Ecological Engineering 72 (2014) 40–46 Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng Long-term denitrification rates in created riverine wetlands and their relationship with environmental factors Keunyea Song a , Maria E. Hernandez b , Jacqulyn A. Batson c , William J. Mitsch d,∗ a Department of Biology, Trent University, Peterborough, ON, Canada b Institute of Ecology, Xalapa, Veracruz, Mexico c USGS National Research Program for Water Resources, Reston, VA, USA d Everglades Wetland Research Park, Kapnick Center, 4940 Bayshore Drive, Florida Gulf Coast University, Naples, FL, USA article info Article history: Received 3 April 2013 Received in revised form 28 June 2013 Accepted 29 June 2013 Available online 14 September 2013 Keywords: Created wetland Nitrogen retention Denitrification Wetland hydrology Aboveground net primary productivity Olentangy River Wetland Research Park abstract Created wetlands that mimic structure and functions of natural wetlands have been widely applied mainly as a means for water quality improvement. Denitrification is a process that is considered to be important, especially in wetlands with their anaerobic soils, for the removal of nitrogen. In this study, we assessed the temporal and spatial patterns of denitrification from created wetlands over a relatively long time scale of 6 years. We found that denitrification rates were highly variable, ranging from 2.1 to 5288 gm -2 h -1 over that 6-year study period. Overall denitrification followed expected seasonal patterns, depending on temperature and nitrate concentrations in the surface water. We also found higher denitrification in open water and deep marsh areas than in shallow and wetland edge areas, likely the result of oxygen depletion in deeper water areas. Denitrification was also regulated by hydrologic regime. The highest mean deni- trification rate (506 gm -2 h -1 ) was observed in 2004 when the wetlands received artificial hydrologic pulses and the lowest rates (217 gm -2 h -1 ) were observed in 2008, when wetlands were drier than in other years. The presence/absence of vegetation had little influence of spatial and seasonal variations of denitrification. However, annual variations of denitrification tended to be related to vegetation produc- tivity as indicated by aboveground net primary productivity. This result suggests that denitrification rates may have been suppressed by plants creating aerobic condition in their rhizospheres. The high spatio- temporal patterns of denitrification seen in these created wetlands were caused mainly by a complex interaction of hydrology, nitrate-nitrogen concentrations and temperature. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Nitrogen, the most prominent non-point pollutant, is dis- charged from agricultural and urban areas and causes eutrophi- cation in aquatic ecosystems, particularly in coastal waters. Given that wetlands are known as significant sinks of nitrogen, partic- ularly nitrate-nitrogen by denitrification and vegetation uptake (Gold et al., 1998; Mitsch and Gosselink, 2007), the creation and restoration of wetlands have been attempted many times to improve water quality (Mitsch et al., 2001, 2005). Created wetlands are self-designing ecosystems which can maintain functions naturally by using natural energy sources, such as sunlight and nutrient inflow (Mitsch and Jørgensen, 2004). This ∗ Corresponding author at: Everglades Wetland Research Park, Kapnick Center, Florida Gulf Coast University, 4940 Bayshore Drive, Naples, FL 34112, USA. Tel.: +1 614 946 6715; fax: +1 239 732 7043. E-mail address: wmitsch@fgcu.edu (W.J. Mitsch). self-designing nature of created wetlands lessens the cost and efforts for wetland operation and management, but also allows temporal variations of environmental conditions over the longer term as the ecosystems self-design. These changes in environ- mental conditions of created wetlands over time further lead to high temporal variability in biogeochemical process rates such as denitrification in wetlands. However, long-term biogeochemical process rates and their relationship with environmental changes in created wetlands are poorly observed and understood in most wetland restoration and creation cases. Denitrification is a microbial process that removes nitrate nitro- gen from wetlands by transforming into the gasses dinitrogen and nitrous oxide (Martin et al., 1999; Mitsch and Gosselink, 2007). This process is considered as a main N removal mechanism in wetlands, particularly in created wetlands for wastewater treat- ment where often over 70% of total nitrogen removal efficiency have been obtained (Kadlec and Knight, 1996). Various factors such as temperature, nitrate concentration, and organic matter con- tent and quality affect the denitrification process, and vegetation 0925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2013.06.041