Karen L. Bushaw-Newton

Dam Removal: Challenges and Opportunities for Ecological Research and River Restoration

W flow is a “master variable” (sensu Power et al. 1995) that governs the fundamental nature of streams and rivers (Poff et al. 1997, Hart and Finelli 1999), so it should come as no surprise that the modification of flow caused by dams alters the structure and function of river ecosystems. Much has been learned during the last several decades about the adverse effects of dams on the physical, chemical, and biological characteristics of rivers (Ward and Stanford 1979, Petts 1984, Poff et al. 1997, Poff and Hart 2002). Increasing concerns about these impacts, together with related social and economic forces, have led to a growing call for the restoration of rivers by removing dams (AR/FE/TU 1999, Pejchar and Warner 2001). For the purposes of this paper, we define restoration broadly as an effort to compensate for the negative effects of human activities on ecological systems by facilitating the establishment of natural components and regenerative processes, although we acknowledge that these efforts rarely eliminate all human impacts (see Williams et al. 1997 for alternative definitions). Interest in dam removal as a means of river restoration has focused attention on important new challenges for watershed management and simultaneously created opportunities for advancing the science of ecology. One challenge lies in determining the magnitude, timing, and range of physical, chemical, and biological responses that can be expected following dam removal. This information is needed to decide whether and how dam removals should be performed to achieve specific restoration objectives (Babbitt 2002). Opportunities for advancing ecological research also exist because dam removal represents a major, but partially controllable, perturbation that can help scientists test and refine models of complex ecosystems. In contrast to the small-scale experiments that traditionally have been employed in stream and river ecology, the unusually large magnitude and spatial extent of dam removal WE DEVELOP A RISK ASSESSMENT FRAME-

Effects of small dam removal on stream chemistry in southeastern Pennsylvania

Abstract We examined changes in stream chemistry following the removal of a 2-m-high dam on Manatawny Creek in southeastern Pennsylvania. Our primary objective was to determine the effect of small dam removal on the concentrations and forms of C, N, and P. Dissolved and particulate constituent concentrations were monitored at sites upstream and downstream of the dam and impoundment. Seasonal changes in alkalinity and N and P concentrations were observed before and after dam removal. However, the proportions of NO3− + NO2−, NH4+, and dissolved organic N (DON), and soluble reactive P (SRP) and dissolved organic P (DOP) in the total dissolved pools of N and P did not change seasonally. The dam and dam removal did not influence C, N, or P concentrations and forms (except for NH4+) in this stream. The lack of significant changes probably was a result of the short hydraulic residence time (<1.5 h at base flow), infrequent temperature stratification, and potential C limitation of bacterial activity in the small impoundment. Our results suggest that alterations in N and P concentrations and forms following dam removal may be site-specific. The characteristics of the dam, watershed, and impoundment (e.g., the amount of wetted streambed, hydraulic residence time, and organic enrichment of sediment and water) probably determine the influence of dam removal on stream water chemistry.

Environmental bacteria produce abundant and diverse antibiofilm compounds

The aim of this study was to isolate novel antibiofilm compounds produced by environmental bacteria.

Nutrients, oxygen dynamics, stable isotopes and fatty acid concentrations of a freshwater tidal system, Washington, D.C.

The Anacostia River in Washington, D.C., USA is an urban waterway contaminated with PAHs, PCBs, metals and sewage. Although several studies have examined the heavy metal geochemistry within the river, no studies have examined basic biogeochemical processes within the Anacostia river system. This study examines nutrients, bacterial biomarkers, organic material, and carbon, nitrogen and sulfur sources in the system. High biological oxygen demand and low nitrogen (0.33-0.56 mg L(-1)) and phosphorus (0.014-0.021 mg L(-1)) concentrations were observed in three areas of the river. Downstream sites had higher nutrient concentrations and dissolved organic matter (up to 13.7 mg L(-1)). Odd-chain length and branched fatty acids (FAs) in the sediments indicated bacterial sources, but long chain FAs indicative of terrestrial primary production were also abundant in some sediments. Sediment carbon stable isotope analyses showed a mix of autochthonous and allochthonous derived materials, but most carbon was derived from terrestrial sources (-23.3 to -31.7 per thousand). Sediment nitrogen stable isotopes ranged from -5.4 to 5.6 per thousand, showing nitrate uptake by plants and also recycling of nitrogen within the river. Sulfur sources were generally between 3 and -5 per thousand, reflecting local sulfate sources and anaerobic sulfate reduction.