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Dietborne bioavailability of copper from cobble coatings in a mining-influenced stream: the effect of organism (L. stagnalis) mass on reverse isotope labeling measurements
Murphy, Jill K.
Murphy, Jill K.
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2018
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Abstract
The legacy impacts of hardrock mining are complex and difficult to fully mitigate. Though the detrimental effects of hardrock mining on environmental quality have been extensively researched, there is a paucity of data documenting the temporal responses of mining influenced waterways (MIW) to remediation efforts. In an effort to bridge this information gap, I examined the bioavailablity of copper (Cu) present in armored metal-oxyhydroxide cobble coatings collected before and after the completion of a high-density-sludge lime treatment plant on the North Fork of Clear Creek (NFCC) in Black Hawk, Gilpin County, Colorado. Using an innovative reverse-labeling stable-isotope method developed by U.S. Geological Survey researchers, I calculated Cu assimilation efficiency (AE) in freshwater snails (Lymnaea stagnalis) that were fed cobble-coating particles. Although Cu bioavailability did not differ significantly between pre- and post-remediation metal-oxyhydroxide particles (~34% AE), high among-replicate variability resulted in low power to infer statistically significant differences. The use of small organisms (~0.5-5 mg dry tissue weight) in early post-embryonic ontogeny may have contributed to the relatively high variability, which may be related to uncertainty in the estimation of differences in tissue Cu concentrations between exposed and background snails. A novel finding was that background Cu concentrations decreased with increasing size, following the relationship: [^63 Cu]_snail=70.088×M_snail^(-0.628) , where the units for [63Cu]snail are mg 63Cu gsnail-1 and the units for Msnail are mg. These size constraints may have important implications for the planned adaptation of this method to smaller benthic organisms that are more ecologically relevant in high-gradient, montane streams (e.g., the midge Chironomus dilutus). Further work is needed to determine whether organism size, growth rate, or developmental stage is the primary source of among-replicate variability.
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