Selenium in Water Management Wetlands in the Semi-arid West

The discovery in 1983 of deformities, reproductive failures, and high waterfowl mortality rates at Kesterson National Wildlife Refuge, western San Joaquin Valley, Calif., due to selenium (Se) -contaminated drainage water, raised concerns that these problems may be occurring in the >600 wetlands and National Wildlife Refuges being utilized to collect irrigation drainage waste water in 17 western states. The waterfowl problems were traced to ingestion of organic Se present as Se-amino acids. Plants assimilate soluble Se into Se-amino acids and release them upon decomposition. Aerobic plant residue decomposition studies showed that 50% of the assimilated Se was mineralized to soluble Se, while the remaining organic Se persisted. This means that each growth cycle results in a steady decrease of soluble Se and an increase in organic Se levels. To test the effect of plant growth on Se accumulation, two types of evaporation ponds were evaluated, one with prolific plant growth, and the second relatively devoid of plant growth. Soil Se analysis showed that plant growth dramatically increased Se accumulation in the surface layers. Evaluation of additional Se-contaminated sites showed that Se accumulation followed an exponential function and accumulated rapidly above a 2% soil organic C content. Without plant growth, the Se remains mobile and diffuses to low concentrations in the underlying soil, suggesting that plant residue cycling is an important factor in Se accumulation and toxicity.

Waterfowl mortality caused by Cyathocotyle bushiensis Khan, 1962 (Trematoda: Cyathocotylidae), St. Lawrence River, Quebec

In St. Lawrence River marshes, fatal sporadic and epizootic typhlitis in breeding populations of black ducks, Anas rubripes; blue-winged teal, A. discors; and migrant green-winged teal, A. carolinensis, is attributed to Cyathocotyle bushiensis Khan, 1962. This is the first report of C. bushiensis in natural definitive hosts, and the first record of the genus Cyathocotyle in North America. Pathogenicity of C. bushiensis was confirmed experimentally by using metacercariae from the most abundant local gastropod, Bythinia tentaculata, to produce cyathocotyliasis in Pekin ducklings.