淡水水生生态系统温室气体排放的主要途径及影响因素研究进展

淡水水生生态系统是全球陆域生态系统的重要组成部分,近年来,关于淡水水生生态系统温室气体排放的研究日益增多。基于国内外目前对湖泊、河流、水库及浅水池塘等淡水生态系统开展的最新研究成果,总结分析了淡水水生生态系统温室气体排放的3个主要途径及相应观测方法。气泡排放的观测方法有倒置漏斗法、开放式动态箱法和超声探测技术;植物传输的观测方法有密闭箱法和植株切割法;扩散途径的观测方法有静态浮箱法、模型估算法/梯度法、微气象学法、TDLAS吸收光谱法等。从物理因素、化学因素、生物因素、水动力因素和人类活动等角度,深入探讨了淡水水生生态系统温室气体排放通量的影响因素。最后根据当前研究中存在的不足,对今后的研究方向提出了建议,以期为我国进一步深入开展相关研究提供借鉴。

Emission paths and measurement methods for greenhouse gas fluxes from freshwater ecosystems:a review

Greenhouse gas (GHGs) emissions from freshwater ecosystems are a major component of global terrestrial landscape budgets. Currently, global warming is affecting these ecosystems and may trigger an increase in GHGs emissions, which may further enhance global warming. The identification and accurate quantification of aquatic ecosystems as sinks/sources of GHGs are vital for evaluating GHGs budgets and assessing possible climate feedback effects in order to improve climate models. In recent years, fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) have been observed from freshwater aquatic environments such as natural lakes, hydropower reservoirs, rivers, ponds, and drainage ditches. This review analyzes and summarizes research developments in GHGs emission paths, observation methods, and key factors affecting emissions from freshwater ecosystems. The mechanism of greenhouse gas production is a complex and interactive process that includes biochemical processes. The main emission paths from aquatic environments are diffusive fluxes across the air-water interface, bubble (ebullition) fluxes resulting from supersaturation of sediment, and plant-mediated fluxes. Attention has been recently been drawn to other emission pathways that contribute to total gas emissions at reservoir surfaces (e.g., gas release immediately below turbines and emissions further downstream in rivers). The monitoring methods vary for aquatic ecosystem emission pathways. Bubble fluxes are measured by funnel techniques, open dynamic floating methods, and ultrasonic detection technologies. Diffusive fluxes are measured by static chamber techniques, model estimations, micrometeorology, and tunable diode laser absorption spectroscopy (TDLAS). GHGs emission is conventionally measured using closed chamber to trap plant-mediated flux components. In addition, we discuss the impacts of physical, biological, hydrodynamic, and anthropogenic factors on GHGs emissions from aquatic ecosystems. We point out that an urgent and key direction for the future is to standardize the observation methods for GHGs fluxes from freshwater aquatic ecosystems and to consider temporal and spatial variability, which rely on long-term field observation.