HIGH-RESOLUTION TEMPORAL VARIABILITY OF NUTRIENT AND SUSPENDED SOLIDS CONCENTRATIONS AND LOADS FROM SEQUENTIAL RUNOFF EVENTS IN THE LITTLE CHAZY RIVER WATERSHED IN NORTHEASTERN NEW YORK

High-resolution temporal sampling for nitrate-N, soluble reactive phosphorus (SRP), total phosphorus and total suspended solids (TSS) through three sequential runoff events in October 2010 provided insights into the fate and transport of nutrients from agricultural lands in the Little Chazy River watershed in northeastern New York. The runoff events were generated by rainfalls of 63.0mm (30 Sep. to 2 Oct.), 25.4mm (6–8 Oct.) and 48.8mm (14–17 Oct.) and resulted in stormflow volumes of 1.34 hm³, 1.01 hm³ and 2.37 hm³, respectively. These runoff volumes were estimated using the Linsley equation to estimate the end of stormflow runoff and correspond to 14.6%, 27.4% and 32.8% of the rainfall volume for each event. The successive increase in percent of stormflow runoff with each event probably relates to increased soil moisture content in the basin. At least two full days of baseflow recession separated the stormflow events, during which little or no additional rainfall occurred. The samples were collected at a U.S. Geological Survey gaging station near Chazy where the river empties into Lake Champlain. Sampling intervals ranged from 3-4 hours during the rainfall events to about 1 day during periods of baseflow recession.

Nutrient concentrations rose sharply during rainfall events, varied closely with rainfall intensity and fell to background levels shortly after the stormflow peak. More than 50% of the stormflow nutrient load was exported from the basin prior to the stormflow peak in all three events, with two events exporting more than 60% of their nutrient loads prior to the peak discharge. Suspended solids loads generally were more closely related to stormflow discharges. The nitrate-N concentration in stormflow for the third event (6–8 Oct.) fell to background levels below those of the two previous events indicating depletion of soil nitrate sources. Total phosphorus and soluble reactive phosphorus did not show similar source-depletion effects. Collectively, these data indicate that nutrient concentrations and loads are more closely related to rainfall characteristics (frequency, intensity and duration) than to stormflow discharge.