Water quality in agricultural lands draining to the Great Barrier Reef: A review of causes, management and priorities

•Processes generating agricultural pollutants were similar to those in temperate environments.•Reducing N losses will primarily be achieved by reducing N applications to high value crops.•Maintaining ground cover and pasture biomass, especially during the dry season, controls erosion.•There are uncertainties over breakdown and fate of pesticides in these tropical environments.•High spatial and temporal rainfall variability complicates management of agricultural pollutants. The environmental consequences of agriculture are of growing concern. One example of these consequences is the effect of agricultural pollutants on the Great Barrier Reef (GBR), a world heritage-listed ecosystem lying off the tropical north-eastern coast of Australia. Pollutants from agricultural lands (fine sediments and attached nitrogen (N) mainly from grazing lands, and dissolved N and pesticides mainly from cropping) in catchments draining into the GBR lagoon threaten the health and resilience of this ecosystem. Government actions are prompting farmers to adopt new management practices to reduce pollutant exports from their farms. However, previous agricultural research has, with the exception of erosion, largely focussed on production rather than environmental impacts. Also, the relevance of research conducted in other regions, e.g. Europe and North America, with different climates, soils and agricultural systems may be limited. Thus, there may not be a strong knowledge base underpinning actions to improve water quality. In this paper, we review research on the relationship between management of agricultural lands and pollutant exports in GBR catchments, and compare this knowledge with experience in other regions. Despite the differences in climate and agricultural systems, there are similarities in the causes and management of N and pesticide losses from cropping lands. Substantial N fertiliser is applied to high value crops in GBR catchments, and the primary path to reducing N losses from cropped lands will be through reducing N applications. Other practices may become effective in these crops once current (high) rates of N application and reduced. Herbicides are widely used, and practices that reduce herbicide runoff have recently been developed and demonstrated in most of the main cropping systems. However, there are still uncertainties over breakdown and fate of pesticides, especially new products, in these tropical environments. The principles of reducing erosion in grazing l