THE INFLUENCE OF RIPARIAN AND HYPORHEIC ZONES ON THE HYDROLOGY AND BIOGEOCHEMICAL RESPONSES IN A STREAM

The stream-riparian-aquifer interface plays a major role in the regional flow of nutrients and contaminants due to a strong physical-chemical gradient that promotes the transformation, retention, elimination or release of biogenic elements. To better understand the effects of the near-stream zones on stream biogeochemistry, we conducted a field experiment on a small groundwater-fed stream located in the rare Charitable Research Reserve, Cambridge, Ontario, Canada. This study focused on monitoring the spatial distributions of nutrient elements in the riparian and hyphoreic zones. Several piezometer nests were installed near stream to obtain data on the groundwater flow system and the samples were taken bi-weekly from May-November 2013. In addition to piezometer groundwater sampling, a series of passive (diffusion) water samplers, known as peepers, were installed along longitudinal and lateral transects centered on the stream. The water samples were analyzed for a suite of inorganic nutrients including; DOC, DIC, SiO₂, NO₃^-, SO₄^2-, NH_3, Mg²⁺, Ca²⁺ and PO₄^3-. The spatial and temporal variation in surface water and groundwater chemistry (carbon, nutrients) was observed between locations. From the headwater to the stream outlet the surface water pH, DO and conductivity consistently increased. Notably, groundwater flow patterns along the stream resulted in distinctly different groundwater types and associated nitrate concentrations. The groundwater nitrate concentrations varied from <0.0081 to 1.1 mmol and the surface water nitrate values varied from 0.070 to 0.97 mmol.