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2004: Variation in Stream Plant Ecology as Related to Hydrological Changes Due to a Migrating Knickpoint

Jeremy Wacksman (Biology)

As previously forested and naturally wild areas are increasingly developed, the amount of impervious surface grows, and as a result there is increased storm water runoff. The result is a phenomenon called channel incision, where the stream channel becomes much deeper in response to the higher velocity and volume of water. Investigations have demonstrated that this has an effect on water table and flooding patterns. In the 2004 Summer Research at the Keck Lab, two Geology students used extensive drilling of wells, stage monitoring, and mapping techniques to create an extensive evaluation of hydrogeological conditions at a stream near the Eastern State Hospital, an urbanized watershed. At the same time, a survey of plant diversity was completed in the floodplain of the stream. The stream has a slowly migrating knickpoint, downstream of which the stream is deeply incised, and above it is a shallow channel which easily floods. The result is a change in water table levels and flooding patterns, which greatly affect herbaceous vegetation. Approximately 200 plots were taken at four different areas along the stream. Herbaceous vegetation was the focus of the study, and was measured using percent cover ratings. In addition, the percent cover of exposed ground and of leaf litter was noted. Results show that there are significant changes in the distribution of certain plant species (Senecio aureus, Microstegium vimineum, Duchesnia indica) as well as in leaf litter, exposed ground, and total herbaceous cover. The areas downstream of the knickpoint, where the stream is incised, tend to be less like wetlands, and more like upland forests. A additional study to see if there is a relationship between woody plant age and incision history has been initiated.

For additional documentation, Jeremy Waxman provided a PowerPoint Presentation entitled "Plant Ecology and Stream Incision," provided here in PDF form.