Promotion function of forest vegetation on the water & carbon coupling cycle in karst critical zone: Insights from karst groundwater systems in south China

Abstract

The earth is gradually turning green due to afforestation, especially in China. Because the carbon cycle is driven by the groundwater cycle in karstification, the process of water & carbon coupling cycle (PWCC) in karst forest area can not only promote vegetation growth but also enhance chemical weathering processes of carbonate rocks to absorb more CO2. Therefore, carbon sequestration can occur during the process of ecological restoration in karst areas. However, forest respiration also increases with the vegetation growth which can produce extra CO2 back to atmosphere. To study the promotion function of forest vegetation during different succession stages on the PWCC in karst critical zone, three karst groundwater systems with different vegetation coverages (a native forest, a secondary forest during reforestation and a crop area in rural land) are chosen in southwest China. Their long-term monitoring of indicators, including precipitation (P), partial pressure of air CO2 (PCO2), groundwater discharge (Q), hydrochemical and isotope components, was conducted. The results indicated that part of CO2 produced by forest respiration diffuses into the atmosphere as a carbon source, and the remaining dissolves into the groundwater, thereby increasing corrodibility. The carbon sequestration mechanism differs at different vegetation succession stages. The secondary forest development stage displays an obvious carbon sequestration effect during the process of rocky desertification control. When the succession stage approaches the top-level ecosystem, the carbon sequestration effect descend sharply until the net carbon sequestration can be ignored.