The unknown role of karst aquatic systems for terrestrial–atmospheric carbon transfer (KarLoss)

内陆水生系统将陆地碳输送到海洋，但也向大气排放二氧化碳。一些研究认为，来自喀斯特地形的河流可能起到碳汇的作用，而另一些研究则表明，这些河流的二氧化碳含量已经高度饱和。由于碳酸盐的大量无机碳储存库，喀斯特地形中的河流和溪流可能成为大气中强大的二氧化碳排放者。然而，喀斯特流域及其各自的泉水和低阶溪流在全球碳循环中的作用在很大程度上仍然未知。此外，到目前为止，人们对二氧化碳模式的变化所起的作用知之甚少。最近发展的便携式激光分析仪可以直接在现场测量逃逸二氧化碳的浓度和稳定同位素比。这可以解开内陆水生系统碳转移的起源、途径和转化过程。该技术的应用还将有助于克服评估二氧化碳逃逸通量的数学模型的局限性。本研究旨在提高我们对温带喀斯特水生系统在全球碳循环中的作用的认识，重点关注低阶溪流及其泉水的二氧化碳逃逸。我们计划通过直接现场测量进行空间和时间量化，以解开和理解驱动岩溶水源集水区二氧化碳梯度的物理和生物地球化学过程。这一目标将通过对德国巴伐利亚北部Wiesent喀斯特试点集水区的详细调查，以及与附近两个花岗岩和砂岩为主的集水区的源头进行比较来实现。我们计划每月定期的实地活动，以日常和事件为基础的抽样。二氧化碳的浓度和稳定同位素将直接在野外测量。这将辅以所有碳相（DIC、DOC和POC）的同位素和浓度的实验室分析。这种多参数方法开辟了通过同位素比率变化来模拟CO2逃逸的新视角。这些新方法有可能更好地限制目前内陆水生系统的二氧化碳转移率，并可能为将碳通量提高到区域或全球估算值奠定基础。

Inland aquatic systems transport terrestrial carbon to the oceans, but also emit CO2 to the atmosphere. Some studies argue that rivers from karst terrains might act as carbon sinks and others show that they are highly oversatured with respect to CO2. Due to the large inorganic carbon reservoir of carbonates, rivers and streams in karst terrains can potentially act as strong CO2 emitters to the atmosphere. However, the role of karst catchments and their respective springs and low-order streams in the global carbon cycle remains largely unknown. In addition, the role of diel changes in CO2 patterns are so far only poorly understood. Recent developments in portable laser-based analyzers allow to measure concentrations and stable istope ratios of evading CO2 directly in the field. This allows to unravel origins, pathways and transformation processes during carbon transfer from inland aquatic systems. The application of this technique will also help to overcome limitations of mathematical models for the assessment of CO2 evasion fluxes. This study aims to enhance our understanding of the role of temperate karst aquatic systems within the global carbon cycle with focus on CO2 evasion from low-order streams and their springs. We plan spatial and temporal quantifications by direct field measurements, to disentangle and understand physical and biogeochemical processes that drive CO2 gradients in karstic headwater catchments. This aim will be reached by detailed investigations of the Wiesent karst pilot catchment in Northern Bavaria, Germany and by comparisons to nearby headwaters of two granite- and sandstone-dominated catchments. We plan regular monthly field campaigns, diel and event-based samplings. Concentrations and stable isotopes of CO2 will be measured directly in the field. This will be complemented by laboratory analyses of all carbon phases (DIC, DOC and POC) for both, isotopes and concentrations. Such a multi-parameter approach opens new modelling perspectives of CO2 evasion via isotope ratio changes. These new approaches have the potential to better constrain current CO2 transfer rates from inland aquatic systems and could establish a basis for upscaling carbon fluxes to regional or global estimates.