Document Type

Conference Proceeding

Publication Date

2003

Conference Title

In proceedings of: Institute of Engineers Australia, 28th International Hydrology and Water Resources Symposium, 10-14 Nov 2003, Wollongong, NSW. Volume 2, 123-130

Place of Publication

Wollongong

Keywords

Eutrophication, BMP, management practices, nutrient pollution, water quality, modelling

Abstract

The ecology of estuaries on the south coast of Western Australia has been disrupted by increased nutrient and sediment discharge from predominantly rural catchments. Seagrass beds have been replaced by macroalgae, and toxic algal blooms threaten human and animal health, and reduce amenity. A range of conventional management actions are available to reduce nutrient loss at source, and it is important to evaluate possible reductions, and costs, so that limited funds can be targeted to realise the greatest moderation of nutrient loss. A lumped landuse nutrient generation rate model was developed for four catchments (Wilson Inlet, Oyster Harbour, Torbay Inlet and Princess Royal Harbour) near Albany Western Australia and the output compared with existing monitoring data. The nutrient moderating effects of five conventional management actions (perennial pastures; vegetated stream buffers; effective fertiliser use; stock control and water management; and effluent management) and their associated costs were implemented at different levels in the model to determine the extent to which these actions could address offsite nutrient pollution, and the cost of doing so. Management actions were implemented in three major scenarios representing the current nutrient reduction efforts, the maximum feasible implementation of each action and the most cost effective set of actions. In each catchment dominated by diffuse nutrient sources, current nutrient reduction efforts amounted to about 10%, whilst the highest possible reductions were of the order of 25-30% above this. In the point source dominated catchment current nutrient reduction efforts amounted to about 40%, with an additional 40% possible. The most cost effective scenarios reduced nitrogen more than phosphorus. Under the most cost effective scenarios, it was estimated that the net cost of management actions over 10 years was budget positive, resulting in a net benefit to the land managers involved. There appears therefore to be limited economic barriers to the adoption of these conventional management actions. However, these maximum possible reductions from the implementation of conventional management actions may not be sufficient to arrest estuarine decline.