Recovery of the water cycle on grazing lands – cumulative impacts of changing pasture condition on retention of water, sediment and nutrients on Burdekin hillslopes.

Summary

Meat and Livestock Australia (MLA) are committed to helping the Beef industry improve the quality and amount of water leaving grazed rangelands and reaching the Great Barrier Reef. This report summarises the findings of a 10 year study at Virginia Park Station in the Burdekin catchment that investigated the role of improved grazing land management (GLM) on hillslope and catchment water quality. The two management practices implemented in this study were: (1) reduced stocking; and (2) rotational wet season spelling. Ground cover and pasture condition were evaluated using on-ground surveys and remote sensing imagery. Subsequent changes to runoff and sediment yield were measured on hillslopes (using flumes) and at the end of the catchment (using automatic water sampling). During this study, average ground cover on hillslopes increased from ~35% to ~80%, although biomass levels are still relatively low for this landscape type, with ~16% of the cover increase attributed (in part) to improved GLM. The increased cover resulted in progressively lower runoff coefficients for the first event in each wet season, however, runoff coefficients were not reduced at the annual time scale. There was a 40 to 90% reduction in hillslope sediment concentrations with the improved cover, although the high runoff meant that total sediment yield did not decline. Similarly, there has not been a reduction in runoff or sediment yield at the catchment outlet (14 km2), as erosion from gullies and streamlines dominate sediment yields in this catchment. This study has shown that GLM in rangelands will potentially reduce impacts on downstream ecosystems, however, because of the multiple erosion sources, it will take more than 10 years for these changes to be detected at the end of the catchment.