Empirical studies have highlighted the important influence of lakes on stream temperature at landscape scales, even when lakes comprise just a small fraction of the catchment area. However, only a few studies have focused on the hydrologic and thermal processes underpinning these landscape patterns. We collected detailed field measurements at a boreal stream that drains a headwater lake and used these data within a process-based stream temperature model to, (a) document the downstream extent of lake influences at both seasonal and event-based timescales, (b) assess the hydrologic and thermal processes that control the observed downstream variability, and (c) compare downstream temperature for streams with and without a headwater lake. Summer and autumn lake outlet temperatures were elevated compared to hillslope lateral inflow temperatures. During periods of low lake outflow, stream temperatures decreased rapidly downstream as local energy fluxes, primarily lateral inflows from the hillslopes and hyporheic exchange, overwhelmed the lake effects. The lake influence on downstream temperature was the greatest during periods of high lake outflow and persisted at least 1.4 km downstream. Since lakes can moderate and delay upstream rainfall runoff response, periods of high lake outflow and high hillslope inflow rates were generally out-of-phase. This difference in timing of warm lake outlet and cool hillslope water creates a dynamic thermal environment downstream of the small lake. Such lakes are ubiquitous in northern landscapes, and accounting for the competing influence of lake and hillslope contributions on downstream water temperature is critical for predicting how network-scale thermal regimes will respond to environmental change.

中文翻译：

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湖泊流出和山坡横向流入决定了小湖泊排水的森林溪流的热规律

实证研究强调了湖泊对景观尺度上河流温度的重要影响，即使湖泊仅占集水区的一小部分。然而，只有少数研究关注支撑这些景观模式的水文和热过程。我们收集了排干源头湖的北方河流的详细现场测量数据，并在基于过程的河流温度模型中使用这些数据，以 (a) 在季节性和基于事件的时间尺度上记录湖泊影响的下游范围，(b)评估控制观察到的下游变化的水文和热过程，和 (c) 比较有和没有源头湖的溪流的下游温度。与山坡横向流入温度相比，夏季和秋季湖泊出口温度升高。在湖泊出水量低的时期，下游的河流温度迅速下降，因为局部能量通量，主要是从山坡和下流交换的侧向流入，淹没了湖泊的影响。湖泊对下游温度的影响在湖泊高流量期间最大，并持续到下游至少 1.4 公里。由于湖泊可以缓和和延迟上游降雨径流响应，因此湖泊高出流和山坡高入流时期通常是异相的。这种暖湖出口和凉山坡水的时间差异在小湖下游创造了一个动态的热环境。这样的湖泊在北方的风景中无处不在，