喀斯特地表水生生态系统生物碳泵的碳汇和水环境改善效应

The role of biological carbon pump in the carbon sink and water environment improvement in karst surface aquatic ecosystems

碳汇研究是全球碳循环研究的重要内容.近年来,陆地水生生态系统的碳汇日益受到重视,被认为是"遗失碳汇"的重要组成部分.最新研究发现,碳酸盐风化碳汇占岩石风化碳汇的94%,因此,喀斯特地表水生生态系统的碳汇显得尤为重要.生物碳泵效应作为一种稳碳和固碳过程,是形成长期稳定碳酸盐风化碳汇的重要机制,是碳循环的重要环节.生物碳泵效应的核心控制元素是碳元素,该效应在富含溶解无机碳(DIC)的喀斯特地表水生生态系统中发挥着重要作用.目前生物碳泵效应的研究主要集中在两个方面:(1)内外源有机碳的区分是准确评价和计算生物碳泵效应碳汇的关键;(2)发现生物碳泵效应影响水环境指标和水质状况.未来,一方面应精确地对陆地水生生态系统碳汇量进行估算,研究不同气候和土地利用对碳汇量的影响;另一方面,揭示生物碳泵效应与水环境的相互作用机制.重点包括以下4个方面:(1)验证地表水生生态系统"元素比值控制假说";(2)生物碳泵效应对水体元素化学计量比的调控潜力;(3)形成不同碳汇机制(生物碳泵效应和富营养化机制)的根本原因;(4)生物碳泵效应通过物理-化学-生物耦合作用改善水环境的可能机制.最后,探究微生物碳泵效应应用于陆地水生生态系统的可能性.

Carbon sink research constitutes a significant topic in the study of the global carbon cycle. Recently, carbon sinks from terrestrial aquatic ecosystems, known as missing carbon, have been attracting increased attention. Since recent studies have found that carbonate-weathering-related carbon sinks comprise 94% of rock-weathering-related carbon sinks, carbon sinks in karst surface aquatic ecosystems play a particularly important role. In addition, the biological carbon pump effect, as a carbon stability and sequestration process, functions as an essential mechanism for the formation of long-term carbonate-weathering-related carbon sinks and a critical part of the carbon cycle. Carbon forms the core of the biological carbon pump, which plays a central role in the karst surface aquatic system, which is replete with dissolved inorganic carbon （DIC）. At present, research into the biological carbon pump mainly focuses on two aspects： （1） the distinction between autochthonous and allochthonous sources for CO2 sinks, which is crucial for accurate evaluation and calculation of carbon sequestration of the biological carbon pump. These methods, including elemental ratio analysis （C/N ratios）, single isotope composition, natural ^14C and ^13C isotopes and biomarker methods, have been utilized to distinguish the OC sources in aquatic ecosystems. Natural ^14C and ^13C isotopes composition and biomarker methods have great development prospects because of good stability and accuracy; and （2） the biological carbon pump effect on water environment indicators and water quality. In this paper, the differences between biological carbon pump and eutrophication, biological carbon pump effect on phosphorus removal and the influence of elemental-coupling relationship on biological species were discussed, which provided further evidence for studying biological carbon pump effect on water environmental improvement. In the future, the amount of carbon sinks of terrestrial aquatic ecosystems should be accurately estimated, and the effects of different climates and land use on carbon sinks should be determined precisely. In addition, it is necessary to elucidate the interaction mechanism between the biological carbon pump effect and the water environment. Important study topics include： （1） the validity of the ＂element ratio control hypothesis＂ regarding the surface aquatic ecosystem（the underlying reasons causing the different biological species in surface aquatic ecosystems are the different elemental-coupling stoichiometric ratios and the differences in biological species further explain the water quality）; （2） the regulation of the biological carbon pump effect on the stoichiometric ratio; （3） the root causes of the formation of different carbon sink mechanisms （biological carbon pump effects and eutrophication）; （4） the possible mechanism of the biological carbon pump effect on water environmental improvement through physical-chemical- bio-coupling, such as colloidal effects and adsorption coprecipitation. Finally, the possibility of applying the microbial carbon pump effect to terrestrial aquatic ecosystems was discussed.