The response of aquatic communities to water quality, land use, flow variability and extraction in an unregulated Australian coastal river

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

C. L. Humphrey, L. Thurtell, R. W. J. Pidgeon, R. A. van Dam & C. M. Finlayson

Made available by the Northern Territory Library via the Publications (Legal Deposit) Act 2004 (NT).Date:199

Change in beta diversity of riverine fish during and after supra-seasonal drought

Context A core theme in ecohydrology is understanding how hydrology affects spatial variation in the composition of species assemblages (i.e., beta diversity). However, most empirical evidence is from research in upland rivers spanning small spatial extents. Relatively little is known of the consequences of hydrological variation for beta diversity across multiple spatial scales in lowland rivers. Objectives We sought to examine how spatial variation in hydrology and fish beta diversity within and among rivers changed over time in response to intensification and cessation of hydrological drought. Methods We used monitoring data of fish assemblages, coupled with hydrological and biophysical data, to test how spatial variation in hydrology and multiple components of fish beta diversity in lowland rivers of the Murray—Darling Basin (Australia) varied across spatial scales during contrasting hydrological phases. Results Spatial variation in hydrology among rivers declined with increasing duration of drought before increasing during a return to above-average flows. Spatial variation in hydrology within rivers did not show consistent changes between hydrological phases. Beta diversity among and within rivers showed variable, river-specific changes among hydrological phases for both incidence- and abundance-based components of assemblage composition. Conclusions Inconsistent hydrology—beta diversity patterns found here suggest that mechanisms and outcomes of drought and flooding impacts to beta diversity are context-dependent and not broadly generalisable. Our findings indicate that hydrological fluctuations occurring in the Murray—Darling Basin in the period analysed here did not cause significant or consistent homogenisation or differentiation of freshwater fish assemblages