题目: Nitrogen purification potential limited by nitrite reduction process in coastal eutrophic wetlands

作者: Chunyu Zhao, Songlin Liu*, Zhijian Jiang, Yunchao Wu, Lijun Cui, Xiaoping Huang, Peter I. Macreadie

刊物: Science of the total Environment

年卷期页: 2019,694:133702

摘要：Coastal wetlands accumulate enormous quantities of nitrogen due to their position at the interface between land and sea and high trapping capacity. Fortunately, they have high nitrogen (N) purifying (removal) capacity, which means that they likely play an important role in mitigating against coastal eutrophication. However studies that empirically measure the degree to which wetlands purify nitrogen and their removal pathways (e.g. denitrification, anammox, plant uptake, microbial immobilization, etc.) are rare. In this study, the N purification potential (denitrification and anammox) and enzyme activities related to denitrification in different subtropical wetlands types were conducted in nitrogen-enriched wetlands of Daya Bay, Southern China. We found the average N purification rate was 11.4 μmol N·kg^-1·h^-1, with denitrification accounting for 84.2%-100% of the total N₂ production in the wetlands of Daya Bay. The N purification potential in the wet season, subtidal areas and mangrove forests were generally observed to be higher than that in the dry season, high and low tidal areas, barren and estuary habitats, respectively. Correspondingly, these differences were mainly driven by the temperature, Eh and NH₄-N, respectively. Additionally, the nitrate reductase (Nar) and nitrite reductase (Nir) activities tended to be similar among different seasons and tidal areas, however, Nir activity in mangrove forest was 1.5-fold and 2-fold of the estuarine and barren areas, respectively. Meanwhile, Nir showed a positive correlation with denitrification rate. These results indicate that NO₂-N reduction, the key control mechanism for N purification, should be the rate-limiting step of the denitrification process in Daya Bay wetlands. Notably, mangroves could improve N removal rates by 48.0% compared to other wetlands. Therefore, protecting and restoring mangrove ecosystems could be an effective way to reduce the risk of coastal eutrophication.