气候变暖和富营养化叠加对深水湖库热力及溶解氧分层的影响机制

Thermal and dissolved oxygen stratification is the fundamental physical process of lake and reservoir ecosystem, which is closely related to topography, optical properties, eutrophication and global climate warming. Meanwhile, thermal and dissolved oxygen stratification plays a vital role in organic matter decomposition, bottom anaerobic environment, nutrients cycle, plankton metabolism, primary production process. This project is aimed to study the superposition effect of climate warming and eutrophication on the thermal and dissolved oxygen stratification in typical deep lake (Lake Fuxianhu) and reservoir (Lake Qiandaohu). Based on the monthly and high-frequency vertical profile measurements of water temperature, underwater irradiance, dissolved oxygen, turbidity etc, this project will present the daily, monthly, seasonal and spatial variations of thermocline and oxycline depth, thickness, strength and Schmidt stability in the typical lake reservoir. The coupling correlations between lake and reservoir area, water depth, air temperature, transparency, diffuse attenuation coefficient and thermocline and oxycline depth, thickness, strength, Schmidt stability will be developed. Climate warming and eutrophication trend will be elucidate based on the long-term meteorological and hydrological observation from 1950s and remote sensing monitoring of transparency and trophic state index from 1980s using Landsat and MODIS data. The effects of climate warming and eutrophication on the thermal and dissolved oxygen stratification will be clarified based on the coupling correlations and long-term trend of climate warming and eutrophication. This project will reveal the driving mechanism of climate warming and eutrophication on the increase of thermal and dissolved oxygen stratification, which will serve water quality and eutrophication management of lakes and reservoirs under the background of global warming.

湖库热力和溶解氧分层是湖库生态系统中最基本的物理过程，对有机物分解、底部厌氧环境形成、营养盐循环、浮游生物的新陈代谢及初级生产过程起着至关重要的作用。本项目针对气候变暖和富营养化对湖库热力和溶解氧分层的叠加效应，以深水湖库抚仙湖和千岛湖为研究区域，通过水温、水下光辐射、溶解氧高频和逐月垂直剖面观测，获得温跃层和氧跃层深度、厚度、强度和热稳定性等湖库热力和溶解氧分层参数时空变化特征；构建湖库面积、水深等地形参数，气温、透明度、漫射衰减系数等光热参数与湖库热力和溶氧分层参数间耦合关系；基于长期气象观测和水温定位观测数据分析抚仙湖和千岛湖地区气候变暖特征，通过透明度和富营养化指数长期定位观测和遥感监测评价其富营养化长期变化趋势，评估长期增温和富营养化对典型湖库热力和溶解氧分层强化的贡献份额，揭示气候变暖和富营养化对湖库热力和溶解氧分层的作用机制，服务于全球变暖背景下湖库水质管理和富营养化治理。

湖库热力和溶解氧分层是湖库生态系统中最基本的物理过程，对有机物分解、底部厌氧环境形成、营养盐循环、浮游生物的新陈代谢及初级生产过程起着至关重要的作用。基于在抚仙湖和千岛湖开展的长期定位观测、短期高频监测，结合长期气象数据，发现抚仙湖和千岛湖过去50年均经历了明显的湖泊增温过程，与此同时过去30年也表现出营养盐和藻类生物量增加，存在从贫营养往贫中营养发展态势；气候变暖和透明度下降均加剧了湖泊热力和溶氧分层，2016年极端高温年造成千岛湖2016-2017年冬季也存在弱分层，底部出现缺氧甚至厌氧状态；流域强降水等水文过程会显著改变湖泊热力和溶氧分层，但暴雨结束后湖泊又会快速形成热力与溶氧分层，预估未来强降雨事件的增加可部分缓解气候变暖导致分层强化带来的水体缺氧效应。综合起来考虑，气候变暖和透明度降低会持续强化湖泊热力和溶氧分层，造成底部缺氧，对生态系统产生不利影响。