湖滨带脱氮效应及关联生物群落对水文恢复的响应特征和机理

Lakeshore wetlands are thought to be effective in intercepting and reducing nitrogen loads entering lake water bodies. Community structure and diversity of plants and microorganisms are thought to be positively related to nitrogen removal effectiveness by influencing several nitrogen cycle processes. In China, restoring lakeshore wetlands and establishing hydrological connectivity between lakeshores and lake water bodies have been considered a best management practice for improving water quality in eutrophic lakes. Previous studies have indicated that hydrological restoration has positive influence on biological community structure in lakeshore wetlands. However, little research has been conducted on the effect of hydrological restoration on lakeshore ecological functions such as nitrogen removal. Moreover, the mechanisms by which hydrologic restoration alters biological community structure and ecological functions are still poorly understood. This proposal includes a meta-analysis and a case study which focuses on the restored lakeshore wetlands around the Lake Dianchi. By meta-analysis, we search the scientific literature containing data on wetland ecological structure and nitrogen removal parameters to identify relationships between nitrogen removal effectiveness and hydrological restoration and associated community structure of macrophytes and microorganisms. In case study, we investigate plant community types, species diversity, and functional diversity in lakeshore wetlands of Lake Dianchi to explore the changes of wetland plant community before and after hydrological restoration. We also analyse the changes of dominant species, species diversity, and gene abundance of microbial communities related nitrogen cycles, based on the nirK, nirS, and hzo genes. The soil denitrification and anaerobic ammonium oxidation are measured by isotope pairing technique and used as an indicator of nitrogen removal capacity. Finally, this study reveals the responses of biological community structure and nitrogen removal capacity of lakeshore wetlands to hydrologic restoration by the use of spatial and temporal comparisons and indicates their formation mechanisms. Results from this study can provide some important information for assessing the ecological benefits of hydrologic restoration and for restoring the degraded lakeshore wetlands in China.

脱氮除磷是湖滨带的重要生态功能之一，脱氮效应与植物和微生物的群落结构特别是多样性密切相关。随着我国富营养化湖泊治理的不断深入，退田（塘）还湖和恢复湖滨带与湖泊水体的水文连通已经成为有效手段，但是关于水文恢复对湖滨带脱氮功能的影响及机理的了解还非常有限。本项目采用整合分析和案例研究相结合的方法，通过整合分析，研究水文恢复对湖滨带和其它湿地类型的脱氮功能及关联生物群落的影响程度、长期趋势及控制因子；以退还的滇池湖滨带为个案，采用空间和时间比较的方法揭示与脱氮功能密切相关的植物和微生物（基于nirK、nirS和hzo等基因分析）的群落结构及物种和功能多样性对水文恢复的响应特征；采用同位素配对技术研究水文恢复及生物群落改变对土壤反硝化和厌氧氨氧化作用的影响；阐明水文恢复对湖滨带脱氮功能的影响机理。本项目的研究成果将为全面评估退田（塘）还湖的生态效应和指导受损湖滨带的生态修复提供理论基础和科学依据。

人类活动导致的湖泊氮磷含量升高对人类健康、生物多样性和水质产生了严重的负面影响。湖泊及其毗邻湿地中的硝化和反硝化作用是调控脱氮的关键生物学过程，然而广泛存在的围湖造田所构筑的混凝土防波堤阻隔了湖泊与湿地间的水文连通，降低了湖泊脱氮能力。目前为止，人们对土壤氮循环过程与水文连通的关联还缺乏深入理解。本项目首先通过整合分析，研究水文恢复对湖滨带和其它湿地类型的生物群落和氮去除效应的影响；然后以滇池正在实施的“湖塘连通”工程为个案，采用空间和时间比较的方法揭示湖滨带脱氮效应及其关联的生物群落对水文恢复的响应特征，阐明水文恢复对湖滨带脱氮效应的影响机理。我们从Web of Science等数据库筛选出了97篇目标文献，挖掘出1600余组数据，44个指标参数，结果表明：水文修复改变了湿地土壤和上覆水的营养动态，导致氮循环参数的总体效应值变化率发生了显著变化，其中真实反硝化速率显著增加了58%，而潜在反硝化速率却下降了30%。作为案例研究，我们从滇池湖滨带选取已修复水文的池塘和滩地各22个和14个作为处理组，未修复水文的池塘和滩地各9个和6个作为对照组。连续2年的4次调查结果表明，水文恢复促进了池塘的土壤N循环速率，但是降低泛滥滩地的土壤N循环速率。路径分析表明，池塘的土壤湿度、土壤总碳和水体中的NH4-浓度是解释潜在硝化速率的最重要因子，其各自效应为34，65和16%；池塘的潜在反硝化速率与土壤湿度和土壤总碳含量正相关，与水体中的NH4-浓度负相关；池塘的真实反硝化速率与土壤湿度、土壤总碳和土壤总氮含量正相关，与水体NH4＋年度负相关。影响滩地潜在消化速率的主要环境因子是土壤湿度、水体NH4+和土壤总碳，潜在反硝化速率和真实反硝化速率与土壤NO3-正相关，与土壤湿度和水体NH4＋负相关。本研究结果表明池塘和滩地两种不同湿地类型对水文连通有完全不同的响应模式。本项目已发表TOP30%SCI期刊论文3篇，正投稿论文2篇；申请发明专利2项；培养博士研究生1名。