Groundwater inflow and nutrient status in agricultural streams during summer and winter base flow

Session: Nutrient Sources, Transport, and Internal Cycling (3)

Max Boreux, University of Western Ontario, [email protected]
James Roy, Environment and Climate Change Canada, [email protected]
Adam Yates, University of Western Ontario, [email protected]
Clare Robinson, The University of Western Ontario, Civil & Environmental Eng., [email protected]

Abstract

Nutrient enrichment of surface waters degrades water quality in the Great Lakes and their tributaries, causing the loss of economic and ecological benefits. Current mitigation efforts focus mainly on reducing surface runoff pathways that supply nutrients to adjacent streams while the role of groundwater in delivering nutrients to streams in agricultural areas remains unclear.

This study evaluated the contribution of groundwater inputs on stream nutrient budgets in agricultural landscapes. Two adjacent headwater streams in the upper Thames River watershed, Ontario were surveyed every ~200 m during summer and winter baseflow for groundwater tracers and nutrients. Two stream segments of ~1.5 km were sampled at ~50 m intervals during different weather conditions to evaluate the temporal dynamics of groundwater and nutrient.

Results from summer baseflow conditions showed that groundwater discharge in streams is primarily located in higher permeability terrain with no clear association between groundwater and phosphorus inputs at large scale. The short-term monitoring of stream segments revealed that groundwater discharge and phosphorus inputs were fairly constant during baseflow conditions. Results from the winter baseflow conditions are compared to the summer baseflow findings. This study provides new insights into the pathways phosphorus is delivered to streams in agricultural landscapes.