RELATIONSHIP BETWEEN NITRATE PROCESSING AND VARIABILITY IN THE VOLUME OF THE HYPORHEIC ZONE

Due to the increased use of nitrogen-rich fertilizers over the last century, the quality of aquatic systems has been significantly degraded. Maintaining and improving surface water quality is contingent on understanding nitrogen dynamics in stream and associated hyporheic zone systems. The goal of this research is to determine how variations in the extent of the hyporheic zone affect nitrate loss within a stream system. Water samples were taken from a Western New York stream from May 2013 through September 2013, while pressure transducers monitored stream stage. In addition to surface water, samples were taken at points 10 cm, 30 cm, 50 cm, 70 cm and 100 cm below the streambed throughout a 255 m reach of stream. Samples were analyzed for major anions, nitrate, dissolved oxygen, pH, and specific conductance. These measurements allow us to quantify net nitrate discharge and [NO₃] patterns relative to a more conservative anion, each of which can indicate nitrate loss. Initial results suggest both seasonal and storm related expansion-contraction cycles in the hyporheic zone. Large storm events result in hyporheic expansion with concomitant declines in nitrate and tracer concentrations at depth suggesting dilution. However, nitrate concentrations also illustrate seasonal patterns at certain locations, decreasing over time. The latter result corresponds with the observed expansion of the hyporheic zone over the study period. At certain locations, patterns in DO and sulfate concentrations suggest that the decline in nitrate concentrations could be an effect of denitrification in groundwater.