高原湖滨河口湿地磷在"水-底质-植物"中的输移关键过程及截留效应定量评估研究

The awareness of lake eutrophication and aquatic ecological degradation worldwide has grown over the last decades. The need for reducing anthropogenic nutrient inputs, especially phosphorus (P), to aquatic ecosystems to restore aquatic ecosystem health has therefore been widely recognized. Lake riparian wetland is viewed as an important component of lake ecological restoration. Its phosphorus retention effect is currently a hot research topic around world. However, there are three challenges when quantitatively measuring the retention effect, including (a) the hydrological variability of the riparian wetland; (b) identification of the key process of phosphorus transporting in the wetland and the source-sink mechanism of sediment; and (c) appropriate quantitative evaluation method of phosphorus retention effect. The Luoshijiang riparian wetland of Lake Erhai, a plateau lake in Yunnan province, southwestern China, is taken as a case study. Temporal and spatial variability of phosphorus retention effect were revealed based on the field monitoring, lab experiments, isotopic tracer and in situ test. Two key biogeochemical processes in the wetland will be focused, including (a) phosphorus transporting in water, sediment and plant; and (b) biochemical kinetic mechanism of sediment under wet or dry conditions. The key process of wetland phosphorus retention, driving factors and dynamic sediment source and sink mechanism were also identified. In order to realize quantitative assessment of phosphorus retention effect, several modules will be developed based on Environmental Fluid Dynamics Code (EFDC), a three-dimensional hydrodynamic, water quality and ecological model platform. The modules are refined hydrological one, phosphorus transporting between water and vegetations, and phosphorus transporting between water and sediment. This proposal aims to explore the key process and driving factors of phosphorus retention and its effect mechanism in lake riparian wetland. The simulation and quantitative evaluation for phosphorus retention mechanisms will be further explored in a typical plateau lake riparian wetland in Yunnan. It is believed that the findings and the approach proposed in this study will provide more interesting and useful hints to support effective riparian wetland management and designing.

湖滨河口湿地是湖泊生态修复的重要组分，对其磷（P）截留效应的研究是目前国内外的热点；但存在2个方面的挑战：磷在湿地中的输移关键过程识别及底质"源-汇"机制；适宜的磷截留效应定量评估方法。本项目以云南高原湖泊洱海罗时江入湖河口湿地为典型对象，基于现场监测、室内模拟、同位素示踪及原位试验，揭示湿地的水文变异性及其对磷截留效应时空分异性的影响；重点研究磷在"水-底质-植物"中的输移、底质在干/湿条件下的地球生化动力学等2个关键过程，识别湿地磷截留的关键过程、驱动因子及底质的"源-汇"动力学机制；基于三维"水动力-水质-生态"模型平台，在合适的模型复杂性程度确定的基础上，开发精细化的水文模块以及"植被-磷"、"底质-水体"的营养动力学模拟模块，实现对磷截留效应的定量评估。本项目旨在通过典型研究，探索高原湖滨河口湿地磷的截留关键过程与驱动因素作用机制，为制定科学的湿地管理与设计对策提供支持。

湖滨河口湿地是湖泊生态修复的重要组分，对其磷（P）截留效应的研究存在2 个方面的挑战：磷在湿地中的输移关键过程识别及底质“源-汇”机制；适宜的磷截留效应定量评估方法。罗时江湖滨河口湿地是洱海北部最主要的补给水源之一，同时也是磷的入湖来源。而过多的营养物入湖会引起水体透明度下降、藻类过量生长、水体中溶解氧浓度下降、鱼类死亡等问题。为了探索磷在罗时江湖滨河口湿地“水生植物-水-底质”中的输移机制，并定量评估湖滨河口湿地对P的截留效应，本研究在进行了为期2年的水质、底质、微生物与水生植物采样、监测的基础上，开发了多种类水生植物模块与营养盐通量、存量平衡追踪模块，并将其与国际上广为接受的环境流体动力学模型进行耦合，形成系统地三维水动力-水质-水生态模型。应用模型于罗时江湖滨河口湿地的实际案例中，研究发现：（1）AOA 群落Shannon和Npshannon指数与土壤中C/N呈显著正相关，认为罗时江流域土壤C/N是影响AOA群落结构的重要环境因子；（2）湿地每年存有0.023t颗粒态有机磷，0.041t溶解态有机磷，0.022t正磷酸盐磷，蓝、绿、硅藻体内每年分别含0.11t、0.23t、0.29t的有机磷，浮叶植物、沉水植物、芦苇、荷花、梭鱼草、香蒲、再力花体内分别含有11.44t、123.35t、288.01t、264.25t、52.30t、66.54t、89.44t有机形态的磷；（3）在罗时江湖滨河口湿地对P的所有去除过程中，荷花的同化吸收与颗粒态磷沉降为最为关键的过程，芦苇、梭鱼草、香蒲、再力花的作用依次降低，最后为藻类；（4）浮叶植物与沉水植物代谢过程会释放出大量的磷，没有表现出明显的截磷作用，因此冬季需将浮叶植物与沉水植物收割，以降低冬季代谢释放的磷浓度，增强其对水体磷的净化作用；（5）与底质会成为磷的源项的富营养化湖泊（如滇池）不同，罗时江湖滨河口湿地的底质为磷的汇项，每天最高贮存2.8kg溶解态磷量。当去掉水生植物后发现，底质将由汇项转变成源项。（6）罗时江湿地对P的截留并不是全年都起作用，在2014年夏季有最高的截留率，而在2014年5月与9-10月却表现为P的输出源，截留率与入湖负荷有关。本研究找到了定量评估高原湖泊入湖河口湿地对磷截留效应的方法，可为高原湖泊河口湿地的工程优化设计提供科学指导。