U.S. Geological Survey, Arizona Water Science Center, Tucson, Arizona, United States of America.
U.S. Geological Survey, Arizona Water Science Center, Flagstaff, Arizona, United States of America.
PLoS One. 2020 Nov 4;15(11):e0241502. doi: 10.1371/journal.pone.0241502. eCollection 2020.
Assessing chemical loading from streams in remote, difficult-to-access watersheds is challenging. The Grand Canyon area in northern Arizona, an international tourist destination and sacred place for many Native Americans, is characterized by broad plateaus divided by canyons as much as two-thousand meters deep and hosts some of the highest-grade uranium deposits in the U.S. From 2015-2018 major surface waters in Grand Canyon were monitored for select elements associated with breccia-pipe uranium deposits in the area, including uranium, arsenic, cadmium, and lead. Dissolved constituents in the Colorado River were monitored upstream (Lees Ferry), in the middle (Phantom Ranch), and downstream (Diamond Creek) of uranium mining areas. Concentrations of uranium, arsenic, cadmium, and lead at these main-stem sites varied little during the study period and were all well below human health and aquatic life benchmark criteria (30, 10, 5, and 15 μg/L maximum contaminant levels and 15, 150, 0.8, and 3.1 μg/L aquatic life criteria, respectively). Additionally, dissolved and sediment-bound constituents were monitored during a wide range of streamflow conditions at Little Colorado River, Kanab Creek, and Havasu Creek tributaries, whose watersheds have experienced different levels of uranium mining activities over time. Samples from the tributary sites contained ≤3.8 μg/L of dissolved cadmium and lead, and ≤17 μg/L of dissolved uranium. Dissolved arsenic also was mostly below human and aquatic life criteria at Little Colorado River and Kanab Creek; however, 63% of water samples from Havasu Creek were above the maximum contaminant level for arsenic. Arsenic in suspended sediment was greater than sediment quality guidelines in 9%, 35%, and 35% of samples from Little Colorado River, Kanab Creek, and Havasu Creek, respectively. At the concentrations observed during this study, tributaries contributed on average only about 0.12 μg/L of arsenic and 0.03 μg/L of uranium to the main-stem river. This study demonstrates how chemical loading from mined watersheds may be reliably assessed across a wide range of flow conditions in challenging locations.
评估偏远、难以进入的流域溪流中的化学负荷具有挑战性。亚利桑那州北部的大峡谷地区是国际旅游胜地，也是许多美国原住民的圣地，其特点是宽阔的高原，被深达 2000 米的峡谷分割，拥有美国一些品位最高的铀矿床。2015 年至 2018 年，对大峡谷的主要地表水进行了监测，以监测与该地区角砾岩筒铀矿床有关的选定元素，包括铀、砷、镉和铅。科罗拉多河的溶解成分在上游（利兹渡槽）、中游（幻影牧场）和下游（钻石溪）的铀矿区进行了监测。在研究期间，这些干流点的铀、砷、镉和铅浓度变化不大，均远低于人类健康和水生生物基准标准（最大污染物水平分别为 30、10、5 和 15μg/L，水生生物标准分别为 15、150、0.8 和 3.1μg/L）。此外，还在小科罗拉多河、卡纳布溪和哈瓦苏溪支流的广泛流量条件下监测了溶解和沉积物结合的成分，这些流域随着时间的推移经历了不同程度的铀矿开采活动。支流点的样品中溶解态镉和铅含量均≤3.8μg/L，溶解态铀含量均≤17μg/L。小科罗拉多河和卡纳布溪的溶解态砷也大多低于人类和水生生物的标准；然而，哈瓦苏溪的 63%的水样超过了砷的最大污染物水平。悬浮沉积物中的砷在小科罗拉多河、卡纳布溪和哈瓦苏溪的 9%、35%和 35%的样本中均高于沉积物质量指南。在本研究中观察到的浓度下，支流平均仅向干流贡献 0.12μg/L 的砷和 0.03μg/L 的铀。本研究表明，如何在具有挑战性的地点的广泛流量条件下可靠地评估矿区流域的化学负荷。
