Environmental Water-Quality Zones for Streams: A Regional Classification Scheme |
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Authors: | DALE M ROBERTSON DAVID A SAAD |
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Institution: | (1) US Geological Survey, 8505 Research Way, Middleton, Wisconsin 53562, USA, US |
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Abstract: | 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 ≥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. |
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Keywords: | : Regionalization Classification Ecoregions Extrapolation Nutrients Regression Tree SPARTA |
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