Coldwater streams are among the most vulnerable habitats to climate change. Changes in precipitation and air temperatures will alter hydrology to the detriment of many coldwater streams. Some coldwater streams are expected to diminish in size, permanently transition to warmer habitats, and or go dry. However, certain watershed characteristics can buffer climate change impacts. Coldwater streams in deep canyons, poleward-facing slopes, thick canopy cover, groundwater-fed areas, and with fewer anthropogenic impacts, are more likely to persist as conditions change. Such areas may act as coldwater refugia, providing long-term habitat to ecologically and economically important species like Brook Trout (Salvelinus fontinalis). The efficacy of conservation strategies to protect coldwater streams and the coldwater-adapted species that rely on them will depend largely on understanding the potential persistence and transition of habitats. We build on existing models (SHEDS-ICE) to map stream reaches in Massachusetts that are likely to remain coldwater refugia, or transition to cool- or warmwater habitats, under different climate scenarios and time scales (2030-2100). Although existing mapping tools incorporate some watershed characteristics (e.g., aspect, impervious surfaces), none directly include flow management, including lake-level management and groundwater inputs, the effects of which have been shown to shape fish assemblages in Massachusetts streams.
Results/Conclusions
Our research is the first to identify coldwater refugia and habitats potentially transitioning to cool- and warmwater at the reach scale in Massachusetts. First, the presence of coldwater species (e.g, Brook Trout, Longnose Sucker Catostomus catostomus, Slimy Sculpin Cottus cognatus) was used to identify stream reaches (~6724 km) most likely to include climate refugia (MDFW, unpublished data). Second, existing models of watershed characteristics and predicted climate scenarios were used to determine changes in the probability of species occupancy before and after potential management actions. Prior to the inclusion of flow management variables, existing models estimated that an increase in July temperatures of 2°C, 4°C, and 6°C would decrease the proportion of streams with high (>50%) probability of Brook Trout occupancy to 43%, 35% and 27%, respectively (ice.ecosheds.org). We are currently modeling the potential impacts of flow management and future stressors (e.g., urban development, water demands) on stream temperatures. The ability to understand the location, speed and duration of changes to stream habitats will guide management decisions that reflect the restoration potential of each reach. Management decisions that benefit directly from this research include prioritization of dam removal, instream flow protection, riparian vegetation management and location and timing of trout stocking.