Document Type

Honors Project On-Campus Access Only

Abstract

Due to their behavior as static, long-lived, filter feeders, freshwater mussels serve as effective proxies of past environments. The sequestration of pollutants and elemental concentrations during the growth of the mussel shell preserves a snapshot of environmental change and anthropogenic influence. Within the Minnesota River Basin, the watersheds of the Cottonwood and Le Sueur rivers exhibit high levels of agricultural influence and anthropogenic alteration, in sharp contrast to the relatively unaltered watershed of the Snake river, within the St. Croix river basin. Here, we utilize the shells of recently deceased freshwater mussels to assess the degree of agricultural impact and habitat alteration within three river systems which varied in their extent of proximal agricultural land use. Using a micro- XRF spectrometer, we analyzed heavy metal bioaccumulation in the shells of freshwater mussels, collected from the Cottonwood, Le Sueur, and Snake rivers. To assess variation in heavy metal presence, the shell nacre was ground and homogenized. Significant differences in the concentrations of manganese (Mn), strontium (Sr), and iron (Fe) were observed in shells between these three rivers. Divergence of the environmental chemistry across these river systems indicates variation in environmental conditions, specifically levels of primary productivity, temperature, and suspended sediment. Though some of these factors may be explained by the underlying geology or system structure, differences can predominantly be attributed to varying effects of agriculturally driven environmental change.

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