Coldwater Stream Refugia
Coldwater Stream Refugia
Small streams beloved by hikers, anglers and nature enthusiasts alike are also crucial for our ecosystems. Headwater streams are the sources of lakes, large rivers, and estuaries. Even though they are smaller and generally cooler than the rivers into which they flow, they are important for feeding fresh water, nutrients, and sediment into the larger bodies of water. Being as though they are so small, streams are highly sensitive to drought and changes in water availability. Thus, the increasing temperatures, particularly in the winter, and shifts in precipitation resulting from climate change have begun to threaten these systems. A greater portion of coldwater habitats (>60%) is likely to be lost in the Northeast than in the rest of the United States by 2100 because regional air temperatures are expected to rise at a faster rate.
Headwater streams support key life stages of important Massachusetts wildlife species. For example, Brook Trout, an economically important game species, are increasingly restricted to cold, clean headwater streams in Massachusetts (Climate Action Tool). Our brightly colored, forest log dwelling Spring Salamander, a species of conservation concern, also frequents the clean, cool, well oxygenated waters of headwater streams. Their larvae as strictly aquatic, so strictly in fact that they live in the stream on average four years before metamorphizing into an adult. Adults are also highly aquatic but are known to leave from time to time in order to forage in riparian zones. Therefore, these salamanders are highly susceptible to changing water temperatures. In MA, spring salamanders do not persist within streams that have been warmed, muddied, or degraded. Since these species are so susceptible to habitat change, it has been suggested that warming of streams as a result from climate change has the potential to reduce and fragment populations of this species.
Another stream-dependent species is the state-listed brook floater, one of the most endangered mussels in northeastern North America; declines may be related to climate and land use change but may also be related to the decline of their host fish brook trout. These guys not only are responsible for keeping the water from being overrun by algae, but also filter feed bacteria, zooplankton, and sediment from the water. These silent super heroes keep our streams turbidity low and oxygenation high in order to support other organisms that rely on high levels of oxygen to grow.
Despite stream vulnerability, there are options for conserving these ecosystems in the face of climate change. MassWildlife is teaming with federal, state, and university partners to map areas of climate change refugia, streams that are most resistant to increases in temperature that can increase persistence of wildlife and fish populations, to prioritize for protection and restoration. For example, brook trout are able to persist in surprisingly small, isolated populations above barriers in headwater streams so there is potential to protect and connect these places to bolster declining populations. Alternatively, areas that are projected to warm but are still well connected could be protected for warmer water species of conservation concern.
In Nash Stream Forest in New Hampshire, crossings were restored from 2007-2016 and other instream work was done from 2008-2017 by Trout Unlimited, NH Fish and Game Department, NH Division of Forests and Lands. This project aimed to restore the natural fluvial processes, such as the natural flow of the water and removing excess sediment in order to increase oxygenation of the water. Streams that had low summer temperatures and good habitat upstream of the culvert were prioritized. Culverts were either removed or replaced with geomorphically compatible crossings that didn't impede an organism's ability to cross, with an emphasis on the native brook trout. Another project was done in the Indian Stream watershed in New Hampshire from 2013 to 2017 for the crossings and 2015-2017 for instream work by Trout Unlimited, NH Fish and Game Department, The Forestland Group, NH Department of Natural and Cultural Resources with the same goals in mind.
A dam removal was also done at Hamant Brookin Massachusetts funded by Millennium Power, The Eastern Brook Trout Joint Venture, and The Massachusetts Environmental Trust. This dam removal aimed to reconnect ¾ of a mile of coldwater habitat for native Eastern Brook Trout and Wood Turtles. It accomplished this by restoring stream and riparian habitat and habitat connectivity, improving water quality. Another example is the collaborative monitoring and mapping efforts led by Dan Isaak of the U.S. Forest Service in the Pacific Northwest. The Cold-Water Climate Shield research project now provides user-friendly digital maps and GIS databases showing which streams throughout the Northwest are most likely to serve as climate change refugia for salmonids this century.