Sources of Soil Water, Carbon, and Nitrogen, and Responses of Karst Carbon Sinks in Peak-Cluster Depression Landscapes Under the Influence of Human Activities

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🔬研究者:Researchers studying carbon sinks, biogeochemistry, or land-use effects on climate can use the isotope tracing and Bayesian modeling approach.

<p indent="0mm"> Karst peak cluster depressions are landscape units within the Southwest Karst Key Zone that exhibit high sensitivity to water–carbon–nitrogen coupling. Investigating the sources of water, carbon and nitrogen in the soils of these depressions, along with the response of karst carbon sinks to human activities, can provide essential data for the precise quantification of karst carbon sinks. This study focuses on a typical karst peak cluster depression in Rong’an, Guangxi. Five land-use types—grassland, scrubland, woodland, cropland, and orchard—were selected for monthly monitoring of soil water and soil CO₂ during the rainy season of 2024 (April to September). By integrating water chemistry, nitrate isotope (<italic>δ</italic>¹⁵N-NO₃^–, <italic>δ</italic>¹⁸O-NO₃^–), and carbon isotopes (<inline-formula id="INLINE2"> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" mathsize="8.0pt"> <mml:mrow> <mml:mspace/> <mml:mrow> <mml:msup other="0"> <mml:mrow other="0"> <mml:mi mathsize="8.0pt" other="0">δ</mml:mi> </mml:mrow> <mml:mrow other="1"> <mml:mn mathsize="5.6pt" other="1">1</mml:mn> <mml:mn mathsize="5.6pt" other="1">3</mml:mn> </mml:mrow> </mml:msup> <mml:msub other="0"> <mml:mstyle mathvariant="normal" other="0"> <mml:mrow other="0"> <mml:mi mathsize="8.0pt" other="0">C</mml:mi> </mml:mrow> </mml:mstyle> <mml:mstyle mathvariant="normal" other="1"> <mml:mrow other="1"> <mml:mi mathsize="5.6pt" other="1">C</mml:mi> <mml:msub other="1"> <mml:mrow other="1"> <mml:mi mathsize="5.6pt" other="1">O</mml:mi> </mml:mrow> <mml:mrow other="2"> <mml:mn mathsize="4.4pt" other="2">2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:mstyle> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> </inline-formula>, <italic>δ</italic>¹³C_DIC), we employed Bayesian mixture models and ion equivalence relationships to analyze nitrate sources and their impact on carbonate rock weathering and carbon sequestration. The results indicate that: (1) Soil water chemistry in the study area is generally controlled by carbonate rock weathering. The natural vegetation zone is dominated by the HCO₃-Ca type, whereas the anthropogenically disturbed zone exhibits significant NO₃^– enrichment. The average concentrations of NO₃^– in soil water from arable land and orchards were <sc>45.26 mg/L</sc> and <sc>100.88 mg/L,</sc> respectively, which are significantly higher than those found in the natural vegetation zone (0.78 to <sc>7.77 mg/L);</sc> (2) Nitrate isotope tracing indicates that NO₃^– in natural vegetation areas primarily originates from the mineralization of soil organic nitrogen and atmospheric deposition. In contrast, concentrations in cultivated and orchard areas are primarily controlled by fertilizer inputs and nitrification processes, with additional contributions from animal manure and wastewater. Bayesian quantitative analysis indicates that nitrate in the study area is predominantly of nitrification origin (including NH₄⁺ fertilizer inputs and soil nitrogen transformation), contributing approximately 65.6%, while animal manure and wastewater account for approximately 27.6%, and rainfall and atmospheric deposition for approximately 6.7%; (3) Ion stoichiometric relationships and carbon isotope results further indicate that carbonate rock dissolution in natural vegetation areas is primarily driven by carbonic acid formed from soil-derived CO₂. In contrast, in human disturbed areas, the involvement of exogenous nitrate is enhanced, leading to an increased proportion of rock-derived carbon in DIC. This phenomenon manifests as enhanced apparent dissolution but a decline in effective carbon sinks. In the study area, nitrate-driven weathering contributes more significantly than carbonate-driven weathering, resulting in a substantial weakening of the effective karst carbon sink. Human activities interfere with and alter exogenous nitrogen inputs and the nitrification-acid production process, thereby weakening the effective carbon sink function of the karst system and exacerbating the complexity of carbon-nitrogen coupling in karst areas as well as the uncertainty in assessing carbon sink effects.

• openalex https://doi.org/10.3724/ee.1672-9250.2026.54.063first seen 2026-07-27 05:08:15