Restoration measures of deteriorated river ecosystems generally aim at increasing the spatial heterogeneity and connectivity of these systems in order to increase biodiversity and ecosystem stability. While this is believed to benefit overall ecological integrity, consequences of such restoration projects on biogeochemical processes per se (i.e. ecosystem functioning) in fluvial systems are rarely considered. We address these issues by evaluating the characteristics of surface water connection between side arms and the main river channel in a former braided river section and the role and degree of connectivity (i.e. duration of surface water connection) on the sediment biogeochemistry. We hypothesized that potential respiration and denitrification would be controlled by the degree of hydrological connectivity, which was increased after floodplain restoration. We measured potential microbial respiration (SIR) and denitrification (DEA) and compared a degraded floodplain section of the Danube River with a reconnected and restored floodplain in the same river section. Re-establishing surface water connection altered the controls on sediment microbial respiration and denitrification ultimately impacting potential microbial activities. Meta-variables were created to characterize the effects of hydrology, morphology, and the available carbon and nutrient pools on potential microbial processing. Mantel statistics and path analysis were performed and demonstrate a hierarchy where the effects of hydrology on the available substrates and microbial processing are mediated by the morphology of the floodplain. In addition, these processes are highest in the least connected sites. Surface water connection, mediated by morphology regulates the potential denitrification rate and the ratio of N2O to N2 emissions, demonstrating the effects of restoration in floodplain systems.

中文翻译：

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对河流泛滥平原潜在呼吸作用和反硝化作用的大规模控制

退化河流生态系统的恢复措施通常旨在增加这些系统的空间异质性和连通性，以增加生物多样性和生态系统稳定性。虽然这被认为有利于整体生态完整性，但很少考虑此类恢复项目对河流系统中生物地球化学过程本身（即生态系统功能）的影响。我们通过评估前辫状河段侧臂与主要河道之间地表水连接的特征以及连接性（即地表水连接的持续时间）对沉积物生物地球化学的作用和程度来解决这些问题。我们假设潜在的呼吸作用和反硝化作用将受水文连通程度的控制，洪泛区恢复后增加。我们测量了潜在的微生物呼吸 (SIR) 和反硝化作用 (DEA)，并将多瑙河退化的洪泛区部分与同一河段中重新连接和恢复的洪泛区进行了比较。重新建立地表水连接改变了对沉积物微生物呼吸和反硝化的控制，最终影响了潜在的微生物活动。创建元变量来表征水文、形态以及可用碳和营养库对潜在微生物加工的影响。进行了 Mantel 统计和路径分析，并展示了一个层次结构，其中水文对可用基质和微生物加工的影响是由漫滩的形态介导的。此外，这些进程在连接最少的站点中最高。由形态介导的地表水连接调节潜在的反硝化速率和 N2O 与 N2 排放的比率，证明了洪泛区系统恢复的效果。