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Department of Geological Sciences, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-7216
* Corresponding author (dbm3{at}po.cwru.edu)
Received for publication August 12, 2000. Trends in climatic variables, streamflow, agricultural practices, and loads of nutrients and suspended solids were estimated for 19761995 in the Maumee and Sandusky watersheds, two large agricultural basins draining to Lake Erie. To understand the contributions that various factors may have made to the trends in loads, earlier results of models linking loads to explanatory variables were combined with estimated trends in those variables. The study period was characterized by increases in temperature, wintertime precipitation and streamflow, conservation farming, and loads of nitrate and total suspended solids; decreases in snowfall and snow cover, fertilizer, manure from livestock, and loads of soluble reactive phosphorus; and relatively steady exports of total phosphorus. After removing the effects of trends in streamflow, nitrate loads increased much less while total suspended solids and total phosphorus loads declined. The analysis suggests that the nitrate increases were due largely to climatic factors, particularly increases in winter streamflow, decreases in snowfall and snow cover, and declining annual precipitation. Decreases in soluble reactive phosphorus were associated with changes in agricultural practices, particularly declines in fertilizer deliveries and head of livestock.
Abbreviations: CRP, Conservation Reserve Program NO2+3, nitrate plus nitrite SRP, soluble reactive phosphorus TP, total phosphorus TSS, total suspended solids
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