BIOWATER’s PhD Student Mette V. Carstensen is first author of a paper on “Reducing adverse side effects by seasonally lowering nitrate removal in subsurface flow constructed wetlands”.
Losses of nitrogen (N) from agricultural lands can be effectively reduced by constructed wetlands (CW). A specific type of CW is a wetland that receives subsurface-flow from drainage, and with a filter of wood chips (SSF-CWs), see the figure. A negative side-effect of these wetlands can be that methane and phosphate may be released during the filtering process.
In this study, two pilot SSF-CWs with wood chips were analysed. It was found that methane production was suppressed when the hydraulic retention time was decreased from on average 82 hours to 11 hours during the low flow period (summer to autumn):
Overall, the SSF-CWs were a net sink of phosphorus, retaining 29 to 33% of the total P loading. However, with respect to phosphate, the wetlands acted as both a sink and source. This study emphasises the importance of employing a holistic approach when designing wetlands in order to diminish negative side effects.
From the field site in Skannerup. Photo: Carl Christian Hoffmann.
Reference:
Carstensen, M.V., S.E. Larsen, C. Kjærgaard and C.C. Hoffmann. 2019. Reducing adverse side effects by seasonally lowering nitrate removal in subsurface flow constructed wetlands. Journal of Environmental Management 240: 190-197. doi:10.1016/j.jenvman.2019.03.081.
Feature image: Mette V. Carstensen.