Nutrient removal and microbial community structure in an artificial-natural coupled wetland system

Abstract An artificial-natural coupled wetland was constructed at an estuary between an upstream river and a downstream lake to transport river water and reduce nutrient input load into a grass-type shallow lake. The removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) were as high as 43 % and 83 %, respectively. Their concentrations were reduced to 30.98 mg/L and 0.79 mg/L, respectively. The lotus pond had high microbial diversity and was key for water purification. It contributed 19 % and 49 % of the removal efficiencies of COD and TN, respectively. Most of the dominant microorganism in wetland were related to the transformation of C and N. Bacterial phyla containing phototrophic members accounted for three-quarters of the microorganisms and significantly contributed to bioactivity. Phylum Proteobacteria, the most abundant microbial species, were involved in both N and C cycling because of the metabolic versatility. The denitrification of the wetland depended on the classes Gammaproteobacteria, Deltaproteobacteria, Bacteroidia and Anaerolineae. Bacteria of the phyla Chloroflexi, Actinobacteria, Firmicutes, Spirochaetes, Bacteroidetes and class Alphaproteobacteria contributed to hydrocarbon mineralization and carbonate decomposition to promote C cycling. Therefore, this study provides insights to develop effective methods for reducing the risks of lake eutrophication and protecting the water ecological health.