INFLUENCE OF A CHANGING HYPORHEIC ZONE ON STREAM NITRATE LOSS

Understanding nitrogen dynamics in aquatic systems is crucial to maintain and improve surface waters. Over the last century, the quality of these systems has been degraded, primarily by the continuous and increased use of nitrogen-rich fertilizers in agriculture. An understanding of the variety of influences on nitrogen processing within a stream can provide insight into how to remediate as well as protect surface water systems.

The goal of this research is to investigate the effects of variations in the extent of the hyporheic zone on nitrate loss within stream systems. We hypothesize that as the extent of the hyporheic zone decreases, the total nitrate loss within the system will also decrease. Weekly water samples were taken from a Western New York stream, from May 2013 through September 2013, while pressure transducers monitored stream stage continuously. Samples were taken from the surface water as well as at points 10 cm, 30 cm, 50 cm, 70 cm and 100 cm below the streambed. Groundwater samples were also taken from monitoring wells on site. Preliminary analyses of tracer test and geochemical data show that hyporheic mixing and the extent (depth and volume) of the hyporheic zone are correlated with stream stage. Samples were analyzed for major anions, nitrate, dissolved oxygen, pH, and specific conductance. These combined measurements will allow us to quantify net nitrate discharge, which acts as an indicator of nitrate loss within the system. Initial results of nitrate analyses show that surface waters have average nitrate concentrations equal to roughly half the average concentration of groundwater (13 mg/L). Additionally, surface water nitrate concentrations are diluted as stream stage increases.