Review of the catchment processes relevant to the Great Barrier Reef region

Abstract

The hydrological processes within catchments set the backbone of all ecological functions and water quality outcomes. These catchment ecosystems and water quality outcomes in turn are in direct connection with the health of the marine environment to which they drain, and have therefore been of increasing concern for the long term health of the Great Barrier Reef World Heritage Area (World Heritage Area) and the Great Barrier Reef Marine Park (Marine Park). This review provides an overview of the relevant hydrological and biogeochemical processes within the Great Barrier Reef catchments, and the important interactions between them from the upper to lower catchment areas. The upper catchment provides all the hydrological services which generate runoff and partition the water balance, setting the tone for the total amount water available downstream and its quality. The lower catchment channel and floodplain network is essentially a buffer between the upper catchment processes and the ocean, and significant alterations to this system also means changes in buffering dynamics, which are critical to understand if catchment impacts on the marine environment are to be properly understood and managed. This review highlights the great number of studies which have contributed to the understanding of the climate, hydrology, and associated processes such as vegetation dependence, catchment erosion, and nutrient dynamics within the Great Barrier Reef catchments. It also collates and analyses some missing aspects of the hydrology between all the Great Barrier Reef catchments. In so doing, it also provides a summary of the key knowledge gaps, which can serve as a guide to further research. The key theme emerging from the majority of these knowledge gaps is a general under appreciation of the importance of catchment hydrology in driving many of the ecosystem health and service outcomes relevant to the Great Barrier Reef. At its core, this is because many of the catchment ecosystem services have a strong inter-dependence on some aspect of catchment hydrology (for example, water balance and tree water use, nutrient export and overland flow and groundwater recharge). Nonetheless, the review also highlights the many research tools that have already been developed to investigate these dependencies, and therefore a research strategy to address these critical gaps is easily developed.