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Effects of relic low-head dams on stream denitrification potential: seasonality and biogeochemical controls

350 210 Stroud Water Research Center

Hripto, J., S. Inamdar, M. Sherman, E. Peck, A.J. Gold, S. Bernasconi, K. Addy, and M. Peipoch. 2022. Aquatic Sciences 84, article number: 60.

https://doi.org/10.1007/s00027-022-00894-z

Abstract

The majority of dams in the contiguous United States are small, low-head dams that are no longer operational but can influence the water quality of contemporary stream ecosystems. Potential effects of low-head dams on stream nitrogen removal (denitrification) have been rarely quantified, and yet they can be an important part of the decision-making process of removing low-head dams. Here, we provide novel empirical data on potential denitrification rates and their biogeochemical controls above and below two mid-Atlantic low-head dams over a 2-year period. Our results show that low-head dams did not increase streambed potential denitrification in comparison to dam-free sections in the same rivers. In our study sites, potential denitrification above low-head dams was generally low (15.7 ± 3.5 µg N [kg sediment]−1 h−1) despite recurring events of water hypoxia (< 50% dissolved oxygen saturation) and high NO3 and DOC concentrations. Overall, we observed higher potential denitrification during winter samplings (9.2 and 50.1 µg N [kg sediment]−1 h−1 on average) and significant effects of sediment surface area and organic matter content on potential denitrification rates above the dams. Results from this study suggest limited effects of relic low-head dams on nitrogen removal and transport in stream ecosystems, and can contribute to the decision-making process of removing low-head dams.