Environmental water-quality zones for streams: a regional classification scheme.
Various approaches have been used to classify large geographical areas into smaller regions of similar water quality or extrapolate water-quality data from a few streams to other unmonitored streams. A combination of some of the strengths of existing techniques is used to develop a new approach for these purposes. In this new approach, referred to here as SPARTA (SPAtial Regression-Tree Analysis), environmental characteristics for each monitored stream are first quantified using a Geographic Information System (GIS) and then regression-tree analysis is used to determine which characteristics are most statistically important in describing the distribution of a specific water-quality constituent. GIS coverages of only the most statistically significant environmental characteristics are then used to subdivide the area of interest into relatively homogeneous environmental water-quality zones. Results from the regression-tree analysis not only define the most important environmental characteristics, but also describe how to subdivide the coverage of the specific characteristic (for example, areas with <26% or >or=26% soil clay content). The resulting regionalization scheme is customized for each water-quality constituent based on the environmental characteristics most statistically related to that constituent. SPARTA was used to delineate areas of similar phosphorus, nitrogen, and sediment concentrations (by including land-use characteristics) and areas of similar potential water quality (by excluding land-use characteristics). The SPARTA approach reduced the variability in water-quality concentrations (phosphorus, total nitrogen, Kjeldahl nitrogen, and suspended sediment) within similarly classified zones from that obtained using the US Environmental Protection Agency's nutrient ecoregions.
US Geological Survey, 8505 Research Way, Middleton, Wisconsin 53562, USA. dzrobert@usgs.gov
Dale M
DM
Robertson
David A
DA
Saad
D000383:Agriculture; D004784:Environmental Monitoring / Q000379:methods*; D040362:Geographic Information Systems; D010758:Phosphorus / Q000032:analysis; D012016:Reference Values; D012044:Regression Analysis; D014873:Water Pollutants / Q000032:analysis* / Q000145:classification*
D014873:Water Pollutants; D010758:Phosphorus