The trends of biological and chemical data collected for 12 years (1969-80) from 46 sites in Chester County were evaluated by using the sea- sonal Kendall test. Brillouin's diversity index was calculated and plotted against time for each site. The diversity index at 7 sites had upward trends significant at the 99-percent confidence level, the index at 9 sites had upward trends significant at the 95 to 98 percent confidence level, and the index at 11 sites had upward trends significant at the 90 to 94 percent con- fidence level. Although the trends were not statistically significant, 17 of the remaining sites had upward trends and 2 had downward trends.
The seasonal Kendall test was used to test the chemical data for temporal trends at eight sites having stream discharge data. Significant trends were found at one or more sites for flow-adjusted values of specific conductance, pH, total nitrate, total phosphorus, dissolved chloride, and dissolved sulfate. The chemical data for 11 sites, which were not flow adjusted, were tested for trends by plotting against time and determining a correlation coefficient. Significant trends were found at one or more sites in nitrate and chloride. Selected chemical constituents were tested by regression analysis for correlation with the diversity index. Only total dissolved solids correlated significantly with diversity index. Several suggestions are made to improve the monitoring program.
Additional publication details
USGS Numbered Series
Determination of benthic-invertebrate indices and water-quality trends of selected streams in Chester County, Pennsylvania, 1969-80