Department of Chemical Engineering and Materials Science, Henry Samueli School of Engineering, University of California, Irvine, 92697-7070, USA.
Environ Sci Technol. 2010 Jan 15;44(2):631-7. doi: 10.1021/es903496m.
Fecal indicator bacteria (FIB) have long been used as a marker of fecal pollution in surface waters subject to point source and non-point source discharges of treated or untreated human waste. In this paper, we set out to determine the source(s) of elevated FIB concentrations in Cucamonga Creek, a concrete-lined urban stream in southern California. Flow in the creek consists primarily of treated and disinfected wastewater effluent, mixed with relatively smaller but variable flow of runoff from the surrounding urban landscape. Dry and wet weather runoff contributes nearly 100% of FIB loading to Cucamonga Creek, while treated wastewater contributes significant loading of nutrients, including dissolved organic carbon (DOC), phosphorus, nitrate, and ammonium. FIB concentrations are strongly positively correlated with DOC concentration in runoff (Spearman's rho >or= 0.66, P <or= 0.037), and microcosm studies reveal that the survival of Escherichia coli and enterococci bacteria in runoff is strongly dependent on the concentration of both DOC and phosphorus. Below threshold concentrations of 7 and 0.07 mg/L, respectively, FIB die off exponentially (die-off rate 0.09 h(-1)). Above these thresholds, FIB either grow exponentially (growth rate 0.3 h(-1)) or exhibit a periodic steady-state in which bacterial concentrations fluctuate around some mean value. The periodic steady-state pattern is consistent with a Lotka-Volterra predator-prey oscillation model, and the clearance rate (20 microL predator(-1) h(-1)) obtained by fitting the model to our data is consistent with the hypothesis that predacious protozoa regulate FIB concentrations in runoff at high DOC concentrations. Collectively, these results indicate that FIB impairment of Cucamonga Creek is best viewed as an ecological phenomenon characterized by both bottom-up and top-down control.
粪便指示菌（FIB）长期以来一直被用作受点源和非点源处理或未处理人类废物排放影响的地表水粪便污染的标志物。在本文中，我们旨在确定加利福尼亚南部混凝土衬砌城市溪流 Cucamonga Creek 中 FIB 浓度升高的来源。溪流中的水流主要由处理和消毒后的废水流出物组成，与周围城市景观中相对较小但变化较大的径流水流混合。干、湿天气径流水对 Cucamonga Creek 的 FIB 负荷贡献近 100％，而处理后的废水则会大量输送养分，包括溶解有机碳（DOC）、磷、硝酸盐和铵。FIB 浓度与径流中 DOC 浓度呈强正相关（Spearman's rho >or= 0.66，P <or= 0.037），并且微宇宙研究表明，大肠杆菌和肠球菌在径流中的存活强烈依赖于 DOC 和磷的浓度。低于分别为 7 和 0.07 mg/L 的阈值浓度时，FIB 呈指数衰减（衰减率为 0.09 h(-1)）。超过这些阈值时，FIB 要么呈指数增长（增长率为 0.3 h(-1))，要么表现出周期性的稳态，其中细菌浓度围绕某个平均值波动。周期性稳态模式与洛特卡-沃尔泰拉捕食者-猎物振荡模型一致，通过将模型拟合到我们的数据中获得的清除率（20 microL 捕食者(-1) h(-1))与捕食原生动物在高 DOC 浓度下调节径流中 FIB 浓度的假设一致。总的来说，这些结果表明，Cucamonga Creek 的 FIB 损害最好被视为一种生态现象，其特征是既有底向上的控制，也有顶向下的控制。
