8017 - Laserfiche WebLink

Home Browse Search

The Recovery Program participants are we77 aware of the potenti al hazard of selenium to the endangered fishes as well as other organisms and authorized studies to determine the levels that may be hazardous to the endangered fishes. Selenium, a nonmeta77ic element, is essential in normal animal nutrition but levels not far above that needed in diets may produce toxic effects in animals (Lemly and Smith 1987). In the Upper Colorado River Basin, relatively high selenium concentrations have been found in tributaries draining Mancos shale formations (Stanford and Ward 1986). Selenium chemistry is complex because it exists in various chemical forms that differ with respect to toxicity (Eisler 1985; Jacobs 1989). Human activities related to irrigated agriculture contribute the largest environmental input of selenium that are above natural background levels in aquatic systems (Maier and Knight 1994). The selenium level in the reach of the Upper Colorado River upstream' from the diversion dam barriers is low (about 2 micrograms per liter of water) and should not adversely affect the endangered fishes. However, selenium concentrations were high in the Gunnison and Uncompahgre rivers -- up to 10 micrograms per liter of water in the Gunnison River and up to 34 micrograms per liter in the Uncompahgre River (Butler et al. 1991). Lemly (1993) stated that "Waterborne selenium concentrations of 2 micrograms per liter. or greater (i.e., parts per billion; total recoverable basis in 0.45 micron filtered samples) should be considered hazardous to the health and long-term survival of fish and wildlife populations due to the high potential for food-chain bioaccumulation, dietary toxicity, and reproductive effects." The endangered fishes evolved in an ecosystem where the marine Mancos shale contain high levels of selenium. Therefore, these fishes may have developed a tolerance for high selenium levels. The sensitivity of the endangered fishes to various chemical forms of selenium may not be constant for the different life stages. At the present time, the toxic levels of selenium to the endangered fishes remains unknown. Ongoing studies by Recovery Program participants have been designed to determine selenium toxicity to these fishes. Selenium concentrations in the Upper Colorado River are at the 2 micrograms per liter where potential adverse impacts could occur (Lemly 1993) to the endangered fish. However, augmentation of streamflows from reservoir releases for the endangered fishes through the Recovery Program will help to dilute selenium concentrations. Not only should this effort help the endangered fishes but other animals win also benefit from selenium reductions in the Upper Basin -- including humans. The selenium levels in some floodplain ponds is high because high levels of selenium from irrigation return flows is concentrated even further. It is beneficial to leave floodplain ponds with high selenium levels fishless because bioaccumulation of selenium could result in adverse impacts to any animals that may eat the fish such as fish-eating birds. 32