Center for Watershed Sciences, University of California, Davis, California, United States of America.
Wildlife, Fish, & Conservation Biology, University of California, Davis, California, United States of America.
PLoS One. 2021 Aug 20;16(8):e0256286. doi: 10.1371/journal.pone.0256286. eCollection 2021.
Stream temperature science and management is rapidly shifting from single-metric driven approaches to multi-metric, thermal regime characterizations of streamscapes. Given considerable investments in recovery of cold-water fisheries (e.g., Pacific salmon and other declining native species), understanding where cold water is likely to persist, and how cold-water thermal regimes vary, is critical for conservation. California's unique position at the southern end of cold-water ecosystems in the northern hemisphere, variable geography and hydrology, and extensive flow regulation requires a systematic approach to thermal regime classification. We used publicly available, long-term (> 8 years) stream temperature data from 77 sites across California to model their thermal regimes, calculate three temperature metrics, and use the metrics to classify each regime with an agglomerative nesting algorithm. Then, we assessed the variation in each class and considered underlying physical or anthropogenic factors that could explain differences between classes. Finally, we considered how different classes might fit existing criteria for cool- or cold-water thermal regimes, and how those differences complicate efforts to manage stream temperature through regulation. Our results demonstrate that cool- and cold-water thermal regimes vary spatially across California. Several salient findings emerge from this study. Groundwater-dominated streams are a ubiquitous, but as yet, poorly explored class of thermal regimes. Further, flow regulation below dams imposes serial discontinuities, including artificial thermal regimes on downstream ecosystems. Finally, and contrary to what is often assumed, California reservoirs do not contain sufficient cold-water storage to replicate desirable, reach-scale thermal regimes. While barriers to cold-water conservation are considerable and the trajectory of cold-water species towards extinction is dire, protecting reaches that demonstrate resilience to climate warming remains worthwhile.
溪流温度科学和管理正迅速从单一指标驱动的方法转变为多指标、溪流景观的热态特征描述。鉴于对冷水渔业（如太平洋三文鱼和其他衰退的本地物种）的大量投资，了解冷水可能存在的地方以及冷水热态如何变化，对于保护至关重要。加利福尼亚州位于北半球冷水生态系统的南端，地理位置和水文条件多变，以及广泛的水流调节，这要求采用系统的方法对热态进行分类。我们使用了来自加利福尼亚州 77 个地点的公开、长期（>8 年）溪流温度数据，对其热态进行建模，计算了三个温度指标，并使用这些指标通过聚合嵌套算法对每个热态进行分类。然后，我们评估了每个类别的变化，并考虑了可能解释类间差异的潜在物理或人为因素。最后，我们考虑了不同的类别如何适应凉爽或寒冷水热态的现有标准，以及这些差异如何使通过监管来管理溪流温度的努力变得复杂。我们的研究结果表明，加利福尼亚州的凉爽和寒冷水热态在空间上存在差异。本研究有几个突出的发现。地下水主导的溪流是一种普遍存在但尚未得到充分探索的热态类型。此外，大坝以下的水流调节会造成连续的不连续，包括对下游生态系统的人工热态。最后，与人们通常的假设相反，加利福尼亚州的水库没有足够的冷水储量来复制理想的、沿程尺度的热态。虽然冷水保护面临着巨大的挑战，冷水物种灭绝的趋势也很严峻，但保护对气候变暖具有恢复力的河段仍然是有价值的。
