The efficient reactivity and mobility of dissolved organic matter (DOM) affect biogeochemical processes. As important components that link aboveground and belowground vertical systems under the binary 3D structure of karst, fissures provide soil–water–nutrient leakage channels and storage spaces. However, reports on DOM properties and drivers in fissured soil are extremely rare. This study characterizes DOM in the fissured soil of different vegetation types under medium-intensity rocky desertification conditions. Soil samples were characterized via ultraviolet (UV)–visible absorption spectroscopy and fluorescence excitation–emission matrix–parallel factor analysis. Five fluorescent fractions were identified. The controlling factors for the optical properties of soil DOM were determined via the redundancy analysis method. Results showed the following: (1) Dissolved organic C/soil organic C < 4.68 + 0.49‰, specific UV absorbance (SUVA)₂₅₄ and SUVA₂₆₀ exhibited low overall performance with the vast majority of the humification index (HIX) < 4, most of the fluorescence index (FI) ≥ 1.7, most of the biological index (BIX) in 0.6 < BIX < 1 and 31.67–41.67% of protein-like fractions. These data indicate that cleaved soil, except for topsoil, has low DOM content, weak aromaticity, and low humification; (2) Rainfall intensity, aperture, and near-surface vegetation type are the major causes of DOM transport and loss; and (3) Most DOM losses are likely to be protein-like and enhance the loss of soil P. In summary, environmental factors and the characteristics of fissures determine DOM content and migration, particularly rainfall intensity and vegetation type. The loss of lighter DOM components will be greater in an area with high karst desertification grade, strong fissure development, weaker soil aromaticity, and lower humification. These results provide a clearer basis for optimizing the fissure nutrient element migration scheme in karst areas.

While vegetation restoration results in increased carbon storage and benefits ecosystems, its effects on water availability in ecologically fragile karst areas are unclear. Here, we investigate the long‐term spatial‐temporal variations of climate parameters, vegetation greenness, hydrological variables (evapotranspiration, runoff, soil moisture), water yield, and terrestrial water storage in the Southwest China Karst (1982–2018), where large‐scale ecological restoration projects (ERPs) were implemented in the past few decades. The generalized linear mixed model (GLMM) was employed to quantify the contributions of climate change and vegetation greening on the changes in water availability in this humid region. We found that vegetation greening in the Southwest China Karst was significant during 1982–2018. Climate change resulted in a remarkable change from a wetting trend to a drying trend during 1993–2013. We show that the vegetation‐greening and climate change across this humid region strongly increased the evapotranspiration (ET, +2.08–2.67 mm yr⁻¹) and reduced the terrestrial water storage (TWS, −2.19–2.96 mm yr⁻¹) over the past almost four decades, while the water yield was almost unchanged. Vegetation greening accounted for a ∼26.43%–52.09% decrease in TWS, and we attribute this water depletion to decreases in soil moisture and groundwater during dry years (1993–2013). These findings show that future “green projects” in humid karst areas should consider the impact of revegetation on the sustainable water supply.

For insight into the productive and storage mechanisms of biogas in the Qaidam Basin, efforts were made to investigate the groundwater recharge and the processes of hydrocarbon generation by CDOM-EEM (fluorescence excitation-emission matrix of Chromophoric dissolved organic matter) spectrum, hydrogen and oxygen isotopes, and geochemical characters in the central depression of the Qaidam Basin, China. The samples contain formation water from three gas fields (TN, SB, and YH) and surrounding surface water (fresh river and brine lake). The results indicate that modern precipitation significantly controls the salinity distribution and organic matter leaching in the groundwater system of the central depression of the Qaidam Basin. Higher salinity levels inhibit microbial activity, which leads to organic matter degradation and to gas generation efficiency being limited in the groundwater. The inhabitation effect is demonstrated by the notable negative correlation between the extent of organic matter degradation and its concentration with hydrogen and oxygen isotopes. The conclusion of this study indicated that modern precipitation emerges as a crucial factor affecting the biogas production and storage in the Qaidam Basin by influencing the ultimate salinity and organic matter concentration in the formation, which provides theoretical insight for the maintenance of modern gas production wells and the assessment of gas production potential.