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Riparian forest degradation alters energy base of headwater stream food webs.
England, Laura*,1, Rosemond, Amy1, 1 University of Georgia, Athens, GA
ABSTRACT- Riparian forests drive a multitude of physical, chemical, and biological dimensions of aquatic ecosystems. Terrestrial carbon inputs from riparian forests support food webs of forested headwater streams. However, human encroachment has converted many riparian forests to narrow, discontinuous corridors of vegetation along streams, which are also impacted by land uses within the catchment. This study assessed the impact of such riparian degradation on the terrestrial dependence of aquatic food webs in headwater streams of the Upper Chattahoochee River, Georgia, USA. GIS techniques were used to classify 1999 color-infrared aerial photographs of study watersheds, and subsequent assessments of riparian degradation were made. Carbon isotope ratios were used to determine the relative importance of terrestrial carbon versus in-stream primary production in supporting aquatic food webs. Basal food resources (algae, leaf litter, fine benthic organic matter, and seston), omnivores (crayfish), and top predators (benthic insectivorous fish) were collected and analyzed for 13C. Basal resource 13C values did not vary with riparian degradation. However, crayfish and benthic insectivore 13C values showed significant enrichment with riparian degradation, such that biota 13C diverged from leaf litter 13C with increasing riparian degradation. These enrichment trends show a decreasing reliance of headwater stream food webs on terrestrial carbon with increasing riparian degradation. The integrity of river systems, which depend on intact headwater food webs, may be compromised by reductions in width, continuity and extent of riparian forests.
KEY WORDS: riparian deforestation, stable carbon isotopes, aquatic food webs, land use