Sullivan Patrick F, Dial Roman J, Cooper David J, Diamond Charles, Tino Christopher J, Gregory Daniel D, Wong Russell E, Lyons Timothy W
University of Alaska Anchorage, Environment and Natural Resources Institute, Anchorage, AK 99508.
Alaska Pacific University, Institute of Culture and Environment, Anchorage, AK 99508.
Proc Natl Acad Sci U S A. 2025 Sep 16;122(37):e2425644122. doi: 10.1073/pnas.2425644122. Epub 2025 Sep 8.
The streams of Alaska's Brooks Range lie within a vast (~14M ha) tract of protected wilderness and have long supported both resident and anadromous fish. However, dozens of historically clear streams have recently turned orange and turbid. Thawing permafrost is thought to have exposed sulfide minerals to weathering, delivering iron and other potentially toxic metals to aquatic ecosystems. Here, we report stream water metal concentrations throughout the federally designated Wild and Scenic Salmon River watershed and compare them with United States Environmental Protection Agency (EPA) chronic (4-d) exposure thresholds for toxicity to aquatic life. The main stem of the Salmon had elevated SO concentrations and elevated SO: Ca relative to a predisturbance baseline for most of its length, consistent with increased sulfide mineral weathering. Most of the tributaries also had elevated SO concentrations and elevated SO: Ca, especially those in the upper watershed. The Salmon River mainstem consistently exceeded EPA chronic exposure thresholds for total recoverable iron, total recoverable aluminum, and dissolved cadmium from its first major tributary to its mouth. Nine of ten major tributaries that we sampled exceeded EPA thresholds for at least one metal on at least one of three sampling dates. Our findings indicate that habitat quality for resident and anadromous fish has been severely degraded in the Salmon River watershed. Loss of important spawning habitat in the Salmon and many other streams in the region might help explain a recent crash in chum salmon returns, which local communities depend upon for commercial and subsistence harvest.
阿拉斯加布鲁克斯山脉的溪流位于一片广袤（约1400万公顷）的受保护荒野之中，长期以来一直为本地鱼类和溯河产卵鱼类提供生存环境。然而，最近几十条历史上清澈的溪流变成了橙色且浑浊不堪。据认为，冻土融化使硫化物矿物暴露于风化作用之下，从而将铁和其他潜在有毒金属带入了水生生态系统。在此，我们报告了联邦指定的野生和风景优美的鲑鱼河流域内溪流水体中的金属浓度，并将其与美国环境保护局（EPA）规定的对水生生物毒性的慢性（4天）暴露阈值进行了比较。鲑鱼河干流在其大部分流程中，相对于扰动前的基线，硫酸根浓度升高，硫酸根与钙离子的比值也升高，这与硫化物矿物风化作用增强一致。大多数支流的硫酸根浓度和硫酸根与钙离子的比值也升高，尤其是流域上游的支流。从其第一条主要支流到河口，鲑鱼河干流中总可回收铁、总可回收铝和溶解镉的含量一直超过EPA的慢性暴露阈值。在我们采样的十条主要支流中，有九条在三个采样日期中的至少一个日期，至少有一种金属超过了EPA的阈值。我们的研究结果表明，鲑鱼河流域内本地鱼类和溯河产卵鱼类的栖息地质量已严重退化。鲑鱼河以及该地区许多其他溪流中重要产卵栖息地的丧失，或许有助于解释近期大麻哈鱼洄游数量的暴跌，而当地社区的商业和自给性捕捞依赖于这些大麻哈鱼。
