Carbon and nitrogen dynamics and greenhouse gas emissions in constructed wetlands treating wastewater: a review

Abstract

Abstract. The removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. 4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs.

Divergent impact of grazing on plant communities of created wetlands with varying hydrology and antecedent land use

“…In order to enhance the success of wetland creation and restoration attempts, a better understanding of abiotic and biotic controls on wetland structure and function is required. Hydrology is the ultimate driver of wetland structure and function, and variations in surface water depth and duration of saturation regulate soil and water chemistry by determining oxygen availability and soil redox status; this indirectly controls nutrient availability for competing plants and microorganisms (Jahangir et al 2016;Song et al 2012), and directly controls the number, type, and distribution of individual plant species (Gurnell et al 2012;Zhang et al 2012). The resulting plant communities provide food and habitat for wetland herbivores, such as waterfowl, which choose their habitats based on water depth and resource availability (Bino et al 2014;Pickens and King 2014).…”

Effect of Different Wastewaters on Carbon and Nitrogen Dynamics in Soils of North Karnataka, India

“…Microbes derive energy and carbon from the organic matter added through the wastewater into the soil. Fluctuation in the microbes' population and diversity are cumulatively influenced by the altering physical and chemical properties of the soil treated with wastewater [20]. Activity of the microbes leads to release of some acids which dissolve the organic carbon compounds to simpler forms.…”

A microbial perspective on balancing trade-offs in ecosystem functions in a constructed stormwater wetland

“…Compared to surface flow wastewater treatment wetlands receiving municipal or agricultural runoff, CO 2 emissions at our study wetland in flooded plots were similar but approximately 95% lower in shallow land plots (Jahangir et al, 2016;Mander et al, 2014). In contrast, CH 4 emissions at our study wetland had similar CH 4 rates in shallow land plots when compared to wastewater treatment wetlands, but approximately 94% greater emissions in flooded plots compared to wastewater treatment wetlands (Jahangir et al, 2016;Mander et al, 2014). In terms of GWP, flooded plots in our study wetland have a GWP that is 98% greater than in wastewater treatment wetlands.…”