Can moderate increases in nutrient loads cause ecological effects in rivers already impacted by nutrients?

Predicting the ecological responses to moderate nutrient additions in systems that are already impacted to some degree by nutrient inputs is an important management task. In this study, we have investigated the responses of phytoplankton and periphyton and macroinvertebrate assemblages to experimental nutrient additions using both laboratory and field bioassays. We looked at six lower river reach/upper estuary sites in two flow seasons (high flow and low flow) in the Glenelg Hopkins Region of Victoria, Australia. Despite the considerable differences in the physical and chemical environments between sites in this study, the results suggest that within the lower river reaches of the Glenelg Hopkins region all systems are likely to have the potential for nutrient limitation. Also, addition of moderate and realistic loads of nutrients are likely to cause ecological changes, including a reduction in diversity H′, increases or decreases in algal growth and increases in densities of consumers. Incorporating this information into land use suitability options for the area will provide mangers an insight into potential outcomes relating to river health in the region.