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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. [ABSTRACT FROM AUTHOR]

The primary productivity of the Salton Sea, California is excessively high, leading to low-oxygen conditions, low clarity, and odors associated with algal decomposition. Treating the inflow water with aluminum sulfate (alum) to remove soluble phosphorus (P), the limiting nutrient, is being considered to improve water quality. The objective of this study was to evaluate the use of alum to remove dissolved phosphorus from New River water, and the potential for the Al-bound P to be released into the Salton Sea. The New River is dominated by agricultural wastewater and has a salinity somewhat higher than normally encountered for alum treatment (total dissolved solids = 2,300 mg l−1), thus, evaluation of alum’s effectiveness is needed. In addition, alum may be dosed directly into the New River and the floc allowed to flow into the Salton Sea if the precipitated P is stable in Salton Sea water. In this study, we evaluated the potential for floc-bound P to be desorbed in Salton Sea water, which has an unusually high salinity (46 g l−1). Aluminum at a 5-mg l−1 dose was effective in removing over 90% of the soluble phosphorus from the New River water. However, when the alum floc was added to Salton Sea water, up to 100% of the Al-bound P was released into the Sea water due to desorption, dissolution, and recrystallization of the alum floc. These results indicate that treatment of agricultural drainage water to reduce P-loading can be effective if the alum floc is settled and not allowed to enter the saline Salton Sea. In addition to alum costs, estimated at US$13 million year−1, settling basin construction and maintenance for floc removal would be required. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article presents a study which states that inflow to the Salton Sea in California, is predominately nutrient-rich agricultural wastewater, which has led to eutrophication. The watershed generates $1.3 billion in agricultural commodities per year. Alum and/or polyacrylamide (PAM) are commonly used in municipal wastewater treatment to remove phosphorus and solids, and then the sludge is collected and disposed. The charge of the polymer and the type of suspended solids in the wastewater influence the degree of flocculation and settling rate. Cationic polymers directly adsorb to the negative surfaces of the clay particles, anionic polymers adsorb through cation-bridging, and nonionic polymers form floc by attaching to the clay surfaces through van der Waals forces. Turbidity reductions were measured in the jar tests to determine the removal efficiency of phosphorus-laden sediment in the tributaries. The PAM treatments resulted in turbidity measurements lower than the control throughout the experiment, showing the PAM was capable of settling suspended solids at higher speeds.

Constructed evaporation ponds are being utilized for disposal of saline subsurface drainage waters in San Joaquin Valley, California. These terminal evaporation ponds are located in hydrologically closed basins and/or regions with no surface drainage out of the valley. The saline drainwaters disposed into the ponds are sodium-sulfate or sodium-sulfate-chloride type waters and upon desiccation produces mirabilite and halite. The drainwaters contain excessive levels of trace elements from geochemical origins. The trace element of most concern, is selenium because it bioaccumulates in the aquatic food chain and causes death and deformity of waterbirds attracted to the pond environment. At the present, the only economic drainwater disposal option in the southern. portion of the valley is evaporation ponds. The operation of these ponds is heavily regulated by waste discharge requirements to reduce and mitigate wildlife impacts. A case study on evaporation ponds and bird usage from a drainage district illustrates the extensive monitoring and mitigation required. The prognosis is evaporation basins will be needed for the foreseeable future unless breakthroughs occur in economic and effective drainwater treatment and drainwater reuse options. [ABSTRACT FROM AUTHOR]

Effective and economical removal of selenium (Se) in agricultural drainage water is very important in Se bioremediation. Zero-valent iron (ZVI) and a redox mediator [anthraquinone-2,6-disulfonate (AQDS)] were assessed for their ability to enhance the removal of Se(VI) or Se(IV) (500 microg/L) in synthetic drainage water by Enterobacter taylorae. The results showed that E. taylorae was capable of using inexpensive sucrose to remove Se from the drainage water. During a 7-day experiment, Se(VI) was almost entirely reduced to Se(0) and transformed to organic Se in the drainage water with sucrose levels of 500 to 1000 mg/L. Addition of ZVI to the drainage water increased the removal of total soluble Se to 94.5-96.5% and limited the production of organic Se. Addition of AQDS to the drainage water with or without ZVI decreased Se(VI) removal, but enhanced the removal of Se(IV), suggesting that E. taylorae only can use anthrahydroquinone-2,6-disulfonate (AHQDS, a reduced form of AQDS) to respire Se(IV), and not Se(VI). These results show that ZVI has promising application potential in the bioremediation of Se in Se-contaminated water.

External loading of phosphorus (P) from agricultural surface discharge (tailwater) is the main cause of excessive algae growth and the eutrophication of the Salton Sea, California. Continuous polyacrylamide (PAM) applications to agricultural irrigation water inflows were evaluated as a means of reducing sediment and P in tailwater. Zero (control) and 1 mg L(-1) PAM (PAM1) treatments were compared at 17 Imperial Valley field sites. Five and 10 mg L(-1) PAM treatments (PAM5, PAM10) were conducted at one site. The particulate phosphorus (Pp) fraction was determined as the difference between total phosphorus (Pt) and the soluble phosphorus (Ps) fraction. We observed 73, 82, and 98% turbidity reduction with PAM1, PAM5, and PAM10 treatments. Although eight field sites had control tailwater sediment concentrations above the New River total maximum daily loads (TMDL), all but one were made compliant during their paired PAM1 treatments. While PAM1 and PAM10 reduced tail water Pp by 31 and 78%, none of the treatments tested reduced Ps. This may have been caused by high irrigation water Na concentrations which would reduce Ca adsorption and Ca-phosphate bridging on the PAM. The PAM1 treatments resulted in <0.5 mg L(-1) drain water polyacrylamide concentrations 1.6 km downstream of PAM addition, while PAM5 and PAM10 treatments produced > 2 mg L(-1) drain water polyacrylamide concentrations. We concluded that, although PAM practically eliminates Imperial Valley tailwater sediment loads, it does not effectively reduce tailwater Ps, the P fraction most responsible for the eutrophication of the Salton Sea.