2011 S3: Noah Jansen-Yee

Food webs and rivers: Importance of floodplain connectivity

In recent years, ecological research in the study of trophic interactions between contiguous ecosystems and microhabitats has begun to develop; however, this topic remains not entirely understood.  These interactions are important because they contribute to healthy ecosystem structure and function.  The focus of this project was to more fully understand and document the dynamic interactions and flow of energy between stream and riparian zones in both a wetland and a cedar (Cedrus spp.) dominated reach.  We hypothesized the base of the aquatic food web would be autotrophic in the wetlands with energy derived mainly from in-stream processes; whereas the cedar-dominated reach would be more heterotrophic due to riparian shading and limited sunlight.  In this reach, energy that sustains the food web should be largely derived from riparian leaf litter inputs.  Because leaf litter enters the stream in the fall, there is a time delay (termed a reciprocal subsidy) such that energy transfers between stream and riparian zones are asynchronous.  We predicted that there would be a stronger energy flux in the cedar reach due to the increased area conferred by the larger and more complex tree structure relative to the wetlands.  We are using stable isotopes of carbon and nitrogen to measure food web structure and to estimate energy transfer rates.  In addition, we are measuring organic matter content of various trophic levels, comparing phosphorous uptake rates and spiraling, and comparing physical habitat between reaches.  Finally, we have conducted extensive sampling of aquatic macrophytes, macroinvertebrates, and fish.  Preliminary results indicate that the cedar reach has more tree cover and significantly higher amounts of leaf litter, with more diverse and abundant macroinvertebrate and fish communities compared to the wetland reach.  Two possible explanations for this include (i) high leaf liter inputs provide significant energy to the stream, and/or (ii) increased tree-fall into the stream has increased physical habitat complexity.  Further results and details are being analyzed as sample processing is still being completed.

Faculty Mentor: Eric Snyder, Biology


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