Biogeochemical hot moments upon flow resumption and coupled sediment transport: A comprehensive approach for temporary and perennial stream ecosystems (FlowReSeT)

该项目将阐明在有和没有泥沙输送的情况下水流恢复的不同年表中调节河床生物地球化学（微生物群落的碳代谢和氮吸收）的机制。干燥后的恢复流动被认为是一个生物地球化学热时刻，由于之前干燥频率的影响，碳代谢和氮吸收的速率很高。调节这一热时刻的机制尚不清楚。迄今为止的研究主要集中在临时溪流和河流生态系统的单因素研究上。然而，在多年生河流生态系统中，水流的间歇和恢复更频繁地发生，地表水流往往意味着泥沙的搬运（如迁移波纹，上层平面床），特别是在砂质河流中。此外，水流恢复可以遵循不同的时间顺序，如降雨瞬间恢复或地下水上升缓慢恢复，并且水流恢复时浸出的营养物质和碳浓度也会影响生物地球化学响应。我们提出了一个新的“间歇溪流栖息地”的一般概念，用于河床的所有区域，尽管各种因素的相互作用不同，但在某个时间点干涸（即缺乏地表水）。本文提出的对各种水流恢复年表、耦合泥沙运移和跨系统比较（临时和长期河流）的机制的研究将表明这种普遍和综合的观点是否适用。本文将通过临时河流和多年生河流间歇生境泥沙群落的微观实验研究水流恢复、泥沙输运和干燥频率的相互作用。需要关注的响应变量有：通过暗、光条件下氧浓度变化测量的碳代谢，通过添加稳定同位素15N （15NH4Cl）测量的净氮吸收率，以及微生物群落的结构和结构（即生物膜）。此外，通过使用数值和水文模型，将评估所获得的结果对河流中碳和氮收支的影响。研究结果将完善易发生严重水流振荡和干旱的生态系统的陆地动力学机制。这些知识是管理地中海和越来越多的温带河流生态系统的关键，这些生态系统由于不断增加的取水和气候变化而经历干燥。

The project shall clarify the mechanisms that modulate streambed biogeochemistry (Carbon metabolism and Nitrogen uptake of the microbial community) at various chronologies of flow resumption with and without sediment transport. The resumption of flow after drying is considered as a biogeochemical hot moment, with high rates of C-metabolism and N-uptake influenced by the frequency of previous drying. The mechanisms modulating this hot moment are not weel understood. Research so far focussed mostly on single factor studies in temporary stream and river ecosystems. However, intermittency and resumption of flow occurs more frequently in perennial stream ecosystems and surface flow often implies sediment transport (e.g. migrating ripples, upper stage plane bed) especially in sandy streams. In addition, flow resumption can follow different chronologies such as instant by rain or slow by rising groundwater, and the concentrations of nutrient and carbon leached upon flow resumption can also influence the biogeochemical response. We suggest a new general concept of “intermittent stream habitats” for all areas of a streambed that dry (i.e. lack of surface water) at some point in time despite variable interactions of factors. The here proposed investigation of the mechanisms at various flow resumption chronologies, coupled sediment transport, and cross system comparison (temporary and perennial streams) will show if such general and integrative view can be applied. The interactions of flow resumption, sediment transport and drying frequency will be studied in microcosm experiments with sediment communities of intermittent habitats from temporary and perennial streams. The response variables under attention are: Carbon metabolism, measured by means of changes in oxygen concentration in darkness and in light, net N-uptake by means of the addition of the stable isotope 15N (15NH4Cl) and the structure and architecture (i.e. biofilm) of the microbial community. Further, by using numerical and hydrological modeling, the implications of the obtained results for C and N budgets in streams will be assessed. The results will complete the mechanistic picture of the Cand Ndynamics of lotic ecosystems prone to severe flow oscillations and drying.. Such knowledgeis key for management of Mediterranean and more and more temperate stream ecosystems that experience drying due to increased water abstraction and climate change.