水利工程对岩溶水体碳循环的影响

Influence of hydraulic project on the carbon cycle in the karst reservoir

为认识水利工程建设对岩溶库区温室气体排放的影响,本文对岩溶区水利工程破坏岩溶水体DIC的稳定性、增加温室气体排放以及水利工程建设所带来的水体富营养化问题进行了初步总结。结果表明,水利工程不仅打破了岩溶水体DIC的自身稳定性,加速水体无机CO2逸出过程,导致CaCO3发生沉淀,而且还通过改变岩溶水动力条件、加速温室气体排放等途径来提高岩溶水体的碳储存、转移、形成与分解过程。与此同时作者还建议:(1)尽快开展岩溶水体温室气体排放的定性分析与定量计算工作,并与不同排放源的温室气体释放效应进行对比;(2)温室气体排放的估算须建立在岩溶碳循环研究基础上,从时间和空间尺度上分析影响岩溶水体温室气体排放过程的关键因素,并把岩溶水体温室气体排放纳入整个岩溶生态系统的生命周期中进行考虑。

In recently,lots of dams are built for hydropower,reservoir and flooding control in China at karst area.To understand the effect of hydraulic project on the greenhouse gas emission from karst water reservoir and the disturbance on the carbon cycle in karst area,this paper presents a comprehensive overview on the greenhouse gas emissions based on relevant published studies.Karst systems are sensitive to changes of many environmental factors,such as the atmospheric CO2 partial pressure.So,the dams will produce the waterfall effect when karst water flows through the spillway or hydraulic turbine,the stability of DIC and the atmospheric CO2 partial pressure will change,which will accelerate the emission of CO2 and promote the precipitation of CaCO3.Concerns about hydroelectric reservoir being important sources of greenhouse gases to the atmosphere have populated the specialized literature.The conversion of terrestrial land to an aquatic area for the creation of a reservoir is a major issue with regard to carbon cycle change in the production of carbon dioxide and methane.The impacts to carbon dynamics of impoundment in karst aquatic systems are mainly the result of three factors,（1） flooding of vegetation; （2） release of carbon from the flooded terrestrial biomass including soil organic matter; （3） the establishment of a new physical-chemical environment for carbon fixation and decomposition.So,the hydro-reservoirs produce biogenic gases through decomposing organic matter underwater.The bottom of the reservoir contains biomass that decomposes anaerobically,emitting principally CH4 and N2O,and secondarily CO2.In aerobic decomposition only CO2 and N2O are emitted.Moreover,the karst hydro-reservoirs will receive allochthonous nutrients from their catchment areas via streams and through groundwater and surface water inflow.Increased nutrient input into karst hydro-reservoirs causes eutrophication.The increased availability of easily degradable autochthonous organic matter increases decomposition and oxygen consumption,promoting oxygen depletion in the water column and sediment.Anoxic conditions can increase CH4 emissions from karst hydro-reservoirs by enhancing the CH4 production and/or decreasing the CH4 oxidation and low oxygen availability can also promote N2O production.Nitrous oxide generation in karst hydro-reservoirs generally requires steep oxygen gradients allowing sequential aerobic nitrification and anaerobic denitrification to take place.This implies that the karst hydro-reservoirs could also be supersaturated with CH4 and N2 O.According to the results,the author provides the suggestion for the future study,（1） the qualitative analysis and quantitative calculation about greenhouse gas emissions from karst hydro-reservoirs must be carried out,and the emission rate from different carbon source should be compared; （2） the space-time analysis of the influence on the greenhouse gas emission should base on the karst carbon cycle and the life-cycle assessment methods for karst hydro-reservoirs should be considered.