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Boston College

Department of Earth and Environmental Sciences


Environmental Studies Program

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Current Research Interests
Downstream changes in water quality and geomorphology around beaver vs. anthropogenic dams in Massachusetts

Beaver Meadow on Pearl Hill Brook Upstream of dam on Pearl Hill Brook

Comparison of an ecogeomorphically diverse beaver meadow (left) and a reservoir upstream of a man-made dam (right) on Pearl Hill Brook.
Both sections of channel are found at Pearl Hill State Park. The differences in geomorphic and ecosystem characteristics upstream of these dams resulted in development of the following research questions: (i) How do beaver versus man-made dams alter trends in water quality? (ii) How do these dams impact geomorphic characteristics such as downstream transport and storage of large wood?

Research Summary:

Beavers are important ecosystem engineers because of their ability to build dams that create low flow zones in the river, causing deposition of sediment, increasing the height of water tables, and often creating wetland habitat adjacent to the channel (Burchsted et al., 2010; Polvi and Wohl, 2013). In Massachusetts, beavers were hunted to extinction soon after settlers established themselves in the region. They were completely absent from the state between the late 1700s and early 1900s. Since their re-establishment in the mid-1900s, beaver populations have grown to close to 70,000 in 2001 (, 2014). The reintroduction of beavers is considered beneficial, because of re-establishment of wetland habitat along with them. Beaver dam habitat can increase the interaction between groundwater and surface water, improving water quality, and increasing the cycling of nutrients. Beaver dams have been shown to alter pH, nutrients, and temperature. It is not well understood if these changes in water quality are unique to beaver dams or if man-made dams can have similar effects (Burchsted et al., 2010).

Massachusetts has a high density of dams, particularly of those built over 100 years ago for industries that no longer exist in the state.

Research Questions:

(1) How do beaver dams alter downstream trends in water quality, such as dissolved oxygen, temperature, and nutrient dynamics? How do these trends differ around beaver versus anthropogenic dams?

(2) How are lateral connections and subsurface flows altered upstream and downstream of a beaver dam (vs. anthropogenic dam)?

Understanding stream health in a dammed watershed

Large wood in Mousam River Large wood in Mousam River

Large wood in the Mousam River in Maine
The picture on the left shows organic material (leaves) accumulating upstream of a log that spans the channel. This is likely a 'hot spot' where there is a high rate of biogeochemical processing of material happening.

Stream health is a concept that links physical and biological diversity and integrity, because the river structure provides the substrate for biogeochemical processes, but it is not yet a quantifiable term. The overarching goal of this project is to develop a metric of stream health that links the physical and biological functions. I propose to use stream metabolism as a proxy for biological diversity and to link the biogeochemical processing of material with the hydraulic and geomorphic diversity within a channel. Wood is recognized as an important geomorphic, hydraulic, and ecologic component of fluvial systems, therefore reaches with a higher density of wood are expected to have high physical diversity and have high rates of biogeochemical cycling. The proposed research will further our knowledge on whether stream metabolism can become a proxy for stream health, while investigating how in-channel wood affects flow patterns, structure, and biogeochemical functions.

Wood transport and distribution in a watershed fragmented by dams

Large wood in Mousam River

Above are results from a study that was part of a senior thesis project by Rhianna James ('14).
She investigated the major sources of wood in the Mousam River using aerial photography, GIS, and field surveys. She found that 33% of the in-channel wood came from large mass wasting events off of the banks. Click on picture to see larger image.

Anthropogenic fragmentation of rivers by dams causes alterations in the movement of water, sediment, organic material, and aquatic organisms. Wood is recognized as an important geomorphic, hydraulic, and ecologic component of fluvial systems, yet the wood dynamics in fragmented rivers are not well understood. The main objective of this project is to identify key sources of wood recruitment, and locations and types of accumulation in a watershed fragmented by multiple dams. Understanding how wood functions in the currently fragmented watershed can assist with prioritizing restoration projects, by determining which sections of the stream are most crucial to biogeochemical processes.

Restoration of hyporheic zone after dam removal

The hyporheic zone (HZ) is a region below the channel where there is an exchange of water, sediment, solutes, and small organisms between the surface and subsurface. The HZ has been found to be an important region for invertebrate production and can strongly influence the volume, temperature, and chemistry of flow in a river channel. Furthermore, the HZ can provide an area of increased biogeochemical processing of material. Therefore, the HZ is an important part of the stream ecosystem and needs to be restored if restoration goals are to be met. In New England, many old dams have reached the end of their functionality and are being removed. The main question for this research project is, does dam removal results in restoration of surface-subsurface exchanges in the hyporheic zone?


Baker, B.W., and Hill, E.P., 2003. Beaver (Castor canadensis). In: Feldhamer, G.A., Thompson, B.C. and Chapman, J.A. (Eds.), Wild Mammals of North America: Biology, Management, and Conservation. Second Edition. The Johns Hopkins University Press, Baltimore, Maryland, 288-310.

Burchsted, D., Daniels, M., Thorson, R., Vokoun, J., 2010. The river discontinuum: applying beaver modifications to baseline conditions for restoration of forested headwaters. Bioscience, 60(11), 908 922., 2014. Managing beavers. Department of Energy and Environmental Affairs, Commonwealth of Massachusetts. (viewed on Sept. 9, 2014).

Naiman, R.J., Johnston, C.A., Kelley, J.C., 1988. Alteration of North American streams by beaver: the structure and dynamics of streams are changing as beaver recolonize their historic habitat. Bioscience, 38(11), 753 762.

Polvi, L.E., Wohl, E., 2013. Biotic drivers of stream planform: implications for understanding the past and restoring the future. Bioscience, 63, 439 452.



Pearl Hill Brooke

Downstream change on Pearl Hill Brook in Pearl Hill State Park, Massachusetts
Investigation on geomorphic and ecologic effects of beaver versus man-made dams on streams in Massachusetts. Click on image for larger picture.

Study Sites

Location of study sites in Massachusetts
Stream surveys were conducted at four locations: Bear Swamp Reservation, Pearl Hill State Park, Harold Parker State Forest, and Noanet Woodlands. Click on picture to see larger image of map. Click on circled areas to see pictures of each stream. GIS data from MassGIS.

Massachusetts Dams

Distribution of dams in Massachusetts
Data from MassGIS. Density of dams in Massachusetts can also be found on the Army Corps of Engineers, National Inventory of Dams website.

Mousam River

Mousam River, Maine
Reservoir upstream of dam.

Mousam River, ME

Large wood in the Mousam River, ME
Large wood deposited in the reservoir along the Mousam River.

Mousam River, ME

Potential sources of wood in Mousam River , ME
Other potential sources of wood include wood input from the floodplain, undercut banks, and blowdowns.

Dam on Mousam River

Dam on Mousam River, ME
The Mousam River has been physically and ecologically impacted by multiple dams. It currently has 15 dams, although in the past it had as many as 24 in the watershed.