Fat cows improve water quality: the benefits of higher forage levels in Great Barrier Reef rangelands (11146)
This paper reviews research informing erosion management in the GBR grazing landscapes, from which most sediment delivered to the GBR is derived. Sediment tracing has identified that fine river sediment predominantly comprises subsoil, derived from a small proportion of total catchment area having very poor vegetation cover. These landscapes have experienced low ground cover and pasture degradation during past droughts. Hillslope scalds, rills, gullies and eroding channel banks are all common features, illustrating areas where the landscape resistance to erosion has been exceeded. River load monitoring also indicates that catchments with these erosion features have sediment yields many times those elsewhere. However, the spatial concentration of erosion features provides the opportunity to concentrate erosion control efforts. For example, 50% of all gullies in the Burdekin basin occur on just 20% of all grazing properties. Therefore it is cost-effective to prioritise investment in erosion management to such areas.
The effectiveness of changing land management on sediment yields is determined in part by the environment, and the GBR rangelands have a more variable climate and more sparse vegetation than the temperate, humid and more intensive agricultural environments in which the bulk of erosion research has occurred. We report on a local before-after-control-impact (BACI) experiment used to quantify the benefits of revegetating gully features on sediment yields. We also demonstrate the effectiveness of reduced forage utilisation and wet-season spelling for starving erosion features of runoff, as well as reducing hillslope erosion and improving forage productivity. We conclude that implementing grazing land management practices at and above industry standards on the properties with erosion features has the potential to deliver considerable long-term reductions in sediment yields to the GBR (public benefit) and forage productivity (private benefit). Remaining knowledge challenges to achieving large reductions in TSS loads are also described.