The Development of Denitrification and of the Denitrifying Community in a Newly-Created Freshwater Wetland
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CONSTRUCTED WETLANDS
The Development of Denitrification and of the Denitrifying Community in a Newly-Created Freshwater Wetland Jordan J. Roose 1 & Judith M. Stribling 1
&
Michael S. Owens 2 & Jeffrey C. Cornwell 2
Received: 28 September 2019 / Accepted: 13 February 2020 # Society of Wetland Scientists 2020
Abstract Agricultural growth and urban development have increased nutrient loading into streams to unnatural levels, negatively affecting estuaries downstream. Wetland creation along streams has the potential to mitigate watershed nutrient loading, providing the necessary conditions to encourage bacterial denitrification. We compared denitrification in two wetland systems, one recently created and one well established, along a branch of the St. Martin River, the largest and most degraded tributary flowing into the Maryland Coastal Bays. Ambient and potential denitrification rates were measured using membrane inlet mass spectrometry, and the denitrifying bacterial communities were compared using qPCR with genes nirK, nirS, nosZ-I, and nosZ-II. For all sites, denitrification rates were highly variable, but similar between the two wetlands, while potential rates increased almost 10-fold after a NO3− amendment, indicating that the denitrifying communities can respond to pulses of NO3− delivered via episodic flow events. Overall, the denitrifying community was more abundant at the created wetland, but the reference site had a higher abundance of the nosZ-I gene and, therefore, a lower genetic potential for N2O production. The created wetland has developed denitrification rates and a denitrifying community similar to those of the established wetland and could successfully remove excess nutrients entering the system. Keywords Created wetland . Denitrification . MIMS . qPCR
Introduction Riverine wetlands are important for improving water quality and provide an environment favorable for microbial nitrogen (N) removal; frequent inundation and high organic matter decomposition rates within wetland sediments create the anoxic conditions necessary for denitrification (Von Korff et al. 2014). While nitrate (NO3−) passing through a wetland may be retained or transformed, bacterial denitrification represents a key removal mechanism for excess NO 3 − (Joye and Anderson 2008). There are two additional pathways for NO3− reduction in aquatic systems, dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (anammox), which reduce NO3− to ammonium (NH4+) and N2, respectively, but denitrification is more * Judith M. Stribling [email protected] 1
Salisbury University, Salisbury, MD 21801, USA
2
University of Maryland Center for Environmental Science, Horn Point Laboratory, Cambridge, MD 21613, USA
commonly observed in freshwater systems (Burgin and Hamilton 2007; Scott et al. 2008; Zhang et al. 2019). The success of wetland restoration and creation projects has been variable and depends on the goals of the project. Wetland restoration involves land that was previously a wetland, whereas cre
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