plains of North America and elsewhere. We discuss 1) how nutrient availability, which may be related to or independent of salinity change, can affect diatom distribution in saline lakes and complicate climate reconstruction; 2) issues related to shifts in geographic distribution of species over geologic time; and 3) how differences in groundwater hydrology can affect lake response to climate.

Baltanás, Angel, Department of Ecology, Universidad Autónoma de Madrid, E-28049 Madrid, Spain

SALINITY AS A MODULATING FACTOR IN INTERSPECIFIC COMPETITION - AN EXAMPLE FROM OSTRACODS FROM SPANISH PLAYA LAKES

Two ostracod species (Crustacea,, Ostracoda) frequently occur in salt lakes in the Ebro Valley (NE Spain): Heterocypris barbara (Gauthier & Brehm 1928) and Prionocypris aragonica (Brehm & Margalef 1948). The former is geographically widespread and seems to have a broad ecological niche; whereas P. aragonica is an endemic species, a specialist of the cold and saline environments it inhabits. But, although their tolerance to temperature and salinity greatly overlaps, both species never co-occur in the field. In order to explain the absence of the supposed generalist Heterocypris barbara from salt lakes inhabited by the highly specialized endemic species Prionocypris aragonica a series of laboratory experiments involving abiotic (salinity) and biotic (competition) factors has been carried out.

Our results indicate that high salinities negatively affect the hatching rate of the H. barbara but, once hatched, juveniles develop at a similar rate than in their own environment. The presence of a competitor results in longer juvenile development and increased juvenile mortality yielding to a numeric superiority of the species that does not experience abiotic stress. This is supposed to be due to the higher feeding efficiencies of the juvenile stages of the specialist species.

Under stressful conditions interspecific competition is found to be more important than intraspecific competition as population densities are controlled by reduced hatching rather than by density dependent processes.

The disjunct distribution of the two species observed in the field is the joint result of abiotic and biotic interactions, each of them affecting different life history components.

Williams, W.D., Department of Environmental Biology, University of Adelaide, Adelaide 5005, Australia, bwilliam@camtech.net.au

PHYSICO-CHEMICAL AND BIOLOGICAL STUDIES OF SOLAR SALT PONDS AT DRY CREEK, ADELAIDE, AUSTRALIA

Major physico-chemical and biological features of a series of solar salt ponds at Dry Creek, Adelaide, Australia, were studied. In these ponds, seawater is progressively evaporated to produce commercial quantities of salt (NaCl). The aim of the study was to provide information to improve the management of salt quantity and quality.

Elements of the marine biota dominated the initial ponds (salinity <55 g/L). In subsequent ponds, crustaceans (principally Artemia and Parartemia, differentially distributed) were the dominant filter feeders, and diatoms (ponds <150 g/L), Cyanobacteria and green algae (Dunaliella, Stephanoptera) (>150 g/l) were the dominant producers.

Benthic mats covered ponds at salinities >150 g/L and were important in increasing evaporation, decreasing seepage of brine, oxygenating brine and recycling organic matter. Synechococcus was a dominant taxon in the benthic mats but produced significant amounts of extra-cellular matter under certain environmental conditions. This is important in the management of the solar salt ponds. Experiments were undertaken in microcosms to determine the effects of salinity and light intensity on the rate of extra-cellular production. Production was highest in conditions of high salinity and high light intensity. An important consequence of increased extra-cellular production was an increase in brine viscosity. This can affect both the quantity and quality of salt produced in the ponds.

Herbst, D.B., Sierra Nevada Aquatic Research Laboratory, University of California, Route 1, Box 198, Mammoth Lakes, CA 93546, USA, herbst@lifesci.ucsb.edu

A PERIODIC TABLE OF HABITAT CHEMISTRY ASSOCIATIONS FOR SALT LAKE ORGANISMS?

The search for pattern in the geographic occurrence of salt lake flora and fauna often reveals strong associations of specific taxa with certain types of water chemistry. Solute composition, along with salinity and habitat stability, may provide a template shaping the distribution of many organisms inhabiting saline lakes. A review of studies demonstrating habitat associations, specific solute tolerance, and ionic and osmotic adaptations provides evidence of fidelity to particular conditions of environmental chemistry across a wide taxonomic spectrum. Under low salinity conditions some species show osmoregulatory adaptability to varied solute composition but the capacity for such flexibility is reduced with increased salinity and only certain taxa are found in hypersaline waters dominated by a particular solute. Anionic ratios of chloride, bicarbonate/carbonate, and sulfate appear to be especially important determinants of distribution. The physiology of solute tolerance has biogeographic significance as an alternative explanation to hydrographic vicariance in explaining certain patterns of distribution in isolated desert aquatic habitats. Use of geochemical evolution principles (e.g. solute branchpoints) may permit paleoecological reconstructions of saline lake ecosystems, and improved understanding of the evolution of saline water taxa.

Blood, B., Sapphos Environmental, 133 Martin Alley, Pasadena, California, 91105, USA.

Salinity-Dependent Changes in the Organization of Aquatic Food Webs in Salt Evaporation Ponds in the Mojave Desert

Three saline evaporation ponds formed by wastewater from a solar energy-generating facility near Harper Dry Lake in the Mojave desert of California were compared for differences in the communities of benthic and planktonic invertebrates and algae present along with avian visitation and foraging activity. Under lower salinity conditions the predatory water boatman Trichocorixa reticulata was abundant and eliminated the planktonic filter-feeding brine shrimp (Artemia franciscana) thus permitting high phytoplankton densities. At high salinities where Trichocorixa could not survive, Artemia were abundant and grazing of phytoplankton kept waters clear except during the winter dormancy of brine shrimp. Intermediate salinity levels support co-existing predator and prey populations early in the growth season (before the Trichocorixa have matured). Salinity controls a cascading trophic effect of predators on consumers on primary producers in the planktonic food chain. Birds foraged primarily on the benthic brine fly Ephydra gracilis, found in greatest abundance at moderate salinity in shallow water. Though winter and spring visitation were greater in the high salinity pond when larvae and pupae were dense (but small), most feeding activity occurred at the moderate salinity pond in summer where biomass of Ephydra was maximum. High salinity inhibited E. gracilis growth rate, body size and emergence success.

Wong, Patricia S., Department of Marine Sciences, University of Georgia, Athens, GA, 30602, USA

STRATIFICATION OF MICROBIAL ASSEMBLAGES IN MONO LAKE, CALIFORNIA, AND RESPONSE TO A MIXING EVENT

Vertical profiles of microbial assemblages were obtained by analyzing (PCR/DGGE) DNA samples collected from the Mono Lake water column in 7/94, 4/95 and 7/95. Microbial assemblages were highly stratified during both July field trips. Vertical distributions of bands in DGGE gels were coherent with temperature, salinity, irradiance and dissolved oxygen distributions. In April 1995, Mono Lake had just re-stratified after a mixing event. Water column gradients were weak and oxygen had just been depleted at depth. The microbial assemblage was uniformly distributed throughout the water column, except at 20 m where a nephthaloid layer was observed by an ROV.

Partial sequences (134 to 161 bp except for one sequence of 79 bp) obtained from DGGE bands revealed affinities (best-match similarity <94%) to known organisms, but no exact matches were found. A band with a partial 16S rDNA sequence (159 bp) having 91% similarity to a Thiomicrospira species was found in the region of the oxic/anoxic interface. A band that was ubiquitous in samples from the oxycline and monimolimnion in July of both years was found throughout the water column in April. The sequence from this band could be attributed to an unusual phytoplankter, Picocystis salinarum.

Beutel, M.W., U.C. Berkeley Civil and Environmental Engineering Department, Univ. of Calif., Berkeley, CA, 94710, USA, beutel@socrates.berkeley.edu

FIXING A BROKEN SALINE LAKE: THE DIFFICULT CHOICES AVAIALBLE FOR ANTHROPOGENICALLY-DESICCATED WALKER LAKE, NEVADA.

Walker Lake is still a large saline terminal desert lake but has shrunk 80% in 100 years due to upstream consumption for profitable agriculture. As salinity increases the lake will soon lose its valuable trout fishery and is already down to only two common zooplankton. Unlike other western lakes, blame cannot be conveniently cast on a distant rich large municipal agency that diverts the water. Those in the basin have created the problem and could find the solution. Thus Walker Lake is similar to the Sea of Aral and perhaps similar in-basin solutions should be sought. The lake could be stabilized by a reduction of consumptive agricultural use of about 30%, similar to those agreed upon in the adjacent Truckee River-Pyramid Lake basin. Even with this agreement, the problem of continual salinity increase due to flushing of salts from agricultural land and small city pollution need to be addressed. The lake’s hypolimnion must be restored to its original oxygenated and non-toxic state to give the Lahontan cutthroat trout a chance to grow to large size. Detailed solutions include windmill-powered lake hypolimnion oxygenation systems, replacement of small dams by ground water galleries, reduction in agricultural water consumptive use, changes in grazing practices, general sanitation improvements for agriculture and housing, advanced solar-powered desalination systems, use of mine water, relocation of hatcheries and created wetlands to outside the basin, changes in the law of water use ("use it or lose it"), and creation of water credits. None of these potential solutions is easy and all require water user concessions. A credo of "a burden shared is a burden lightened" may be a most appropriate solution for this lightly populated region. An alternative is imposition of federal control as has occurred in the Sacramento-San Joaquin Delta. The third equally likely alternative is that the lake will be destroyed as in the case of Winemucca Lake about 3 hours north.

Melack, John M., Donald Bren School of Environmental Science and Management, Univ. Calif., Santa Barbara 93106 and the Marine Science Institute, Univ. Calif., Santa Barbara 93106, melack@lifesci.ucsb.edu

INVESTIGATING THE PRESENCE OF AMMONIA OXIDIZING BACTERIA IN MONO LAKE, CA

Mono Lake is a hypersaline lake, located on the eastern slope of the Sierra Nevada of California, characterized by stratified conditions with high ammonia concentrations in the hypolimnion and low ammonia concentration in the epilimnion. Past studies on the flux of ammonia across the anoxic boundary have shown a rapid rate of consumption of the ammonia, attributed to photosynthetic algal activity. Alternatively, autotrophic ammonia oxidizing bacteria (AOB) could be contributing to the consumption.

We investigated the presence of AOB belonging to the beta subdivision of the Proteobacteria by molecular techniques. Total nucleic acids were extracted from water samples at 12 depths in the lake, ranging from 3 to 18 meters, in August 1997 and April 1998. The nucleic acid samples were subjected to molecular probing using oligonucleotide probes specific for known beta subdivision AOB, as well as nucleic acid probes for the domains Archaea, Eukarya and Eubacteria. The PCR, with primers specific for known beta subdivision AOB, was also performed on the extractions. Samples were analyzed by denaturing gradient gel electrophoresis (DGGE). Lastly, clone libraries were constructed from samples from two depths.

Results demonstrated that known AOB of the beta subdivision were below the limits of detection for the molecular probes. Group specific PCR primers failed to detect beta subdivision AOB. Furthermore, ribosomal DNA fragments of planktonic bacteria did not co-migrated with those of pure cultures of known beta subdivision AOB in DGGE analyses. Finally, no sequences retrieved from the clone libraries were related to known AOB. In total, the data suggest that organisms other than known beta subdivision AOB are responsible for the consumption of ammonia in Mono Lake at the times of our sampling.

Hurlbert, S. H., Department of Biology and Center for Inland Waters, San Diego State University, San Diego CA 92182, USA. shurlbert@sunstroke.sdsu.edu

MICROCOSM EXPERIMENTS HAVE ASTOUNDING RELEVANCE FOR COMMUNITY AND ECOSYSTEM ECOLOGY OF SALINE LAKES

Microcosm experimentation represents the greatest methodological advance in limnology since the invention of the plankton net. This is demonstrated by the revolution in our understanding of community and ecosystem level processes in lakes since outdoor microcosm studies began in the 1960s. This progress may be contrasted with the much slower progress in oceanography, where the dominating influence of physical and biological factors operating at large spatial scales prohibits any semi-realistic mimicking of the open water ecosystem in enclosures of any sort.

Yet between 1996 and 1999, four rather different articles, three by limnologists, appeared in the journal Ecology, all bearing Microcosm experiments have limited relevance for community and ecosystem ecology as the title, or first portion thereof. Numerous errors in two of these reports will be discussed, along with their implications for the editorial process. Limitations of whole-lake experiments with respect to their feasibility and conclusiveness will be discussed. A brief survey of the few microcosm experiments carried out in relation to saline lakes follows. Such experiments serve multiple functions and can usefully be carried out prior to, during, or after detailed observational study of a given lake, or even without reference to any specific lake.

Jehl, Joseph R., Jr., Hubbs-Sea World Research Institute, 2595 Ingraham Street, San Diego, Ca 92106

THE BIOLOGY OF EARED GREBES IN MIGRATION

The Eared Grebe (Podiceps nigricollis) is the dominant bird species at the hypersaline lakes of North America. After the breeding season, virtually the entire population ( 4 million) stages at either Mono Lake, CA or Great Salt Lake, UT for several months to exploit the abundant crop of brine shrimp. They remain until food supplies run out and then make a nonstop flight to wintering areas in southern California or Mexico. The flight is hazardous, as is crosses hundreds of miles of arid land with no suitable stopping place. The energetic demands on these chunky and poor-flying birds are high, and before they can start off the grebes must ose weight and reorganize their body composition.

I will review the importance of salt lakes to this species and the major features of their fall migration, to include recent radar studies that enable us to follow the migrants over much of their route from Great Salt Lake to southern California.

Jehl, Joseph R., Jr., Hubbs Sea-World Research Institute, San Diego, CA, USA, jjehl@hswri.org

THE SURVIVORSHIP AND LIFE HISTORY OF CALIFORNIA GULLS REVEALED BY BANDING STUDIES

The California Gull (Larus californicus) colony at hypersaline Mono Lake, CA was discovered in the 1850s and has been studied since the 1930-60s, when gulls were banded to study movement patterns.

Streams feeding Mono Lake were diverted to provide a municipal water supply in 1940. By 1980 the lake elevation had dropped 40 feet, causing gull nesting islands to become connected to the mainland, where they were susceptible to invasion by coyotes. This prompted concern for the colony and elicited a broad spectrum of studies on the lake’s ecology and future to include population studies involving banding, life history, and survivorship.

An early "finding"—that the colony as not self-sustaining—was paradoxical because the colony (which reached 65,000 breeding adults in 1994)-- had been growing for decades. The notion derived from a 1988 population model that included an estimated life span of 8 years at Mono Lake, even though California Gulls elsewhere breed into their twenties. The problem was band loss. Gulls banded in 1938-1963 (the only ones, at that time, that might have lived long enough for consideration) had aluminum bands, which have a half life of about 6 years. When banders switched to durable (monel, stainless steel) bands (1979-1993) adult longevity assumed an expected pattern.

Aluminum bands, however, do not impair short-term studies. To maintain a self-sustaining population, large gulls need to fledge about 0.6 chicks/pair/year. To do this, chicks at Mono Lake need to weigh >540 g at banding time. Their subsequent survivorship is also affected by body condition.

Only rarely will a bird that weighed < 500g survive long enough (36-48 mos.) to enter the breeding population.

Productivity is usually sufficient to sustain the Mono Lake colony, except when the lake becomes meromictic. It is ironic that the current period of meromixis (1995-present) is unnatural, stemming from increased stream flows mandated by the State to "restore" Mono Lake. The degree to which meromixis and gull productivity are causally related is under study.

Melack, John M., Donald Bren School of School of Environmental Science and Management, University of California, Santa Barbara, CA, 93106

PLANKTON DYNAMICS IN HYPERSALINE MONO LAKE DURING DIFFERENT HYDROLOGICAL REGIMES, 1979-98.

Human-caused changes in salinity and the annual mixing regime of hypersaline Mono Lake have affected all three trophic levels of this relatively simple, but highly productive ecosystem. Beginning in 1941, diversion of freshwater out of the basin resulted in a 14-m drop in surface elevation and a doubling of salinity by 1982. During this period, rotifer species disappeared from the plankton, declines in primary and secondary productivity were hypothesized based on salinity bioassays, and the nesting gull colony disrupted by coyotes when Negit Island became connected to the mainland. During 1982 and 1983, record high runoff and reduced diversions resulted in large inputs of freshwater and the onset of a 5-yr period of meromixis (1984–88). In 1995, the second largest recorded runoff, coupled with the reduced size of the lake and the halt of diversions led to the onset of a second period of meromixis (1995– ) which has persisted through the present. During both these meromictic periods, vertical mixing was reduced, and the annual replenishment of nutrients to the euphotic zone during winter holomixis absent. These changes in nutrient availability resulted in three-fold differences in primary production. While effects on the Artemia population were less pronounced, reduced algal biomass resulted in slower maturation of the spring generation of Artemia and individual fecundity was reduced. Low rates of gull chick production during the 1^st year of the 1980s episode of meromixis and during all years of the current episode of meromixis suggest the timing and magnitude of the Artemia population may be critical to breeding gulls. Also, Artemia abundance declined more rapidly in the autumn during meromixis and may impact migrating grebe populations. In contrast to the 1980s episode of meromixis in which the resumption of diversions and evaporative concentration of the mixolimnion led to the breakdown of meromixis after 5 years, the current episode of meromixis is predicted to persist for decades.

John, Jacob, School of Environmental Biology, Curtin University of Technology, GPO Box U1987, Perth WA 6845 Australia, RJACOBJO@cc.curtin.edu.au

LIMNOLOGY OF LAKE CAREY - AN INLAND EPHEMERAL HYPERSALINE SYSTEM IN THE ARID REGION OF WESTERN AUSTRALIA

Lake Carey, located 700 km east of Perth on the eastern edge of the Great Victoria Desert in Western Australia, is about 1000 km2, gets filled only during the tropical cyclone period. With an annual precipitation of 220 mm and an annual evaporation of 3,500 mm, the lake remains dry for most of the year. Lake Carey is part of a palaeodrainage network which was active during the tertiary period. The system seems to have dried up in the late pleistocene. The lake bed is characterised by several island outcrops with well established fauna and flora.

The limnological properties of the lake were investigated in August 1998 and in March 1999, when the lake was filled for a few weeks following tropical cyclone events. The salinity ranged from 59 to 230 mg/l in 1998 and 8 to 297 in 1999 with Na dominating the cations and Cl, the anions but with sulphate in high concentration. The pH of water ranged from 7 to 9.3. The maximum depth was less than 50 cm and salinity increased as depth declined.

A total of 30 taxa of algae and 15 taxa of insects and crustaceans were recorded. A species of Parartemia and three species of ostracods were most common. There were six species of cyanobacteria, two species of green algae, and 22 species of diatoms. True phytoplankton were sparse and the vast majority of algae were periphyton or benthic mat made of Schizothrix sp. The primary biomass ranged from one to 10 µg/l indicating the low productivity of the standing water. Water temperature reflected ambient air temperature ranging from 12.6oC to 30.90C. Reactive silica showed large fluctuation with the highest concentration of 15 mg/l in the least saline part of the lake. Nitrate and phosphate levels were low and on the increase.

Among the invertebrates, the cladocerans and copepods were mostly associated with lower salinity whereas Parartemia continued to occur in higher saline areas. This hypersaline systems appeared to respond to filling events rapidly by triggering pulses of biological activities.

John, Jacob Shane Chaplin, School of Environmental Biology, Curtin University of Technology, GPO Box U1987, Perth 6845, Australia, RJACOBJO@cc.curtin.edu.au

BIODIVERSITY OF LAKE LEFROY - A SALT ENCRUSTED HYPERSALINE LAKE IN THE SALINALAND OF WESTERN AUSTRALIA

Lake Lefroy is part of a salt lake system located 580 km east of Perth, mostly covered by salt crust, with an area of 554 km2. Lake Zot and Lake Cowan are other large salt lakes located close to Lake Lefroy. The climate of the region is semiarid with a mean annual rainfall 242 mm and evaporation of 2,701 mm. The lake is completely dry for more than one fourth of a year. With the biomodal rainfall distribution in February and June, the lake becomes partially inundated up to a mean depth of 20 mm. There are islands within the lake. The margins of the lakes and islands are colonised by halophytic plant communities. The paper describes the biota in and around the lake bed in relation to water chemistry, observed in February and April-May 1999. The biota were investigated by incubating the sediment in February when the lake bed was dry, and later in April to May when the lake was filled by rain events.

While the salt encrusted region of the lake was devoid of aquatic fauna and flora, the ephemeral pools and margins of the pools were productive with distinct groups of fauna and flora.

Bacteria, cyanobacteria, diatoms, and ciliates were abundant in the ephemeral pools of the peripheral regions of the lake. Parartemia cysts were present in high numbers at some sites in the sediments. There were three species of ostracods, two species of nematodes, one calanoid copepod species, a cladoceran and a species of rotifer. With the rains the animal diversity increased in April to May.

Benthic algal mats consisting of Schizothrix was present in the ephemeral pools adjacent to Lake Lefroy. The vast catchment was sparsely vegetated and the carbon source for supporting the diverse animal forms was presumably derived from the algal mat. In terms of diversity, the region is poor in species richness. The salt encrusted lake bed was colonised by some terrestrial invertebrates like spiders and ants.

The challenges posed by human activities such as mining on the biodiversity of the lakes and their fringing ecosystems are discussed in this paper.

Jones, B., U.S. Geological Survey, MS 432, 12201 Sunrise Valley Dr., Reston, VA 20192, USA, bfjones@usgs.gov

GEOCHEMICAL EVOLUTION OF CLOSED BASIN WATERS: A REVIEW

In the twenty plus years since the publication of comprehensive, semi-quantitative descriptions of closed basin brine evolution, much effort has gone into the further development of computer simulation models, in contrast to detailed examination of the highly variable reaction mechanisms. This focus is quite suitable for the majority of the principal solute constituents, which are exclusively or predominantly affected by straightforward solubility considerations accompanying evaporative concentration, such as is the case for chlorides or sulfates. However, the situation can appear more complicated with complex carbonates and silicates, which exert major influence particularly on the alkaline earth cations (Ca, Mg, Sr). The general association of the major solute anions with principal lithology, such as the association of carbonate species with silicate (crystalline or pyroclastic) as well as carbonate rocks, or sulfate with sulfide weathering or ancient evaporites, has been further documented in a number of areas, including Death Valley. The simplest early quantitative predictor of major solute evolution is still the "chemical divide" of Eugster and Hardie (1978), based on the mass-action equivalence of cation and anion required for the simple direct precipitation of calcite and gypsum. The principle can be easily applied through the use of the "Spencer triangle" (Jones & Bodine, 1987), such that the simple plot position of a water composition in terms of Ca, SO₄, and CO₃ species determines the ultimate major cation-anion dominance in the resulting brine. The most important deviations caused by complex carbonate (e.g., dolomite) and silicate (e.g., interstratified smectite) reactions from simple concentration trends primarily affect Mg, Sr, and K. Information on the influential kinetics of formation of these phases and their affects on general solute evolution is only slowly emerging. The knowledge of redox phenomena, principally affecting metals and sulfate, is also largely qualitative at present.

Chris Holmden, Dept. Geol. Sciences, Univ. of Saskatchewan, Saskatoon, Canada S7N 5E2

GEOCHEMISTRY OF GROUNDWATER ASSOCIATED WITH ECONOMIC DEPOSITS OF SODIUM SULFATE (MIRABILITE) IN SALINE LAKES OF SASKATCHEWAN, CANADA

Sodium sulfate has been mined from evaporite deposits in post-glacial, groundwater-fed, endorheic lake basins in Saskatchewan since 1918. Sodium sulfate is used in the manufacture of detergents, fresheners, glass, paper and textiles. Recently, Saskatchewan companies have pioneered the use of sodium sulfate in the value-added manufacture of potassium sulfate used as a fertilizer for chloride-sensitive crops.

We have begun a five-year project to advance understanding of the origin of these deposits as modern ore-forming systems. Because groundwater continues to supply ions to the lake basins through spring discharge, our approach is hydrogeological, with the major objective of quantifying fluid and chemical mass balances.

Our initial efforts are focused on evaluating which portion of the groundwater flow system supplies ions to the lake basins. Hydrogen and oxygen isotopes demonstrate that relatively shallow (<200m) systems are the source of groundwater that discharges in springs near sodium sulfate deposits. Preliminary work with strontium isotopes shows that different inter-till aquifers appear to have different ⁸⁷Sr/⁸⁶Sr ratios. In some cases the lake brine isotopic composition matches that of groundwater discharging from springs. The challenge ahead is to determine whether strontium isotopes can be used to fingerprint specific aquifer inputs in a context of potential ⁸⁷Sr/⁸⁶Sr evolution along groundwater flow paths.

Matey, V. E., Department of Biology and Center for Inland Waters, San Diego State University, San Diego, CA, 92182-4614, USA, kuperman@sunstroke.sdsu.edu

PARASITES OF FISH FROM THE SALTON SEA, CALIFORNIA, USA

Massive fish mortalities have been registered for some decades at the Salton Sea, a desertic lake in southeastern California. These events have been associated with crucial combinations of high salinity ( 46 g/l), high temperatures (up to 40š C), elevated nutrient levels, low oxygen tension, and microbial pathogens. Until recently, the possible role of parasites in the Salton Sea ecosystem was unstudied. In 1997-1999, we conducted the first systematic parasitological examination of fish at the Sea. We examined 840 tilapia, Oreochromis mossambicus, 186 croakers, Bairdiella icistia, 158 longjaw mudsuckers, Gillichthys mirabilis, and 175 sailfin mollies, Poecilia latipinna. Three species of parasitic protozoans, Amyloodinium ocellatum, Ambiphrya ameiuri, and Cryptobia sp., and one parasitic metazoan, Gyrodactylus spp, were found in high densities on fish gills and skin. In 1997-98, massive infestation of tilapia by the dangerous dinoflagellate, A. ocellatum , were detected in nearshore waters from May to November. Heavy infection of tilapia and croaker by ciliate A. ameiuri occurred from April to December, 1997-98. An outbreak of fish infestation by the flagellate Cryptobia sp. was registered in September, 1997. Monogeneans of the genus Gyrodactylus were found on mudsuckers, tilapia, and mollies in 1997-99. SEM and LM studies show some of these infestations cause severe distortion of fish respiratory epithelium which can depress respiration. In combination with other environmental factors, parasites may cause fish suffocation and death.

Tiffany, M.A., Department of Biology and Center for Inland Waters, San Diego State University, San Diego, San Diego, CA, 92182-4614, USA, tiffany@sunstroke.sdsu.edu

INVERTEBRATES OF THE SALTON SEA, CALIFORNIA, USA: A SCANNING ELECTRON MICROSCOPY PORTFOLIO

The last detailed examination of the biota of the Salton Sea was carried out at late 1950s. A biotic inventory is currently being conducted by researchers at the Center for Inland Waters, SDSU, and other universities. Modern technology is used for the identification, description and catologing of organisms inhabiting the Salton Sea. We are attempting to document all invertebrates in the Sea with scanning electron microscopy (SEM) and light microscopy(LM). General morphology and ultrastructure of representatives of 8 major taxonomic groups of invertebrates will be demonstrated in this portfolio of images and brief descriptions. Forms illustrated in the different stages of their development include the rotifer Brachionus rotundiformis, the polychaetes Neanthes succinea and Streblospio benedicti, the copepods Apocyclops dengizicus and Cletocamptus deitersi, the barnacle Balanus amphitrite saltonensis, the amphipod Gammarus mucronatus, and the insects Trichocorixa reticulata and Ephydra sp. Charts showing seasonal variation in the zooplankton assemblage will also be presented.

Last, William M., Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2; WM_Last@UManitoba.ca

REDISCOVERING SALT LAKES OF THE GREAT PLAINS OF WESTERN CANADA: WHAT ADVANCES HAVE WE MADE & WHAT CHALLENGES DO WE FACE IN THE NEW MILLENNIUM?

The millions of extant salt lakes as well as ancient lacustrine deposits of the Great Plains of western Canada are important features of the landscape in this vast region of North America. Despite their elevated salinities, these lakes and their sediments serve a variety of uses, and form the cornerstone of a multimillion dollar minerals industry. Scientific investigation of salt lakes in western Canada extends back over 100 years, although segmented disciplinary research contributed to generally slow progress in our understanding of the lakes throughout most of this century. It has now been nearly two decades since Professor Ted Hammer used the 2^nd International Conference on Salt Lakes to showcase these saline lacustrine environments. What have we accomplished in the intervening two decades? With a geochemical database now comprising over 700 lakes, our knowledge of the lacustrine hydrochemical systems in the Prairies has increased significantly. Similarly, the rudimentary understanding of modern sedimentary processes has matured with considerable effort having been directed toward unravelling the complexities and dynamics of various interactive physical, chemical, and biological processes.

Investigation of the Quaternary stratigraphic records in these basins is still in its infancy. Many avenues of paleoenvironmental investigation offer promise. Some approaches, such as deciphering paleochemistry and paleohydrology from the endogenic mineral record and isotopic composition, have already been shown to be successful; others are essentially untried. Challenges for both fundamental and applied researchers are to integrate the sedimentological and geochemical complexities exhibited by the modern lakes with the preserved stratigraphic records on a regional basis.

De Deckker, Patrick, Department of Geology, Australian National University, Canberra, ACT, Australia, Patrick.DeDeckker@anu.edu.au

LATE HOLOCENE HISTORY OF EAST BASIN LAKE, VICTORIA, AUSTRALIA

The Western Plains District of Victoria, Australia is a large (40,000 km²) region of Quaternary volcanics having low relief and poorly integrated surface drainage. There are a large number of small cones and eruption centers in the area, some of which contain relatively deep, perennial lakes (maars). East Basin occupies the larger of two adjacent maars. Maximum depth is ~12 m, although water levels in this 30 ha closed basin lake can fluctuate by over a meter on a seasonal basis. The water in East Basin is saline (~50 ppt TDS), alkaline (pH: 9-9.5) and, like most other lakes in the vicinity, strongly dominated by Na⁺ and Cl^-. Unlike that of neighboring West Basin Lake, the East Basin water column is not chemically stratified. The lake is highly productive, due largely to the fact the basin was used as site for liquid waste disposal from a dairy located at the rim of the crater for over sixty years.

The modern offshore sediments consist of equal proportions of organic matter and inorganic material. The nearshore and shoreline sediments are noteworthy because of the occurrence of a variety of modern and penecontemporaneous hardgrounds, crusts, beachrocks, microbialites, and phytoherm framestones. The sedimentary sequence recovered from the offshore spans about 6000 years, and consists of indistinctly organic-rich, clayey silt and silty clay.

The general lack of fine lamination in the recovered sedimentary sequence of East Basin suggests the lake’s water column has remained mainly nonstratified throughout much of its 6000-year history. The presence of Mg-calcite and monohydrocalcite in the lowermost sediment indicates somewhat fresher water conditions (lower E/P) prevailed between about 6000 and 4500 BP. Beginning ~4500 BP, aridity increased, initiating more saline conditions and lower water levels as reflected by the presence of magnesite, dolomite, hardgrounds and crusts. A change in mineral composition at 1500 BP suggests a return to freshening conditions, a lower Mg/Ca ratio in the water, and a trend toward greater influence of surface runoff versus groundwater in the hydrologic budget of the lake.

Vance, Robert E., Natural Resources Canada, 580 Booth Street, Ottawa, ON., Canada K1A 0E4, rvance@gsc.nrcan.gc.ca

ORO LAKE: THE HOLY GRAIL OF WESTERN CANADA PALEOLIMNOLOGY? THE QUATERNARY EVOLUTION OF ONE OF WESTERN CANADA’S LONGEST CONTINUOUS LACUSTRINE RECORDS

Oro Lake is a small, saline, perennial lake occupying a closed basin on the Missouri Coteau in southern Saskatchewan, Canada. The water column is periodically chemically stratified with ~30 ppt salinity surface water and ~50 ppt at depth. Unlike most other salt lakes in the vicinity, Oro brine is dominated by Mg²⁺ rather than Na⁺. The surficial offshore bottom sediments consist of a complex mixture of hydrated magnesium sulfates, magnesium+sodium sulfates, calcium sulfate, magnesium carbonate, and detrital components. The stratigraphic variation exhibited by these various endogenic components in a ²¹⁰Pb dated short core suggests the basin has experienced considerable hydrochemical changes in the past several decades.

The Holocene stratigraphic sequence recovered from the basin consists of well bedded, calcareous and gypsiferous clayey silts. Endogenic and authigenic components dominate over detrital material. With its long, apparently uninterrupted record of laminated sediment, Oro Lake is clearly one of the most important lacustrine sections yet retrieved from the Canadian Great Plains. Our interpretation of stratigraphic changes in the chemical precipitates suggests that although the overall salinity and depth of the lake probably did not change dramatically after deposition of the basal clastic unit, ion ratios of the brine did undergo significant variation. An early Holocene gypsite was deposited in an Ca-SO₄ dominated saline lake. Water depths were sufficiently great to preserve lamination or the lake was chemically stratified. An abrupt change in water chemistry occurred at ~6900 BP with the lake becoming considerably more alkaline and having Mg/Ca ratios of not less than 10 to over 100. Another sharp change occurred ~3500 BP. The previous 3400 yr long episode of stable but high Mg/Ca ratios and alkalinities was replaced by 2500 years of rapidly fluctuating but still saline waters. Beginning ~1000 years ago, episodic hypersaline conditions became more common, coincident with decreased concentrations of Mg²⁺ and complementary increased proportions of Na⁺ and Mg²⁺ ions.

Kis-Papo, T., Moshe Shilo Minerva Center for Marine Biogeochemistry, Div. Microbial and Molecular Ecology, Institute of Life Sciences, Hebrew University of Jerusalem, 91904, Jerusalem, Israel. Present address: Institute of Evolution, University of Haifa, Mt. Carmel, Haifa 31905, Israel

MICROBIAL DIVERSITY IN SOLAR SALTERNS: CARBON UTILIZATION PATTERNS

The metabolic diversity of solar salterns has not to date been examined over a range of salinities and seasons. The purpose of our study, therefore, was to compare the metabolic diversity of the whole microbial community in an oligotrophic saltern (Eilat, Israel) and in a saltern with a more enriched source water(Newark, California). Between 1993 and 1998 water samples were taken from selected locations within the solar salterns of the Cargill Solar Salt Plant, Newark, California and the Israel Salt Co. solar saltern in Eilat, Israel. To examine the whole community metabolic diversity, we used the 96-well BIOLOG GNÔplates which contain 95 different carbon sources and a control well. The plates were inoculated directly within 48 hours of sample collection and incubated at either room temperature (California samples) or 35 C (Eilat samples). The plates were examined visually for up to four weeks and color changes in the redox dye noted. Plates from >15% salt were excluded from the final analyses because of a lack of reproducibility when multiple plates were inoculated with the same sample. The data were analyzed by simple matching coefficient and principle component analysis. Both methods gave essentially identical results. Two distinct clusters were formed based on the geographic origins of the samples although several samples, especially from California, were not included in either major group. Several carbon sources were used by 85% of the microbial community from the California samples, while 85% of the Eilat samples had no commonly used carbon sources. These results suggest that ponds in different geographic locations may have communities with different microbial communities despite the similarities in salt content and processing for salt production.

Kis-Papo, T., Moshe Shilo Minerva Center for Marine Biogeochemistry, Div. Microbial and Molecular Ecology, Institute of Life Sciences, Hebrew University of Jerusalem, 91904, Jerusalem, Israel. Present address: Institute of Evolution, University of Haifa, Mt. Carmel, Haifa 31905, Israel

COMPARISONS OF THE POLAR LIPID AND PIGMENT PROFILES OF TWO SOLAR SALTERNS LOCATED IN NEWARK, CALIFORNIA AND EILAT, ISRAEL

The whole community pigments and lipids have been examined over a three to five-year period in two commercial solar salterns located in the United States and in Israel. There were significant differences in the complexity of the lipid and pigment patterns within the California saltern system, and these differences were not consistent over the sampling period despite examination of ponds with the same salinities. Halophilic Archaea and halophilic Bacteria have been isolated in both systems. The solar salt system in Eilat, Israel showed greater consistency during this sampling period and in the crystallizers compared directly with previous studies. The complexity of the lipid patterns in the saltern in Newark, California could be explained on the basis of the prevailing weather conditions (cooler and more rainfall) and the nutrient enriched source water, the San Francisco Bay and Sacramento River. These conditions permit a complex and diverse microbial population to exist throughout the saltern. The Eilat saltern, however, has an oligotrophic water source and has a considerably warmer and drier climate. It appears that the microbial community here is less diverse and fewer in number than found in the California saltern. These differences resulted in more complex pigment and lipid patterns in the Newark, California plant than in the saltern in Eilat, Israel indicating the potential for significant differences in solar salterns worldwide.

Takekawa, J.Y., U. S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, P. O. Box 2012, Vallejo, CA, 94592, john_takekawa@usgs.gov

BIRD COMMUNITIES IN SALT EVAPORATION PONDS AND BAYLANDS OF THE NORTHERN SAN FRANCISCO BAY ESTUARY

Bayland habitats surround the San Francisco Bay estuary between the high and low tide lines and compose 85,830 ha. Fragmented wetlands within the baylands landscape range from fresh to salt water, and support a diverse waterbird community. Much of the baylands has been altered by development, agriculture and salt production. Natural salt pans were common historically in the baylands and likely provided invertebrates for migratory waterbirds as well as protected waters for roosting during high winds or tides on the open Bay. In the past century, artificial salt evaporation pond systems have become an integral habitat component for wildlife in the estuary. These hypersaline systems typically support simple assemblages of macroalgae and macroinvertebrates. Although salt ponds comprise a seemingly uniform habitat with little variation, they support a surprisingly diverse avian community. Ponds vary from brackish to saturated, but many species representing different foraging guilds are represented across the different ponds. We have identified six waterbird foraging guilds using the salt pond systems including: 1) sweepers -- American avocet (Recurvirostra americana), black-necked stilt (Himantopus mexicanus); 2) shallow probers -- (Calidris spp.); 3) deep probers -- marbled godwit (Limosa fedoa), long-billed dowitcher (Limnodromus scolopaceus), 4) surface feeders --northern shoveler (Anus clypeata), red-necked phalarope (Phalaropus lobatus); 5) diving benthivores -- lesser and greater scaup (Aythya marila, Aythya affinis), ruddy duck (Oxyura jamaicensis), eared grebe (Podiceps nigricollis); and 6) piscivorous birds -- American white pelican (Pelecanus erythrorhynchos), Caspian and Forster’s terns (Sterna caspia, Sterna forsteri), double-crested cormorant (Phalacrocorax auritus). We discuss the differences in the abundance and diversity of the avian communities found in the baylands compared with salt ponds.

McQuilkin, G., Mono Lake Committee, Lee Vining, CA, geoff@monolake.org

SAVING WATER, SAVING MONO LAKE: A MODEL FOR LAKE PROTECTION

Mono Lake is a 180-km² saline lake located in California’s Eastern Sierra. Endemic brine shrimp, Artemia monica, and alkali flies, Ephydrya hians, thrive in its waters, in turn supporting millions of migratory and nesting birds, including phalaropes, grebes, gulls, and waterfowl. Diversion of its tributary streams for use in Los Angeles began in the 1940s and by the 1980s had caused the lake to drop over 40 vertical feet, halving the lake’s volume and doubling its salinity. Continued diversions threatened the survival of the Mono Lake ecosystem.

Extensive citizen efforts have led to a positive management and protection plan for the lake. These protection efforts were successful because they found solutions that met the urban water needs while keeping more water in Mono Lake. Specifically, water recycling and conservation in Los Angeles have reduced the city’s water consumption to 1970s levels, despite a million-plus person population growth. A portion of these savings are directly credited to Mono Lake, and funding for the water recycling and conservation programs was provided in part to create a solution to the Mono Lake problem. Lake protection organizations can use the Mono Lake model to look for solutions which meet real water needs and protect environmental resources in order to create stable, long term strategies for lake protection.

Sally MacIntyre, Marine Science Institute, University of California, Santa Barbara, CA 93106, USA, macintyr@lifesci.ucsb.edu

RECENT ADVANCES IN REMOTE SENSING AND IN SITU MEASUREMENTS OF LIMNOLOGICAL CONDITIONS IN MONO LAKE

As part of a long-term investigation of seasonal and interannual dynamics of plankton in Mono Lake, we have developed a methodology using airborne imaging spectrometry to synoptically measure chlorophyll concentrations. A series of images of Mono Lake were acquired with NASA's Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) during the 1990s. Each image was atmospherically corrected, and we developed a predictive equation for the calculation of chlorophyll based on remote sensing reflectances derived from AVIRIS radiances and field measurements of chlorophyll concentrations. Conspicuous spatial patterns in the distribution of chlorophyll are evident in the images. Broad east to west gradients in concentration are common, and large swirls are apparent on several dates.

Temperature-gradient microstructure and nutrient profiling at inshore and offshore sites demonstrated the importance of boundary mixing for vertical mixing of nutrients in Mono Lake. Turbulent mixing was two to three orders of magnitude higher at the inshore site where the pycnocline intersected the bottom than at the same depths at an offshore station. Calculated ammonium fluxes at the inshore site were sufficient to support daily rates of primary productivity in the deep chlorophyll maximum throughout the lake. Vertical flux of nutrients across the nutricline in Mono Lake occurs over a limited area during intense mixing events initiated by high winds.

Peralta, L., Limnology Lab., Environmental Conservation & Improvement Project, UIICSE, UNAM Campus Iztacala, Av. de los Barrios s/n, Los Reyes Iztacala, 54090 Tlalnepantla, Edo. de Mexico, Mexico

PHYTOPLANKTON DYNAMICS IN A TROPICAL, HYPOSALINE DEEP LAKE.

Lake Alchichica, Puebla, is the deepest known natural lake in Mexico. Lake’s water is hyposaline (l 8.5 g/L), sodium chloride type, and alkaline (pH = 8.6-9.4). This research studied the composition and structure dynamics of the phytoplankton community, related to the environmental variability in the lake. Five sampling levels were selected along the water column in a single sampling station located in the central and deepest portion of the lake. Water samples were obtained for nutrient (N-NH₃, N-NO₂, N-NO₃, PO₄) and chlorophyll a analyses. Simultaneously, vertical profiles of temperature, dissolved oxygen concentration, and PAR were measured. Alchichica is a warm-monomictic lake, with a circulation period during the dry and cold season and a stratification period along the warm rainy season. A well-established stratification develops an anoxic hypolimnion. N-NH₃ ranges between N.D. (non detectable) and 0.98 mg 1^-1, N-NO₂ between N.D. and 0.007 mg 1^-1, N-NO₃ between 0.1 and 0.5 mg 1^-1, and PO₄ between N.D. and 1.68 mg 1^-1. Highest nutrient concentrations are found during the circulation period and the lowest at the end of the stratification period. Chlorophyll a varies from < 1 to 20 µg 1^-1 however, in most cases the chlorophyll a concentration is < 5 µg 1^-1. Alchichica is a clear water lake. The euphotic zone usually comprises the upper 15 to 20 m. Phytoplankton is composed by nineteen species. Most of them are typical inhabitants of saline lakes. Diatoms show the highest species richness (10 species). In spite of this fact, the small cyanobacteria Merismopedia minutum and Synechocystis aquatilis as well as the colonial chlorophyte Oocystis parva are numerically dominant along the annual cycle. Other species, as the diatom Chaetoceros elmorei are abundant during the stratification period. The profuse –bloom-presence of Nodularia spumigena, a nitrogen-fixing cyanobacteria, during a brief period at the end of the circulation and the beginning of the stratification period, suggests nitrogen deficit conditions in the lake. Succession of phytoplankton species in Lake Alchichica shows a close relationship to lake’s hydrodynamics (circulation-stratification) through its influence on stability and nutrient and light availability.

Oren, A., Division of Microbial and Molecular Ecology, The Institute of Life Sciences, and The Moshe Shilo Minerva Center for Marine Biogeochemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, orena@shum.cc.huji.ac.il

THE BIOENERGETIC BASIS FOR THE DECREASE IN METABOLIC DIVERSITY AT INCREASING SALT CONCENTRATIONS: IMPLICATIONS FOR THE FUNCTIONING OF SALT LAKE ECOSYSTEMS

Examination of the microbial diversity in hypersaline lakes of increasing salt concentrations shows that certain types of dissimilatory metabolism do not occur at the highest salinities. Examples are methanogenesis from hydrogen and carbon dioxide or from acetate, dissimilatory sulfate reduction with oxidation of acetate, and autotrophic nitrification. The observations can be explained on the basis of the energetic cost of haloadaptation used by the different metabolic groups and the free-energy change associated with the dissimilatory reactions. All halophilic microorganisms spend large amounts of energy to maintain steep gradients of Na⁺ and K⁺ concentrations across their cytoplasmic membrane. Most Bacteria and also the methanogenic Archaea produce high intracellular concentrations of organic osmotic solutes at a high energetic cost. The halophilic aerobic Archaea (order Halobacteriales) and the halophilic fermentative Bacteria (order Haloanaerobiales) use KCl as the main intracellular solute. This strategy, while requiring far-reaching adaptations of the intracellular machinery, is energetically more favorable than production of organic compatible solutes. By combining information on the amount of energy available to each physiological group and the strategy used to cope with salt stress, a coherent model emerges that provides explanations for the upper salinity limit at which the different microbial conversions occur in Nature.

Peterson, J., The Nature Conservancy of Utah, 559 East South Temple, Salt Lake City, UT, 84102, USA, jpeterson@tnc.org

CONSERVATION OF SHOREBIRDS AND DYNAMIC HABITATS AT MULTIPLE SCALES, GREAT SALT LAKE, UTAH, USA

The Nature Conservancy (TNC), a private, non-profit conservation organization, typically has protected areas of rich biological diversity by buying land from willing sellers or protecting biologically important land and waters through cooperative projects with public management agencies. The Layton Wetlands Preserve at the Great Salt Lake (GSL) was the first TNC real estate action in Utah, and now totals ca. 1215 hectares of wetland habitats.

However, a land acquisition strategy alone is expensive and cannot keep pace with losses of habitat and degradation of ecological systems at the GSL. In particular, there is not enough local land for sale, nor money to buy it, to protect a broad array of conservation targets. On a larger scale, agency planning efforts currently underway are aimed at resolving GSL management conflicts with a multiple-use approach for the entire GSL below its surveyed meander line--an area of about 3885 square kilometers. An even more comprehensive management effort involving the entire GSL watershed has been entertained, covering an area of approximately 57,000 square kilometers and involving three states.

This poster presentation demonstrates how current community-based, landscape-scale conservation planning strategies of TNC are being employed at multiple spatial and functional scales to protect conservation targets at the GSL.

Peng, Qiming, China Geological Survey, Beijing, China.

Sedimentary Setting of the paleoproterozoic Borate in Northeast China

The borate deposits in Liaoning and Jijin, northeast China are hosted in a 2.0 Ga. evaporite sequence. The deposits have experienced amphibolite facies metamorphism and granite intrusion. Detailed geological and geochemical study suggests that they are metamorphosed evaporites that were originally deposited in salt lakes. Two types of evaporite sequences have been identified: Fe-poor and Fe-rich borate deposits, which indicates different sedimentary settings,

Formation of these deposits involved two major stages. During evaporation and diagenesis, waters with 

d¹¹B values of +5 to +23 ‰, (that were derived from mixing of hot springs and marine sources) flowed into basins. The Fe-poor deposits were deposited in shallow and wide basins, where the waters precipitated Ca and Fe minerals at the basin margins and B was partly adsorbed onto clays or precipitated as (e.g. searlesite). This led to evolution of the fluids towards Na, K and Mg-rich brines with increasing B contents and d¹¹B values. Further evolution of the brine resulted in the final brines with high K, B and Mg levels. With desiccation of the basins, the brine evolution produced lateral zoning in alteration. Boron was enriched in the final stage, hence it is associated with the K-Mg zone. Brine evolution increased d¹¹B values to up to 33 ‰, from which borate with d¹¹B values of +8+17‰ were deposited. In deep and narrow basins where the Fe-rich deposits were deposited, the above brine evolution was not well developed, so the K-rich zone is missing. For this reason boron is associated with Na-rich zone and Fe was introduced into basin along with B instead of being precipitated along basin margins. Boron source in such basins might have lower starting d¹¹B values than the shallow ones, which means a larger portion of volcanic hot springs than marine sources.

Both alteration patterns and boron isotope data are in support of a non-marine setting for deposition of the borate deposits. Input of marine source fluids does no necessarily indicate a marine setting. The marine components could be derived from either deep-seated marine evaporites or brines, or from cyclic B sources.

Reddy, Michael M., U.S. Geological Survey, 3215 Marine Street, Boulder, CO 80303, mmreddy@usgs.gov

CARBONATE PRECIPITATION IN PYRAMID LAKE, NEVADA. PROBABLE CONTROL BY MAGNESIUM ION

Magnesium ion inhibition of calcium carbonate (calcite) formation explains present-day controls on carbonate formation in Pyramid Lake. Concentrations of magnesium ion are sufficient to reduce calcium carbonate nucleation rates and calcite formation rates in present-day supersatuated lake water. Calcium carbonate nucleation and crystal growth measurements in the presence of magnesium ion are consistent with whole-lake whitings and carbonate mound formation in Pyramid Lake. Calcium carbonate nucleation is reduced by millimolar magnesium ion concentrations. Induction times, compared with magnesium free solutions, increase in solutions containing millimolar magnesium ion. Whitings in Pyramid Lake result from calcium carbonate nucleation and are influenced by water column supersaturation and by magnesium ion concentration levels. Massive lake whitings, observed during the 1980’s, indicate that at that time supersaturations were well above 10. Elevated Pyramid Lake supersaturations may reflect high calcium ion loads transported to the lake during peak discharge. Carbonate nucleation studies of lake water may have application in characterizing and predicting Pyramid Lake whiting episodes.

Present-day Pyramid Lake maximum supersaturation occurs in late summer, corresponding to the maximum lake water temperature, and is below the value necessary for nucleation. An increase in maximum summer supersaturation appears to be necessary to cause whiting episodes now (1999). Whitings in other large lakes (i.e., the North American Great Lakes) occur at lower supersaturations, presumably because inhibitor concentrations in these lakes are lower than in Pyramid Lake. Crystal growth kinetic characterization is the key to understanding carbonate formation in Pyramid Lake, and at other Great Basin lakes.

Costa-Pierce, B., Dept. Biology, San Diego State University, San Diego, CA 92182, Dept. Coastal Sciences, Institute of Marine Sciences, University of Southern Mississippi, Ocean Springs, MS 39564.

Fisheries Ecology of the Salton Sea

Beginning in 1929, large introductions of striped bass, longjaw mudsuckers, salmon, and over 20 other marine species were planted into the Salton Sea, CA from offshore San Felipe, Gulf of California. Of these, only the orangemouth corvina (Cynoscion xanthulus), bairdiella (Bairdiella icistia) and sargo (Anisotremus davidsoni) established and flourished in the Sea. In 1964-65, an aggressive exotic species from Africa, the tilapia (family Cichlidae), escaped to the Sea by two routes: (1) an aquarist fish farm near Niland, and (2) from irrigation ditches where it was stocked purposefully by California and Arizona fisheries agencies for the control of nuisance aquatic weed and insect species (Costa-Pierce and Doyle 1997). In the 1970’s-80’s, the tilapias quickly dominated the fish community of the Salton Sea as the salinity rose to hypersaline levels. We have initiated a large, bimonthly fisheries sampling program of the Salton Sea Ecosystem (SSE) that will conclude its work in May 2000. The team sets four, 50-m long multi-panel, multi-mesh gill nets overnight (two bottom and two surface nets at each station) at nine stations in the Sea. Our preliminary observations from samplings between January-June 1999 are: (1) eight species have been sampled, and their size and age distributions determined, (2) the Alamo and New Rivers are not refugia for any of the fish species in the Sea, (3) highest catch per unit efforts (CPUEs) of 1 kg/hour are in nearshore and estuarine stations, (4) a remnant threadfin shad population is present at southern stations, (5) tilapia CPUEs are higher than reported in tropical lakes worldwide, (6) there is a narrow population size-frequency distributions for bairdiella and tilapia, and many tilapia are 3 years old, (7) there is evidence for seasonal in/offshore movements for some species, (8) there is evidence of habitat preference for the water column, and (9) there is no evidence of widespread deformities or external abnormalities in the corvina, sargo, tilapia, or croaker populations.

Faulkner, D. J., Scripps Institute of Oceanography, University of California, San Diego, CA, 92093-0212, USA, jfaulkner@ucsd.edu

PLEUROCHRYSIS PSEUDOROSCOFFENSIS IN THE SALTON SEA, CALIFORNIA, USA

The Salton Sea is a saline (46g/L), highly eutrophic lake in the southeast corner of California, USA. Since January 1997, the phytoplankton of the Salton Sea have been under investigation. Some species observed in previous studies when the lake was at 35g/L are still present; however, new species have also come to dominate at times. A coccolithophore not previously reported from the Salton Sea, identified as Pleurochrysis pseudoroscoffensis (Prymnesiophyceae), has been found in moderate numbers in the plankton and in much higher densities in surface material. Accumulations of P. pseudoroscoffensis on the surface film were seen at several locations around the Salton Sea in February, June, and July of 1999. During these times, the water was supersaturated with oxygen in the top few meters, and specific conductivity was much lower in the surface (27 mS/cm) than one meter below (53 mS/cm). Also, rafts of dead fish tended to be associated with these surface scums.

Coccolithophorids are noted for producing blooms that are non-toxic. In a preliminary study, however, P. pseudoroscoffensis collected from a surface scum caused high mortality in a brine shrimp assay (100% lethality at 400 m g/mL). Several large samples have since been collected for toxicity analysis using both the brine shrimp assay and standard mouse bioassay. Taxonomic composition of these surface scum samples was examined using the Utermöhl method. These samples were also analyzed for pigment spectra using high performance liquid chromatography (HPLC).

Sada, Donald W., Univ. of Calif., White Mountain Research Station, Bishop, CA, USA, dwsada@aol.com

BADWATER SNAIL (ASSIMINEA INFIMA) HABITAT USE AND HUMAN DISTURBANCE AFFECTING ITS ABUNDANCE, DEATH VALLEY, CALIFORNIA.

Springs in North American deserts support diverse fish and macroinvertebrate assemblages, with many relictual populations surviving since the Pleistocene Epoch. Although Death Valley wetlands are small, isolated, and comparatively harsh environments, they also provide habitat for a diversity of fishes and macroinvertebrates. One species is the Badwater snail (Assiminea infima Berry), a semi-aquatic species that is endemic to the valley’s low elevation, spring-fed wetlands. It is known to occur beneath salt crust that is adjacent to valley floor springs (at Badwater and Cottonball Marsh) and decaying vegetation beside low elevation canyon springs. Habitat at Cottonball Marsh is remote and infrequently visited, Badwater is visited by more than 600,000 people annually, and many canyon springs have been diverted to supply municipal water. Taxonomy of this species is well understood, however, knowledge of its ecology has been limited to qualitative observations.

Fritz, Sherilyn C., Dept. of Geosciences, University of Nebraska, 214 Bessey Hall, Lincoln, NE 68588 USA

THE EFFECT OF SALINITY AND BRINE TYPE ON THE RESOURCE PHYSIOLOGY OF SALINE-LAKE DIATOMS

In saline lakes of the Northern Great Plains (NGP) of North America, diatom species distributions are highly correlated with salinity and anion composition, however the mechanisms behind these correlations are unknown. These two parameters may influence diatom physiology directly, e.g. by exerting an osmotic stress, but they may also interact with other factors and thus indirectly affect species composition. We investigated the effect of salinity and brine type on the resource physiology of saline-lake diatoms in a series of growth rate and resource competition experiments. The growth rates of 4 saline-lake diatom taxa were measured under varying conditions of salinity, brine type, and nitrogen form. Brine type affected growth rates when nitrogen was supplied as nitrate, such that rates were consistently depressed in the sulfate versus bicarbonate media, but had no impact on growth rates on ammonium . The 2 taxa that are associated with bicarbonate lakes in the NGP exhibited consistently higher growth rates in the bicarbonate media, suggesting that these taxa may have higher carbon requirements. Along with results from the resource competition experiments, this suggests that bicarbonate-associated taxa may be less abundant in sulfate systems due to the lower total carbon concentrations in these systems, while sulfate-associated taxa may be less abundant in bicarbonate systems due to competitive interactions.

Stradling, Frank R. Jr. Agrarian Research and Management Company, Provo, UT USA 84604 frank@agrarian.org

RECLAMATION OF OWENS (DRY) LAKE PLAYA SOILS USING VEGETATION AND SHALLOW FLOODING FOR CONTROL OF FUGITIVE DUST

Managed vegetation and shallow flooding are two measures approved for controlling dust emissions from the Owens (Dry) Lake playa surface. Goals in the development of mitigation measures are control effectiveness and efficiency of resource use, including water.

The playa soils are characterized by extreme salinity and sodicity, as well as exceedingly high levels of phytotoxic elements such as arsenic and boron. Active reclamation is required to provide suitable substrate for even the most hardy locally-adapted plant species. Reclamation activities including mechanical surface preparation, leaching, and drainage have permitted the successful introduction of saltgrass (Distichlis spicata var. stricta) to both sand and clay soils of the playa. Both basin flooding and drip lines have been used for leaching and irrigation. Recent demonstration projects including shrubs and trees may result in an emission reduction strategy using vegetation that is water efficient, highly sustainable, and with a spatial configuration that is aerodynamically optimal for dust control.

The shallow flooding control measure relies on maintaining a saturated or flooded surface during the high wind events of the winter and early spring. Water-conserving techniques including drainage and recycling of waste-water offer the potential to make this measure resource efficient as well as highly effective.

Sharpe, Saxon E., Nevada State Division of Water Planning, 1550 E. College Parkway, Suite 142, Carson City, NV 89706, ssharpe@govmail.state.nv.us

THE RELATION BETWEEN SOLUTE COMPOSITION AND MOLLUSCAN OCCURRENCE

A strong relation exists between the solute, or ionic, composition of water and the occurrence of mollusks. Water and mollusks collected from 90 lakes, springs, and wetlands throughout the northwestern quarter of the U.S. suggest that 1) solute composition appears to be at least as important as concentration (total dissolved solids, TDS) for species occurrence, 2) the relative proportion of HCO₃ and Ca can serve as an isolating mechanism for the distribution of these taxa, and 3) the underlying cause for this distribution appears to be closely linked to the geochemical solute branchpoint process. For example, Pisidium, Sphaerium, and Valvata inhabit only waters where HCO₃ > Ca. Fossaria occurs in waters where Ca > HCO₃ at higher TDS levels, whereas Physella, Stagnicola, Gyraulus, and Planorbella are found in waters with either greater HCO₃ or Ca. Additionally, the absence of mollusks from lakes in this data set occurs abruptly between 4,000 and 5,000 mg l ^-1 TDS. This absence may coincide with the loss of HCO₃ or Ca from water rather than a TDS tolerance limit.

Mollusks recovered from a sediment core from Lower Pahranagat Lake in Nevada show changes in species assemblages with stratigraphy over the last 2,000 years. Corroboration with the pollen and isotope record from this core suggests that hydrologically-driven changes in solute characteristics can be identified in the fossil mollusk record.

Hill, R. E., 3900 Central Avenue, Fair Oaks, CA 95628, USA, rehill@ix.netcom.com

ANOSTRACAN CYSTS FOUND IN CALIFORNIA SALT LAKES

The salt lakes of California are home to four genera and seven species of Anostraca (fairy shrimp). The cysts (= resting eggs) of these species are readily distinguished using a combination of cyst and geographic characters. Cyst identification is a valuable tool that can allow a look at fairy shrimp ecology when adults are not available. For example, fossil anostracan cysts from 500-year old Mono Lake sediments show more character variation that currently exists in extant Artemia monica cysts, indicating a greater diversity in the Mono Lake Anostraca at that time. Thus, continuing desertification in that area over the last 500 years is associated with decreased diversity in the anostracan fauna.

Stephens, Doyle W., U.S. Geological Survey, 1745 W. 1700 S., Salt Lake City, Utah, 84104, USA, stephens@usgs.gov

DYMAMICS OF THE ARTEMIA FRANCISCANA POPULATION IN GREAT SALT LAKE DURING THE BOOM AND BUST PERIOD OF 1995-98

Brine shrimp (Artemia franciscana Kellogg) from Great Salt Lake provide food for large numbers of migrating and nesting water birds and have been commercially harvested as adults since 1950 and as cysts since 1952. Changes in lake salinity, local climatic patterns, and in the quantities of cysts harvested resulted in large variations in artemia populations in the lake between 1995 and 1998.

From October 1995 to June 1998, the water elevation of Gilbert Bay (south bay of the lake) rose nearly 1.2 m and the salinity declined from 130 g/L to 85 g/L. Record artemia harvests of about 6,600 metric tons occurred in 1995 and 1996. Limnological conditions in 1995 and 1996 were characterized by salinities of 150 to 107 g/L, rapidly warming water temperature in springtime, abundant but small-sized phytoplankton, and presence of small numbers of artemia at the beginning of the growing season in March.

In 1997, declining salinity coupled with a large springtime population of artemia resulted in changes in phytoplankton species from a system dominated by small chlorophytes and centric diatoms to one dominated by pennate diatoms too large to be ingested by artemia nauplii. The few small chlorophytes or centric diatoms present were quickly consumed by the rapidly growing nauplii eliminating competition for light and nutrients and allowing the large pennate diatoms to dominate throughout the year. Commercial harvest of artemia cysts was halted by the State in 1997 and 1998 and only 2,700 metric tons were taken. Conditions during these years included declining salinities of 115 g/L to 85 g/L, phytoplankton dominance by large diatoms in 1997, and presence of large numbers of artemia in March of 1997, and slowly warming water temperature in 1998.

Servant-Vildary, S. IRD-MNHN, Laboratoire de Géologie, 43 Rue Buffon, 75005 Paris, France. mone@mnhn.fr

A SALINE SHALLOW LAKE IN THE SALAR OF COIPASA (SOUTHERN BOLIVIAN ALTIPLANO) DURING THE LAST GLACIAL MAXIMUM. A RECONSTRUCTION BASED ON DIATOM STUDIES.

The " salar " of Coipasa (19°S, 68°W) is presently mainly occupied by a salt crust, except in the northern part, where a temporary shallow saline water body persisted near the Lauca river mouth.

The studied core is located in the southern part of the salar. Diatom rich sediments, dated from 21 000 BP to 17 750 BP, indicate that wetter conditions prevailed during this period in the southern Altiplano, while drier conditions are evidenced in the northern Altiplano by a lower level than presently in the Lake Titicaca (~16°N).

The weighted-averaging partial least squares regression (WA-PLS) is used to estimate optimal and tolerance of modern diatoms to ionic concentration and salinity and gives an estimate of paleosalinities in Lake Coipasa during the LGM.

From 21,000 BP to 20,700 BP, periphitic diatoms indicate shallow water body, with a salinity less than 10 gL^-1. Between 20,700 BP and 18,680 BP, planktic Chaetoceros spp. show a water level increase. This diatom is presently abundant in Lake Poopo, a 2 m depth lake with a salinity of 10 to 40 gL^-1 . At the end of this period, the lake-level is unstable as shown by the alternation between Chaetoceros spp. and the epiphytic Amphora coffaeformis which is presently abundant on the border of Salar de Uyuni (~18 gL^-1). From 18,680 BP to 17,750 BP, laminated sediments rich in mainly periphitic diatoms suggest salinity and water level decrease.

The Coipasa lake was mostly of Cl-Na type during all the LGM period.

Threloff, Douglas, Resources Management Division, Death Valley National Park, Death Valley, CA 92328, doug_threloff@nps.gov

BIOLOGICAL RESOURCE VALUES ON AND ADJACENT TO THE DEATH VALLEY SALTPAN IN DEATH VALLEY NATIONAL PARK, CALIFORNIA

The saltpan in the central valley of Death Valley National Park, California is the largest playa feature that occurs on lands that are administered by the National Park Service. The playa is relatively unique in that portions of the playa are damp on a constant basis even during years when rainfall is absent. The perennially damp portion of the playa is 8,622 hectares in size, while intermittently wet portions of the playa measure approximately 33,210 hectares in area. A diversity of moisture gradients and chemical constituents on the Death Valley saltpan have created a complex landscape mosaic that varies on temporal and spatial scale. The playa receives water through upward movement of groundwater that is derived from a regional aquifer that extends into the southern third of the state of Nevada. The playa also receives surface water on an intermittent basis from the Amargosa River.

The biological communities in and adjacent to the saltpan have only been superficially studied due to National Park Service funding constraints. The playa area does possess plant and animal communities that are characterized by a number of endemic species. The more notable vertebrate taxa include the Salt Creek pupfish (Cyprinodon salinus salinus) and the Cottonball Marsh pupfish (Cyprinodon salinus milleri). A number of endemic invertebrate species also are present in aquatic and mesic habitats, and include a variety of snail and tiger beetle species. Mapping of vegetation around the playa has recently begun, and will document that presence of an extensive riparian plant community.

Environmental conditions around the playa are characterized by high evaporation rates, low precipitation, and high summer temperatures (>125º C). This unique combination of factors makes the Death Valley saltpan a unique environment for conducting research that involves biological, chemical, and geophysical studies.

Hurlbert, S. H., Department of Biology and Center for Inland Waters, San Diego State University, San Diego CA 92182, USA. sbarlow@sunstroke.sdsu.edu

CHATTONELLA CF. MARINA, A POTENTIALLY TOXIC RAPHIDOPHYCEAN ALGA IN THE SALTON SEA, CALIFORNIA

Chattonella cf. marina was abundant in the Salton Sea from April-November in 1997 and 1998. It was not detected from January 1997-March 1997 or from December 1997 to March 1998. Algae in this genus are known to be toxic and produce brevetoxins and superoxide radicals, both of which may be lethal to fish. The species has been associated with massive fishkills in the coastal waters of Japan and Australia. Fish kills occur frequently in the Sea and some may be due to this organism. The cells are 40-50 µm long with two heterodynamic flagella emerging from the anterior of the cell, one projecting anteriorly and one lying close to the body. TEM studies show the typical Chattonella features; a tear drop shaped nucleus, numerous chloroplasts with thylakoids extending into the pyrenoids and lack of a cell wall. No mucocysts were observed. To our knowledge this is the first report of Chattonella from any lake.

Timms, B.V., Department of Geography and Environmental Science, University of Newcastle, Callaghan, NSW, 2265, Australia. ggbvt@cc.newcastle.edu.au

A STUDY OF THE WEREWILKA INLET OF THE SALINE LAKE WYARA, AUSTRALIA: A HARBOUR OF BIODIVERSITY FOR A SEA OF SIMPLICITY.

Lake Wyara receives most of its water from Werewilka Creek, with the area between the two forming Werewilka Inlet which is highly variable in area, salinity and has high habitat heterogeneity. In a study spanning twelve years, 83 species of macroinvertebrate were found in the inlet but only 34 in the lake. Halobiont and halophilic species were the same in each, but there were many fewer salt-tolerant species in the lake and no freshwater species. The later were excluded by salinity, but habitat homogeneity due to strong wave action in the lake seems to limit many salt-tolerant species to the inlet. This factor, together with salinity and the poor speciation opportunities provided by episodic lakes, is important in limiting species richness of large saline lakes in inland Australia.

Hemming, S. R., Lamont-Doherty Earth Observatory of Columbia University, Rt. 9W, Palisades, NY 10964 USA, sidney@LDEO.columbia.edu

LITHIUM ISOTOPE GEOCHEMISTRY OF MONO LAKE, CALIFORNIA

Because of the large relative mass difference, the two isotopes of lithium are fractionated by many common near-surface processes. However, the specifics of Li isotope behavior at low temperatures are virtually unexplored. We measured the Li isotopic composition of samples from the Mono Lake area to constrain the paramount mechanisms of Li isotope fractionation under these conditions. We anticipate that Li iso-topes may be useful as tracers of source or process in this environment, and hence they may be a valuable tool to study the paleogeochemistry of this long-lived lake system. Mono Lake water samples from Fall 1996 and Spring 1999 (10 ppm Li at surface, and 12 ppm at 24 m depth) are isotopically homogeneous at +20 permil (all data are Li-7/Li-6 normalized to the NIST L-SVEC standard). This is lighter than 1999 samples from Pyramid (+24 permil) and Walker Lake (+26 permil). This is substantially heavier than all examined rivers in the area, which average +12 permil. Although ~85% of the Mono Lake water budget derives from streams, our concentration measurements indicate that springs currently provide the bulk of the Li. The springs show both light (+8 permil) and heavy (+30 permil) Li. The light values may reflect source components in young volcanic rocks (e.g., Mono Craters obsidian: 41 ppm Li; +4 permil). The heavy value from one groundwater spring is similar to the composition of water-soluble efflorescent salts from the eastern flank of the lake (10 ppm Li; +32 permil). Recently-crystallized carbonates at lake-spring mixing zones also show isotopic variability (14 to 32 ppm Li; +12 to +23 permil), perhaps due to contamination by lake water in the untreated samples. Whether Li will serve as a sensitive proxy for hydrogeochemical processes or ambient climatic variations is not known. Similarities between the isotopic offsets of Mono Lake and its inputs compared to modern seawater and its principal inputs suggests that if the fractionation mechanisms can be determined at Mono, this would benefit our comprehension of the global Li isotopic budget, several aspects of which remain poorly understood.

Sorgeloos, P., Laboratory of Aquaculture & Artemia Reference Center, University of Gent, Rozier 44, B-9000, Gent, patrick.sorgeloos@rug.ac.be

Field study of Artemia urmiana population in Lake Urmiah, Iran

Lake Urmiah is a large (total surface 4750-6100 km² in recent times) thalassohaline hypersaline lake (150-180 ppt in the period 1994-’96) located in northwestern Iran. It is the habitat of the endemic Artemia urmiana. Over the period July 1994-January 1996 a sampling campaign was organized. Thirty-six fixed sampling stations, distributed over the entire lake’s area, were sampled weekly to determine water temperature, salinity and transparency. At each sampling occasion a filter net was dragged over a distance of 400 m in the superficial water layer to assess the density and composition of the Artemia population. A more limited sampling campaign aimed at the annual fluctuations in chlorophyll concentration and at the reproductive behaviour of the brine shrimp population.

Different stages of brine shrimp survived during winter months (water temperature 3°C), be it at low densities. Compared to available data for the Great Salt Lake, USA, Lake Urmiah shows a limited primary production and low overall Artemia density. Contrary to other natural Artemia habitats, the grazing pressure of the expanding brine shrimp population in spring seems to prevent the phytoplankton to reach high blooming concentrations, and oviparity is the dominant reproductive mode throughout the reproductive season.

Hurlbert, S.H., Department of Biology and Center for Inland Waters, San Diego State University, San Diego, CA, 92182, USA, shurlbert@sunstroke.sdsu.edu

MIXING REGIME AND OXYGEN DYNAMICS OF THE SALTON SEA, CALIFORNIA, 1997-1999

The Salton Sea is a polymictic, 980 km² lake located in the arid southwest United States. Formed in 1905 as a fresh water lake, the salinity is now 46 g/L and is increasing at a rate of 0.4 g/L/year. The Salton Sea has a mean depth of 8m and a maximum depth of 15m. Temperature and dissolved oxygen were measured at three mid-lake stations at 2 - 5 week intervals from January 1997 to August 1999. Two additional near shore stations were added in January 1999. Daily climate data was obtained from 5 meteorological stations surrounding the Salton Sea. We use this 32 month data set to assess the temporal, vertical, and horizontal variations of temperature and dissolved oxygen in the Salton Sea, the physical processes that produce them, and their significance to life in the lake.

The lake has a warming period from early January to July-September, followed by a 4-5 month cooling period. Thermal stratification exists during most of the warming period but this is interrupted by periodic wind-driven mixing events, especially in early spring. Mixing events are less frequent in the summer, but when they occur they sometimes result in the entire water column becoming anoxic. For a large part of the warming period, most of the lake bottom is anoxic and free of macroinvertebrates. By the end of the warming period mean water column temperature in midlake is 31-34°C. During the cooling period, convectional circulation supplements wind-generated turbulence and the whole water column mixes more or less daily. Oxygen levels during this period are almost always > 3 mg/L at all depths. By the end of the cooling period mean midlake water column temperature is 13-15°C. Lake hydrodynamics are complex, influenced by freshwater inflows at the south end and a double-gyre current system, and produce large differences in temperature and oxygen profiles between the northern and southern basins.

Williams, W.D., Department of Environmental Biology, University of Adelaide, Adelaide 5005, Australia, bwilliam@camtech.net.au

SALINISATION OF FRESH WATERS

Regions with a mean annual rainfall of between 25 and 500 mm (‘drylands’) cover about one-third of total land area. Despite their relatively low rainfall, many freshwater lakes, wetlands and rivers occur in such regions. A major threat to their natural character and economic use is secondary salinisation, i.e. rising salinities following anthropogenic activities. The excessive clearance of natural vegetation from catchments and the discharge of saline waste water from agricultural regions is particularly important in this respect. Rising saline groundwaters are also important in some areas, as is increasing climatic aridity.

The salinisation of fresh waters has many important impacts. All are deleterious and usually irreversible. Lower biodiversities, changes to the nature of the ecosystem, and lower production are usual ecological effects. In some countries in drylands, salinisation is seen as the most important hazard facing water resources. However, globally, the extent and significance of salinisation of fresh waters has been underestimated thus far. Global climatic change is likely to increase further the volume of fresh water effected by salinisation.

Gliwicz, Z. Matthew, Department of Hydrobiology, University of Warsaw, Nowy Swiat 67, Warsaw, Poland, gliwicz@hydro.biol.uw.edu.pl

POPULATION DYNAMICS AND ENVIRONMENTAL FACTORS CONTROLLING BRINE SHRIMP CYST PRODUCTION IN THE GREAT SALT LAKE, UTAH

Because brine shrimp (Artemia franciscana Kellogg) in the Great Salt Lake are important for commercial harvest and migrant birds, seasonal fluctuations in abundance and cyst production were monitored in 1994 and 1995 in a 4290 km2 basin of the lake. Temperature, salinity and chlorophyll levels were measured, and ancillary experiments were done in order to understand factors controlling production. Salinity during the study varied from 130-160 g/L, providing optimal conditions for brine shrimp, and excluding other macroinvertebrates. In spring, nauplii hatched from cysts as early as March when temperatures reached 10 C and chlorophyll a levels were near 30 ug/L. As the first cohort matured in May with densities of 0.4 females/L and clutch sizes of 170, production of ovoviviparous eggs reached 8 L-1 d -1. Grazing by juveniles maturing from this production decreased chlorophyll levels to < 1 ug/L in late May, and despite higher temperatures, brine shrimp population levels decreased from 8/L in spring to mid-summer levels near 3/L. This suggests that algal resources are controlling maximum production levels. In a laboratory experiment, interbrood intervals decreased from 20 d at 10 C to 4 d at 25 C. Decreasing chlorophyll levels decreased the proportion of ovoviviparous eggs produced and increased the proportion of cysts. Using predicted interbrood intervals, and field data on temperature, chlorophyll and brood size, we estimate that the lake produced 380,000 cysts m-2 yr-1, or 4,500 tonnes dry weight in 1994. Reported commercial cyst harvest was near 2,300 tonnes of dry cysts, or 51% of the 1994 production. Consequently, commercial harvest can have a significant impact on cysts available for subsequent cohorts, and the impact of this harvest must be carefully modeled and monitored.

Liu, Danyang, R &D Center of Saline Lakes and Epithermal Deposites, C.A.G.S. , Beijing 100037; Open Laboratory of Saline Lake Resources and Environment, C.A.G.S., Beijing 100037

STUDY ON ISOTHERMAL 15C EVAPORATION EXPERIMENT OF BRINE OF ZABUYE SALT LAKE, TIBET, SOUTHWEST CHINA

Zabuye Salt Lake is located at the center of the Tibetan Plateau and at 31°21´N and 84°04´E with an elevation of 4421m of lake level. It is a tectonic lake which is separated into two parts--the South Lake and the North Lake. The special brine in the lake is a kind of Na⁺,K⁺,Li⁺//Cl^-, SO₄^2-, B₄O₇^2-, CO₃^2-,HCO₃^---H₂0 complex 8-element brine system, its type is carbonated and characterized by the rich in Li, B and K. The composition of the brine changes with season. The brine of 10000ml for this experiment was taken from the South Lake in July of 1998. The evaporation experiment had been run under a 15C-controlled constant temperature box in lab in the end of 1998.

It is the first time for this isothermal evaporation experiment at a low temperature of 15? to the study on the special kind of most complex 8-element brine system in the area of the Tibetan Plateau. This paper first announces the relationship between the evaporation rate (Er) and the concentration change of each element in the liquidus facies and the salt mineral composition in the solid facies to the brine system. So it is of certain theoretic and applied significance for the study on this kind of complex brine system.

Zheng, Mianping, R&D Center of Saline lake and Epithermal Deposits, CAGS, Open Laboratory of Saline Lake Resources and Environment, CAGS, Beijing 100037

ON SALINOLOGY

Saline lakes are a group of comprehensive natural resources, including large diversity of mineral resources, salt-liking biological resources and tourism resources. These resources are also database and field laboratories for study of global change and mineralization processes. In traditional classification, saline lake study was part of limnology that studies physics, chemistry and biology of lakes (W.G. Moor, 1975). Limnology, however, focuses on the physical, chemical and biological properties of lake, and does not include resource engineering concept. In the field of geological sciences, saline lake geology does not include study of biological resources and ecology. Hence, neither traditional limnlogy nor saline lake geology could cover the comprehensive meaning of research and development of saline lakes. To meet the needs of development of saline lake research and society’s demands, there is a need to set up a new research system that could be named as "salinology". This new branch deals with chemistry, physics, biology and their interaction with resources and environment, which is a marginal and application discipline of research. The basic mission of salinology is to conduct comprehensive, multidisciplinary research and exploration of saline lakes, providing data for rational management and exploitation of saline lakes and make contributions to sustainable development of saline lake agriculture, saline lake mining and tourism business.

Zhang, Yongsheng, Open Laboratory of Saline Lake Resources and Environment, C.A.G.S., Beijing, China.

THE CLIMATIC HISTORY OF ZABUYE LAKE ON THE TIBETAN PLATEAU

Zabuye Lake is situated at the edge of Himalayan fold belt of Gandise. It is a tectonic lake in S-N direction. During 40-28 Ka B. P., the Lake belonged to Zhabuye-Zhari Namco ancient Pan-lake. By the end of Pleistocen, 28 Ka B. P., the climate in the centre of the Tibetan Plateau changed into semiarid. The Pan-lake shramk and disintegrated Sub-lake tuned into some chain-lakes that included Zhabuye-Lagkor Co Chain-lake.

During about 40-28 B. P., the ancient Pan-Lake were very extensive. In combination with micropale-ontological and geochemical data, it is inferred that the annual precipitation at that time was at least 2-3 times highter than that at present. It represented a very strong wet monsoon event on the Qinghai-Tibet Plateau.

According to the features of the climatic evolution of Zabuye Lake since 40 Ka B. P., the period may be divided into six phases.

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