Temporal variations in water quality of farm dams : impacts of land use and water sources

Three farm dams near Raglan, New South Wales (Australia), were compared to investigate diurnal and seasonal patterns in water quality over a period of 1 year. The source of water in one dam was predominantly influenced by groundwater, another showed links with both groundwater and agricultural runoff, and the third collected runoff from urban and agricultural lands with no apparent groundwater input. Patterns in chemical profiles were compared to identify level of similarity in macro-trends of water quality. Within dams, micro-trends were contrasted with known chemical relationships in dam waters to explore links between land use and water quality. The three dams were shown to have quite distinct patterns of water chemistry. Within dams, trends were strongly linked with the differing water sources, evidenced by chemical patterns that matched those expected from the different dominant ion transfer pathways associated with surface water and groundwater flow processes. Phosphates were primarily linked with groundwater fluctuations, nitrogen as ammonium ions with urban runoff, and nitrates with storm events resulting in runoff from pastures. We conclude that, for farm dams, the combination of land use and preferential flow paths gives a more complete description of water quality impacts than land use alone.