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A 3D ecosystem model was used to quantify changes in water quality brought about by salmon aquaculture in the D'Entrecasteaux Channel and Huon Estuary in southeast Tasmania. Macroalgae-based integrated multitrophic aquaculture (IMTA) was simulated and showed that IMTA is capable of reducing the increased chlorophyll concentration attributable to fish farming by up to 10–15% in large areas of the region, during the season of highest production. Kelp farms ( Macrocystis pyrifera ) recovered between 6 and 11% of the dissolved inorganic nitrogen (DIN) input by salmon aquaculture over a nine month period, with DIN remediation increasing linearly with farm size. Under a ten-fold increase in aquaculture to very high loads, a much lower remediation effect was found for both chlorophyll and DIN. Model results indicate that IMTA could have an important impact on reducing negative effects of finfish aquaculture on water quality providing that stocking rates are not too high. [ABSTRACT FROM AUTHOR]

The fine-scale (< 100 m; < 1 day) skill of a 3D biogeochemical estuarine model cannot be assessed by traditional discrete monitoring programmes. Whilst continuous temperature, salinity, chlorophyll, turbidity and oxygen sensors based on electrical and optical properties have been deployed at individual sites, in underway and in profiling configurations, continuous estuarine nutrient sensors are in their infancy. In this paper we present data from 3 continuous nutrient observing systems deployed in a temperate estuary: a Systea Wet Chemistry analyser deployed at the head of the estuary to characterise river water entering the estuary; an in situ ultra-violet optical nitrate analyser deployed on a benthic lander at the mouth of the estuary to ascertain the marine nitrate concentrations entering the estuary; and a rapid reverse flow injection analysis system to achieve a high resolution spatial survey of conditions throughout the estuary. Our observations capture seasonal and synoptic timescale variability in marine and river nutrient concentrations and characterise plumes of nutrient enrichment associated with point source discharge against a background estuarine gradient. At the head of the estuary nutrient concentrations were greater and varied in ratio compared to previous observations. Results from a fine-scale 3D biogeochemical model (Wild-Allen et al., 2013) captured 66% of the observed synoptic timescale variability in nitrate concentration at the mouth of the estuary, but did not propagate the observed synoptic timescale fluctuations in river nutrients into the domain when forced with an upstream boundary condition of interpolated monthly observations. The absence of proxies for observing river nutrients dictates further investment in automated nutrient analysis to better inform the model and characterise evolving river conditions. Modelled surface nutrient fields matched observed spatial snapshots of estuarine conditions in contrasting years with surprising accuracy and suggest persistent spatial patterns that might usefully be characterised with neural network self organising maps. [ABSTRACT FROM AUTHOR]

Abstract: A method for the spatial selection of sites for a coastal environmental monitoring system is described. The study was completed in southeastern Tasmania, Australia, but the method can be applied in all regions with validated biogeochemical models. A 3-dimensional coupled hydrodynamic, sediment and biogeochemical model with high spatial and temporal resolution was validated against observations collected throughout 2002 and found to capture the essential features of the biogeochemical dynamics of the system. The model was used to predict the possible quantitative environmental impact of a projected increase in fish farming activity in the region. Integrated impacts of fish farm waste on labile nitrogen, phosphorus, chlorophyll and dissolved oxygen concentrations in the water column were spatially ranked to identify the most likely places to detect environmental change due to fish farming activities. Priority sites were found to be grouped in the Huon Estuary and northern part of the D''Entrecasteaux Channel consistent with the residual northward current in the region. The final monitoring program synthesized model and field understanding to ensure adequate spatial and temporal sampling of the region. [Copyright &y& Elsevier]