Cyclic utilization of reed litters to enhance nitrogen removal efficiency in simulated estuarine wetland

Reed is a common species in China's estuarine wetlands, contains high carbon and low nitrogen, and its litters have potential to be reused as external carbon source to achieve denitrification efficiency enhancement in estuarine wetlands. In this study, leaching experiments of reed leaf and stem under estuarine wetland salinity were conducted, and a certain amount of reed litters was then added into simulated estuarine wetlands under 0‰ and 7‰ salinity respectively. It was observed that reed litters had a higher release of total organic carbon (TOC) under 7‰ salinity than 0‰ salinity, and reed leaf litters released more TOC than stem litters did. Meantime, it was found that salinity had a more significant effect on TOC leached from stems than from leaves. In simulated estuarine wetlands, NO₃^--N removal rates were found to be improved about 20% under 7‰ salinity and 25% under 0‰ salinity in average after the addition of mixed litters, and almost no additional improvement in NO₃^--N removal was found after leaf-only litter addition compared with mixed litter addition. Besides, mixed litter addition could work two weeks longer than leaf-only litter addition. Moreover, the microbial community change was analyzed by high-throughput sequencing and found that litter addition could increase the denitrification-related genera and then increased the NO₃^--N removal efficiency. For simulated estuarine wetland, reed litter addition could achieve better nitrogen removal efficiency.