Establishing estuarine condition and response to catchment activities is complex, although many of the extreme symptoms are by now well known such as algal blooms and fish kills. A harder task is to understand the vulnerability of estuaries and the rate at which they respond to both improvements and deteriorations in catchment stressors.
Traditional water quality variables are not always the best indicator of the condition of an estuary. For example, while these are important indicators of eutrophication, on their own they do not describe the overall estuarine condition especially when nutrients are stored in sediments or plant biomass. Instead, a combination of indicators is required to establish condition. These include changes in the extent and distribution of estuarine submerged aquatic vegetation and differences in the physical properties, and nutrient flux and metabolism in estuarine sediments, both of which are reflective of changes in catchment loading and estuarine dynamics.
The role of the department is to develop these condition indicators and to incorporate them into long-term monitoring programs so that condition targets can be set for the estuaries. The major challenges are to distinguish changes in submerged aquatic vegetation in response to a change in the estuarine condition from those which might be due to natural variability, and to better understand the processes controlling the nutrient flow in the estuaries, especially the role that estuarine sediments play.