In conclusion, our findings suggest that the location of the CHLa maximum in the tidal freshwater James River is determined in part by natural geomorphic features of the channel. The transition from a riverine-type (narrow, deep) cross-sectional morphometry to a broad channel with shallow lateral areas provided favorable light conditions and resulted in increased phytoplankton production and
abundance. Greater cross-sectional area also likely reduced local water velocities allowing more efficient phytoplankton utilization of nutrients from the catchment and local point sources. Zooplankton grazing rates were low suggesting that other food quality factors may offset high CHLa concentrations such as the presence of cyanobacteria and non-algal particulates. Estimates of whole ecosystem respiration indicate that the bulk of algal production was respired in the region of the CHLa maximum and comparisons to water column rates suggest that the bulk of respiration occurred in the sediments. Thus the shallow, high light environment favored net autotrophy within the water column but also likely enhanced the export of chlorophyll biomass to the benthic detrital food web.