Date of Defense

4-22-2015

Date of Graduation

5-2015

Department

Geosciences

First Advisor

Carla Koretsky

Second Advisor

Michael Barcelona

Third Advisor

Heather Petcovic

Abstract

Road salt deicers, especially NaCl and CaCl2, are used throughout the world on paved areas during the winter. Previous studies suggest that road salt deicers can alter the biogeochemistry of sediment located near roadways and influence the mobility of heavy metals. The goal of this study is to investigate the influence of CaCl2 on wetland soil biogeochemistry, especially trace metal speciation. Sediment cores were collected in the fall from a freshwater wetland near an urban kettle lake (Asylum Lake, Kalamazoo, MI) and incubated for 100 days in deionized water (control), 5 g/L of CaCl2, or 5 g/L of CaCl2 with approximately 1 ppm each of Cd, Cr(VI), and Pb. At 25 day intervals, two cores were sacrificed from each treatment and pore waters were extracted for analysis of pH, total alkalinity, and dissolved Mn(II), Fe(II), PO4-3, Na, K, Mg, Ca, Pb, Cr(VI), and Cd. The change in percent organic matter in the solid phase was also measured over time. Addition of CaCl2 stimulated a significant growth of microbial mats on the surface of the cores and led to increased Mn(II) and Fe(II) in the pore waters due to anaerobic respiration of Fe(III) and Mn(IV). Siderite, rhodochrosite, calcite, and aragonite were supersaturated in the CaCl2 and may have precipitated, decreasing the alkalinity and pH. This study demonstrates that the use of road salt deicers may have a significant impact on biogeochemical cycling in wetland sediments.

Access Setting

Honors Thesis-Open Access

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