Spatiotemporal variability of fluvial carbon components under different land use types in a mountainous karst region, Southwest China

Abstract

Rivers export inorganic and organic carbon derived from various landscapes. Land use thus can significantly impact the spatiotemporal variations in river carbon species. However, the impact of land use, especially agricultural land, on riverine carbon species and dissolved organic matter (DOM) compositions in carbonate areas remains poorly explored. In this study, we collected water samples from a typical karst river in Southwest China, and analyzed the dissolved organic and inorganic (DOC and DIC) and particulate organic carbon (POC) concentrations, δ¹³C_DIC, and DOM compositions. The DIC concentration and δ¹³C_DIC value ranged from 7.9 to 41.4 mg L^–1 and −11.2 to −7.4 ‰ in the wet season, and from 7.4 to 48.7 mg L^–1 and −9.5 to −5.7 ‰ in the dry season, respectively. During the wet season, the tributaries from the catchments with high proportions of forest coverage have relatively low DIC concentrations, and negative δ¹³C_DIC values, indicating the larger contribution of soil CO₂. The forest-dominated group exhibited the highest proportions of humic-like C1 (21.1 ± 0.7 %). The cropland-dominated group displayed the highest proportions of protein-like C3 (44.6 ± 7.6 %), indicating the organic matter inputs from terrestrial and anthropogenic sources. The POC% and C/N ratio ranged from 0.1 % to 0.8 % and 1–16.6 in the wet season, respectively. The proportion of cropland is positively correlated with POC and C/N, indicating the loss of soil rich in organic matter in farmland. These results further highlighted that land use and biological processes have an important impact on carbon transportation in the karst rivers. Therefore, considering alterations in carbon component dynamics resulting from climate and land use changes is crucial for river ecosystem assessments and sustainable development.