天目湖流域沟塘湿地脱氮速率的时空差异

Temporal and Spatial Characteristics of Nitrogen Removal in Ditches and Ponds in Tianmuhu Lake Basin

湿地是陆地生态系统重要的脱氮热点,其对削减流域面源氮负荷具有重要意义.为探究水库流域沟渠、池塘等湿地的脱氮速率及其影响因素,分别于2021年春季(3月)与夏季(6月)采集了天目湖沙河水库流域内典型土地利用类型下沟塘湿地的原状泥-水柱,利用同位素示踪技术进行室内流动培养,测定了不同沟塘湿地的反硝化速率和厌氧氨氧化速率.结果表明:①各沟塘湿地沉积物均具有较高的脱氮速率,春季脱氮速率范围为10.59~107.65μmol/(m^(2)·h),平均值为70.73μmol/(m^(2)·h),夏季脱氮速率范围为32.07~150.10μmol/(m^(2)·h),平均值为112.36μmol/(m^(2)·h),春季果园排水沟渠的脱氮速率最高,夏季茶园退水池塘的脱氮速率最高.②春季和夏季不同沟塘湿地厌氧氨氧化作用对脱氮的贡献率(简称“厌氧氨氧化贡献率”)平均值分别为45.45%、36.26%,其中生活污水排放池塘和茶园退水池塘的厌氧氨氧化贡献率在夏季分别下降26.82%、14.98%,春季和夏季果园排水沟渠和入湖口河流湿地的厌氧氨氧化贡献率变化不大,平均值分别为21.17%、48.99%.③统计分析表明,水体溶解性无机氮(DIN)浓度和沉积物有机碳含量与沉积物脱氮速率均呈显著相关,且高温与低溶解氧浓度条件下也有利于脱氮作用的进行.研究显示,水库流域沟塘湿地具有较好的脱氮能力,通过有效调控管理能够大大增加流域氮的截留能力,对水库水质保障具有重要作用.

Wetlands are important hotspots of nitrogen removal in land ecosystems,and are great significance for reducing nitrogen load from non-point source in basins.In order to explore the nitrogen removal rate of different wetlands and their controlling factors,undisturbed sediment column cores of ponds and ditches with different typical land use types were collected in the spring(March)and summer(June)of 2021,in the Tianmuhu Lake Basin,China.The denitrification and anammox rates of different ponds and ditches were determined through the isotope matching technology with indoor continuous-flow incubations.The results showed that,the ponds and ditches had a high nitrogen removal rate,ranging from 10.59 to 107.65μmol/(m^(2)·h)in spring,with an average of 70.73μmol/(m^(2)·h),and from 32.07-150.10μmol/(m^(2)·h)in summer,with an average of 112.36μmol/(m^(2)·h).The orchard ditch showed the highest nitrogen removal rate in spring and the tea garden retreat pond showed the highest nitrogen removal rate in summer.The average contribution of anammox to nitrogen removal was 45.45%in spring and 36.26%in summer.In summer,the contribution of anammox to nitrogen removal in domestic sewage discharge pond and tea garden retreat pond decreased 26.82%and 14.98%,respectively.The contribution of anammox in orchard ditch and river discharging to Tiamuhu Lake had little change between spring and summer,the mean value were 21.17%and48.99%,respectively.Statistical analysis shows that the concentration of dissolved inorganic nitrogen(DIN)in water and the content of organic carbon in sediment were significantly correlated with the sediment nitrogen removal rate.In addition,the nitrogen removal rate of ditches and ponds was higher under the conditions of high temperature and low dissolved oxygen.Our results indicates that the ditches and ponds in the reservoir basin have a good nitrogen removal capacity,so effective regulation and management can greatly increase the nitrogen retention capacity of the reservoir basin,which plays an important role in water quality assurance of the reservoir.