浅水湖泊草源性“湖泛”发生过程特征及其机理

Currently, the pollution phenomenon "colored zone" in shallow lakes in China leads to the deterioration of water quality in partial area of lakes, and then caused the serious damage to the lake function. The pollution "colored zone" resulting from the quick decomposition of decayed macrophytes often occurs in heavily macrophyte-growing areas in shallow lakes in China. Investigating the mechanism of "colored zone" from decayed macrophytes in lakes will benefit the assessment of the environmental effects from decayed macrophytes as well as the prediction of disaster even from those decayed macrophytes, and also will be helpful for the development of the prevention and emergency treatment technologies for "colored zone" in shallow lakes. This project proposal provides a new idea to better understand the mechanism of "colored zone" from decayed macrophytes in lakes, with research focusing on both the microbial community structure for quick decomposition of aquatic plant residues and the response of microbial processes in sediments to the quick decomposition of those plant residues. Through selecting the macrophyte-type region in Taihu lake as the research area, the main contents in the project include the study of quick decomposition process for decayed macrophytes in shallow lakes; analysis of process characteristics of "colored zone" from decayed macrophyte in lakes; and application of metagenomic technology to analyze the microbial community for quick decomposition of plant residues during the occurence of "colored zone" in lakes. Based on those above studies, finally, this project will obtain the mechanism for occurence of "colored zone" from decayed macrophytes in shallow lakes. The project has important application in environmental treatment, disaster control, and management of lakes, also has reference and guidance significance for the utilization of biological resources in lakes.

目前我国浅水湖泊发生的"湖泛"污染现象，使局部水域水质恶化，严重影响到湖泊功能的发挥。由水生植物残体分解而产生的草源性"湖泛"在我国浅水湖泊水生植物生长密集区时常发生。研究草源性"湖泛"发生机理，既有助于水生植物死亡后的环境效应评估及其致灾预测，也有利于"湖泛"预防和应急去除的技术和工艺的研发。本项目提出通过研究快速分解水生植物残体的微生物群落结构、以及沉积物生物过程联动响应来认知草源性"湖泛"发生过程机理的一种新思路。项目以太湖中草型湖区为研究对象，其主要内容包括研究水生植物残体在水体中快速分解过程；分析浅水湖泊草源性"湖泛"发生过程特征；再应用宏基因组技术分析"湖泛"时植物残体快速分解的微生物群落，从而获得浅水湖泊草源性"湖泛"发生机理。该项目在湖泊环境治理、湖泊灾害控制和湖泊管理方面有重要的应用价值，同时对于湖泊生物资源开发利用方面也有参考与指导意义。

通过单因素实验和曲面响应实验相结合，系统研究了影响植物残体快速分解的主要驱动因子，明确了温度、溶解氧、光照强度是影响水生植物残体降解的主要环境因素。植物残体快速分解时将释放大量草源性溶解性有机质，除了大部分为非有色可溶性有机物外，还有少量为有色可溶性有机物，这些溶解性有机质（DOM）是促进甚至诱发草源性“湖泛”的发生的主要物源基础。为了进行DOM生物可利用性快速检测，自行设计构建了一组四级推流式生物膜反应装置。与普通生物接种法相比，此生物检测装置可在4天内得到等同于传统接种法56天的DOM降解率，同时还能用于分析DOM组分与其分解微生物群落特征间的关系。通过应用四级推流式生物反应装置，发现湖泊内生DOM中活性和半活性部分占总体的79%。进而利用本项目组设计研制的“湖泛”室内模拟中型装置，发现草源性“湖泛”暴发的前一天内，植物形态、微生物群落结构和功能都发生显著改变，厌氧木质纤维素降解菌大量增殖，表明木质纤维素的降解也和“湖泛”发生有密切关联。需要特别强调的是，项目研究还首次发现我国湖泊的高硫酸根浓度对致黑物质产生有较大作用，有机质在水体中的分解过程导致了水柱中的硫还原菌数量显著地增加，使得水柱中的还原态总硫浓度显著升高。另外，还发现湖流对草源性“湖泛”的消退有重要作用，补偿流能更快地使“湖泛”水体褪黑，但不能系统持续地提供溶解氧，而表面流对湖体充氧能力大，因此，“表面流”是恢复“湖泛”水体中溶解氧水平的主要湖流。本项目对认识草源性“湖泛”的发生过程机理及环境效应、及湖泊生态灾害预测预警和防控治理都具有重要的科学意义和应用价值。