Collins R, Elliott S, Adams R
National Institute of Water and Atmospheric Research Limited (NIWA), Hamilton, New Zealand.
J Appl Microbiol. 2005;99(1):126-32. doi: 10.1111/j.1365-2672.2005.02580.x.
To quantify and derive statistical relationships with which to predict the delivery of faecal bacteria (Escherichia coli) to a pastoral stream, by overland flow.
A large-scale (1050 m2) rainfall simulator, located upon a steep (18 degrees) grazed hillside in New Zealand, was used to simulate 11 heavy rainfall events. Overland flow was generated and sampled throughout each event, before discharging to a headwater stream. The samples were subsequently analysed to determine the concentration of E. coli. Statistical analysis showed that the time elapsed since the last period of grazing was a statistically significant predictor of both the total number (load) and concentrations of E. coli in overland flow. Between 10(5) and 10(8)E. coli per m2 of hillside were delivered to the stream within overland flow during each event, and peak concentrations ranged between 10(3) and 10(7) most probable number per 100 ml.
Under heavy rainfall on steep pastoral land, overland flow can transport substantial levels of faecal bacteria to streams. Under such conditions, it is unlikely that vegetated buffer strips will be particularly effective at attenuating bacteria within overland flow.
This work has improved understanding of the importance of overland flow as a process contributing to the contamination of pastoral streams by faecal bacteria. In addition, the predictive relationships derived can be incorporated within catchment models.
通过地表径流来量化并推导统计关系，以此预测粪便细菌（大肠杆菌）进入田园溪流的情况。
在新西兰一处陡峭（18度）的放牧山坡上，使用一个大型（1050平方米）降雨模拟器来模拟11次强降雨事件。在每次降雨事件中，产生地表径流并进行采样，之后排放到源头溪流中。随后对样本进行分析以确定大肠杆菌的浓度。统计分析表明，自上次放牧期以来经过的时间是地表径流中大肠杆菌总数（负荷）和浓度的一个具有统计学意义的预测指标。在每次降雨事件期间，每平方米山坡有10⁵至10⁸个大肠杆菌通过地表径流进入溪流，峰值浓度范围为每100毫升10³至10⁷个最可能数。
在陡峭的田园土地上遭遇强降雨时，地表径流可将大量粪便细菌输送到溪流中。在这种情况下，植被缓冲带不太可能特别有效地减少地表径流中的细菌。
这项工作增进了对地表径流作为粪便细菌污染田园溪流的一个过程的重要性的理解。此外，所推导的预测关系可纳入集水区模型。
