Keeping it Cool

Résumé du livre

Stream temperature is a major aspect of stream ecology. For ecosystems that depend on cold water, major disturbances from water extraction, dam regulation, and climate change have blocked or eliminated critical cold-water habitat. In California, cold-water conservation in streams is particularly critical as it is the southern extent of many cold-water species currently at risk of extinction. Research showing the importance of managing stream temperature from a regime-based perspective is disconnected from the more common practice of managing streams for threshold-based temperature criteria. This research connects the conceptual framework of regime-based stream temperature management and practice. Classifying California streams' thermal regimes identifies unique temperature patterns in groundwater-dominated stream reaches, suggesting that they should be prioritized for long-term cold-water conservation. The resilience of groundwater-dominated stream reaches contrasts with thermal regimes below dam outlets and in regulated reaches, which show an artificial pattern unable to replicate desirable cold-water regimes. A case study of Big Springs Creek, one stream in the classification analysis, shows that its thermal regime is controlled by a previously undocumented mechanism: aquatic macrophytes. Extensive, emergent aquatic macrophyte growth provides seasonal cover to over 70% of the stream surface, creating a riverine canopy. This riverine canopy is the dominant seasonal control of Big Springs Creek's thermal regime. Spatial and temporal growth was quantified with Unmanned Aerial Vehicle (UAV) imagery and used to develop a numerical model, which showed that monthly surveys were sufficient to accurately simulate the effects of the seasonal canopy on the thermal regime. The results of this research show that modeling thermal regimes to identify thermally resilient reaches, and numerical modeling of stream reaches to assess alternative management actions, is a viable strategy to prioritize conservation investments to restore and sustain cold-water ecosystems.