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MODELING MERCURY DYNAMICS IN STREAM SYSTEMS WITH WASP7: CHARACTERIZING PROCESSES CONTROLLING SHORT AND LONG TERM RESPONSE
Citation:
WOOL, T. A., R. B. AMBROSE, AND C. D. KNIGHTES. MODELING MERCURY DYNAMICS IN STREAM SYSTEMS WITH WASP7: CHARACTERIZING PROCESSES CONTROLLING SHORT AND LONG TERM RESPONSE. Presented at Eighth International Conference on Mercury as a Global Pollutant, Madison, WI, August 06 - 11, 2006.
Impact/Purpose:
The objective of this task is to develop, support and transfer a wide variety of tools and mathematical models that can be used to support watershed and water quality protection programs in support of OW, OSWER, and the Regions.
Description:
Mercury transport through stream ecosystems is driven by a complicated set of transport and transformation reactions operating on a variety of scales in the atmosphere, landscape, surface water, and biota. Riverine systems typically have short residence times and can experience large fluctuations in flow, depth, and velocity. Rivers are intimately connected to their drainage basins from which they receive both pollutant loads and dilution water. Important components of a riverine mercury modeling system include the upland watershed through the flood plains, riparian wetlands, the drainage network, and the underlying sediments. WASP7 is a dynamic, mass balance framework for modeling contaminant transport and fate in surface water systems. The WASP7 mercury module simulates Hg0, Hg(II), and MeHg, as well as silt, sand, and particulate organic matter. Linkage is provided through external files from watershed loading models, including WCS and GBMM, and to aquatic food web models, including BASS. The relative importance of watershed loading, in-stream transport, and mercury transformation processes in controlling short and long-term mercury response is investigated in a case study of mercury fate in Brier Creek, Georgia. WASP7 first simulated long-term mercury buildup in the sediment layers. Finer scale simulations were then run, calculating mercury dynamics under current conditions. Model parameters were calibrated to available water column and sediment mercury data, and sensitivity analyses were conducted to determine the key parameters and forcing functions controlling short and long-term mercury fate in this stream. This case study provides a realistic example of the capabilities and limitations of stream mercury simulations. Data needs to support WASP7 applications to mercury dynamics in riverine ecosystems are itemized, and a collaborative monitoring, process science, and model development program is recommended.