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Australian National University (2008)

Groundwater-surface water interactions : implications for nutrient transport to tropical rivers

Dixon-Jain, Prachi

Titre : Groundwater-surface water interactions : implications for nutrient transport to tropical rivers

Auteur : Dixon-Jain, Prachi

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 2008

Description partielle
The interaction between groundwater and surface water systems is a key component of the hydrological cycle and an understanding of their connectivity is fundamental for sustainable water resource management. Water is a vehicle for mobilising dissolved constituents, including nutrients, between surface and subsurface waters and between terrestrial and marine systems. Therefore, knowledge of surface-subsurface linkages is critical not only for water quantity allocation, but also for water quality and its implications for ecosystem health. In particular, ascertaining the significance of groundwater fluxes for river nitrogen budgets is an important motivation for characterising river-groundwater connectivity. This overarching theme is developed through the course of the thesis. The marked seasonality of tropical river systems provides a unique opportunity to investigate groundwater contributions to surface waters, especially when there are minimal overland flows. The Herbert River in northeast Queensland represents a useful case study in the Australian tropics for assessing the potential for transport of agricultural contaminants, such as dissolved forms of nitrogen, between surface and subsurface waters, and between terrestrial and marine systems, including the ecologically significant Great Barrier Reef World Heritage Area. Whilst the lower Herbert River catchment, dominated by sugarcane production, is the focus for this thesis, the research methodology and policy implications for nutrient monitoring and management are applicable to other tropical catchments. An extensive water quality sampling program was instigated to collect river and groundwater samples during low flow conditions, for analysis of a range of conservative and nonconservative environmental tracers including major ions, stable isotopes of water, radon, and dissolved inorganic forms of nitrogen. Grab samples were collected during months representing the beginning and end of the dry season to compare connectivity relationships at contrasting stages of the stream hydrograph. Hydrochemical data at the end of the dry season is particularly useful for isolating the groundwater signal in the river and its tributaries. Existing physical and chemical datasets are also an important source of high temporal resolution information to supplement the more detailed water quality data collected specifically for this investigation. An understanding of the dynamics of water movement between river and aquifer storages is critical for assessing the mobility of dissolved nitrogen between them

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