A spatially intensive approach to water quality monitoring in the Rous River catchment, NSW, Australia

The Rous River catchment northern NSW, Australia was used as a case study to evaluate a spatially intensive approach to water quality monitoring, which involved the collection of water quality data from a large number of sample sites over a short period of time. Despite a few potential limitations, the spatially intensive water quality monitoring methodology should allow environmental managers to rapidly and cost-effectively (in the long term) identify point and non-point source impacts on water quality. Three point sources, the Murwillumbah Sewage Treatment Plant, a dairy shed and horse stables had the largest impact on water quality in the Rous River catchment during baseflow conditions. The poorest water quality in the Rous River catchment, due to non-point source inputs, was associated with cane land, which had elevated total nitrogen, total particulate nitrogen, and dissolved organic nitrogen concentrations and temperatures that were significantly greater (Kruskal-Wallis, u>0·05) than other land uses. High oxidized nitrogen concentrations were associated with bananas, most likely due to leaching of N-fertilizers, and oxidized nitrogen concentrations in the pristine areas appear high because oxidized nitrogen concentrations are low in other parts of the catchment (excluding horticulture areas) due to algal uptake and removal of inorganic nutrients. At the time of sampling, low flows were reflected by the dominance of instream processes which had converted most of the inorganic nutrients to organic nutrients. These findings evoked an immediate management response, where Environmental Health Officers were sent into the field to inspect the dairy shed and horse stables. This contrasts with previous Routine water quality studies in the Rous that identified a water quality problem, but not the exact causes, as a such there was no immediate management intervention. Long-term management efforts in the Rous River catchment need to be firstly directed at reducing point source inputs (particularly nitrogen), secondly at reducing non-point source inputs (particularly nitrogen) from cane land and bananas and thirdly at improving the catchment water quality for human health by reducing direct cattle access to streams.