CONTROLS ON SELENIUM DISTRIBUTION IN WETLAND SEDIMENT, BENTON LAKE, MONTANA

The distribution of selenium in sediment in Benton Lake is mainly cont rolled by the location of the dissolved selenium inputs. Selenium conc entrations in sediment decrease along how paths downgradient within th e wetland system. Construction in 1961 of a pump station to increase w ater supply and dikes to facilitate water management, along with curre nt water management, has increased the rate of selenium accumulation i n sediments as compared to the pre-1961 natural lake. Agricultural pra ctices (alternate crop/fallow rotation) in the non-irrigated farm land of the seleniferous Benton Lake basin also have increased selenium lo ading to Benton Lake. Carbon content is an important factor affecting selenium distribution in sediment but this relationship is greatly aff ected by dissolved selenium inputs. Amelioration of selenium contamina tion in Benton Lake will require a combination of land and water manag ement modifications. Within the wetland system, minimizing the duratio n of inlet-perennial ponds would minimize selenium accumulation and in crease the life of the refuge.