Citation:

TSIROS, I. X., R. B. AMBROSE, AND C. D. KNIGHTES. CHALLENGES AND SUCCESSES MODELING THE INFLUENCES OF LAND USE CHANGES ON MERCURY DYNAMICS. 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:

Linked sets of atmospheric, watershed, water body, and food web models and supporting data are required to evaluate the effectiveness of proposals to regulate atmospheric mercury emissions. Simulating mercury dynamics in watersheds is a key step linking changes in atmospheric deposition with changes in stream loading rates. This step is challenged by uncertainties in mercury fate process descriptions, incomplete empirical datasets, and gaps in simulation technology. Case studies indicate that land use and vegetative cover strongly influence mercury accumulation and subsequent runoff and erosion loading rates. Land use changes, then, significantly complicate long-term hind casts and forecasts of watershed mercury fate. A small number of field-scale and watershed-scale models have been developed and applied to watershed mercury cycling, including WARMF, WCS-Mercury, GBMM, and GLEAMS-Hg. The loading, transport, and transformation processes controlling mercury cycling through watersheds are summarized, and their implementation in this set of simulation models is reviewed. Uncertainties and differences in process descriptions are highlighted, and areas of convergence are noted. Most of these watershed mercury cycling processes are strongly affected by land use and vegetative cover. Simple example calculations of mercury accumulation and delivery rates are provided for different land use scenarios. In particular, disturbed and impervious surfaces should more efficiently deliver mercury deposited from the atmosphere. Modeling case studies are reviewed to highlight the relative contributions of different land uses on watershed loading rates. Calculations of watershed mercury loading rates under changing land use patterns are presented. These calculations are suggestive, but highly uncertain. Given present uncertainties, watershed models can be used to bound the timing and extent of load reductions following changes in mercury deposition rates, and to explore factors that might complicate the watershed response. Additional watershed mercury data would help to constrain model calibrations somewhat, giving more accurate runoff and loading calculations. To reduce predictive uncertainties, however, better descriptions of processes controlling mercury transport and fate processes are needed.

Record Details: