The water quality impact of a herd of 246 dairy cows crossing a stream ford was documented. Two cow crossings produced plumes of turbid water associated with very high concentrations of faecal indicator bacteria (Escherichia coli) and high suspended solids (SS) and total nitrogen (TN). On the first crossing, towards the milking shed, the cows were tightly-bunched and produced a sharp spike of contamination (E. coli peaking at 50 000 cfu/100 ml). After milking, the cows wandered back across the stream as individuals or small groups, and contaminants were less elevated, albeit for a longer period. Light attenuation, measured continuously by beam transmissometer, correlated closely with E. coli, SS, and TN, permitting the total yield of these contaminants to be estimated. Contaminant yields for M04005; Online publication date

Storm-induced Escherichia coli pulses in the Motueka River (2074 km 2 ) and the Sherry River (78.4 km 2 ) are modelled. The model focuses on the catchment outlets, representing key processes, including E. coli transfer to and from the river bed, with account taken of the hysteresis in, and non-linear, non-stationary, response of E. coli concentrations to river stormflows. The model fits the Motueka River observations well, but less well in the Sherry River. A greatly simplified description of headwater and riparian inputs is satisfactory at the larger catchment scale where near-field, in-channel processes dominate the response. Spatial heterogeneity in rainfall-run-off and faecal sources probably contribute to the poorer fit in the smaller catchment. Despite using a relatively small number of driving variables and parameters, the model has the potential to predict real-time E. coli input to Tasman Bay in river plumes causing shellfish and bathing beach contamination.

The Sherry River, a tributary of the Motueka River (Tasman District, upper South Island, New Zealand), has somewhat degraded water quality related to a high proportion of the catchment being used for pastoral agriculture (which comprises 30% dairying). We undertook a campaign to estimate loads of phosphorus, nitrogen and Escherichia coli for comparison with other dairy-impacted catchments and against which to measure future reductions in pollutants in the Sherry River, expected from changed management practices. Monthly water quality sampling in the Sherry River was augmented with storm chasing for one year (October 2008 to October 2009). Loads of pollutants in events increased disproportionately with event peak flow, probably because the proportion of overland flow increases systematically with increasing event size. Stormflows (occurring 9.5% of the time) transported 33% of the total flow from the Sherry River, and between 22% (for nitrate) and 92% (for E. coli) of pollutant loads.