Suncook River

Title: Physical, biological, and biogeochemical response of a northeastern river to a severe flood
Principal Investigators: William H. McDowell

Statement of critical regional or state water problem
On May 15, 2006 the Suncook River in Epsom, New Hampshire dramatically changed course, creating one entirely new stream reach, drastically reducing flow in a second reach, and delivering large amounts of suspended sediments to an otherwise un-impacted downstream reach. The May 25, 2006 issue of the New York Times included a feature-length article reporting on the event (http://www.nytimes.com/2006/05/29/us/29river.html). We now have an unparalleled opportunity to study the effects of sedimentation and dewatering on stream ecology and biogeochemistry, and to examine the process by which a new stream becomes established.

An examination of the effects of persistent dewatering on the biota and on ecosystem processes is particularly important in New England, which has only recently recognized the importance of instream flow issues. In New Hampshire, a pilot program was recently established for instream flow protection on the Lamprey and Souhegan Rivers, two of the state’s fourteen designated rivers. Water quality is intrinsically tied to water quantity; dissolved nutrients and pollutants can be concentrated or diluted depending on instream flow. Stream temperature is regulated, in part, by instream flow, and water quantity determines the extent of instream habitat. The direct and indirect impacts of drought can greatly reduce population densities, species richness and alter life-history schedules, species composition, patterns of abundance, type and strength of biotic interactions (predation and competition), food resources, trophic structure and ecosystem processes (Lake, 2003). Recreational activities such as fishing and boating can also be impacted by significant reductions in stream flow.

Documentation of the effects of continuously elevated sediment loads is also increasingly important in New England and nationally, due to relentless increases in construction activities and the creation of impervious surfaces. Sedimentation of streams affects organisms in two major ways: through physical and chemical changes to the water, and through blanketing of the stream bottom. Specific effects of siltation on aquatic systems include screening out light, changing heat radiation, smothering the stream bottom, and retaining organic material and other substances, which create unfavorable conditions at the bottom (Ellis, 1936). By reducing the stream bottom’s permeability to water movement, an increased amount of fine sediments in the streambed can affect the delivery and removal of gases, nutrients and metabolites, and potentially movement of animals (Allan, 1995).

Primary succession, involving site-specific, temporal change occurring after a disturbance that is so intense that no trace of the previous community remains (Fisher, 1990), has rarely been documented in streams at the spatial scale of whole river segments (Milner, 1994). With the proliferation of stream restoration activities that attempt to recreate natural channels (e.g. bypass channels and restored meanders), an understanding of the course and speed of the establishment of structure and function in a new stream would be timely. By advancing knowledge of the way that stream ecology and biogeochemistry respond to large-scale disturbances, this research has practical applications for stream conservation and restoration practices in New England.