Chemical and physical characteristics of the Salton Sea, California

A 1-year sampling program was conducted to assess current chemical and physical conditions in the Salton Sea. Analyses included general physical conditions and a suite of water quality parameters, including nutrients, trophic state variables, major cations and anions, trace metals and organic compounds. Samples were collected from three locations in the main body of the lake and from the three major tributaries. Nutrient concentrations in the Salton Sea are high and lead to frequent algal blooms, which in turn contribute to low dissolved oxygen concentrations. The tributaries consist primarily of agricultural return flows with high nutrient levels. Concentrations of trace metals and organic compounds do not appear to be of major concern. Two geochemical models, PHRQPITZ and PHREEQC, were used to evaluate potential chemical reactions limiting the solubility of selected water quality variables. Modeling indicated that the Salton Sea is supersaturated with respect to calcite, gypsum, and other minerals. Precipitation of these minerals may serve as a sink for phosphorus and limit the rate of salt accumulation in the Salton Sea.     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.     

Transport and distribution of trace elements and other selected inorganic constituents by suspended particulates in the Salton Sea Basin, California, 2001

In order to examine the transport of contaminants associated with river-derived suspended particles in the Salton Sea, California, large volume water samples were collected in transects established along the three major rivers emptying into the Salton Sea in fall 2001. Rivers in this area carry significant aqueous and particulate contaminant loads derived from irrigation water associated with the extensive agricultural activity, as well as wastewater from small and large municipalities. A variety of inorganic constituents, including trace metals, nutrients, and organic carbon were analyzed on suspended material isolated from water samples collected at upriver, near-shore, and off-shore sites established on the Alamo, New, and Whitewater rivers. Concentration patterns showed expected trends, with river-borne metals becoming diluted by organic-rich algal particles of lacustrine origin in off-shore stations. More soluble metals, such as cadmium, copper, and zinc showed a more even distribution between sites in the rivers and off-shore in the lake basin. General distributional trends of trace elements between particulate and aqueous forms were discerned by combining metal concentration data for particulates from this study with historical aqueous metals data. Highly insoluble trace metals, such as iron and aluminum, occurred almost entirely in the particulate phase, while major cations and approximately 95% of selenium were transported in the soluble phase. Evidence for greater reducing conditions in the New compared to the Alamo River was provided by the greater proportion of reduced (soluble) manganese in the New River. Evidence of bioconcentration of selenium and arsenic within the lake by algae was provided by calculating “enrichment” concentration ratios from metal concentrations on the algal-derived particulate samples and the off-shore sites. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005 Roy A. Schroeder—Retired.     

Properties and distribution of sediment in the Salton Sea,California: an assessment of predictive models

The Salton Sea is the largest lake, on a surface area basis, in California (939 km²). Although saline (>44 g/l) and shallow (mean depth approximately 9.7 m), it provides valuable habitat for a number of endangered species. The distribution of sediments and their properties within the Salton Sea are thought to have significant influence on benthic ecology and water quality. Sediment properties and their distribution were quantified and compared with predicted distributions using several sediment distribution models. Sediment samples (n = 90) were collected using a regular staggered-start sampling grid and analyzed for water content, organic carbon (C), calcium carbonate, total nitrogen (N), total phosphorus (P), organic phosphorus, and other properties. Water content, total N, and total and organic P concentrations were all highly correlated with organic C content. The organic C concentration showed a non-linear increase with depth, with low organic C contents (typically 1–2%) present in sediments found in depths up to 9 m, followed by a strong increase in organic C at greater depths (to about 12% at 15 m depth). The models of Hakanson, Rowan et al., Blais and Kalff, and Carper and Bachmann yielded very different predicted critical depths for accumulation (10.5–22.8 m) and areas of accumulation (0–49.5%). Hakanson’s dynamic ratio model more reasonably reproduced the observed zone of elevated organic C concentrations in the Salton Sea than either exposure- or slope-based equations. Wave theory calculations suggest that strong winds occurring less than 1% of the time are sufficient to minimize accumulation of organic matter in sediments that lie at depths less than 9 m in this system. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Salinity and fish effects on Salton Sea microecosystems: water chemistry and nutrient cycling

A 15 month long experiment was undertaken to document responses of the Salton Sea biota to experimentally manipulated salinity levels (30, 39, 48, 57, and 65 g l-1) in 312-liter fiberglass tanks maintained outdoors. At two salinities (39 and 57 g l-1) microcosms were set up each having one small tilapia ( Oreochromis mossambicus) in order to assess its influence on the system. To 28 tanks filled with Salton Sea water diluted to 30 g l-1, different salts (NaCl, Na2SO_4, MgSO4 · 7H2O, KCl) were added in constant proportions to produce the desired salinity levels. Salton Sea shoreline sediment was added to the bottom of each tank, and inocula of algae and invertebrates were added on several occasions. Invertebrate populations, phytoplankton, periphyton, and water chemistry were monitored at regular intervals. This article present the results concerning water chemistry and nutrient cycling. There was no apparent increase in salinity over time, though ∼ 1190 l of tapwater with a salinity of ∼ 0.65 g l-1 were added to each tank during the experiment. Ionic composition varied both among treatments and over time to some degree. Ca2 concentrations were the same at all salinities, while K1 concentrations were >3 times greater at the highest salinity than at the lowest. pH showed little consistent variation among salinities until the last few months when it was higher by ∼ 0.4 units at the two higher salinities than at the lower ones; it was unaffected by fish. Absolute oxygen concentrations were negatively correlated with salinity, and occasionally depressed by the presence of fish. PO3-4, dissolved organic phosphorus, and particulate phosphorus concentrations were often reduced by 30–80% at 65 g l-1 relative to lower salinities and by the presence of fish. Early in the experiment NO2-3 concentrations were >2 times higher at 57 and 65 g l-1 than at lower salinities, but otherwise effects of salinity on dissolved forms of nitrogen were not marked; particulate nitrogen was much lower at 65 g l-1 than at other salinities and also was reduced by up to 90% by the presence of fish. Silica concentrations increased over time at all salinities, but, relative to those at lower salinities, were reduced by 60–90% at 65 g l-1 by abundant periphytic diatoms. The TN:TP ratio (molar basis) was 24–30 initially and 35–110 at the end of the experiment; it was positively correlated with salinity and the presence of fish. Mechanisms accounting for the above patterns involve principally the biological activities of phytoplankton and periphyton, as modified by grazing by Artemia franciscana and Gammarus mucronatus, and the feeding and metabolic activities of the tilapia. The large reduction in water column TN and TP levels brought about by the fast-growing, phyto- and zooplanktivorous tilapia suggest that amelioration of the Salton Sea's hypereutrophic state might be assisted by a large scale, sustained yield fish harvesting operation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evidence for salt diffusion from sediments contributing to increasing salinity in the Salton Sea, California

Geochemical investigations of interstitial waters from the Salton Sea, CA reveal evidence of concentrated brines in the sediments underlying the lakes two basins. The brines are likely caused by the gradual dissolution of evaporite deposits. The chemical composition of the brine in the northern basin is dominated by magnesium and sulfate and differs from the southern basin where the dominant components are sodium and chloride. Sediment depth distributions of major ions and porosity indicate diffusion of salts from the sediments into the overlying waters in both basins. Benthic fluxes have been calculated for the four most abundant ions: magnesium, sodium, sulfate and chloride. For the northern basin we calculate diffusive fluxes of 3.7 × 10^–2, 8.2 × 10^–2, 44 × 10^–2, and 5.4 × 10^–2 g cm^–2 yr^–1 for magnesium, sodium, sulfate and chloride, respectively. For the southern basin we calculate diffusive fluxes of 0.9 × 10^–2, 9.7 × 10^–2, 6.9 × 10^–2, and 25 × 10^–2 g cm^–2 yr^–1 for these same ions. By scaling up our results we estimate the salinity flux from the sediment to the water column to be between 3.6 × 10⁴ and 3.6 × 10⁵metric tons per year, equivalent to 1–10% of the riverine input. These results are important for developing strategies to combat rising salinity in the Salton Sea, CA.     

Summer movements of desert pupfish among habitats at the Salton Sea

Summer movement behavior of native desert pupfish (Cyprinodon macularius Baird and Girard) was evaluated among various habitats around the Salton Sea, located in southern California. Agricultural drains, shoreline pools, and Salt Creek were sampled six times between June 28 and September 16, 1999. Collected pupfish were marked using fluorescent elastomer implants. Unique marks were used at each site. Movements were detected from locations of recaptured pupfish. Desert pupfish were found in 10 of 12 sites sampled. Of 3239 pupfish captured during the study, 278 were recaptures, including 27 recaptures at areas different from where they were initially marked. The best evidence of pupfish movements was in the southwestern area of the Salton Sea between a drain and a connected shoreline pool. Movements were also observed from lower Salt Creek into a shoreline pool at the mouth of the creek as the water level dropped. The use of the Salton Sea as a migration corridor between habitats was not documented during this short study. The marking technique was successful and showed promise for future mark and recapture studies of desert pupfish.     

Fish biology and fisheries ecology of the Salton Sea, California

Studies of the fisheries ecology and fish biology of the Salton Sea, California, were conducted in 1999 and 2000 using 50 m gill nets in river, nearshore, pelagic, and estuarine areas. Total lengths and weights were measured for all fish captured, and sub-samples were dissected for gonad weights and aging. Ten fish species were captured of which a hybrid tilapia (Oreochromis mossambicusx O. urolepis hornorum) was dominant by number and weight. Nearshore and estuarine areas had highest catch rates (over 11 kg h^–1 net^–1 for tilapia). Rivers were richest in the number of species (6 of 10 species were exclusively riverine), but lowest in fish abundance. Orangemouth corvina (Cynoscion xanthulus), bairdiella (Bairdiella icistia), sargo (Anisotremus davidsoni), and tilapia grew faster, but had shorter life spans than conspecifics elsewhere and Salton Sea conspecifics of 50 years ago. Reproduction occurred mostly in the nearshore and estuarine areas. Onset of reproduction of bairdiella and sargo was in the spring and extended through the beginning of summer. Reproduction of orangemouth corvina started in the summer and of tilapia in the spring. Reproduction of orangemouth corvina and tilapia extended through the fall. Gender ratios of tilapia were skewed toward males in all areas, except the rivers, where females predominated. All four species aggregated along the nearshore and estuarine areas in the summer when dissolved oxygen in the pelagic area was limited. Any restoration alternative for the Salton Sea should consider areas close to shore as primary areas for fish reproduction and survival.     

Salinity tolerance of the copepod Apocyclops dengizicus (Lepeschkin, 1900), a key food chain organism in the Salton Sea,California

The copepod Apocyclops dengizicus is a key item in the food chain of the Salton Sea where the salinity is currently 45 g 1^–1. The salinity of the Salton Sea may reach 90 g 1 ^–1 within the next 20 years. This study examined the salinity tolerance of this copepod.Large copepodite and adult A. dengizicus were introduced into various salinities with and without acclimation. The 96 h LC₅₀ without acclimation was 101 g 1^–1. Mortality (at 96 h) without acclimation was low at salinities of 90 g 1 ^–1 or less.Copepod cultures were maintained, with successful reproduction of at least one new generation, at salinities of from 0.5 to 68 g 1 ^–1 for at least 120 days. Copepods maintained at higher salinities, up to 79 g 1 ^–1, remained alive up to 90 days, but a new generation was not produced. In laboratory studies of larval production and survivorship, few nauplii were released at salinities of 68 g 1 ^–1 or higher, and none survived to the copepodite stage.     

Reconstruction of prehistoric Lake Cahuilla in the Salton Sea Basin using GIS and GPS

During prehistoric times, the Colorado River occasionally meandered into and filled the Salton Sea Basin, creating several huge inland lakes, variously called Lake LeConte and Lake Cahuilla. Previous researchers have identified high stands of these ancient lakes using standard survey methods. The objective of this investigation was to further delineate the prehistoric shorelines using satellite imagery, global positioning system (GPS) and geographic information system (GIS) technologies. Using one-meter digital orthophotographs, points were selected in the laboratory and were located in the field using a GPS. Point data were integrated with a digital elevation model (DEM) and elevation contours were plotted on Landsat-TM images, generating a range of prehistoric shorelines. Contours were then correlated with archaeological site data, geomorphic features, and other factors to reconstruct Early American settlement patterns for Lake Cahuilla. The combined GIS coverages of ancient Lake Cahuilla and cultural resources may be used together as a model for cultural resource constraints, identifying areas of high cultural resource sensitivity for evaluation of potential impacts as a result of implementation of Salton Sea restoration project alternatives.     

Biology and migration of Eared Grebes at the Salton Sea

The Eared Grebe (Podiceps nigricollis Brehm) is the North American bird species most closely associated with highly saline habitats, and in winter and early spring it is the most abundant waterbird at the Salton Sea. During the fall, the great majority of the North American population stages at hypersaline lakes in the Great Basin, departing in early winter for wintering areas in southern California and Mexico, principally in the central Gulf of California. On the northward return flight, nearly all the population passes through the Salton Sea, where concentrations of >1 million have been reported in February–March. After staging for several weeks, grebes leave in March–April and migrate toward breeding grounds in the northern United States and southern Canada. The Sea's development as the species' major spring staging area may be as recent as the 1960s, and presumably awaited the establishment of appropriate prey populations of marine worms. In the past decades, two major dieoffs at the Sea each resulted in the undiagnosed death of tens of thousands of birds. Whether the cause(s) are endemic to the Sea or involve the grebes' migration routes and stopover locations is unknown. Because of problems in estimating numbers, the significance of these mortality events is hard to evaluate. Population trends are better studied at fall staging areas, especially Mono Lake, where population turnover is inconsequential, grebes are virtually the only species present, and numbers can be ascertained by aerial photography.     

Invertebrates of the Salton Sea: a scanning electron microscopy portfolio

Scanning electron microphotographs of 16 Salton Sea invertebrate species are presented within this portfolio. A wide spectrum of invertebrates was investigated including foraminiferans, a flatworm, a rotifer, annelids, crustaceans and insects. Additional information is provided on the morphology and function of structures visible in the images.     

Influence of river inflows on plankton distribution around the southern perimeter of the Salton Sea,California

The influence of river inflows (2.5–5 g l⁻¹) on phytoplankton and zooplankton was assessed with samples collected at 17 sites around the 50 km perimeter of the southern basin of the Salton Sea (41–45 g l⁻¹) along the 5 m isobath on 2 September and 11 December 2000. Phytoplankton generally increased in abundance downcurrent of the points of inflow, but patterns in downcurrent abundance varied widely among species. Several diatom species showed large increases; Chaetoceros muelleri var subsalsum, Cylindrotheca closterium and Thalassionema sp. increased up to 800-fold in abundance by ca. 20 km downcurrent from inflow points in September. In contrast, the dinoflagellates Gyrodinium uncatenum and Prorocentrum minimum increased 6- and 4-fold, respectively, in December, and Gonyaulax grindleyi actually decreased downcurrent of the rivers in September. In September, patterns in downcurrent abundance were correlated with the ratio of cell surface area to cell biovolume, with species with high ratios showing the largest increases. Zooplankton abundances did not show regular trends downcurrent of river inflows except for the larvae of Balanus amphitrite, which increased in density ca. 100-fold. This increase most likely reflected the abundance of adult-colonized rocky substrates near river inflow points. The strong upcurrent trends documented for some species seemed to have been due to the injection of nutrient-rich water from central to nearshore areas and near-site mortality due to the presence of hydrogen sulfide. This study gives a first glimpse of the complexity of the responses of nearshore plankton to river inflow and provides evidence for how changes in factors such as current speed, nutrient supply and salinity stratification may influence plankton dynamics. Guest Editor: John M. Melack Saline Waters and their Biota     

Geochemistry of iron in the Salton Sea,California

The Salton Sea is a large, saline, closed-basin lake in southern California. The Sea receives agricultural runoff and, to a lesser extent, municipal wastewater that is high in nutrients, salt, and suspended solids. High sulfate concentrations (4× higher than that of the ocean), coupled with warm temperatures and low-redox potentials present during much of the year, result in extensive sulfate reduction and hydrogen sulfide production. Hydrogen sulfide formation may have a dramatic effect on the iron (Fe) geochemistry in the Sea. We hypothesized that the Fe(II)-sulfide minerals should dominate the iron mineralogy of the sediments, and plans to increase hypolimnetic aeration would increase the amount of Fe(III)-oxides, which are strong adsorbers of phosphate. Sequential chemical extractions were used to differentiate iron mineralogy in the lake sediments and suspended solids from the tributary rivers. Iron in the river-borne suspended solids was mainly associated with structural iron within silicate clays (70%) and ferric oxides (30%). The iron in the bottom sediments of the lake was associated with silicate minerals (71% of the total iron in the sediments), framboidal pyrite (10%), greigite (11%), and amorphous FeS (5%). The ferric oxide fraction was <4% of the total iron in these anaerobic sediments. The morphological characteristics of the framboidal pyrite as determined using SEM suggest that it formed within the water column and experiences some changes in local redox conditions, probably associated with alternating summer anoxia and the well-mixed and generally well-aerated conditions found during the winter. The prevalence of Fe(II)-sulfide minerals in the sediments and the lack of Fe(III)-oxide minerals suggest that the classic model of P-retention by Fe(III)-oxides would not be operating in this lake, at least during anoxic summer conditions. Aeration of the hypolimnion could affect the internal loading of P by changing the relative amounts of Fe(II)-sulfides and Fe(III)-oxides at the sediment/water interface. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Pore water nutrient profiles and dynamics in soft bottoms of the northern Baltic Sea

Chemical profiles of nutrients at the sediment–water interface were measured in the northern Baltic Sea. A whole core squeezer technique capable of mm-scale resolution was used to obtain the vertical profiles of NO₃ ^–, NO₂ ^–, o-P, NH₄ ⁺ and Si in the soft bottom sediments. The profiles were compared with nutrient flux and denitrification measurements. In the Gulf of Finland, the profiles revealed a marked chemical zonation in NO₃ ^– and NO₂ ^– distribution indicating strong potential of nitrification just under the sediment surface followed by a layer of denitrification down to a depth of 30 mm. Below the depth of 20 mm NO₃ ^– was usually absent, whereas other nutrients were increasing steadily in concentration. A distinct minimum of NO₃ ^– was observed at the sediment–water interface, suggesting NO₃ ^– uptake by a microbial biofilm and/or active denitrification at the suboxic microniches usually present in organic-rich sediments. At the deep stations in the Baltic Proper, the NO₃ ^– concentration in pore water, as well as denitrification, were very low. The concentrations of NH₄ ⁺, o-P and Si were usually increasing steadily with depth.     

The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics

The Salton Sea, California's largest inland water body, is an athalassic saline lake with an invertebrate fauna dominated by marine species. The distribution and seasonal dynamics of the benthic macroinvertebrate populations of the Salton Sea were investigated during 1999 in the first survey of the benthos since 1956. Invertebrates were sampled from sediments at depths of 2–12 m, shallow water rocky substrates, and littoral barnacle shell substrates. The macroinvertebrates of the Salton Sea consist of a few invasive, euryhaline species, several of which thrive on different substrates. The principal infaunal organisms are the polychaetes Neanthes succinea Frey & Leuckart and Streblospio benedicti Webster, and the oligochaetes Thalassodrilides gurwitschi Cook, T. belli Hrabe, and an enchytraeid. All but Neanthes are new records for the Sea. Benthic crustacean species are the amphipods Gammarus mucronatus Say, Corophium louisianum Shoemaker, and the barnacle Balanus amphitrite Darwin. Neanthes succinea is the dominant infaunal species on the Sea bottom at depths of 2–12 m. Area-weighted estimates of N. succinea standing stock in September and November 1999 were two orders of magnitude lower than biomass estimated in the same months in 1956. During 1999, population density varied spatially and temporally. Abundance declined greatly in offshore sediments at depths >2 m during spring and summer due to decreasing oxygen levels at the sediment surface, eventually resulting in the absence of Neanthes from all offshore sites >2 m between July and November. In contrast, on shoreline rocky substrate, Neanthes persisted year round, and biomass density increased nearly one order of magnitude between January and November. The rocky shoreline had the highest numbers of invertebrates per unit area, exceeding those reported by other published sources for Neanthes, Gammarus mucronatus, Corophium louisianum, and Balanus amphitrite in marine coastal habitats. The rocky shoreline habitat is highly productive, and is an important refuge during periods of seasonal anoxia for Neanthes and for the other invertebrates that also serve as prey for fish and birds.     

Possible importance of algal toxins in the Salton Sea, California

In response to wildlife mortality including unexplained eared grebe (Podiceps nigricollis) die-off events in 1992 and 1994 and other mortality events including large fish kills, a survey was conducted for the presence of algal toxins in the Salton Sea. Goals of this survey were to determine if and when algal toxins are present in the Salton Sea and to describe the phytoplankton composition during those times. A total of 29 samples was collected for toxicity analysis from both nearshore and midlake sites visited biweekly from January to December 1999. Dinoflagellates and diatoms dominated most samples, but some were dominated by a prymnesiophyte (Pleurochrysis pseudoroscoffensis) or a raphidophyte (Chattonella marina). Several types of blooms were observed and sampled. The dinoflagellate Gyrodinium uncatenum formed an extensive, dense (up to 310000 cells ml^–1) and long-lasting bloom during the winter in 1999. A coccolithophorid, Pleurochrysis pseudoroscoffensis, occurred at high densities in surface films and nearshore areas during the spring and summer of 1999. These surface films also contained high densities of one or two other species (an unidentified scrippsielloid, Heterocapsa niei, Chattonella marina). Localized blooms were also observed in the Salton Sea. An unknown small dinoflagellate reached high densities (110000 cells ml^–1) inside Varner Harbor, and an unidentified species of Gymnodinium formed a dense (270000 cells ml^–1) band along part of the southern shoreline during the summer. Three species known to produce toxins in other systems were found. Protoceratium reticulatum (=Gonyaulax grindleyi) and Chattonella marina were found in several samples taken during summer months, and Prorocentrum minimum was found in low densities in several samples. Extracts of most samples, including those containing known toxic species, showed a low level (<10% mortality across all concentrations) of activity in the brine shrimp lethality assay and were not considered toxic. All sample extracts tested in the mouse bioassay showed no activity. One sample extract taken from the bloom of the small dinoflagellate was highly active (100% mortality across all concentrations) in the brine shrimp lethality assay, but the active material could not be isolated. While dense algal blooms are common at the Salton Sea, no evidence gathered in this study suggests that algal toxins are present within phytoplankton cells; however, toxins actively excreted by cells may have been missed. Blooms of phytoplankton likely contribute to wildlife mortality at the Salton Sea. Possible mechanisms including intoxication due to ingestion of feathers in grebes and waterlogging caused by changes in surface tension are discussed.     

Flagellate Cryptobia branchialis (Bodonida: Kinetoplastida), ectoparasite of tilapia from the Salton Sea

An infestation of young tilapia, Oreochromis mossambicus Peters, by the flagellate Cryptobia branchialiswas observed at the Salton Sea, California, in September, 1997. This is the first report of C. branchialis in a highly saline water-body (43 g l^–1). Ultrastructure of C. branchialis as well as its effect on the gills of tilapia were studied using the scanning and transmission electron microscopy. No direct effect of C. branchialis on the epithelial cells of fish gills was observed. However, alterations of gill general structure, such as deposition of copious mucus on the gill surface, swelling of filaments, reduction of respiratory lamellae and their transformation into short club-shaped structures were found in infected fish. This suggests mortality of young tilapia may arise from decreased gill function in response to Cryptobia infestation.     

Naked amoebae (Protozoa) of the Salton Sea, California

The Salton Sea is an inland lake in California with an average salinity of ca. 44 g l^–1. This productive water body, which supports substantial fish and migratory bird populations, is under threat because of increasing salinity levels. The present study was the first to examine the naked amoeboid protozoa of the Salton Sea and provide a first estimate of their numerical importance. Over a six-month sampling period (June–December, 1999), 45 different morphospecies (considered to be species) of amoebae were isolated. Wherever possible, isolates were identified to species or genus using diagnostic features recognizable by light microscopy. For each isolate, illustrations and brief notes on the diagnostic characters used in the identifications are given. These will allow this paper to be used as an identification guide to amoebae of the Salton Sea in future studies. Of the 45 taxa, around 18 of the isolates (i.e. 40%) are probably new to Science. Preliminary counts, based on enrichment cultivation methods, showed that amoebae in shoreline waters ranged from 14560 to 237120 cells l^–1 (mean 117312 ± 86075 S.D.). The ecological importance of high numbers and high diversity of amoebae is unknown. But it should be noted that several of the amoebae were actively grazing cyanobacterial and algal filaments and filaments of the bacterium Beggiatoa. Others were predominately associated with suspended particulates. As such, amoebae may be important in the cycling of carbon and nutrients in the Salton Sea.     

Long-term changes in the phosphorus loading to and trophic state of the Salton Sea,California

The Salton Sea (Sea) is a eutrophic to hypereutrophic lake characterized by high nutrient concentrations, low water clarity, and high biological productivity. Based on dissolved phosphorus (P) and nitrogen (N) concentrations and N:P ratios, P is typically the limiting nutrient in the Sea and, therefore, should be the primary nutrient of concern when considering management efforts. Flows in the major tributaries to the Sea have been measured since 1965, whereas total P (TP) concentrations were only measured intermittently by various agencies since 1968. These data were used to estimate annual P loading from 1965 to 2002. Annual loads have increased steadily from ∼940,000 kg around 1968 to ∼1,450,000 kg in 2002 (∼55% increase), primarily a result of increased TP concentrations and loads in the New River. Although the eutrophic condition of the Salton Sea is of great concern, only limited nutrient data are available for the Sea. It is difficult to determine whether the eutrophic state of the Sea has degraded or possibly even improved slightly in response to the change in P loading because of variability in the data and changes in the sampling and analytical methodologies. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005