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

点击翻译按钮获取中文摘要

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.