Response in the water quality of the Salton Sea,California, to changes in phosphorus loading: an empirical modeling approach

Salton Sea, California, like many other lakes, has become eutrophic because of excessive nutrient loading, primarily phosphorus (P). A Total Maximum Daily Load (TMDL) is being prepared for P to reduce the input of P to the Sea. In order to better understand how P-load reductions should affect the average annual water quality of this terminal saline lake, three different eutrophication programs (BATHTUB, WiLMS, and the Seepage Lake Model) were applied. After verifying that specific empirical models within these programs were applicable to this saline lake, each model was calibrated using water-quality and nutrient-loading data for 1999 and then used to simulate the effects of specific P-load reductions. Model simulations indicate that a 50% decrease in external P loading would decrease near-surface total phosphorus concentrations (TP) by 25–50%. Application of other empirical models demonstrated that this decrease in loading should decrease near-surface chlorophyll a concentrations (Chl a) by 17–63% and increase Secchi depths (SD) by 38–97%. The wide range in estimated responses in Chl a and SD were primarily caused by uncertainty in how non-algal turbidity would respond to P-load reductions. If only the models most applicable to the Salton Sea are considered, a 70–90% P-load reduction is required for the Sea to be classified as moderately eutrophic (trophic state index of 55). These models simulate steady-state conditions in the Sea; therefore, it is difficult to ascertain how long it would take for the simulated changes to occur after load reductions. 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.     

Laboratory studies on the coprecipitation of phosphate with calcium carbonate in the Salton Sea, California

The Salton Sea is a hypereutrophic, saline lake in the desert of southern California. Like many lakes, the primary productivity of the Sea is limited by phosphorus. However, unlike most lakes, the release of P from the sediments is not controlled by the reductive dissolution of Fe(III)-oxide minerals. Most of the iron in the sediments of the Salton Sea is present as Fe(II)-sulfides and silicates. Rather, the sediments are dominated by calcite which is actively precipitating due to alkalinity production via sulfate reduction reactions. We hypothesized that calcite could be an important sink for phosphorus released from the decomposing organic matter. In this work we evaluated the potential for phosphate to coprecipitate with calcite formed in simulated Salton Sea sediment pore water. At calcite precipitation levels and P concentrations typical for the Salton Sea pore water, coprecipitation of P removed 82–100% of the dissolved phosphorus. The amount of P incorporated into the calcite was independent of temperature. The results of this work indicate that the internal loading of P within the Salton Sea is being controlled by calcite precipitation. Management of external P loading should have an immediate impact on reducing algae blooms in the Salton Sea. 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     

Organochlorine pesticides, polychlorinated biphenyls, metals, and trace elements in waterbird eggs, Salton Sea, California, 2004

The Salton Sea is a highly eutrophic, hypersaline terminal lake that receives inflows primarily from agricultural drainages in the Imperial and Coachella valleys. Impending reductions in water inflow at Salton Sea may concentrate existing contaminants which have been a concern for many years, and result in higher exposure to birds. Thus, waterbird eggs were collected and analyzed in 2004 and compared with residue concentrations from earlier years; these data provide a base for future comparisons. Eggs from four waterbird species (black-crowned night-heron [Nycticorax nycticorax], great egret [Ardea alba], black-necked stilt [Himantopus mexicanus], and American avocet [Recurvirostra Americana]) were collected. Eggs were analyzed for organochlorine pesticides, polychlorinated biphenyls (PCBs), metals, and trace elements, with current results compared to those reported for eggs collected from the same species and others during 1985–1993. The two contaminants of primary concern were p,p′-DDE (DDE) and selenium. DDE concentrations in night-heron and great egret eggs collected from the northwest corner of Salton Sea (Whitewater River delta) decreased 91 and 95%, respectively, by 2004, with a concomitant increase in eggshell thickness for both species. Decreases in bird egg DDE levels paralleled those in tissues of tilapia (Oreochromis mossambicus × O. urolepis), an important prey species for herons and egrets. Despite most nests of night-herons and great egrets failing in 2004 due to predation, predicted reproductive effects based on DDE concentrations in eggs were low or negligible for these species. The 2004 DDE findings were in dramatic contrast to those in the past decade, and included an 81% decrease in black-necked stilt eggs, although concentrations were lower historically than those reported in night-herons and egrets. Selenium concentrations in black-necked stilt eggs from the southeast corner of Salton Sea (Davis Road) were similar in 1993 and 2004, with 4.5–7.6% of the clutches estimated to be selenium impaired during both time periods. Because of present selenium concentrations and future reduced water inflow, the stilt population is of special concern. Between 1992 and 1993 and 2004 selenium in night-heron and great egret eggs from the Whitewater River delta at the north end of the Sea decreased by 81 and 55%, respectively. None of the night-heron or egret eggs collected in 2004 contained selenium concentrations above the lowest reported effect concentration (6.0 μg/g dw). Reasons for selenium decreases in night-heron and egret eggs are unknown. Other contaminants evaluated in 2004 were all below known effect concentrations. However, in spite of generally low contaminant levels in 2004, the nesting populations of night-herons and great egrets at Salton Sea were greatly reduced from earlier years and snowy egrets (Egretta thula) were not found nesting. Other factors that include predation, reduced water level, diminished roost and nest sites, increased salinity, eutrophication, and reduced fish populations can certainly influence avian populations. Future monitoring, to validate predicted responses by birds, other organisms, and contaminant loadings associated with reduced water inflows, together with adaptive management should be the operational framework at the Salton Sea. 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     

Barnacle growth rate on artificial substrate in the Salton Sea,California

The Salton Sea is one of the few saline, inland lakes in the world with a population of barnacles, Balanus amphitrite. It is also one of California’s most impaired water bodies due to excessive nutrient loading which leads to phytoplankton blooms and low dissolved oxygen. Currently, B. amphitrite growth is limited due to lack of hard substrate in and around the Sea. We have hypothesized that artificial substrate could support the growth of B. amphitrite and their filter-feeding would lead to improved water quality. Periodic harvesting of the barnacles would result in the permanent removal of nitrogen and phosphorus from the Sea. A 44-day in-situ experiment was carried out in the Salton Sea to assess the rate of barnacle growth and phosphorus and nitrogen sequestration on burlap sheets suspended vertically from a floating line. Burlap panels were collected weekly and the barnacles analyzed for Ca, total-P, inorganic-P, total-N, total-C, CaCO₃, and organic matter content. After 44 days of growth, the barnacle mats weighed 7.4 kg m⁻² on a dry weight basis, with 80% of the mass as shell material. The nutrient sequestration was 9.4 g P m⁻² and 100 g N m⁻². Approximately half of the P was inorganic and appears to be coprecipitated with the calcium carbonate shell material. Results indicate that harvesting barnacles grown on artificial substrate in the Salton Sea would not be an effective method for removing N or P from the lake because of the relative proportions of shell material and organic material. 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     

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.     

Spatial and temporal variability of internal and external phosphorus loads in Mona Lake,Michigan

A study was conducted in Mona Lake, a small eutrophic lake located in western Michigan (USA) to address the temporal and spatial variability of external and internal phosphorus loading. External P load varied among subbasins, which was mostly related to discharge, but also to land use. Black Creek, which drains lands with natural cover and agriculture, accounted for the majority of flow, and total phosphorus (TP) and soluble reactive phosphorus (SRP) load, to Mona Lake. However, the relative contribution of SRP load was greater in Little Black Creek, which flows through a mostly urbanized subbasin, than in Black Creek. The relative importance of internal loading was strongly related to season, as internal TP loads contributed only ∼9% of the overall P load in April 2005, but ∼68–82% of the overall P load in the summer and early fall seasons. Internal TP and SRP loading was greater under anaerobic than aerobic conditions. Mean anaerobic TP release rates ranged from 0.80 to 15.56 mg P m⁻² d⁻¹, varying with site and season. Spatial variability in both internal phosphorus loading and sediment P concentration was also evident. By taking into account the spatial and temporal variability of different loading sources, management practices can be targeted to optimize nutrient source control strategies.     

Fundamentals of estimating the net benefits of ecosystem preservation: the case of the Salton Sea

This article, both theoretical and methodological in nature, argues the potential merits of using a net benefits’ framework as a tool to aid policy makers in their efforts to compare Salton Sea restoration alternatives and inform the public as to the potential magnitude and distribution of trade-offs associated with each alternative. A net benefits’ approach can provide a more accurate comparison and evaluation of the potential net returns from public spending on Salton Sea restoration than what would be provided under the suggested criteria of current legislative mandates. Furthermore, a net benefits’ framework provides a more lucid and systematic accounting framework by which to enumerate the full array of benefits and costs of each alternative for policy analysis. Finally, net benefits’ analysis serves to add transparency to the decision-making process so that the public gains an understanding of how its scarce resources, including both financial and natural capital, are being appropriated. Additionally, we illustrate and emphasize the importance of estimating the non-market values associated with many of the ecosystem services provided by the Salton Sea and describe the major techniques that do so. 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     

Chemical evolution of the Salton Sea, California: nutrient and selenium dynamics

The Salton Sea is a 1000-km² terminal lake located in the desert area of southeastern California. This saline (44000 mg l^–1 dissolved solids) lake started as fresh water in 1905–07 by accidental flooding of the Colorado River, and it is maintained by agricultural runoff of irrigation water diverted from the Colorado River. The Salton Sea and surrounding wetlands have recently acquired substantial ecological importance because of the death of large numbers of birds and fish, and the establishment of a program to restore the health of the Sea. In this report, we present new data on the salinity and concentration of selected chemicals in the Salton Sea water, porewater and sediments, emphasizing the constituents of concern: nutrients (N and P), Se and salinity. Chemical profiles from a Salton Sea core estimated to have a sedimentation rate of 2.3 mm yr^–1 show increasing concentrations of OC, N, and P in younger sediment that are believed to reflect increasing eutrophication of the lake. Porewater profiles from two locations in the Sea show that diffusion from bottom sediment is only a minor source of nutrients to the overlying water as compared to irrigation water inputs. Although loss of N and Se by microbial-mediated volatilization is possible, comparison of selected element concentrations in river inputs and water and sediments from the Salton Sea indicates that most of the N (from fertilizer) and virtually all of the Se (delivered in irrigation water from the Colorado River) discharged to the Sea still reside within its bottom sediment. Laboratory simulation on mixtures of sediment and water from the Salton Sea suggest that sediment is a potential source of N and Se to the water column under aerobic conditions. Hence, it is important that any engineered changes made to the Salton Sea for remediation or for transfer of water out of the basin do not result in remobilization of nutrients and Se from the bottom sediment into the overlying water.     

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.     

A linked hydrodynamic and water quality model for the Salton Sea

A linked hydrodynamic and water quality model was developed and applied to the Salton Sea. The hydrodynamic component is based on the one-dimensional numerical model, DLM. The water quality model is based on a new conceptual model for nutrient cycling in the Sea, and simulates temperature, total suspended sediment concentration, nutrient concentrations, including and DO concentration and chlorophyll a concentration as functions of depth and time. Existing water temperature data from 1997 were used to verify that the model could accurately represent the onset and breakup of thermal stratification. 1999 is the only year with a near-complete dataset for water quality variables for the Salton Sea. The linked hydrodynamic and water quality model was run for 1999, and by adjustment of rate coefficients and other water quality parameters, a good match with the data was obtained. In this article, the model is fully described and the model results for reductions in external phosphorus load on chlorophyll a distribution are presented. 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     

Evaluation of potential impacts of perchlorate in the Colorado River on the Salton Sea,California

Ammonium perchlorate, a component of rocket fuel, entered Lake Mead through drainage and shallow groundwater in the Las Vegas Valley, Nevada, and is now found in the lower Colorado River from Lake Mead to the international boundary with Mexico. Perchlorate is a threat to human health through reduction of thyroid hormone production. Perchlorate has been found in water throughout the lower Colorado system and in crops in the California’s Imperial Valley, as well as in several other states, but it has not previously been included in investigations of the Salton Sea. Because perchlorate behaves conservatively in the Colorado River, it was postulated that it could be accumulating at high levels along with other salts in the Salton Sea. Results show that perchlorate is not accumulating in the Sea, although it is present in tributaries to the Sea at levels similar to those found in the Colorado River. Bacterial reduction of perchlorate is the most likely explanation for the observed results. The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 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     

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     

Role of the polychaete <Emphasis Type="Italic">Neanthes succinea</Emphasis> in phosphorus regeneration from sediments in the Salton Sea,California

The Salton Sea currently suffers from several well-documented water quality problems associated with high nutrient loading. However, the importance of phosphorus regeneration from sediments has not been established. Sediment phosphorus regeneration rates may be affected by benthic macroinvertebrate activity (e.g. bioturbation and excretion). The polychaete Neanthes succinea (Frey and Leuckart) is the dominant benthic macroinvertebrate in the Salton Sea. It is widely distributed during periods of mixing (winter and spring), and inhabits only shallow water areas following development of anoxia in summer. The contribution of N. succinea to sediment phosphorus regeneration was investigated using laboratory incubations of cores under lake temperatures and dissolved oxygen concentrations typical of the Salton Sea. Regeneration rates of soluble reactive phosphorus (SRP) were lowest (−0.23–1.03 mg P m⁻² day⁻¹) under saturated oxygen conditions, and highest (1.23–4.67 mg P m⁻² day⁻¹) under reduced oxygen levels. N. succinea most likely stimulated phosphorus regeneration under reduced oxygen levels via increased burrow ventilation rates. Phosphorus excretion rates by N. succinea were 60–70% more rapid under reduced oxygen levels than under saturated or hypoxic conditions. SRP accounted for 71–80% of the dissolved phosphorus excreted under all conditions. Whole-lake SRP regeneration rates predicted from N. succinea biomass densities are highest in early spring, when the lake is mixing frequently and mid-lake phytoplankton populations are maximal. Thus, any additional phosphorus regenerated from the sediments at that time has potential for contributing to the overall production of the lake. Guest Editor: John M. Melack Saline Water and their Biota     

Occurrence,distribution and transport of pesticides into the Salton Sea Basin,California, 2001–2002

The Salton Sea is a hypersaline lake located in southeastern California. Concerns over the ecological impacts of sediment quality and potential human exposure to dust emissions from exposed lakebed sediments resulting from anticipated shrinking of shoreline led to a study of pesticide distribution and transport within the Salton Sea Basin, California, in 2001–2002. Three sampling stations—upriver, river mouth, and offshore—were established along each of the three major rivers that discharge into the Salton Sea. Large-volume water samples were collected for analysis of pesticides in water and suspended sediments at the nine sampling stations. Samples of the bottom sediment were also collected at each site for pesticide analysis. Sampling occurred in October 2001, March–April 2002, and October 2002, coinciding with the regional fall and spring peaks in pesticide use in the heavily agricultural watershed. Fourteen current-use pesticides were detected in water and the majority of dissolved concentrations ranged from the limits of detection to 151 ng/l. Diazinon, EPTC and malathion were detected at much higher concentrations (940–3,830 ng/l) at the New and Alamo River upriver and near-shore stations. Concentrations of carbaryl, dacthal, diazinon, and EPTC were higher in the two fall sampling periods, whereas concentrations of atrazine, carbofuran, and trifluralin were higher during the spring, which matched seasonal use patterns of these pesticides. Current-use pesticides were also detected on suspended and bed sediments in concentrations ranging from detection limits to 106 ng/g. Chlorpyrifos, dacthal, EPTC, trifluralin, and DDE were the most frequently detected pesticides on sediments from all three rivers. The number of detections and concentrations of suspended sediment-associated pesticides were often similar for the river upriver and near-shore sites, consistent with downstream transport of pesticides via suspended sediment. While detectable suspended sediment pesticide concentrations were more sporadic than detected aqueous concentrations, seasonal trends were similar to those for dissolved concentrations. Generally, the pesticides detected on suspended sediments were the same as those on the bed sediments, and concentrations were similar, especially at the Alamo River upriver site. With a few exceptions, pesticides were not detected in suspended or bed sediments from the off-shore sites. The partitioning of pesticides between water and sediment was not predictable from solely the physical–chemical properties of individual pesticide compounds, but appear to be a complicated function of the quantity of pesticide applied in the watershed, residence time of sediments in the water, and compound solubility and hydrophobicity. Sediment concentrations of most pesticides were found to be 100–1,000 times lower than the low-effects levels determined in human health risk assessment studies. However, maximum concentrations of chlorpyrifos on suspended sediments were approximately half the low-effects level, suggesting the need for further sediment characterization of lake sediments proximate to riverine inputs. 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     

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.     

Eutrophication of the Dutch Wadden Sea: External nutrient loadings of the Marsdiep and Vliestroom basin

The increasing P and N content in the two main tidal basins in the western Dutch Wadden Sea, the Marsdiep and the Vliestroom basin, has been reconstructed from the 50s onwards. The area is enriched with nutrients by two sources both originating from the river Rhine, one being the discharge from Lake IJssel and the other the exchange with the coastal zone of the North Sea. Due to a buffering by Lake IJssel for about 15–20 years, the eutrophication of the western Wadden Sea showed a time lag compared with the continuously increasing nutrient concentrations in the river Rhine and the coastal zone of the North Sea. At present, the primary production in part of the area still seems to be nutrient limited in summer, while loadings have already been decreasing in recent years. So far, no severe, negative effects on the ecosystem have been reported. Some remarks are made on the eutrophication in other parts of the Dutch' Wadden Sea in relation to the hydrographic characteristics of these areas. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988) Publication No. 18 of the project “Ecological Research of the North Sea and Wadden Sea” (EON)     

A northern Italian shallow lake as a case study for eutrophication control

Lake Varese (northern Italy) has shown deterioration in water quality since the 1960s and, as a result of the long duration of direct discharge of untreated sewage into the lake, it was classified as being hypertrophic. To recover the lake water quality, a series of externally and internally remedial actions were implemented in subsequent years. The applied sewage collecting system induced a reduction of the external P loads from 50 t P year⁻¹ to 16t P year⁻¹ and the weighted mean annual TP concentration decreased from 352 μg P l⁻¹ to 85 μg P l⁻¹, typical of eutrophic conditions. The hypolimnetic water withdrawals, adopted in the years 2000–2003, allowed a reduction of the internal P loads of about 3–5 t P. In the same years, 500t O₂ were injected at depths of 4.5–8 m during the summer months. In spite of these internal remedial actions, no significant reduction of the weighted mean annual concentration of the TP could be observed, and during the summer stratification period no significant reduction of the volumes of anoxic water and of the duration of the anoxia were detected. The anoxic conditions are still the prevailing force driving the lake P-budget, maintaining the lake in eutrophic status.     

STRUCTURE, COMPOSITION AND BIOGENESIS OF PRASINOPHYTE SCALES

The species composition of phytoflagellates in the Salton Sea has recently been the subject of intense investigation as part of an analysis of the Salton Sea ecosystem. The Salton Sea, an inland sea occupying 980 km² in southern California, has become a major stopping point for migratory birds along the Pacific Flyway. The increasing salinity of the sea, currently at 44 gm L⁻¹, and its eutrophic condition (average depth is nine meters, with a high nutrient load contributed by agricultural drainage from the surrounding farmlands) have contributed to a stressed ecosystem. Massive fish kills and bird kills, including such endangered birds as the brown pelican, have become a recurring problem. Although previous investigations have noted the presence of at least two phytoflagellates implicated in fish mortality, little attention has been paid the to the identities of the smaller flagellates observed growing in the sea and their possible contribution to the fish and bird population mortality. Using freshly collected field samples as well as enrichment culture techniques, we report the occurrence of several genera of cryptomonads in the Salton Sea, including representatives from the genera Chroomonas , Hemiselmis , Leucocryptos , Plagioselmis , Storeatula and Teleaulax.     

PHYTOFLAGELLATES OF THE SALTON SEA: CRYPTOPHYCEAE

The species composition of phytoflagellates in the Salton Sea has recently been the subject of intense investigation as part of an analysis of the Salton Sea ecosystem. The Salton Sea, an inland sea occupying 980 km² in southern California, has become a major stopping point for migratory birds along the Pacific Flyway. The increasing salinity of the sea, currently at 44 gm L^?1, and its eutrophic condition (average depth is nine meters, with a high nutrient load contributed by agricultural drainage from the surrounding farmlands) have contributed to a stressed ecosystem. Massive fish kills and bird kills, including such endangered birds as the brown pelican, have become a recurring problem. Although previous investigations have noted the presence of at least two phytoflagellates implicated in fish mortality, little attention has been paid the to the identities of the smaller flagellates observed growing in the sea and their possible contribution to the fish and bird population mortality. Using freshly collected field samples as well as enrichment culture techniques, we report the occurrence of several genera of cryptomonads in the Salton Sea, including representatives from the genera Chroomonas, Hemiselmis, Leucocryptos, Plagioselmis, Storeatula and Teleaulax.