Water-Resources Investigations Report 03-4251
In January 2002, the U.S. Geological Survey began a study to collect water-quality and habitat-assessment data at 50 sites located in the Mississippi River Alluvial Plain. Forty-three sites in northwestern Mississippi and seven sites in eastern Arkansas were sampled during winter and summer 2002. Water-quality analyses included physical-property measurements, nitrogen and phosphorus species, chlorophyll-a, and chloride. Water-quality data collected during this study compared well to data collected for ongoing studies located in the study area and collected by similar sampling techniques.
Statistical analyses were performed to determine whether the water-quality and/or habitat-assessment data could be used to detect ranges in stream conditions for the sampled sites. These analyses compared the data sets based on sample index period, site location, drainage-area size, and subjectively evaluated stream conditions (sites that were considered to have good or poor water quality and habitat). Of the water-quality data analyzed, turbidity was the most practical in indicating ranges in stream conditions among the sites sampled. Habitat-assessment total scores were similarly practical.
The statistical results were also evaluated to determine the value of data analysis by category. Sample index period and site location categories provided the strongest results. For example, the mean turbidity value for northwestern Mississippi sites sampled during the winter index period (213 NTU) was about three times the mean turbidity value for the summer index period (68 NTU). The median turbidity value for the eastern Arkansas sites (17 NTU) was about one-fifth the median value for the northwestern Mississippi sites (89 NTU). Drainage-area size and subjectively evaluated stream conditions were the weakest categories with respect to statistical results. None of the comparisons were statistically significant for water-quality or habitat-assessment data from northwestern Mississippi sites categorized as good to data from sites categorized as poor.
First posted May 21, 2010
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Rebich, R.A., Welch, H.L., and Coupe, R.H., 2004, Evaluation of water-quality and habitat assessment data to determine ranges in stream conditions in the Mississippi River alluvial plain of northwestern Mississippi and eastern Arkansas: U.S. Geological Survey Water-Resources Investigations Report 03-4251, 47 p.
WATER-QUALITY AND HABITAT-ASSESSMENT DATA SUMMARIES
RESULTS OF STATISTICAL ANALYSIS