This work presents data on a suite of\ud diffuse pollutants, monitored in a stream draining an intensively managed grassland on a 30 min time step during a period of intense rainfall to better understand their sources and pathways. Nitrite (92 μg l−1), particulate phosphorus (107 μg l−1) and soluble phosphorus (74 μg l−1) exceeded environmental limits during base flow. Concentrations of nitrate and nitrite were decreased during the storm event, whereas all\ud other pollutants generally increased and exceeded\ud environmental limits where specified, especially when associated with a small subsidiary hydrograph on the rising limb of the main hydrograph. Total pollutants loads, when using a 60 min sampling frequency, would have led to significant over and underestimations depending on which 60 min sample set was used. In the worst case, loads of ammonium could have been under-estimated by 35% or over estimated by 25% with errors being associated with loads on the rising limb of the hydrograph and more specifically a small subsidiary hydrograph. This subsidiary hydrograph may have occurred as a result of runoff from the farm hard standings within the\ud catchment. Incidental transfer of pollutants associate with this runoff have masked the overall grassland pollutant response. To better understand these different source areas and pollutant dynamics, there is a need for novel tracing techniques to elucidate their relative contribution and pathways
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