Concentration Variations and Flux Estimation of Dissolved Carbon in Karst Spring of a Typical Karst Area

Abstract

Dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) are two important indices for studying karstification, carbon sinks, and the carbon cycle. In order to further understand the migration characteristics of DIC and DOC in karst springs in small watersheds and improve the estimation accuracy of carbon flux under conditions of discrete and limited water quality monitoring data, the concentration variations of DIC and DOC were studied in karst outlet springs of Chenqi small watershed in Puding County, Guizhou Province, China. The flux estimation regression equations of DIC and DOC were established by the LOADEST model, and the carbon sink intensity in Chenqi karst spring basin was estimated. The results showed that the concentrations of DIC and DOC were 16.47-42.31 mg·L-1 and 0.87-6.89 mg·L-1, which displayed exponential decrease and increase with increased instantaneous runoff, respectively. Based on the regression equations constructed by the LOADEST model, the daily flux load of DIC was mainly affected by runoff, whereas that of DOC was affected by both time and runoff. The estimated total fluxes of DIC and DOC were 9490.01 kg·a-1 (95% confidence interval of 11293.58-7972.33 kg·a-1) and 1704.87 kg·a-1 (95% confidence interval of 1895.24-1553.24 kg·a-1), respectively. The carbon sink intensity of the Chenqi karst spring basin was 3.40 g·(m2·a)-1[95% confidence interval of 2.85-4.05 g·(m2·a)-1]. The LOADEST model fully utilized discrete and limited water quality data to improve flux estimation accuracy from the monthly average to the daily average. Therefore, it is an effective tool to estimate the fluxes of DIC and DOC in karst springs under low frequency water quality monitoring conditions.