Journal article

Publication year: 2019

Pages: 55-63

Journal: Ecological Engineering: The Journal of Ecosystem Restoration

Volume number: 126

ISSN: 0925-8574

DOI Link: https://doi.org/10.1016/j.ecoleng.2018.10.021

Publisher: Elsevier

Abstract: 
Using earthen liners at the base of an integrated constructed wetland (ICW) maintains a hydraulic continuum between the ICW and the underlying groundwater body. This may enable migration of reactive carbon (dissolved organic and inorganic carbon (DOC, DIC)) and reactive nitrogen (N-r) across this liner to groundwater along this continuum to groundwater. Therefore, in terms of a holistic assessment of ICWs, quantification of these losses is important and indeed from an environmental perspective comparing such losses to other ICW dis-connected areas within the same groundwater body is critical. The main objective of the present study on an ICW site in SE Ireland was to compare reactive forms of C and N in groundwater (three piezometer nests) representing the continuum end point of ICW Cell 2 and 3 with that of groundwater dis-connected to the ICW system. For this purpose two control planes consisting of shallow and deep groundwater piezometer nests were installed and monitored at 1 and 4 m depths, respectively underneath the earthen liners at 0.2 m adjacent to the ICW cells. Fieldwork was conducted between Nov 2013 and Nov 2014 and results showed that groundwater beneath the ICW liner had a highly reduced signal with C and N concentrations being significantly higher to those of the disconnected up-gradient groundwater. The DOC, DIC and dissolved CO2 and CH4 concentrations in groundwater beneath the ICW cells were significantly higher than the up-gradient groundwater. All the reactive forms of C were higher in Cell 2 than in Cell 3. With respect to depth, all forms of reactive C were higher in deeper groundwater than the shallow equivalents except for DOC. Equally, N-r concentrations (NH4+, DON, NO3--N and N2O) were higher in groundwater beneath the ICW cells than the up-gradient groundwater. They were higher in Cell 2 than in Cell 3 and higher in shallow rather than deep groundwater. The fate of the reactive C and N is unknown. Typically DOC delivery from groundwater to surface water drives many biogeochemical processes as an electron donor to microbes or can be converted to CO2 and CH4 emissions and the dissolved CO2 and CH4 can be indirectly exchanged to the atmosphere. The results suggest that nutrient delivery from the ICW cells to the underlying groundwater needs to be evaluated and the design of earthen-lined ICWs should consider this nutrient loss continuum across the liner.

Harvard Citation style: Jahangir, M., Fenton, O., McAleer, E., Johnston, P., Harrington, R., Müller, C., et al. (2019) Reactive carbon and nitrogen concentrations and dynamics in groundwater beneath an earthen-lined integrated constructed wetland, Ecological Engineering: The Journal of Ecosystem Restoration, 126, pp. 55-63. https://doi.org/10.1016/j.ecoleng.2018.10.021

APA Citation style: Jahangir, M., Fenton, O., McAleer, E., Johnston, P., Harrington, R., Müller, C., & Richards, K. (2019). Reactive carbon and nitrogen concentrations and dynamics in groundwater beneath an earthen-lined integrated constructed wetland. Ecological Engineering: The Journal of Ecosystem Restoration. 126, 55-63. https://doi.org/10.1016/j.ecoleng.2018.10.021