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Impacts of Land Use on Mercury in Urban Stormwater RunoffEPA Grant Number: F07B20467
Title: Impacts of Land Use on Mercury in Urban Stormwater Runoff
Investigators: Creswell, Joel
Institution: University of Wisconsin - Madison
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2007 through January 1, 2010
RFA: STAR Graduate Fellowships (2007) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Chemistry , Mercury , Academic Fellowships
Mercury is a pollutant that poses a serious threat to human and ecosystem health. It is present in the atmosphere worldwide in measurable concentrations, primarily as a result of human activities such as coal burning and waste incineration. The primary pathway of human exposure to mercury is through the consumption of contaminated fish, therefore, understanding the process of mercury transport from atmospheric to aquatic systems is important to the protection of human health. Several recent studies suggest that urban areas are sites of high mercury input to aquatic systems. This is due both to a high density of emissions sources and a high percentage of impervious surface area, which generates stormwater runoff into lakes and streams. The aim of this study is to investigate the impacts of different types of urban land use and land cover on mercury pollution in stormwater runoff, and to determine if stormwater management measures, such as green roofs, retention ponds, and rainwater gardens, have a positive or negative effect on the problem. This issue will be investigated in areas close to mercury-emitting point sources as well as in areas that are not near any point sources.
Samples will be collected in the city of Milwaukee, WI, at points where overland flow or storm sewer effluent is discharged into a stream or lake. Sites will be chosen within watersheds that encompass a wide variety of land use types and stormwater management measures. At each site, water will be collected from the stream or lake under dry and rainy conditions, and surface runoff will be collected during rainy weather. In addition, treated effluent from Milwaukee’s Jones Island wastewater treatment plant will be collected both when it is treating only sanitary sewage, as well as when it is treating water from the combined sanitary and storm sewer systems. The concentrations and chemical forms of mercury will be determined in all of these samples, as well as a number of other physical parameters, in order to determine the differences in mercury contributions between each watershed. Samples of wet- and dry-deposited material on all sites will also be collected and analyzed for mercury species. Using Geographic Information Systems (GIS) software and existing datasets, the relative contribution of different land use types and stormwater management areas to the surface area of each watershed will be computed. Using statistical methods to examine the correlations between the geographic and chemical data, the extent to which mercury concentrations are predicted by land use will be estimated.
It is expected that the watersheds with higher percentages of impervious surface cover and fewer stormwater control measures will exhibit the highest concentrations of mercury in stormwater runoff, while those with less impervious cover and/or more stormwater control will have less mercury. Higher overall concentrations of mercury, especially reactive forms of mercury, are likely to be seen in areas close to emissions point sources. The treated wastewater effluent from the combined storm and sanitary sewer system will most likely contain the highest levels of organic species of mercury, due to its high organic matter content and the fact that it travels through deep, possibly anoxic pipes, before reaching the treatment plant.