Sources and processes of contaminant loss from an intensively grazed catchment inferred from patterns in discharge and concentration of thirteen analytes using high intensity sampling

SummaryContaminants in water from intensively grazed catchments have been shown to cause significant environmental impacts. Effective intervention to reduce contaminant loads depends on identifying their sources and processes of mobilisation and transport. In this study, flow (Q) and analyte concentrations (CA) from a 12 ha catchment in north-west Tasmania used for grazing dairy cattle were monitored at a fine temporal scale and used to infer sources and processes of loss. Three groups of analytes identified based on CA–Q relationships, which included hysteresis loops, demonstrated that the TP group (TP, DRP, TSS, TN, E.coli and Enterococcus) was transported by surface runoff processes while the behaviour of the NO3 group (NO3, TDS, Ca, Mg, Na) was explained by subsurface processes and pathways. The NH4 group (NH4, K) was dominated by the addition of large quantities of analyte from grazing. In addition to the CA–Q relationships, concentrations of most analytes decreased linearly over each season of runoff. NH4 and K concentrations decreased exponentially following grazing events while TP concentrations decreased linearly. The study demonstrated the importance of understanding surface water and groundwater interactions and that relationships between runoff events, analyte concentrations and management as revealed by a fine temporal sampling regime may yield significant insights to sources and processes of loss of analytes in surface flow, at a given scale.