State Water Resources Research Institute Program

Project ID: 2007ID72B
Title: Wetlands as Sinks for Metal(loid)s in Mining-contaminated Coeur d'Alene Basin Soils
Project Type: Research
Start Date: 3/01/2007
End Date: 6/30/2008
Congressional District: First
Focus Categories: Geochemical Processes, Wetlands, Water Quality
Keywords: Metals, mine tailings, mine contamination
Principal Investigator: Morra, Matthew
Federal Funds: $ 14,686
Non-Federal Matching Funds: $ 32,653
Abstract: Mining activities within the Coeur d'Alene (CDA) Basin have resulted in large areas of metal contamination far beyond the designated Bunker Hill Mining and Metallurgical Superfund Site, contaminating the CDA River and CDA Lake. It will be impossible to remove and dispose of contaminated sediments within the CDA Basin and Lake CDA, and thus management decisions that protect the environment and human health are required. Our recent investigations indicate that continuously reduced sediments of ponds located in CDA River flooplain tailings contain soluble metal(loid) concentrations far less than similarly contaminated lake sediments experiencing active redox cycling. Analyses of plant tissues obtained from aquatic macrophytes within these ponds have confirmed that this stable redox environment decreases metal(loid) bioavailability. However, in preliminary investigations we observed that seasonal redox changes occurring in surrounding agricultural fields appear to mobilize metal(loid)s such that pond waters experience severe contaminant inputs during the spring. We propose that ponds strategically placed with respect to hydrologic gradients might be used as sinks to sequester metal(loid)s released from contiguous agricultural fields, thus decreasing contaminant mobility and bioavailability. Our objective is to determine the potential for ponds located within the floodplain of the CDA River to act as a sink for Cd, Zn, As, Cu, and Pb mobilized during seasonal changes in soil redox. We will achieve this goal by characterizing changes in soluble metal concentrations in three ponds located in the contaminated floodplain during the course of one calendar year. Total metal(loid) concentrations in the sediment of three contaminated ponds within the Coeur d'Alene Basin will be determined on sediment digests using ICP-AES. Pond waters will be secured on a monthly basis and total metal(loid) concentrations measured using ICP-MS. Our overall goal is to suggest management strategies for contaminated floodplain soils that will decrease the mobility and bioavailability of harmful metal(loid)s. We ultimately wish to 1) determine if wetlands in metal(loid)-contaminated areas can be used as contaminant sinks, 2) delineate spatial and temporal variables that control the extent of metal(loid) sequestration, and 3) elucidate the responsible biogeochemical processes. Studies as proposed here are the first step in determining whether the creation of wetlands might be used to sequester metals, thereby preventing their further dispersal in the environment.

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