Shi Liangxing, Zhao Yuhao, Zeng Sibo, Liu Zaihua, Shao Mingyu, Zhao Min, He Haibo, Zeng Cheng, Han Yongqiang, Hao Pengyun, Tang Liguo
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 550081, Guiyang, China; University of Chinese Academy of Sciences, 100049, Beijing, China.
Chongqing Key Laboratory of Karst Environment & School of Geographical Sciences of Southwest University, Chongqing 400715, China.
Water Res. 2025 Sep 15;284:124031. doi: 10.1016/j.watres.2025.124031. Epub 2025 Jun 15.
The carbon flux involved in aquatic metabolism in karst surface waters is an important component of both regional and global carbon cycling. Yet, the mechanisms of how aquatic metabolism and the related carbon flux respond to human land use and climate change in a high-pH aquatic environment remain unclear. To address this, we conducted continuous high-frequency (15-min interval) monitoring of hydrochemical parameters, combined with a bookkeeping model and gas transport velocity model, to estimate the aquatic net ecosystem primary (NEP) and water-air CO exchange flux (FCO) under different land-use types at a simulation test site. We then used a structural equation model (SEM) and Random Forest model (RF) to determine the relationship between NEP, land-use type, and climatic factors, and to determine how NEP variations alter the FCO. The results showed that the annual NEP of karst surface water systems under bare rock (0.01 g C m day) was significantly lower than under vegetated land (shrubs, grass and cropland, 0.38-0.75 g C m day). This high NEP demonstrates a strong autotrophic capacity and the potential to reduce CO emissions in these aquatic systems. Our results also suggest that differences in groundwater HCO inputs between bare rock/soil and vegetated land can explain their NEP differences. We applied the RF model to predict the variation of the NEP of different land-use systems by the end of this century, under different CMIP6 scenarios. The results suggested that land-use regulation (the conversion from bare rock or soil to grass or shrubs) can increase the autotrophic capacity of karst surface systems by 42.3 % (SSP126) and 51.5 % (SSP585). The results of this study indicate that human land-use change can potentially enhance the autotrophic capacity and lower the CO emissions of high-pH karst aquatic ecosystems.
岩溶地表水水生代谢过程中的碳通量是区域和全球碳循环的重要组成部分。然而，在高pH值的水生环境中，水生代谢及相关碳通量如何响应人类土地利用和气候变化的机制仍不清楚。为了解决这一问题，我们对水化学参数进行了连续高频（间隔15分钟）监测，并结合簿记模型和气体传输速度模型，在一个模拟试验场估算了不同土地利用类型下的水生生态系统净初级生产力（NEP）和水-气CO₂交换通量（FCO₂）。然后，我们使用结构方程模型（SEM）和随机森林模型（RF）来确定NEP、土地利用类型和气候因子之间的关系，并确定NEP变化如何改变FCO₂。结果表明，裸岩（0.01 g C m⁻² day⁻¹）下岩溶地表水系统的年NEP显著低于植被覆盖土地（灌木、草地和农田，0.38 - 0.75 g C m⁻² day⁻¹）。这种高NEP表明这些水生系统具有很强的自养能力和减少CO₂排放的潜力。我们的结果还表明，裸岩/土壤和植被覆盖土地之间地下水HCO₃⁻输入的差异可以解释它们的NEP差异。我们应用RF模型预测了在不同CMIP6情景下，到本世纪末不同土地利用系统NEP的变化。结果表明，土地利用调控（从裸岩或土壤转变为草地或灌木）可使岩溶地表系统的自养能力提高42.3%（SSP126）和51.5%（SSP585）。本研究结果表明，人类土地利用变化可能会增强高pH值岩溶水生生态系统的自养能力并降低其CO₂排放。
