Water quality and greenhouse gas fluxes for stormwater detained in a constructed wetland

Constructed wetlands (CWs) have been extensively used to deal with stormwater runoff and prevent flooding, as well as to improve water quality. However, some studies indicate that runoff from CWs can be a source of greenhouse gas (GHG) emissions to the atmosphere, as well as have increased levels of organic matter and nitrogen that may affect the environment and water quality of receiving waterways. We collected water samples at five different locations within a constructed stormwater detention wetland and determined dissolved organic carbon (DOC) and nitrate (NO3-), as well as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) concentrations and fluxes. Results showed that the water had high levels of DOC and NO3-. Analysis of DOC quality showed that the organic matter is mainly derived from soil and plant litter, but it has some contribution from microbial sources as well. Additionally, the water was supersaturated with CO2 and CH4 with respect to the atmosphere, which resulted in high evasion fluxes of 4.1 g CO2 -Cm(-2)d(-1)and 45 mg CH4-Cm(-2)d(-1). N2O flux was low, 36.6 mu g N2O-N m(-2) d(-1), and varied between uptake and emission throughout the study period. Consideration of water quality and GHG emissions is key to evaluate the environmental performance of stormwater management systems.