Centre for Sustainable Water Management, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
Centre for Sustainable Water Management, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.
Environ Int. 2010 Jan;36(1):1-7. doi: 10.1016/j.envint.2009.08.006. Epub 2009 Sep 26.
Dung-pats excreted directly on pasture from grazing animals can contribute a significant burden of faecal microbes to agricultural land. The aim of this study was to use a combined field and modelling approach to determine the importance of Escherichia coli growth in dung-pats when predicting faecal bacteria accumulation on grazed grassland. To do this an empirical model was developed to predict the dynamics of an E. coli reservoir within 1ha plots each grazed by four beef steers for six months. Published first-order die-off coefficients were used within the model to describe the expected decline of E. coli in dung-pats. Modelled estimates using first-order kinetics led to an underestimation of the observed E. coli land reservoir, when using site-specific die-off coefficients. A simultaneous experiment determined the die-off profiles of E. coli within fresh faeces of beef cattle under field relevant conditions and suggested that faecal bacteria may experience growth and re-growth in the period post defecation when exposed to a complex interaction of environmental drivers such as variable temperature, UV radiation and moisture levels. This growth phase in dung-pats is not accounted for in models based on first-order die-off coefficients. When the model was amended to incorporate the growth of E. coli, equivalent to that observed in the field study, the prediction of the E. coli reservoir was improved with respect to the observed data and produced a previously unquantified step-change improvement in model predictions of the accumulation of these faecal bacteria on grasslands. Results from this study suggest that the use of first-order kinetic equations for determining land-based reservoirs of faecal bacteria should be approached with caution and greater emphasis placed on accounting for actual survival patterns observed under field relevant conditions.
动物在牧场上直接排泄的粪便可能会对农业用地造成大量粪便微生物的负担。本研究旨在采用现场调查和模型模拟相结合的方法，确定在预测放牧草地中粪便细菌积累时，粪便堆中大肠杆菌生长的重要性。为此，开发了一个经验模型，以预测每个被 4 头肉牛放牧 6 个月的 1 公顷地块中大肠杆菌储库的动态。该模型使用已发表的一级衰减系数来描述粪便堆中大肠杆菌的预期衰减。使用现场特定的衰减系数，使用一级动力学进行模拟估计导致对观察到的大肠杆菌土地储库的低估。同时进行的实验确定了在现场相关条件下肉牛新鲜粪便中大肠杆菌的衰减曲线，并表明粪便细菌在暴露于温度、紫外线辐射和水分水平等环境驱动因素的复杂相互作用后，可能会在粪便排泄后的时期经历生长和再生长。在基于一级衰减系数的模型中，未考虑到这种粪便堆中的生长阶段。当模型被修改为纳入大肠杆菌的生长时，与田间研究中观察到的生长相当，就大肠杆菌储库的预测而言，与观察数据相比有所改善，并且对这些粪便细菌在草地上积累的模型预测产生了以前未量化的阶跃式改进。本研究的结果表明，在确定基于土地的粪便细菌储库时，应谨慎使用一级动力学方程，并更加重视在现场相关条件下观察到的实际生存模式。
