Data from: Accounting for groundwater in stream fish thermal habitat responses to climate change

Forecasting climate change effects on aquatic fauna and their habitat requires an understanding of how water temperature responds to changing air temperature (i.e., thermal sensitivity). Previous efforts to forecast climate effects on brook trout (Salvelinus fontinalis) habitat have generally assumed uniform air–water temperature relationships over large areas that cannot account for groundwater inputs and other processes that operate at finer spatial scales. We developed regression models that accounted for groundwater influences on thermal sensitivity from measured air–water temperature relationships within forested watersheds in eastern North America (Shenandoah National Park, Virginia, USA, 78 sites in nine watersheds). We used these reach-scale models to forecast climate change effects on stream temperature and brook trout thermal habitat, and compared our results to previous forecasts based upon large-scale models. Observed stream temperatures were generally less sensitive to air temperature than previously assumed, and we attribute this to the moderating effect of shallow groundwater inputs. Predicted groundwater temperatures from air–water regression models corresponded well to observed groundwater temperatures elsewhere in the study area. Predictions of brook trout future habitat loss derived from our fine-grained models were far less pessimistic than those from prior models developed at coarser spatial resolutions. However, our models also revealed spatial variation in thermal sensitivity within and among catchments resulting in a patchy distribution of thermally suitable habitat. Habitat fragmentation due to thermal barriers therefore may have an increasingly important role for trout population viability in headwater streams. Our results demonstrate that simple adjustments to air–water temperature regression models can provide a powerful and cost-effective approach for predicting future stream temperatures while accounting for effects of groundwater.

预测气候变化对水生动物及其栖息地的影响，需明晰水温对气温变化的响应规律（即热敏感性（thermal sensitivity））。此前针对气候变化对溪红点鲑（Salvelinus fontinalis）栖息地影响的预测研究，通常假设大尺度区域内气-水温关系均一，却未考虑地下水输入及其他精细空间尺度过程的作用。我们基于北美东部森林流域（美国弗吉尼亚州谢南多厄国家公园，9个流域共78个监测点位）实测的气-水温关系，构建了可表征地下水对热敏感性影响的回归模型。我们利用这些河段尺度模型，预测了气候变化对溪流水温及溪红点鲑热栖息地的影响，并将本研究结果与此前基于大尺度模型得到的预测结果进行了对比。实测溪流水温对气温的敏感性普遍低于此前的假设，我们将这一现象归因于浅层地下水输入的调节作用。通过气-水温回归模型预测的地下水温度，与研究区域内其他点位的实测地下水温度吻合度较高。基于本研究精细尺度模型得到的溪红点鲑未来栖息地丧失预测结果，远较此前采用较粗空间分辨率模型得到的结果乐观。但本研究模型同时揭示了流域内部及不同流域间的热敏感性空间异质性，这使得适宜热栖息地的分布呈现斑块状特征。因此，由热屏障引发的栖息地破碎化，对源头溪流中溪红点鲑种群的存续可能会发挥愈发重要的作用。本研究结果表明，仅需对气-水温回归模型进行简单调整，即可在考虑地下水影响的前提下，为未来溪流水温预测提供一种高效且经济的可行方案。