Adding Corbicula fluminea altered the effect of plant species diversity on greenhouse gas emissions and nitrogen removal from constructed wetlands in the low-temperature season

Abstract

Plant species diversity is crucial in greenhouse gas emissions and nitrogen removal from constructed wetlands (CWs). However, previous studies have overlooked the impact of benthos on cumulative greenhouse gas emissions during the low-temperature season in CWs. In this study, we established 66 vertical flow CWs with three levels of species richness (1, 2, and 4 species) and eleven species compositions. The Corbicula fluminea was added or not added at each diversity level and monitored greenhouse gas emissions and effluent nitrogen concentration. Our findings indicated that (1) in microcosms without C. fluminea, high species richness significantly increased effluent nitrogen concentrations (NO₃^--N, NH₄⁺-N, and TIN), but plant species richness did not affect cumulative CH₄, N₂O, and CO₂ emissions. The presence of Hemerocallis fulva significantly increased cumulative CO₂ emissions, while the presence of Iris tectorum significantly increased effluent nitrogen (NO₃^--N and TIN) concentrations and cumulative N₂O emissions; (2) in microcosms with C. fluminea, the lowest cumulative CH₄ emissions occurred when there were two species, but plant species richness did not affect cumulative CO₂ and N₂O emissions. The presence of H. fulva significantly increased cumulative CH₄ emissions, while the presence of Reineckea carnea significantly increased effluent nitrogen (NO₃^--N, NH₄⁺- N, TIN) concentrations; (3) at the same diversity level, the addition of C. fluminea significantly increased cumulative CH₄ and N₂O emissions, as well as effluent nitrogen concentrations. These results demonstrate that C. fluminea alters the effect of plant species diversity on cumulative greenhouse gas emissions and nitrogen removal from CWs during the low-temperature season. We recommend using a two-species mixture to reduce greenhouse gas emissions. However, we caution against using plant compositions with H. fulva or I. tectorum for effective wastewater treatment and greenhouse gas reduction in CWs.

Keywords: Benthos; Carbon dioxide; Methane; Nitrous oxide; Species identity; Species richness.