岩溶湖库生产力的溶解无机碳施肥及碳增汇和富营养化缓解效应

DIC fertilization of primary production in karst lake-reservoirs and its effects on carbon sequestration and mitigation of eutrophication

内陆水体在全球碳循环中的作用日益受到关注,特别是喀斯特地表水体与水生光合作用有关的生物泵(biological pump,BP)将溶解无机碳(dissolved inorganic carbon,DIC)转化为有机碳沉积,是形成长期稳定碳酸盐风化碳汇的关键.富营养化作为BP的特殊阶段,是地表水环境面临的主要环境问题之一.然而,通常认为富营养化的控制元素是磷(P)和氮(N),而BP的控制元素还包括碳(C),如喀斯特湖库尽管DIC浓度高,但其碱性环境使得水中的CO_(2)很低,因此BP效率受到C限制.同时BP产生的碳酸钙促进了水中P的共沉淀,缓解了水体向蓝藻型富营养化的发展,可能促成水质安全和水体碳增汇的双赢.未来需通过对不同气候(温度、降水差异)、不同土地利用(N-P营养输入差异)和不同岩性(碳酸盐岩-硅酸盐岩风化产生pH和DIC差异)条件下的喀斯特地表水体BP的DIC施肥及其碳增汇和富营养化缓解效应进行系统研究,重点揭示以下关键科学问题:(1)DIC对BP施肥的机制及控制因素;(2)水体C:N:P:Si与浮游-沉水植物群落结构/组成的耦合关系及机制;(3)DIC施肥下BP的碳增汇和富营养化缓解效应.系统研究将为HCO_(3)-Ca型地表水体碳增汇和水质安全调控提供新的理论依据和科学支撑.

The role of inland water bodies in the global carbon cycle is receiving more and more attention.It was found that in karst surface water ecosystems,phytoplankton and/or submerged plants can fix some of the carbonate weathering-related carbon and form stable carbon sinks.The higher the concentration of dissolved inorganic carbon(DIC),the higher the aquatic productivity,showing a“DIC fertilization effect”on the biological pump(BP)that improves the environment.Both BP and aqueous eutrophication are based on the formation of organic matter by aquatic photosynthesis.It is usually believed that N-P plays the limiting role in eutrophication,but both CO_(2)and water may be limiting factors in photosynthetic reactions on land,while abundance of CO_(2)is the only constraint in water.Previous studies have supposed that CO_(2)can be obtained continuously from the atmosphere but,in fact,air-water atmospheric CO_(2)exchange is a slow process and in alkaline karst aquatic ecosystems,(especially at pH>8),the limited CO_(2)is important.Aqueous CO_(2)concentrations also affect the biological composition in water bodies.Cyanobacteria can adapt to lower CO_(2)concentrations than other algae,while green algae,diatoms and submerged plants tend to demand CO_(2)-rich water environments.In addition,when the BP utilizes DIC to build autochthonous organic matter,the precipitation of calcium carbonate due to high concentrations of Ca2+also induces co-precipitation of phosphorus,removing the latter from the water and thus suppressing eutrophication of cyanobacteria.In short,the DIC fertilization effect on the biological pump and its inhibition of cyanobacterial eutrophication provides a new perspective on the climate-change win-win case of increased carbon sequestration plus reduced eutrophication.Future studies should try to focus on the following key scientific issues through integrated investigation on DIC fertilization,carbon sequestration enhancement and eutrophication mitigation effects of karst lake and reservoir BP in different nutrient states by combining with control experiments:(1)Mechanisms and controlling factors of DIC fertilization on BP;(2)coupling relationship and mechanism between water body C:N:P:Si and phytoplankton-submerged plant community structure/compositions;(3)effects of BP on carbon sink increase and eutrophication mitigation under DIC fertilization.