Assessment of the Effects of Land Use Changes on Lower St. Johns River Basin Watershed Detrital Input (Phase 2). Final Report

摘要

The research conducted from September 2003 to August 2005 addressed the central question of what effects changing land use have played in detrital dynamics of small, headwater tributaries to the lower St. Johns River. The work was subdivided into three major tasks: (1) quantifying detrital inputs along an urban-rural gradient, (2) assessing trophic changes in stream food-webs along an urban-rural gradient and (3) assessing downstream effects of altered detritus dynmics on stream communities. In addressing detrital inputs along an urban-rural gradient, we quantified inputs of coarse particulate organic matter, estimated export of leaf litter, quantified standing crop of benthic organic matter, and measured processing rates for coarse detritus. Trophic changes along an urban-rural gradient were measured using both functional and structural assessments of benthic invertebrates. These included preliminary measures of whole-stream metabolism and stable isotope analysis. Both methods showed potential to assess the relative importance of autochthonous and allochthonous organic matter. Assessment of downstream effects was limited to measure of coarse organic matter export.