2006 BES Annual Meeting Presentation and Poster Abstracts
Mercury dynamics in an urban watershed ecosystem
Co-Authors: Joseph T. Bushey, Peter M. Groffman, Charles T. Driscoll, Gary T. Fisher
Abstract: Metal cycling within an ecosystem is affected by land use. However, studies concerning urban/suburban ecosystems are limited, as watershed cycling studies for low-level mercury (Hg) have focused on non-urban, remote ecosystems. In this study, we investigated the effects of urban land use on watershed Hg loading in a series of nested, increasingly-urbanized watersheds centered on the Gwynns Falls watershed (Baltimore, MD). Samples were collected monthly, without targeting specific flow conditions, and were analyzed for total Hg (THg), methyl Hg (MeHg) and ancillary water quality characteristics. THg and MeHg concentrations varied from 0.17-207 ng/L (mean ± SD, 4.5 ± 1.2) and 0.01-5.5 ng/L (0.10 ± 0.03), respectively. Somewhat surprisingly, Hg concentrations and fluxes in urban and suburban watersheds were lower than those in a forested reference watershed during base flow conditions. Changes in carbon cycling associated with urbanization appear to have altered the tight coupling among dissolved organic carbon, THg, and MeHg dynamics that strongly influences watershed Hg exports from forested ecosystems. Within the urban and suburban watersheds studied, Hg concentrations and fluxes increased with the intensity of urbanization, suggesting that urbanization supplies additional sources of Hg within the watershed. Urban and suburban land use change thus alters both the sources and dynamics of Hg in complex ways.