Gently-sloping Cool Streams

Slow-flowing in small watershed valleys with some connection to groundwater. Substrates are dominated by sand and gravel with some adjacent floodplain wetlands and the potential for rooted aquatic vegetation.

This habitat has been identified in the Massachusetts State Wildlife Action Plan because it supports a variety of plants and wildlife.

Habitat description

Meandering, cool streams with some groundwater inflows usually running through relatively wide alluvial floodplains, with substrate often dominated by silt, sand and gravel. This habitat is very important for groundwater exchange and floodwater retention. These streams move laterally in the floodplain, resulting in a series of oxbows and other wetlands that may support aquatic invertebrates typically associated with the stream. Beavers are often found in these streams, except on Cape Cod, and can create extensive stream-associated wetlands. These wetlands tend to increase solar exposure and cause general stream warming, but also enhance groundwater recharge and contribute to coldwater refugia within the reach. 

Characteristic communities and species

Fish communities in these reaches will vary depending on watershed but will typically be more diverse than gently sloping coldwater streams. Western watersheds will include white suckers, creek chubs, longnose and blacknose dace. Eastern watersheds include cool and warmwater species like fallfish, common shiner, bridle shiners, tessellated darter, and redfin pickerel. A wide variety of native and introduced pond species will also be present, especially when downstream of large impoundments. These streams can have additional species like brook trout in springs or areas where groundwater is upwelling. Mussels include eastern elliptio, eastern pearlshell, creeper, triangle floater, brook floater, dwarf wedgemussel, eastern lampmussel, and eastern pondmussel. Typical dragonfly species include spring and fawn darners, spiketails, snaketails, clubtails from the Phanogomphus and Hylogomphus genus, eastern least clubtail, and several striped emerald species where streams flow through wetlands.

Associated Habitat Types 

It is typical to have reaches of small low gradient coolwater streams adjacent to high gradient reaches, following changes in valley slope. This habitat is associated with riparian and floodplains, forests, and palustrine habitats. These reaches can vary widely over time, becoming a series of beaver ponds for a decade and then reverting to meandering streams with emergent grasslands for additional extended periods of time until enough food is once again present, in the form of young forest, for beaver colonies. This habitat is one of the most diverse aquatic stream habitats and is most closely associated with all other floodplain habitats and species. 

Ecological Processes 

Beavers are often the primary ecosystem engineers in these streams as they bring large woody habitat and organic material into streams that have seen 300 years of tree clearing and stream simplification. These organic inputs increase the natural productivity of the system. Unlike their high gradient counterparts, these streams can retain beaver dams for many years, eventually providing enough substrate even for mature trees to grow on old dams. The low energy and power that allows these dams to persist, also allows encroachment by invasive species. These reaches serve a critical role in flood storage, retaining water in adjacent side-channel wetlands.  

Threats

Climate change, water withdrawal, and floodplain encroachment are threats that will continue to increase in these habitats without protection and restoration measures. Existing impacts include channelization, disconnection from adjacent floodplain habitats, dams, and floodplain encroachment.

Restoration & management recommendations

This habitat is one of the most sensitive to the threats associated with climate change. Efforts to restore and manage these habitats will need to address climate change and also connect climate refugia.

• Floodplain restoration: Many streams in this category have been historically channelized, severing the connection between stream channel and floodplain. Restoring the connection is particularly important for gently sloping habitats and can have immediate flood storage benefits. Increased flood connection will also enhance groundwater infiltration and promote climate resilience and water quality.
• In-stream structure placement - Large woody habitat: The low energy of these streams makes them an excellent choice for the reestablishment of large woody habitat. The material will stay in place, provide variability in stream current, and will over time facilitate the reestablishment of sinuosity, reversing the historical trend of channelization, and further enhance flood storage
• Channel restoration - Benches, backwaters and side channels: Historical channelization dramatically reduces complexity of available habitat and exacerbates flooding. Channel restoration can be expensive and a challenge from a permitting perspective but can have great benefits for people and wildlife. In-stream structure placement and floodplain connectivity restoration can achieve many of the same goals, but over a much longer period of time than active channel restoration. This option might not be available in many instances, but is a more holistic approach to restoration.
• Dam removal: Gently-sloping streams were historically less of a target for damming as they could provide little vertical head and had little power. However, in places where dams exist, their removal can connect large reaches of stream between dams. Dam removal will allow fish and sediment transport, connect coldwater climate refugia, and allow streambank vegetation to shade the stream, providing further climate resilience. Because these streams are slow to heal from the presence of dams, active channel restoration might be needed in conjunction with this technique.

Examples

• West River
• Nemasket
• Farmington River (upper)

Additional resources

• Coming soon