Hydrological, Chemical, and Biological Characterization of the Snake River and Associated Tributaries and Irrigation Drains from River Mile 448 to 346, 2022

This dataset includes field hydrologic measurements and laboratory analyses of surface and pore waters, sediments, benthic plants/biofilms, and biota along the Middle Snake River upgradient of the Hells Canyon Complex. The study region for this work focuses on a section of the Snake River heavily utilized for agriculture, with complex systems of irrigation diversion and return drainage, spanning 164 km above the Hells Canyon Complex (Idaho, Oregon). The goal of this study was to identify potential loading sources of methylmercury from the upgradient Snake River into the reservoir complex, with a focus on the tributaries, irrigation return drains, and riparian zones adjacent to agricultural lands along the river. To this end, 16 locations along the Snake River between River Miles 448 and 346 were sampled over a four-day period, July 11 ? 14, 2022. At each sampling site, pore water and sediment cores were collected in the shallow riparian zones along the edge of the river, surface waters were collected from cross-sections of the river, river flow and velocity were measured, submerged macrophytes and associated biofilm was collected, and biota (snails, amphipods, clams, periphyton, dragonfly larvae) were sampled from shallow riparian margins using a boat-mounted benthic suction dredge. Concurrently, water samples were collected from the six major tributaries that enter the Snake River in the study reach (Succor Creek, Owyhee River, Boise River, Malheur River, Payette River, Weiser River) and from six irrigation return drains that were actively discharging to the Snake River. Data from additional irrigation return drains to the study reach, sampled in June 2021 and May 2022, are also included. All water samples (surface and pore water) were processed and analyzed for filter-passing total mercury and methylmercury, dissolved organic carbon (DOC), dissolved organic matter (DOM) composition (UV-vis absorption and fluorescence), inorganic anions (chloride, nitrate, sulfate), and filter acidified metals (iron, manganese). In addition, the surface waters were analyzed for total suspended solids (TSS), particulate total and methylmercury, particulate organic carbon (POC) and stable isotopic composition, particulate nitrogen (PN) content and stable isotopic composition, and particulate metals (iron, manganese); and the pore waters were analyzed for inorganic sulfide (S(-II)). Sediment, submerged macrophytes and biofilms, and biota samples were dried, ground, and analyzed for total and methylmercury. Loss on ignition was also measured on the sediment samples. This data release includes metadata and eight tables in machine readable format (*.csv). All data columns in tables 3-8 are defined in Table 2. Reference Table 2 for associated units, abbreviation definitions, laboratory information, and method citations. Table_1_Site_Descriptions.csv - site descriptions Table_2_Analysis_Descriptions.csv - data dictionary defining column headings in Tables 3-8 Table_3_Water_SW.csv - surface water chemistry data Table_4_Water_PW.csv - pore water chemistry data Table_5_Sediment.csv - sediment chemistry data Table_6_Macrophytes_and_Biofilms.csv - submerged macrophyte and biofilm data Table_7_Hydrology.csv - hydrologic data Table_8_Biota.csv - biota data

本数据集涵盖了地狱谷综合体（Hells Canyon Complex）上游段中蛇河沿线的野外水文测量数据，以及地表水、孔隙水、沉积物、底栖植物/生物膜和生物群的实验室分析结果。本研究的区域聚焦于中蛇河一段农业开发强度极高的河段，该河段拥有复杂的引水灌溉与退排水系统，范围覆盖地狱谷综合体上游164公里的河段（位于爱达荷州、俄勒冈州境内）。本研究的目标为识别中蛇河上游向该水库综合体输入甲基汞的潜在来源，重点关注沿河农业用地毗邻的支流、灌溉退水渠以及河岸带。为此，研究团队于2022年7月11日至14日的四天时间内，对河道英里数448至346之间的中蛇河沿线16个采样点开展了采样工作。在每个采样点，研究人员于沿河浅滩河岸带采集孔隙水与沉积物岩芯，从河道断面采集地表水样本，测量河道流量与流速，采集沉水大型植物及其附着生物膜，并使用船载底栖抽吸式挖泥机从浅滩河岸带采集生物群样本（涵盖螺类、端足类、蚌类、周丛生物、蜻蜓幼虫）。与此同时，研究人员还采集了研究河段内汇入中蛇河的6条主要支流（萨克溪、奥怀希河、博伊西河、马卢尔河、佩埃特河、韦瑟河）的水样，以及6条正向中蛇河排放的灌溉退水渠的水样。本数据集同时纳入了2021年6月与2022年5月采集的研究河段其他灌溉退水渠的相关数据。所有水样（地表水与孔隙水）均经过处理并分析了以下指标：滤过态总汞与甲基汞、溶解有机碳（dissolved organic carbon, DOC）、溶解有机质（dissolved organic matter, DOM）组成（紫外-可见吸收与荧光光谱）、无机阴离子（氯化物、硝酸盐、硫酸盐）以及滤后酸化金属（铁、锰）。此外，研究人员还对地表水开展了以下指标分析：总悬浮颗粒物（total suspended solids, TSS）、颗粒态总汞与甲基汞、颗粒有机碳（particulate organic carbon, POC）及其稳定同位素组成、颗粒态氮（particulate nitrogen, PN）含量及其稳定同位素组成，以及颗粒态金属（铁、锰）；孔隙水则被分析了无机硫化物（S(-II)）指标。沉积物、沉水大型植物与生物膜以及生物群样本均经过干燥、研磨处理，并分析了总汞与甲基汞含量；沉积物样本还测定了烧失量。本数据发布包包含元数据以及8个机器可读格式（*.csv）的数据表。数据表3至8中的所有数据列均在表2中予以定义。如需了解相关单位、缩写定义、实验室信息以及方法引用，请参考表2。各数据表详情如下：Table_1_Site_Descriptions.csv：采样点描述表；Table_2_Analysis_Descriptions.csv：数据表3至8列名定义的数据字典；Table_3_Water_SW.csv：地表水化学数据表；Table_4_Water_PW.csv：孔隙水化学数据表；Table_5_Sediment.csv：沉积物化学数据表；Table_6_Macrophytes_and_Biofilms.csv：沉水大型植物与生物膜数据表；Table_7_Hydrology.csv：水文数据表；Table_8_Biota.csv：生物群数据表。