A LABORATORY EVALUATION OF TRACE-ELEMENT MOBILITY FROM FLOODING AND NUTRIENT LOADING OF COEUR-DALENE RIVER SEDIMENTS

The main stem (MSCDR) and south fork (SFCDR) of the Coeur d'Alene Rive r, Idaho, are contaminated with heavy metals from many years of mining , To assess the potential impacts of flooding on water quality in the river system, contaminants in undisturbed sediments were subjected to selective extraction, and their rates of release measured in simulated laboratory flooding experiments. To simulate flooding, 18 columns wer e constructed allowing the sediment-water interfere to be monitored fo r pH, E-h, and dissolved concentrations of As, Fe, Mn, Ph, and Zn, The se columns were subjected to four types of treatments, The first two i nvolved overlaying the columns with N-2(g)- or air-purged river water, whereas the latter two involved overlaying sediment columns with N-2( g)- or sir-purged river water amended with C and N. Treatment with una mended river water resulted in the immediate release of Zn at an avera ge concentration of 10.4 mg L-1 from sediment taken along the MSCDR at Cataldo, ID. Treatment with either oxic or anoxic river water amended with glucose and N resulted in an order of magnitude increase in sedi ment microbial density, These biotic changes correlated with fivefold to 100-fold increases in the release of trace elements into the aqueou s phase, Our results suggest that heavy metal loading of Haters in the Coeur d'Alene system occurs not only as a result of the resuspension of particulate matter, but also;Is a result of transformations that ar e either directly or indirectly mediated by sediment microbiota. Undis turbed sediments currently situated in the riverbanks of the MSCDR and SFCDR have the capacity to release contaminants into the river system during flooding. This release could be dramatically enhanced by incre ased nutrient levels into the CDA river system.