Abstract:This study investigated the effect of benthic macrofauna on nutrient fluxes. The influence of the macrofauna on nutrients released from the sediments was investigated experimentally in the laboratory using sediment cores from the Swan-Canning Estuary. Excretion rates of common benthic species were also measured to quantify the role of the macrofauna in estuarine nutrient cycling.The presence of macrofauna increased the release of phosphate and ammonium into the water column but decreased the release, or resulted in uptake, of nitrate by the sediments. There were no significant differences in porewater concentrations of ammonium, nitrate or phosphate between treatments with and without macrofauna. The macrofauna clearly had an important role in nutrient fluxes, as nutrient release differed between cores with and without fauna, and nutrient fluxes were significantly correlated with increased faunal biomass.Other factors, such as season and dissolved oxygen concentrations, influenced the concentration of nutrients released. Ammonium was released into the overlying water column at higher rates in winter than summer, while nitrate was released at higher rates in summer than winter. Aeration did not have a significant effect on nutrient fluxes, however there was a significant increase in filterable reactive phosphorus, and decrease in nitrate, in the porewater of cores which were not aerated.Benthic species excreted phosphate, nitrate and ammonium, with ammonium present in the largest amounts. Comparison of excretion rates to the amount of nutrients released into the water column in the core experiments revealed that excretion could account for 30% of the phosphate and >200% of the ammonium measured in the water column.Clearly the benthic macrofauna have a significant role with respect to benthic nutrient fluxes within the Swan-Canning Estuary, with benthic regeneration of nutrients estimated to equal external loading of nutrients. However, further work is required to more precisely define the influence of seasonality, dissolved oxygen, microbial activity and sediment characteristics on nutrient fluxes.

Freshwater aquatic ecosystems are in decline due to intensifying land use, salinisation, water abstraction and climate change. Understanding compositional patterns in aquatic biota is a useful step towards better management of aquatic ecosystems. We used generalised dissimilarity modelling (GDM) to predict compositional turnover in riverine invertebrate fauna (primarily insects) as a function of environment. Conceptual understanding of major drivers of aquatic invertebrate species distribution helped decide which predictor variables to source and include. Five groups of environmental variables—waterscape, local habitat, climate, landscape and disturbance—were derived from either spatial layers or in situ (site) measurements. Predictive models and variance partitioning tests of variable groups demonstrated the importance of representing all conceptual drivers of ecological pattern and process. As expected, waterscape variables were independently the most important group, followed by local habitat and landscape variables; with complex interactions between groups. Climate variables independently contributed the least. To determine the information content for mapping patterns, we investigated the independent and combined contribution of site‐measured and spatial predictors. Even though predictive models developed using only site‐measured variables or only spatial variables explained around the same amount of deviance (DE), combined they increased explained model DE by 11.2%. Compositional dissimilarities between the 51 surveyed site pairs predicted by the model using only spatial variables were highly correlated (r2 = .85) with dissimilarities predicted using site and spatial variables. These results support the use of the spatial model for conservation decisions. The spatial model was used to evaluate representativeness of both the conservation reserve network and biological monitoring locations. The location of aquatic monitoring sites was uneven, with comprehensive coverage south and coastward, and less representative of inland environments. Proportional protection of ecological environments (scaled by riverine invertebrate taxa) was found to vary between 20% and 30%, being higher in southern parts where more land has been allocated to reserves and less in northern and inland parts. This demonstrated local progress towards achieving the Convention on Biological Diversity's Aichi Target 11 for inland waters. These results provide a focus for improving the robustness of information used in decisions affecting the conservation of aquatic biodiversity, including places to target to fill gaps in the reserve network and additional aquatic monitoring locations (supporting Convention on Biological Diversity's Aichi Target 19). The GDM‐based approach to characterising ecological environments, provided a first quantitative foundation for comprehensively evaluating the conservation status of freshwater ecosystems in south‐western Australia. Potential future applications include assessing the ecological implication...