Food Chain Organisms in Hypersaline, Industrial Evaporation Ponds
Evaporation ponds are becoming widely used by industry and agriculture for the disposal of brines as a result of increasingly strict regulations pertaining to off-site disposal methods. Migratory waterfowl and other wildlife can become reliant on such ponds, which can present biological hazards depending on the chemicals they receive. This study examined the algae, invertebrates, and chemistry of two large, hypersaline, industrial wastewater ponds near Phoenix, Arizona, at which waterfowl die-offs (primarily eared grebes, Podiceps nigricollis) were reported. The objectives were to determine what attracted birds to the ponds and whether the ponds were directly responsible for bird deaths. High levels of total salts and nitrate were detected in both ponds, but selenium (16 to 41 μg/L) was the only potentially toxic element that reached levels of concern in the water column. Dominant algae were diatoms, Chaetoceros sp. and Nitzschia frustrulum (Kurtz.) Grun. (up to 6.5 × 105 cells/mL), and cyanobacteria. Synechococcus Nageli 1849 (up to 8.8 × 106 cells/mL). These are normal components of hypersaline ponds and natural salt lakes. However, Chaetoceros levels were negatively correlated with salinity levels in the ponds and a species turnover is expected as ponds age. Primary aquatic fauna were Artemia franciscana (brine shrimp), a filter feeder that consumes algae, and Trichocorixa sp. (waterboatman), a carnivorous insect that presumably feeds on brine shrimp. Brine shrimp were the primary attractant of birds; they were harvested by numerous resident and migratory waterfowl. Selenium levels in brine shrimp (2 to 10 mg/kg) were above recommended levels for food chain organisms in aquatic ecosystems but were well below levels that can cause acute toxicity. Brine shrimp fed to zebra danios fish (Brachydanio refio) in a bioassay were nontoxic. As at other locations where grebe mortality events have been reported in recent years, the cause of death of birds visiting these evaporation ponds is unknown. Therefore, it is concluded that these ponds may not be directly toxic to visiting wildlife, but that evaporation ponds such as these are attractants for wildlife and may pose a long-term hazard through the accumulation of selenium in the food chain. Zero-discharge evaporation ponds may be useful as an interim solution to the brine disposal problem but do not represent a safe, permanent solution.
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Document Type: Research Article
Publication date: 1999-07-01
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Water Environment Research (WER) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year. Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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