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如何影响优胜美地国家公园荒野中的水质。在2012-2014年夏季,我们收集并分析了地表水样品的水质指标,包括粪便指示细菌大肠杆菌,营养物质 (氮,磷,碳),悬浮沉积物浓度,药物和激素。在每周至每两周的间隔以及夏季风暴期间,从不同类型的访客使用的上游和下游收集样本。我们在夏季2014进行了公园范围的天气采样活动,并从草甸的上游和下游采样,以评估草甸对水质的缓解作用。在pack种群流过境处,从过境处下游的大肠杆菌浓度高于上游 (三个菌落形成单位100   mL-1的大肠杆菌的下游中位值增加),其中最大的增加发生在风暴期间 (大肠杆菌的下游中位值增加32 CFU 100   mL-1)。在背包客使用地点,在下游地点检测到激素和药物 (例如,驱虫剂),并且在下游地点检测到大肠杆菌浓度更高 (大肠杆菌的下游增加中位数为1 CFU 100 mL-1)。对于大多数水质指标,无法检测到填鸭式草甸下游与上游的水质差异,但是,下游的大肠杆菌浓度降低,表明草甸中粪便指示细菌的截留和死亡。我们的结果表明,在当前使用水平下,包装库存的使用和背包客的使用与可检测但相对较小的水质影响有关,这在暴风雨期间最为明显。

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