Date of Graduation

Spring 2005

Degree

Master of Science in Geospatial Sciences

Department

Geography, Geology and Planning

Committee Chair

Robert Pavlowsky

Keywords

mercury, fluvial sediments, Wilson Creek, Springfield, urban pollution

Subject Categories

Hydrology | Sedimentology

Abstract

Mercury (Hg) is a pollutant affecting aquatic environments and human health world wide. Sediments in urban streams can store Hg from historical industrial waste releases in channel and floodplain deposits. Subsequent erosion of these deposits can remobilize sediment-bound Hg impacting downstream receiving waters. This study describes the distribution of Hg in floodplain and channel sediments of Wilson Creek and its tributaries using geochemical sediment analysis and cesium-137 dating. The upper Wilson Creek watershed drains the southern two-thirds of Springfield, Missouri. Results indicate that Hg concentrations in overbank and active channel sediments along the entire stream length are elevated above the mean background level of 20 ppb measured in pre-settlement overbank deposits. Background Hg levels are possibly associated with organic and iron content in these deposits. Historically-contaminated post-settlement overbank deposits are ~ 1 m thick with sedimentation rates ranging from 0.5 to 1 cm per year. In the upper watershed, these deposits have Hg contamination deep in the overbank profile. Mercury stored in these deposits serves as a nonpoint source to channel sediments as indicated by a contamination trend originating within the historical industrial center. This trend reaches a peak concentration of 1,240 ppb Hg downstream of a closed waste water treatment plant and landfill site. In the lower watershed, historically contaminated sediment combines with recent mercury releases to produce a second trend characteristic of both nonpoint and point source releases. This trend reaches 1,940 ppb Hg downstream of two municipal utility facilities. Surface to stream karst connections complicate source identification in the lower watershed. Even with current reductions in the use and emission of mercury, historically contaminated sediment stored within the Wilson Creek watershed may be a source of Hg to receiving waters for decades to centuries.

Copyright

© Willard E. Rodgers II

Open Access

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