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 perta ining to off-site disposal methods. Migratory waterfowl and other wildlife can become reliant on such ponds, which can present biological hazards depe nding on the chemicals they receive. This study examined the algae, inverte brates, and chemistry of two large, hypersaline, industrial wastewater pond s near Phoenix, Arizona, at which waterfowl die-offs (primarily eared grebe s, Podiceps nigricollis) were reported. The objectives were to determine wh at attracted birds to the ponds and whether the ponds were directly respons ible for bird deaths. High levels of total salts and nitrate were detected in both ponds, but selenium (16 to 41 mu g/L) was the only potentially toxi c element that reached levels of concern in the water column. Dominant alga e were diatoms, Chaetoceros sp. and Nitzschia frustrulum (Krutz.) Grun. (up to 6.5 X 10(5) cells/mL), and cyanobacteria, Synechococcus Nageli 1849 (up to 8.8 x 10(6) cells/mL). These are normal components of hypersaline ponds and natural salt lakes. However, Chaetoceros levels were negatively correl ated with salinity levels in the ponds and a species turnover is expected a s 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 we re the primary attractant of birds; they were harvested by numerous residen t and migratory waterfowl. Selenium levels in brine shrimp (2 to 10 mg/kg) were above recommended levels for food chain organisms in aquatic ecosystem s but were well below levels that can cause acute toxicity. Brine shrimp fe d to zebra danios fish (Brachydanio refio) in a bioassay were nontoxic. As at other locations where grebe mortality events have been reported in recen t Fears, the cause of death of birds visiting these evaporation ponds is un known. Therefore, it is concluded that these ponds may not be directly toxi c to visiting wildlife, but that evaporation ponds such as these are attrac tants for wildlife and may pose a long-term hazard through the accumulation of selenium in the food chain. Zero-discharge evaporation ponds may be use ful as an interim solution to the brine disposal problem but do not represe nt a safe, permanent solution.