Developing an Optimal Strategy for Monitoring Nutrients in an Agricultural Watershed

This study, which is part of a larger Tasmanian study on water quality and nutrient export, examines nutrient status and flux in a small agricultural basin where the dominant land uses are dairy, sheep and free range pig farming. This is the first such study to be carried out in Tasmania. Routine monitoring was on a monthly basis and several flood events were also sampled. Various monitoring strategies exist to describe the nutrient status of rivers and it was found that a strategy of monitoring based on flow yields a very different picture to that based on lime. Methods for calculating nutrient export loads were tested and it was found that there can be considerable differences in load estimates between methods. It was also found that confounding factors such as preceding climatic conditions will influence the resulting calculations and that methods may need careful examination before application to a particular catchment. Nutrient export studies need to be carefully designed to quantify the concentration discharge relationship. Based upon the above results, various sampling options for water resource agencies are discussed. Optimal sampling strategies are suggested based upon consideration of resource constraints, accuracy of results and the expected outcomes of a nutrient sampling program. Turbidity is found to be an excellent surrogate for Total Phosphorus and Suspended Solids loads in this catchment.