Estimation of karst carbon sink in typical karst system in pediment of Taihang Mountain, northern China.

Abstract

The increase of global carbon dioxide concentration leads to climate change and accurate estimation of carbon sink fluxes from rock weathering in karst regions is of great significance to the current global carbon cycle and climate change. However, sulfide oxidation in coal-bearing strata in karst areas of northern China forms sulfuric acid that enters the karst groundwater system and participates in the dissolution of carbonate rocks, making carbon sink estimates potentially too high. To accurately estimate carbon sinks, we selected a typical foothill karst system in northern China. The effects of sulfuric acid on carbonate weathering and carbon sink flux were quantitatively evaluated by applying the Galy model and water chemistry methods. Twenty-nine data sets were analyzed for the dry and wet seasons. The results show that the karst groundwater ions in the spring area mainly originated from the weathering and dissolution of carbonate rocks and partly from the weathering and dissolution of silicate rocks. The total HCO₃^- flux in the spring area is 296.49´10³mol/km²·a^-1. When only carbonic acid dissolution was considered, the rock dissolution rate was 300.83´10³mol/km²·a^-1 and the total consumed CO₂ flux was 191.82´10³mol/km²·a^-1. When carbonic acid and sulfuric acid were jointly involved, the rock dissolution rate was 364.33´10³mol/km²·a^-1 and the total consumed CO₂ flux was 162.17´10³mol/km²·a^-1. With the participation of sulfuric acid, the rock dissolution rate was elevated by 21.11%, while the consumed CO₂ flux decreased by 15%, and the sink reduction effect of sulfuric acid dissolution on karst carbon sinks was obvious. And the carbon sink rate in wet season more than doubled compared with that in dry season. This study provides a basis for the evaluation of carbon sinks in northern China.