都市区小型湖库群温室气体排放特征及其对陆域人类活动的响应机理

Lake and reservoir, as the typical lentic ecosystem, serving a dual role by receiving and sequestering carbon (C) and nitrogen (N) from terrestrial system while acting as bioreactor of the biogeochemical process, are well known as sources of greenhouse gases (GHGs) to the atmosphere and get widespread attention especially now with the changing environment. However, due to the increasing influence of human activity, GHGs emissions from small lentic ecosystems become highly variable and uncertain, resulting in the challenge of the accurate estimate of lake and reservoir systems. In this project, Chongqing metropolitan area, the super-large city in the west region of China, will be selected as a typical study area because of its obvious human activity disturbance gradient following the natural area to agricultural area, to urban area. We choose 75 lakes and reservoirs that located in Chongqing metropolitan area to perform a high spatial resolution investigation on aqueous GHGs concentrations and fluxes and water-quality parameter throughout an entire hydrological year, and to carry out a simulating cultivating experiment for the gases process and physiochemical parameters of sediments from 40 representative lakes or reservoirs. Combining with the geostatistical methods and multivariate statistical models, we will examine that (1) the spatial and temporal pattern of GHGs concentrations and fluxes across the metropolitan lakes and reservoirs, and clarify the coupling relationship between of human activity and GHGs emissions; (2) the possible environmental factors dominating such spatial and temporal pattern and the potential predictors; (3) the effect of human activity on the GHGs emissions from sediments and its regulatory factors. The aim of our project is to explore the response of the GHGs emissions from regional lake and reservoirs group to the terrestrial human activities, and to assess the total GHGs evasion from regional lake and reservoirs group and their regional contribution. The results of the project will provide scientific basis for the protection and greenhouse gas emission reduction of the lake and reservoir in metropolitan area.

湖库生态系统是大气温室气体的重要排放源。都市区小型湖库群是自然过程与城市建设共同作用形成的特殊景观单元，受人类活动干扰强烈，其温室气体排放特征及关键影响因素尚不清楚，是全球湖库排放研究中最具不确定性的关键区域。本项目以重庆都市区小型湖库群为研究对象，开展水体溶存温室气体浓度、排放速率、水环境、沉积物等采样分析及室内培养试验，结合地统计学方法及多元分析模型，研究(1)都市区小型湖库群温室气体排放时空特征及其与陆域人类活动的空间耦合关系；(2)都市区小型湖库群温室气体排放差异的关键影响因子及其与温室气体通量的数学模型关系；(3)都市区小型湖库群沉积物产气潜势及调控因子。为湖库系统温室气体排放清单制定提供一批都市区小型湖库群的基础数据，并估算重庆都市区小型湖库群温室气体排放总量，阐明都市区小型湖库群温室气体排放特征及其对陆域人类活动响应机理，为变化环境下湖库系统生态功能研究提供基础科学依据。

淡水水体是大气重要的温室气排放源，在全球气候变化及碳氮循环过程中发挥重要作用。流域环境变化是影响淡水生态系统外源物质输入和内部物质循环的重要因素，进而间接或直接影响水体碳、氮生物地球化学循环过程，导致水体温室气体排放出现较大的变异。揭示高强度流域环境变化下不同类型水体温室气体排放规律及调控机制对全球或区域温室气体排放清单的精确估算及人为控制具有重要意义。本研究围绕重庆大都市区小型溪流、水库、湖泊等淡水水体网络，开展了不同流域环境背景下水体温室气体溶存浓度及水气界面通量的时空变异规律及关键控制因素，主要结论如下：（1）重庆主城区71个湖库水体CO2、CH4、N2O浓度均为过饱和状态，是大气温室气体净排放源；其中，CO2排放通量为-354~895 mmol•m-2•d-1（平均84.6），CH4、N2O排放通量为0.030~3.29 mmol•m-2•d-1（1.07±1.58 mmol•m-2•d-1）与-55.74~241.57 μmol•m-2•d-1（79.06±36.08），城市区小型湖、库CO2、CH4、N2O排放通量均显著高于城市郊区和非城市区，是整个区域温室气体排放的热点；（2）水环境污染是导致不同类型水体温室气体排放强度增加的关键因素，水体碳、氮、磷含量的累积对温室气体通量具有较好的解释效益；（3）湖库水体综合整治对水体温室气体排放具有一定的缓解效应，但对CO2排放的缓解效应有限；但不同功能型水体温室气体排放强度差异，城市小型景观水体是温室气体排放的热点，未利用的自然湖库温室气体排放较低；（4）城市湖库群温室气体排放总量的空间特征与湖库沉积物产气潜势之间具有明显的非线性关系，城市污水排放及城市下垫面径流过程的差异是导致这种非线性关系的主要机制。（5）城市扩展过程显著增强了溪流水体温室气体排放通量，城市郊区河流水体温室气体通量呈现强烈的空间分异，且与流域土地利用类型具有显著的线性关系；（6）山区场镇发展对河流水体碳、氮、磷含量呈连续的增加效应，进而导致水体温室气体沿程梯级增长。本研究未区域城市淡水水体温室气体排放总量估算及调控提供了重要参考。