Abstract：
The presence of bacteria and viruses in freshwater represents a global health risk. The substantial spatial and temporal variability of microbes leads to difficulties in quantifying the risks associated with their presence in freshwater. Fine particles, including bacteria and viruses are transported and accumulated into shallow streambed (i.e., benthic) sediment, delaying the downstream transmission during baseflow conditions but contributing to their resuspension and transport downstream during stormflow events. Direct measurements of pathogen accumulation in benthic sediments are rare. Until now, the dynamic role of benthic sediment as both a store and source of microbes, has not been quantified. In this study, we analyze microbial abundance in benthic sediment along a 1 km reach of an intermittent Mediterranean stream receiving inputs from the effluent of a wastewater treatment plant, a known point source of microbes in streams. We sampled benthic sediment during a summer drought when the wastewater effluent constituted 100 % of the stream flow, and thus, large accumulation and persistence of pathogens along the streambed was expected. We measured the abundance of total bacteria, Escherichia coli (as a fecal indicator), and presence of enteric rotavirus (RoV) and norovirus (NoV). The abundance of E. coli, based on qPCR detection, was high (4.99∙102 gc /cm2) along the first 100 m downstream of the wastewater effluent input and in general decreased with distance from the source, with presence of RoV and NoV along the study reach. A particle tracking model was applied, that uses stream water velocity as an input, and accounts for microbial exchange into, immobilization, degradation, and resuspension out of benthic sediment during baseflow and stormflow. Rates of exchange into benthic sediment were 3 orders of magnitude higher during stormflow, but residence times were proportionately lower, resulting in increased longitudinal connectivity from up to downstream during stormflow. Model simulations demonstrated mechanistically how the rates of exchange into and out of the benthic sediment resulted in benthic sediment to act as a store during baseflow and a source during stormflow.
摘要：
淡水中细菌和病毒的存在代表了全球健康风险。微生物的巨大时空变化导致难以量化与它们在淡水中的存在相关的风险。细颗粒,包括细菌和病毒在内的细菌和病毒被运输和积累到浅层河床(即，底栖)沉积物，在基流条件下延迟下游传输，但在暴风流事件期间导致其重新悬浮和向下游传输。很少直接测量底栖沉积物中病原体的积累。直到现在,底栖沉积物作为微生物的储存和来源的动态作用，还没有量化。在这项研究中,我们分析了底栖沉积物中的微生物丰度，沿着间歇性地中海河流的1公里范围，从污水处理厂的废水中接收输入，溪流中已知的微生物点源。我们在夏季干旱期间采样了底栖沉积物，当时废水占水流的100％，因此，预计沿河床的病原体会大量积累和持续存在。我们测量了总细菌的丰度，大肠杆菌（作为粪便指示剂），以及肠轮状病毒（RoV）和诺如病毒（NoV）的存在。大量的大肠杆菌,基于qPCR检测，是高的（4.99*102gc/cm2）沿着废水排放输入的第一个100m下游，在一般减少与来源的距离，沿着研究范围存在RoV和NoV。应用了粒子跟踪模型，使用水流速度作为输入，并考虑到微生物交换，固定化，降解，并在基流和暴雨期间从底栖沉积物中再悬浮。在暴风流期间，底栖沉积物的交换率高出3个数量级，但是停留时间成比例地更低，导致在暴雨期间从上至下游的纵向连通性增加。模型模拟从机械上证明了进出底栖沉积物的交换速率如何导致底栖沉积物在基流期间充当储存物，并在暴雨中充当源。
