Soil Fluid Biogeochemical Response to Climatic Events
Soil Fluid Biogeochemical Response to Climatic Events
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土壤流体对气候事件的生物地球化学响应
DOI：
10.1029/2019jg005216
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
J. Chorover
中科院分区：
文献类型：
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作者：
Y. Olshansky;J. Knowles;G. Barron‐Gafford;C. Rasmussen;N. Abramson;J. Chorover
由于温度、湿度和生物活性等多种控制因素随时间的变化，预测渗透带中的流体生物地球化学是困难的。此外，土壤是多组分、非均质多孔介质，其中多种反应可能影响溶液的化学性质。我们假设生态系统尺度的过程，如碳固定和生态水文分配，控制地下生物地球化学反应，包括矿物风化。为了验证这一假设，我们采用了一种新的“仪器化pedon”研究方法。对数据流的分析表明，脉冲润湿事件与土壤剖面和地下水流动路径上的生物地球化学过程之间存在相互作用。湿润锋向干燥土壤的快速传播导致深层土壤CO2分压的脉冲增加，而湿润锋向预湿土壤剖面的传播则表现出相反的效果。根据CO2和O2通量计算的表观呼吸商（ARQ）偏离预期的氧化比，特别是在土壤湿润事件期间。这些偏差与孔隙水地球化学响应及时相关，揭示了在伴随湿锋传播的脉冲硅酸盐风化事件中，部分呼出的二氧化碳被局部消耗。然而，大部分二氧化碳溶解在土壤孔隙水中，并沿着土壤-基岩界面向下梯度输送，其中一部分在硅酸盐风化反应中进一步消耗，另一部分被脱气到大气中。这些结果强调了物理、生物和化学过程之间存在的紧密耦合，在事件时间尺度上，在关键区域的增量共同进化过程中，特别是在水限制系统中。
Predicting fluid biogeochemistry in the vadose zone is difficult because of time‐dependent variation in multiple controlling factors, such as temperature, moisture, and biological activity. Furthermore, soils are multicomponent, heterogeneous porous media where manifold reactions may be affecting solution chemistry. We postulated that ecosystem‐scale processes, such as carbon fixation and ecohydrologic partitioning, control subsurface biogeochemical reactions, including mineral weathering. To test this hypothesis, we applied a novel “instrumented pedon” research approach. Analysis of the data streams demonstrates the interactions between pulsed wetting events and biogeochemical processes in the soil profile, and along groundwater flow paths. Rapid wetting front propagation into dry soil resulted in a pulsed increase in CO2 partial pressure in deeper soil layers, whereas wetting front propagation into a premoistened soil profile showed the opposite effect. The apparent respiratory quotient (ARQ), calculated from CO2 and O2 fluxes, deviated from expected oxidative ratios particularly during soil wetting events. These deviations were correlated in time with pore water geochemical responses, revealing that a fraction of the respired CO2 was consumed locally in pulsed silicate weathering events that accompanied wetting‐front propagation. However, most of this CO2 was dissolved in the soil pore water and transported downgradient, and along the soil‐bedrock interface, where a portion of it was further consumed in silicate weathering reactions, and another portion was degassed to the atmosphere. These results highlight the tight coupling that exists between physical, biological, and chemical processes, on event time scales, during incremental co‐evolution of the critical zone, particularly in water‐limited systems.