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Managing pollutant inputs from pastoral dairy farming to maintain water quality of a lake in a high-rainfall catchment

2013; CSIRO Publishing; Volume: 64; Issue: 5 Linguagem: Inglês

10.1071/mf12296

1448-6059

Robert J. Wilcock, R. M. Monaghan, R. W. McDowell, Piet Verburg, Jonny Horrox, Catherine Chagué‐Goff, Maurice J. Duncan, Alison Rutherford, Gil Zemansky, Mike R. Scarsbrook, Aslan E. Wright‐Stow, Clive Howard‐Williams, Sue Cotton,

Soil erosion and sediment transport

A study (2004–11) of a dairy catchment stream entering an oligotrophic lake in an area of very high rainfall (~5 m year–1) yielded median concentrations of total nitrogen (TN), total phosphorus (TP), suspended sediment (SS) and Escherichia coli (E. coli) of 0.584, 0.074 and 3.7 g m–3, and 405/100 mL (most probable number method), respectively. Trend analysis indicated significant (P < 0.01) decreases for TN (–0.08 ± 0.02 g m–3 year–1), TP (–0.01 ± 0.005 g m–3 year–1) and SS (–0.45 ± 0.14 g m–3 year–1) and were partly attributable to improved exclusion of cattle from the stream. Water balance calculations indicated that approximately one-half the rainfall left as deep drainage that by-passed catchment outlet flow recorders. Estimates of catchment yields for TN were improved by taking into account groundwater hydrology and concentrations from well samples. Storm-flow monitoring inflows exceeding the 97.5th percentile contributed ~40% of total loads leaving the catchment so that specific yields for SS, TN and TP augmented by groundwater inputs and storm flows were ~960, 45 and 7 kg ha–1 year–1, respectively. These compared well with modelled results for losses from dairy farms in the catchment of 40–60 kg N ha–1 year–1 and 5–6 kg P ha–1 year–1 and indicated that attenuation losses were relatively small.