Urbanization drives geographically heterogeneous freshwater salinization in the northeastern United States

Rising trends in freshwater salinity, collectively termed the Freshwater Salinization Syndrome (FSS), constitute a global environmental concern. Given that the FSS has been observed in diverse settings, key questions regarding the causes, trend magnitudes, and consequences remain. Prior work hypothesized that FSS is driven by state factors, such as human-centered land use change, geology, and climate. Here, we identify the fundamental overriding factors driving FSS within the northeastern United States and quantify the diversity of FSS severity within the region. Specifically, we analyzed decadal-scale trends in specific conductance (a salinity proxy) for 333 lotic sites over four  decades. Next, we quantified potential variables driving the rising or falling trends, including impervious surface cover (ISC), winter temperature and precipitation, watershed size, and ambient conductance. Temperature and ISC were considered the most likely candidates for predicting FSS severity because roa..., All water quality data were collected from the Water Quality Portal, an online database maintained by the National Water Quality Monitoring Council. Data were collected using the following filters (selected options as listed on the portal provided in italics): states inclusive of the 10 listed above, site type = Stream (NWIS, STEWARDS, STORET), sample media = Water (NWIS, STEWARDS, STORET), characteristic = Specific conductance (NWIS, STORET), a date range between 1 Jan.1980 and 12 Jan. 2021, and minimum results per site = 100. Sites with records that spanned <10 yr were omitted from further analyses. Included here are also metrics depicting land use and climate attributes for each site.,

淡水盐度持续上升的趋势，统称为淡水盐化综合征（Freshwater Salinization Syndrome, FSS），已成为全球性的环境关切问题。鉴于该综合征已在多种环境场景中被观测到，关于其成因、趋势强度与生态影响的核心科学问题仍未得到充分解答。既往研究提出假说，认为FSS由各类状态因子驱动，例如人类主导的土地利用变化、地质条件与气候。本研究旨在明确美国东北部地区驱动FSS的核心主导因子，并量化该区域内FSS严重程度的多样性特征。具体而言，本研究针对40余年间333个流水生境样点的比电导率（specific conductance，盐度替代指标）的年代际变化趋势展开分析。随后，本研究量化了驱动趋势升降的潜在变量，包括不透水面覆盖率（impervious surface cover, ISC）、冬季气温与降水量、流域面积以及环境比电导率。研究认为气温与ISC是预测FSS严重程度的最具潜力的因子，原因在于……所有水质数据均取自水质门户（Water Quality Portal）——这是由美国国家水质监测委员会（National Water Quality Monitoring Council）维护的在线数据库。数据采集时应用了以下筛选条件（数据库页面标注为斜体的可选配置）：涵盖上述10个州、样点类型=溪流（NWIS、STEWARDS、STORET）、采样介质=水体（NWIS、STEWARDS、STORET）、监测指标=比电导率（NWIS、STORET）、时间范围为1980年1月1日至2021年1月12日，且每个样点的有效观测数不少于100。记录时长不足10年的样点被排除在后续分析之外。本数据集还包含各对应样点的土地利用与气候属性指标。