Coldwater streams are shaped by the interaction of groundwater, surface water, surrounding landscapes, physical habitat, and biological communities. Even relatively small changes in hydrology, temperature, riparian condition, or watershed development can alter habitat for thermally sensitive organisms such as brook trout and many aquatic macroinvertebrates.

Research in the Stoll Lab examines the physical, chemical, and biological processes that create and maintain healthy coldwater stream ecosystems. We are particularly interested in identifying which characteristics allow coldwater communities to persist in increasingly altered landscapes and how that information can be used to prioritize conservation and restoration.

Our approach integrates continuous temperature monitoring, physical habitat assessments, fish and macroinvertebrate communities, riparian vegetation, water quality, hydrology, GIS, and watershed-scale landscape characteristics. By examining these components together, we aim to understand not only whether a stream is impaired, but also why—and which management actions are most likely to improve ecological condition.

Assessing coldwater streams across Southwest Michigan

We are conducting comprehensive assessments of coldwater streams across Southwest Michigan to identify relationships among physical habitat, thermal conditions, and biological integrity. Field assessments include fish communities, macroinvertebrates, stream habitat, substrate, channel characteristics, riparian condition, and continuous water-temperature monitoring. We are also contributing to the Great Lakes Road-Stream Crossing Inventory. 

A major goal of this work is to translate ecological data into data-driven restoration priorities. Rather than applying the same restoration approach everywhere, we want to identify the factors actually constraining ecological condition within individual streams and determine where conservation investments are most likely to produce meaningful ecological benefits.

Protecting remnant brook trout populations

Small, isolated populations of brook trout persist in coldwater streams throughout Michigan, sometimes within watersheds substantially altered by agriculture, urban development, infrastructure, and other land uses.

We are interested in understanding what allows these remnant populations to persist. By examining stream temperature, groundwater influence, habitat quality, connectivity, surrounding land use, and other environmental characteristics, we aim to identify both vulnerable populations and opportunities for targeted protection.

Ultimately, this work asks an important conservation question: What needs to be protected today to ensure that coldwater species remain on the landscape in the future?

Stormwater, bioretention, and stream temperature

Urban stormwater presents a different challenge for coldwater ecosystems. During warm weather, runoff from roads, parking lots, rooftops, and other impervious surfaces can become substantially warmer than receiving streams.

Bioretention cells are increasingly used to capture and treat this runoff, but their effects on stream temperature remain poorly understood. Our research asks whether bioretention cells mitigate thermal pollution by retaining and cooling stormwater or contribute warm surface-water effluent to receiving coldwater streams during storm events.

By monitoring temperature and hydrologic responses throughout a small coldwater watershed, this work will help determine how green stormwater infrastructure functions within thermally sensitive watersheds and could ultimately inform stormwater design and management practices that better protect coldwater ecosystems.

Groundwater withdrawal & coldwater stream resilience

Groundwater is fundamental to many coldwater streams because groundwater inputs help maintain streamflow and buffer streams against high summer temperatures. Consequently, changes in groundwater availability have the potential to alter both the hydrology and thermal suitability of coldwater habitat.

An emerging direction of our research examines how groundwater withdrawal may influence coldwater stream health and how biological and habitat data can be incorporated into water-management decisions. We are particularly interested in connecting changes in hydrology with ecological responses rather than evaluating water availability solely from a physical perspective.

Beaver Management & Coldwater Stream Ecosystems

Beavers are ecosystem engineers that can substantially alter stream hydrology, geomorphology, temperature, and aquatic habitat. While beaver activity can create valuable habitat and increase ecological complexity, dams can also cause extensive flooding that creates conflicts with roads, infrastructure, private property, and other land uses. These conflicts often result in removal of beavers or their dams, creating a need for management approaches that allow beavers to remain on the landscape while reducing unwanted flooding.

We are evaluating “beaver deceivers” and related flow-control devices as an alternative approach to beaver management in Michigan. These structures are designed to regulate water levels and maintain flow through or around beaver dams, reducing severe flooding without requiring removal of the beavers or complete elimination of the dam.

Our research assesses streams with these management structures by monitoring conditions upstream and downstream of beaver dams through time. We are examining changes in stream substrate and geomorphology, physical habitat, fish communities, and aquatic macroinvertebrate communities to determine how both beaver dams and flow-control structures influence stream ecosystem condition. An important goal is to understand whether the ecological effects of these management approaches differ among stream types. By comparing responses across systems, we can identify where flow-control devices successfully balance flood management with the ecological benefits associated with beaver activity—and where their use may create unintended consequences for stream habitat or biological communities.

Beaver management remains challenging in Michigan because the ecological benefits of beavers must often be balanced against flooding and infrastructure concerns. Removing beavers can eliminate the source of the immediate conflict but also removes an important ecosystem engineer and may substantially alter stream habitat. This research will provide Michigan EGLE with direct, field-based information on how beaver flow-management structures function across different stream settings. By documenting their physical and biological effects through time, our goal is to help determine when and where these approaches are appropriate and potentially support their expanded use as a tool for coexistence with beavers while protecting stream ecosystems and surrounding infrastructure.

Questions we're interested in

• What physical and biological characteristics distinguish healthy coldwater streams?

• Which habitat characteristics best predict fish and macroinvertebrate community condition?

• What allows remnant brook trout populations to persist in altered watersheds?

• How important are groundwater inputs for maintaining thermal refugia and summer coldwater habitat?

• How does riparian vegetation influence in-stream habitat and thermal condition?

• Do bioretention cells reduce or exacerbate thermal pollution during storm events?

• How might groundwater withdrawal affect coldwater stream ecosystems?

• Which restoration and conservation actions are most likely to produce meaningful ecological improvements?

• Can beaver flow-control structures reduce flooding while maintaining the ecological benefits of beaver activity and protecting stream biological communities?

Why it matters

Coldwater streams support ecologically and recreationally important species while providing ecosystem services including water filtration, nutrient processing, and high-quality aquatic habitat. Climate change, groundwater demand, watershed development, habitat degradation, and altered stormwater delivery increasingly threaten these systems.

By identifying the mechanisms that sustain healthy coldwater ecosystems, our goal is to provide conservation organizations, natural resource managers, and decision-makers with information they can use to protect high-quality streams, prioritize restoration, and increase the resilience of coldwater ecosystems to future environmental change.