Extreme dry climate conditions undermine the benefits of ecological restoration on carbonate weathering: A case study from 7 years of monitoring data for an underground river in a typical karst trough valley, in Southwest China

Study region: Longtan Trough Valley, Youyang, Chongqing, China Study focus: Carbonate weathering and associated carbon sinks are sensitive to climate change and vegetation dynamics. In recent decades, climate change-induced extreme events and human-driven ecological restoration efforts have intensified globally, yet their impacts on carbonate weathering remain underexplored. To address this, we conducted seven years of monthly monitoring at an underground river outlet in a typical karst trough valley in Southwest China, aiming to investigate individual influences. New hydrological insights for the region: The dissolved inorganic carbon (DIC) and δ13CDIC were measured from 2017 to 2023 at the seasonal scale in a carbonate-dominated watershed subject to significant ecological restoration and extreme climate conditions. The fixed drought threshold (FDT) and normalized difference vegetation index (NDVI) were employed in this study. We found that vegetation restoration under the humid climate conditions increased the DIC and reduced the δ13CDIC by around 34.6 mg L−1 and 1.7 ‰ from 2017 to 2021. In the same period, the enhancement of carbonate dissolution increased the carbonate weathering carbon sink flux (CCSF) by 5.49 tC km−2, and the rise in runoff increased the CCSF by 6.00 tC km−2. However, in 2022 and 2023, extreme droughts led to a 6.1 % decline in the DIC, a 5.9 % decrease in the NDVI, and a 28.4 % decrease in runoff. We estimate that the lower carbonate weathering intensity reduced the CCSF by 1.06 tC km−2 during this period, while the decline in runoff reduced the CCSF by 8.54 tC km−2. Therefore, we suggest that less extreme events and vegetation restoration efforts are both crucial for enhancing carbonate weathering carbon sinks in the future.