Hydrological intermittency affects sediment biogeochemistry, organic carbon (OC) metabolism and carbon dioxide (CO 2 ) emission but the study of the effects of drying is generally confined to natural ecosystems. Agricultural canals are artificial, widespread elements in irrigated floodplains, and regularly subjected to water level fluctuations. The aim of this study was to quantify the CO 2 emissions along water saturation gradients in artificial canals to understand the environmental factors regulating these fluxes. CO 2 measurements were performed in five replicated canals within the Po River basin (Northern Italy). In each canal we analysed three sites: (i) a spot with exposed, dry sediments; (ii) a spot with inundated, saturated sediments and (iii) a spot with an intermediate level of saturation. Besides dark CO 2 flux measurements, net potential nitrification and denitrification rates were measured as proxies of sediment redox potential and due to their CO 2 sink and source role, respectively. We hypothesized a site-specific regulation of CO 2 emission, depending on the interplay among water saturation, sediment oxidation and organic matter content. Our results suggest that desiccation stimulates mineralization processes and CO 2 fluxes, that were mainly dependant on water and organic matter content and correlated with microbial N transformations. CO 2 emissions tended to increase along the considered water saturation gradients, almost tripling rates from inundated, saturated (158.2 ± 24.1 mmol CO 2 m −2 days −1 ) to dry, exposed sediments (416.5 ± 78.9 mmol CO 2 m −2 days −1 ). Results also suggest that net potential nitrification and denitrification allow tracing the effects of drying on N microbial communities involved in CO 2 fluxes. Net potential nitrification rates produce little effects on CO 2 fluxes, but is a good proxy of oxygen (O 2 ) availability, whereas potential denitrification may be responsible for variable fractions (up to 100%) of CO 2 production, in wetter sediments.

中文翻译：

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沿灌溉渠沉积物中水饱和度梯度的 CO2 通量调节

水文间歇性影响沉积物生物地球化学、有机碳 (OC) 代谢和二氧化碳 (CO 2 ) 排放，但对干燥影响的研究通常仅限于自然生态系统。农业运河是人工灌溉的泛滥平原中广泛分布的元素，经常受到水位波动的影响。本研究的目的是量化人工运河中沿水饱和度梯度的 CO 2 排放，以了解调节这些通量的环境因素。CO 2 测量在波河流域（意大利北部）内的五个重复运河中进行。在每条运河中，我们分析了三个地点：(i) 一个有暴露的干燥沉积物的地点；(ii) 一个被淹没的饱和沉积物的地点和 (iii) 一个中等饱和度的地点。除了暗 CO 2 通量测量，净电位硝化和反硝化速率分别作为沉积物氧化还原电位的代表和由于它们的 CO 2 汇和源作用进行测量。我们假设特定地点的 CO 2 排放调节取决于水饱和度、沉积物氧化和有机物含量之间的相互作用。我们的结果表明，干燥刺激矿化过程和 CO 2 通量，这主要取决于水和有机物含量，并与微生物 N 转化相关。CO 2 排放倾向于沿着所考虑的水饱和梯度增加，从淹没、饱和（158.2 ± 24.1 mmol CO 2 m -2 天 -1 ）到干燥、暴露的沉积物（416.5 ± 78.9 mmol CO 2 m -2 天）的速率几乎增加了三倍-1 )。结果还表明，净潜在硝化和反硝化允许追踪干燥对参与 CO 2 通量的 N 微生物群落的影响。潜在的净硝化速率对 CO 2 通量几乎没有影响，但它是氧 (O 2 ) 可用性的良好代表，而潜在的反硝化作用可能导致更潮湿沉积物中 CO 2 产生的不同部分（高达 100%）。