Pathways of contaminant transfers to water from an artificially-drained soil under intensive grazing by dairy cows

• Published in: Agriculture, ecosystems & environment Vol. 220; pp. 76 - 88
• Main Authors: Monaghan, R.M., Smith, L.C., Muirhead, R.W.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-03-2016
• Subjects: Dairy pasture grazing; Escherichia coli (E. coli); Mitigation; Mole-pipe drainage; Nitrogen; Phosphorus and sediment fluxes; Surface runoff; PSE, New Zealand; Mitigation; Mole-pipe drainage; Escherichia coli (E. coli); Phosphorus and sediment fluxes; Dairy pasture grazing; Nitrogen; Surface runoff
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2015.12.024

•We measured pollutant losses in drainage and surface runoff from pasture grazed by cattle.•Artificial (mole-pipe) subsurface drainage was the most important pathway of nitrogen (N) loss.•Restricting autumn grazing times reduced N losses in subsurface drainage by 43%.•Surface runoff and subsurface drainage were equally important pathways of P and sediment fluxes.•Fluxes of Escherichia coli in surface runoff were greater than in mole-pipe drainage.
There is limited quantitative understanding of the pathways and temporal patterns involved in the transfer of nitrogen (N), phosphorus (P), faecal bacteria and sediment from grazed temperate pastoral land to water. Because these transfers have the potential to significantly impair water quality, many catchment and community groups want to identify farming systems and management strategies that minimise the risks that farming activities pose for their water quality goals. Here we document the concentrations and loads of N, P, sediment and the faecal indicator bacteria E. coli (E. coli) measured in mole-pipe drainage (3-year monitoring period) and surface runoff (2-year monitoring period) collected from hydrologically-isolated plots grazed by dairy cattle in southern New Zealand. We also evaluate the effectiveness of restricted autumn grazing management as a strategy that could potentially reduce these losses. Monitoring indicated that 62 and 25% of estimated surplus rainfall was captured as mole-pipe drainage and surface runoff, respectively. Mole-pipe drainage was the most important pathway of N loss, accounting for c. 80% of the total soluble N discharged in the combined flows from mole-pipe drainage and surface runoff. In contrast, surface runoff proved to be an important pathway for P and sediment movement, and contributed 68% of the calculated flux of the faecal bacteria E. coli. Temporal patterns of loss suggest that the management of urinary N deposited in the months preceding winter drainage events is key for reducing potential N losses in drainage. A restricted autumn grazing strategy reduced losses of dissolved N in subsurface drainage by 43% on average, although statistically significant reductions were only observed for 2 of the 3 measurement years. Temporal patterns of P, sediment and E. coli fluxes suggest that management strategies which can reduce surface runoff generated during spring on these poorly-drained soil types may be the most effective approach for reducing the impacts of these contaminants on surface water quality.