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Mapping the biological condition of USA rivers and streams
Citation:
Hill, R., M. Weber, S. Leibowitz, AND Tony Olsen. Mapping the biological condition of USA rivers and streams. Society for Freshwater Science, Milwaukee, WI, May 17 - 21, 2015.
Impact/Purpose:
We will present a model that predicts the probable (pr) biological condition (BC) of ~5.4 million km of streams within the conterminous USA. We developed this model to aid the USEPA’s Office of Water in understanding how BC varies spatially and the anthropogenic stressors associated with poor BC. A spatially explicit map of stream resources and their prBC would provide a powerful tool for the USEPA Office of Water to prioritize sampling, monitoring, and restoration. To model BC, we linked 1,883 streams that were previously determined by the EPA’s National Rivers and Stream Assessment to be in ‘good’ or ‘poor’ condition to a spatially extensive dataset of watershed-level landscape metrics. This dataset contains a suite of natural (e.g., climate, geology, soils) and anthropogenic (e.g., urbanization, agriculture, dams) watershed features and is linked a pre-existing geospatial framework (National Hydrography Dataset Plus version 2; NHDPlusV2). Random forest modeling correctly classified 70% of sites as being in good or poor BC. prBC was best predicted by 3 natural (elevation, air temperature, and sand content of soils) and 4 human-altered (% riparian naturalness, population density, and % of watershed composed of forest cover or agriculture) landscape metrics. We then applied the model to the ~2.7 million NHDPlusV2 catchments. The USA-wide map of prBC provided a unique way to assess model performance. Large-scale patterns of prBC were consistent with human-related land use. However, patterns of local prBC were sometimes unrealistic. The maps will help to guide future modeling and suggest that regional models may be more appropriate than a single, national-scale model. This presentation will introduce the spatially extensive GIS database and our model of USA-wide BC to scientists and managers at one of the premier conferences in stream ecology.
Description:
We predicted the probable (pr) biological condition (BC) of ~5.4 million km of stream within the conterminous USA (CONUS). National maps of prBC could provide an important tool for prioritizing monitoring and restoration of streams. The USEPA uses a spatially balanced survey design to estimate the proportion of streams that fail to support healthy BC, but does not infer BC at un-sampled locations. To model BC, we developed a GIS database of >100 anthropogenic and natural watershed metrics for streams within the CONUS. We combined these data with 1,883 USEPA-sampled streams that were previously assessed as having ‘good’ or ‘poor’ BC. prBC was best predicted (70% correctly classified) with random forest modeling using elevation, % riparian naturalness, population density, air temperature, watershed % forest and % agriculture as predictors. National maps of prBC provided a unique assessment of model performance. Specifically, lower prBC was consistent with large-scale patterns of human-related land use. However, local prBC was sometimes unrealistic, suggesting that predictions could be improved with regional, rather than national, models. Models will soon be extended to also include 356,044 lakes.