We investigated how visitor-use affects water quality in wilderness in Yosemite National Park. During the summers of 2012-2014, we collected and analyzed surface-water samples for water-quality indicators, including fecal indicator bacteria Escherichia coli, nutrients (nitrogen, phosphorus, carbon), suspended sediment concentration, pharmaceuticals, and hormones. Samples were collected upstream and downstream from different types of visitor use at weekly to biweekly intervals and during summer storms. We conducted a park-wide synoptic sampling campaign during summer 2014, and sampled upstream and downstream from meadows to evaluate the mitigating effect of meadows on water quality. At pack stock stream crossings, Escherichia coli concentrations were greater downstream from crossings than upstream (median downstream increase in Escherichia coli of three colony forming units 100 mL-1), with the greatest increases occurring during storms (median downstream increase in Escherichia coli of 32 CFU 100 mL-1). At backpacker use sites, hormones, and pharmaceuticals (e.g., insect repellent) were detected at downstream sites, and Escherichia coli concentrations were greater at downstream sites (median downstream increase in Escherichia coli of 1 CFU 100 mL-1). Differences in water quality downstream vs. upstream from meadows grazed by pack stock were not detectable for most water-quality indicators, however, Escherichia coli concentrations decreased downstream, suggesting entrapment and die-off of fecal indicator bacteria in meadows. Our results indicate that under current-use levels pack stock trail use and backpacker use are associated with detectable, but relatively minor, effects on water quality, which are most pronounced during storms.

译文

:我们调查了游客的使用方式如何影响优胜美地国家公园荒野的水质。在2012-2014年夏季,我们收集并分析了地表水样品中的水质指标,包括粪便指标细菌大肠杆菌,营养物质(氮,磷,碳),悬浮沉淀物浓度,药物和激素。每周至每两周一次,在夏季暴风雨期间,从不同类型的访客使用的上游和下游采集样本。我们在2014年夏季进行了公园范围的天气抽样活动,并从草甸的上游和下游进行了采样,以评估草甸对水质的缓解作用。在打包种群的过境点处,下游的大肠杆菌浓度比上游的浓度高(三个集落形成单位100-1mL-1的大肠杆菌的中间下游增加),在暴风雨期间发生的最大增加(大肠杆菌的下游中间增加32个) CFU 100 mL-1)。在背包客使用地点,在下游地点检测到激素和药品(例如驱蚊剂),并且下游地点的大肠杆菌浓度更高(大肠杆菌中下游增加1 CFU 100?mL-1)。对于大多数水质指标而言,用包装纸放牧的草甸下游和上游的水质差异是无法检测到的,但是,大肠杆菌浓度在下游下降,表明粪便指示菌在草甸中被捕获和死亡。我们的结果表明,在当前使用水平下,背包径和背包客的使用与可检测到的但相对较小的对水质的影响相关,这在暴风雨期间最为明显。

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