ABSTRACT

Contaminant loss from grazed pasture can negatively affect freshwater quality. There is, however, little data on the impact of different levels of grazing/treading on contaminant loss measured under field conditions. This study quantified phosphorus (P), sediment and Escherichia coli (E. coli) loss in surface runoff from plots grazed by cattle for 0, 16 or 28 h to create different pasture/treading damage. Results showed an increase in grazing/treading duration decreased soil macroporosity (30%) and saturated hydraulic conductivity (96%), and increased surface roughness (71%) and depression water storage capacity (388%). These changes in soil physical condition contributed to greater volumes of surface runoff in the 16 h (31%) and 28 h (55%) treatments. Contaminant concentrations and loads in runoff also tended to increase with grazing/treading, although the increases were not statistically significant. An exception was total P (TP) which increased from 0.323 to 1.222 kg ha⁻¹, principally due to increased dissolved P, probably released from plants due to grazing and from the deposition of dung. Management of animals to minimise the number, duration and frequency of grazing wet soils that are vulnerable to physical damage are likely key factors to reducing TP, and probably SS and E. coli transport in surface runoff.

摘要

放牧草场的污染物损失会对淡水质量产生负面影响。然而，关于不同程度的放牧/踩踏对田间条件下测量的污染物损失的影响的数据很少。本研究对磷 (P)、沉积物和大肠杆菌( E. coli) 牛放牧 0、16 或 28 小时的地表径流损失，造成不同的牧场/踩踏损害。结果表明，放牧/踩踏持续时间的增加降低了土壤大孔隙率 (30%) 和饱和导水率 (96%)，并增加了表面粗糙度 (71%) 和洼地储水能力 (388%)。土壤物理条件的这些变化导致 16 小时（31%）和 28 小时（55%）处理的地表径流量增加。径流中的污染物浓度和负荷也随着放牧/踩踏而增加，尽管这种增加在统计上并不显着。一个例外是总磷 (TP)，它从 0.323 增加到 1.222 kg ha ⁻¹，主要是由于溶解的磷增加，可能是由于放牧和粪便沉积从植物中释放出来的。管理动物以最大程度地减少易受物理损坏的潮湿土壤放牧的数量、持续时间和频率可能是减少 TP 的关键因素，并且可能是减少地表径流中SS 和大肠杆菌运输的关键因素。