Relationship of nitrogen discharge to land use on Rhode River [USA] watersheds
1980
Correll, D.L. | Dixon, D. (Smithsonian Inst., Edgewater, MD (USA). Chesapeake Bay Center for Environmental Studies)
Eight Rhode River subwatersheds were monitored with flow volume-integrating apparatus for area yield discharge of total nitrogen, total Kjeldahl nitrogen and nitrate nitrogen. Land use data for each subwatershed were also estimated from aerial photographs and ground truth surveys. Regression analyses of area yield discharge for the year versus percent managed land (row crops + pasture + residential) have high (R('2) = 0.65-0.68) correlations for all three nitrogen parameters. Correlations were relatively high for nitrate nitrogen in each season; however, little relationship was found between percent disturbed land and total Kjeldahl nitrogen in the spring. Correlations were higher in five variable multiple linear regressions utilizing four land use categories. Nitrate nitrogen had a strong correlation with percent row crops, the highest correlation being in the winter and the lowest in the fall. Total Kjeldahl nitrogen had a high correlation with row crops in the summer when this form of nitrogen was discharged at high rates. Variations in percentages of four land use categories were sufficient to explain 98 per cent of the variation between watersheds in dischages of total nitrogen for the year. High percentages of the variability in discharge of Kjeldahl and of nitrate nitrogen between watersheds were also explainable by land use variation for the year and for most season-parameter combinations. A second set of multiple linear regressions utilizing basin characteristics related to transport mechanisms resulted in generally similar coefficients of determination for all three parameters.
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