Stream incision is the increased erosion of a stream channel from its natural setting and has been shown to lower the water table leading to a variety of adverse affects. Increasing impervious surface in a watershed has been shown to cause stream incision. Previous studies related to stream incision have focused on the hydrology, soil nutrients, or surface water qualities. Groundwater quality has not been examined as extensively with respect to stream incision. This study examines the groundwater quality in relation to the hydrology at a knickpoint, or a small discontinuity in a stream, where incision is found just below the knickpoint. This provides for a control, upstream, and an experimental variable downstream. Dissolved inorganic phosphate (DIP), ferrous iron, ammonium, nitrate and nitrite, and hydrogen sulfide were nutrients measured to access the groundwater quality of the site. All nutrients were expected to have higher concentrations upstream with the exception of nitrate which was expected to be higher downstream. With over 60 monitoring wells installed encompassing both upstream and downstream of the knickpoint, 59 groundwater samples were collected in the same day and tested for their nutrient concentrations. The results showed that there was a significant difference in the nutrient concentrations above the knickpoint versus below it. DIP, ammonium, and ferrous iron had higher concentrations further upstream of the knickpoint and a much lower concentration downstream. Hydrogen sulfide however demonstrated the opposite, with higher concentrations downstream versus lower amounts upstream. Nitrate and nitrite were not found in either group. The results imply that all groundwater was anoxic and that other factors affected by stream incision may cause the difference in nutrient concentrations, such as change in vegetation. With urbanization continually expanding, understanding the effects of stream incision will become more critical to ecological studies, resource management, and future planned developments.
For additional documentation Logan Reid provided a PowerPoint Presentation entitled "The Effects of Stream Incision on Groundwater Quality in a Riparian Zone" provided here in PDF form.