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Recovery of the water cycle on grazing lands - cumulative impacts of changing pasture condition on retention of water, sediment and nutrients on Burdekin hillslopes
Degradation of grazing land resulting from unsustainable grazing practices can increase water, sediment and nutrient yields to downstream ecosystems. This report presents the results of a 10-year field study (2002-2011) that evaluated the impact of improved grazing land management (GLM) on ground cover, runoff and erosion at hillslope and catchment scales. The study was located in the Weany Creek catchment within the Burdekin River basin, on eucalypt woodland with a native pasture understorey dominated by the invasive exotic grass, Bothriochloa pertusa. The two management practices implemented to improve pasture condition were reduced stocking (i.e., reduced pasture utilisation) and rotational wet season spelling. Vegetation cover was measured using botanical field surveys and remote sensing techniques. Rainfall, runoff and sediment concentration were measured using flumes on three hillslopes ranging in size from 0.2 -1.1 ha, and using a stream gauge at the end of the 14 km2 catchment. The annual average rainfall for the 10 year period (670 mm) was slightly more than the long term average rainfall (of 606 mm) for the area. Over the 10 year study period the ground cover increased by ~46% across the whole catchment.
Following a comparison of cover data with a similar sized catchment that did not undergo changed GLM, ~16% of this cover increase can be attributed to GLM (and not increased rainfall). At one of the flume sites, the amount of rainfall required to initiate runoff for the first event in each wet season increased significantly with the increase in ground cover. However, at the annual scale, the total amount of runoff increased during the study despite the increase in cover. This was because annual runoff is largely controlled by the storage capacity of the soil profile, and thus high rainfall years result in high runoff regardless of the amount of ground cover. Although there was no response to annual runoff with improved ground cover, there was a statistically significant reduction in total suspended sediment (TSS) concentrations on hillslopes that do not have large bare (
This page was last updated on 24/07/2017
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