Evaluation of the utility of water quality based indicators of estuarine lagoon condition in NSW, Australia

Environmental indicators must have a predictable relationship with stressors to be of value in ecological assessments. We evaluated the information provided by commonly implemented monitoring indicators as a means of assessing of the level of ecological impact experienced by coastal lagoons in New South Wales, Australia. Existing data for environmental variables in coastal lagoons were correlated with independent estimates of catchment disturbance. There were few relationships between the monitoring variables (particularly water chemistry) and nutrient loads and catchment land use. Data from NSW catchments and lagoons were compared to analogous data from published northern hemisphere studies and it was clear that stressor variables were up to one to two orders of magnitude smaller in NSW, potentially explaining the lack of relationships with recognised indicators. Our study has highlighted the importance of using a range of indicators to assess trends in ecological condition of an estuarine ecosystem, particularly where stressor levels are not great. Using water quality as the sole means of determining lagoon condition was simply inadequate in NSW lagoons. We recommended that ecological outcome indicators such as algal abundance (macro and micro) and turbidity were most likely to show interpretable patterns at low to moderate nitrogen loadings (<40 kg Ha 1 yr 1) and that these should form the basis of estuarine trend monitoring in NSW lagoons. The demonstrated value of seagrass and macroalgal monitoring in estuaries with moderate to high nutrient loadings suggests that these indicators should not be overlooked when planning monitoring programs, recognising, however, they will not have strong discrimination at lower catchment loadings.