The U.S. Geological Survey is leading a nutrient criteria study of 46
streams in Pennsylvania, Maryland, Virginia and West Virginia. Sampling
took place during the summers of 2004 and 2005 and a subset of these data
was used for this study to test the hypothesis that the direct in-stream
response of primary productivity can be predicted by phosphorus and
nitrogen supply rates and light levels. The best results of a bivariate
linear regression analysis of the 2 years of data found gross primary
productivity to have a strong correlation with the supply rate of total
nitrogen (r²=0.42), total phosphorus (r²=0.74) and light (r²=0.51). A
multivariate stepwise regression analysis with the same parameters yielded
a stronger correlation (r²=0.88). This study suggests that for shallow
flowing waters, primary productivity shows a better correlation with
nutrient supply rates instead of nutrient concentrations that doesn't take
into account the effects of stream discharge and channel surface area.