Stream ecosystems are greatly influenced by their catchments through the contribution of water and nutrients. While nutrients are an essential component in driving biological stream functions and processes, the continuing impact of changing land use and diffuse inputs has increased nutrient loads within most aquatic environments around the world. These increasing nutrient loads have resulted in artificial or cultural eutrophication, impairing water quality and aquatic ecosystem function. It is hypothesised in this thesis that catchment properties and agricultural land use increase total nutrient concentrations within the Manning River system on the north coast of New South Wales, Australia. Increases in nutrient concentrations, coupled with reduced flows, will have ecological impacts through increases in primary productivity and algal biomass. To assess how land use and river discharge influences biogeochemical processes, this study measured water quality under various flow conditions and assessed the responses of biota to flow and water quality changes. Regionally-derived nutrient thresholds were identified, as was the influence of discharge on in-stream nutrient concentrations and ratios. Nutrient enrichment experiments, nocturnal water quality investigations and assessments of macroinvertebrate community structure responses were also undertaken to better understand ecosystem functioning
