River chemistry in cleared and pristine catchments: Where does the salt come from? Kangaroo Island, Australia

摘要

The surface waters of Kangaroo Island have an extremely wide range of salinities (specific electrical conductance varied from 221 to 63500 μS cm-1), in general being less saline in the western part of the island. The river waters display large variations in chemistry, both spatially and with time, reflecting the complex sources, pathways and residence time ofthe waters within individual catchments. Natural tracers were measured in river waters and provide evidence that groundwater discharge forms an important control of river flow. A comparison of river waters in a cleared and pristine catchment suggests that there is a link between vegetation clearance and the flow paths of water through the soil and regolith. Preliminary data in the Rocky River show that there are large stores of salt present at shallow depth. Despite this, the river water is remarkably fresh, and in places continues to flow throughout the year. It is suggested that flow via macropores, effectively by-passing the salt store, and lateral flow in deeper regolith or bedrock, is an important pathway for flow to the river.However, further more focused research is necessary to establish precise mechanisms of streamflow generation,the importance of surface water - groundwater interactions and impacts on surface ecosystems.