Monday, May 26, 2008 - 9:15 AM
12

Stream food web responses to watershed land use

Brian Helms and Jack W. Feminella. Biological Sciences, Auburn University, Auburn, AL 36849

In 2006, we examined the role of watershed land use / land cover on stream food webs in the Lower Piedmont ecoregion, near the city of Columbus, GA, USA.  We quantified elements of food web structure in 12 small streams varying in degree of watershed disturbance from urbanization and pasture using stable C and N isotope signatures of food web components (fishes, amphibians, macroinvertebrates, producers, organic matter).  Overall N signatures (δ15N), particularly those of fishes, were more enriched with increasing anthropogenic disturbance as evidenced by negative relationships between δ15N and  % of watershed as forest cover (% forest). Similarly, C signatures (δ13C) also decreased with increasing % forest and were highly enriched in urban watersheds.  Overall food chain length was highest in heavily forested watersheds and was significantly correlated with in-stream habitat quality scores.  Further, mean trophic position in study food webs increased with % forest and decreased with increased spate flow frequency.  Not surprisingly, food chain length and mean trophic position were both positively correlated with overall species richness.  Our results suggest that, through alterations of instream physicochemical conditions, agriculture and urbanization cause predictable shifts in basal resources, size, and structure of food webs across this landscape.

 



Web Page: urbanization, agriculture, disturbance

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