Temporal and spatial dynamics of organic carbon in intermittent springs – Environmental drivers and connectivity to headwater streams

泉水是源头溪流的发源地。它们代表着河流连续体的起点，是地下水和地表水之间的重要交错带。断断续续的泉水来自近地表的无承压含水层。它们表现出地下水暂时不连通的流动状态，停留时间短，并可能作为源头溪流的有机碳(OC)来源。因此，断断续续的泉水有可能显著影响源头溪流中的碳通量。然而，只有少数生态水文学研究将泉水作为有机碳的不同来源，目前仍不清楚可变的水流状况如何影响这些不同交错带的时间变异性或有机碳，这些交错带在低山山脉是典型的。因此，这项建议的目的是调查间歇性泉水有机碳的时空动态，这些过程的环境驱动因素，以及它们在不同低山山脉的下游影响。系统地调查了不同低山山脉(莱茵板岩山脉、矿石山脉、黑森林)的44个间歇性泉水，利用水文和生物地球化学资料进一步阐明了不同时空尺度上的有机碳动态。除了对泉水流量、电导率和水温进行长期监测外，还将对有机碳、营养物质和稳定同位素进行季节性和基于事件的测量。使用一系列最先进的实验室设备和方法(C/N-和TOC-Analyzer，Picarro)，我们将分析DOC、POC、光学性质(荧光、吸光度)、营养物质(PO4、NO3、NO2、NH4)和稳定同位素(18O、2H)的时空变异性。我们将使用一系列多变量统计技术(例如，主成分分析、CCA)来识别空间和时间模式、过程和驱动因素。我们将对弹簧OC的来源和流量进行建模(PARAFAC、SIMMR混合模型、LOADEST、机器学习)。这项对间歇性泉水的水文和生物地球化学性质及其时空动态的跨尺度研究将填补关于间歇性泉水在河流连续体概念中的作用的现有知识空白。这将进一步有助于理解气候变化引起的降水和径流变化引起的泉水动态的潜在变化，以及它们的变化对泉水生态系统以及相关源头溪流的影响。

Springs are the birth of headwater streams. They represent the starting point of the river continuum, and are important ecotones between groundwater and surface water. Intermittent springs originate from near-surface, unconfined aquifers. They display a temporarily groundwater disconnected flow regime, short residence times and may act as sources of organic carbon (OC) to headwater streams. As a result, intermittent springs have the potential to significantly impact carbon fluxes in headwater streams. However, only a few eco-hydrological studies have addressed springs as distinct sources of OC, and it is still unclear how the variable flow regime impacts the temporal variability or organic carbon in these diverse ecotones, which are typical for low mountain ranges. Therefore, the objective of this proposal is to investigate the spatial and temporal dynamics of OC in intermittent springs, environmental drivers of these processes, and their downstream impact in different low mountain ranges. Systematically investigating 44 intermittent springs in different low mountain ranges (Rhenish Slate Mountains, Ore Mountains, Black Forest), we will use hydrological and biogeochemical data to further elucidate OC dynamics at different temporal and spatial scales. In addition to the permanent monitoring of spring discharge, electrical conductivity and water temperature; seasonal and event-based measurements of OC, nutrients and stable isotopes will be carried out. Using an array of state-of-the-art laboratory equipment and methods (C/N- and TOC-Analyzer, Picarro), we will analyse the temporal and spatial variability of DOC, POC, optical properties (fluorescence, absorbance), nutrients (PO4, NO3, NO2, NH4) and stable isotopes (18O, 2H). We will employ a range of multivariate statistical techniques (e.g., PCA, CCA), to identify spatial and temporal patterns, processes and drivers. We will model the sources and fluxes of spring OC (PARAFAC, SIMMR mixing model, LOADest, machine learning). This cross-scale study of the hydrological and biogeochemical properties of intermittent spring and their spatial and temporal dynamics will close the existing knowledge gap regarding the role of intermittent springs within the river continuum concept. This would further contribute to the understanding of potential shifts in the dynamics of springs due to climate change induced variations in precipitation and runoff, and the impact of their changes on both the spring ecosystem, as well as related headwater streams.