@misc{AltenkirchZlatanovićWoodwardetal., author = {Altenkirch, Nora and Zlatanović, Sanja and Woodward, K. Benjamin and Trauth, Nico and Mutz, Michael and Molkenthin, Frank}, title = {Untangling hyporheic residence time distributions and whole stream" "metabolism using a hydrological process model}, series = {Procedia Engineering}, volume = {154}, journal = {Procedia Engineering}, issn = {1877-7058}, doi = {10.1016/j.proeng.2016.07.598}, pages = {1071 -- 1078}, abstract = {The interaction of the water residence time (RT) in hyporheic sediments with the sediment metabolic rates is believed to be a key factor controlling whole stream metabolism. However, due to the methodological difficulties, there is little data that investigates this fundamental theory of aquatic ecology. Here, we report on progress made to combine numerical modelling with a series of modification to laboratory flumes overcoming methodological difficulties e.g. by creating steady flow paths for assessment of metabolic rates. To model the biogeochemical performance and to validate the model results, sediment structures were introduced in both, the model and the flumes, leading to differing RT distributions. Furthermore, the DOC supply in the flumes was manipulated to test the whole stream metabolic response with regard to RT distributions. In the flumes, hydraulic conditions were assessed using conservative tracer and heat as tracer. Metabolic activity was assessed using oxygen dynamics as a proxy of community respiration (CR). Residence time and metabolic processes were modelled using a multicomponent reactive transport code called MIN3P and calibrated with regard to the hydraulic conditions using the results obtained from the flume experiments. Monod type expressions were used to implement metabolic activity terms in the model. Using the results of the hydrological process model, a sensitivity analysis of the impact of RT distributions on the metabolic activity could yield supporting proof of an existing link between the two.}, language = {en} } @inproceedings{ReichertMolkenthin, author = {Reichert, Nora and Molkenthin, Frank}, title = {Which numerical model is suitable for the simulation of hyporheic residence times and metabolic activity? FE model vs. FV model}, series = {European Geosciences Union, General Assembly 2018, Vienna, Austria}, booktitle = {European Geosciences Union, General Assembly 2018, Vienna, Austria}, publisher = {European Geophysical Society}, address = {Katlenburg-Lindau}, abstract = {Numerical models have experienced a steady increase in popularity in the scientific community, espe-cially where historically isolated disciplines more and more acknowledge their need for interdisciplinarity. A frequently mentioned example is the interstitial between surface water and ground water in lotic systems, referred to as hyporheic zone. Due to its temporal and spatial heterogeneity, the prediction of hydraulic properties e.g. the residence time remains a challenge in science. Moreover, the hyporheic zone is often described as a reaction chamber due to its repertoire of chemical reactivity, which in turn is highly influenced by the residence times. Ecologically, this habitat is populated by a microbial community that has the potential to alter the chemical characteristics of their environment under the right hydraulic conditions. This small example illustrates the complexity of interdisciplinary research and elucidates the growing requirements concerning numerical models. While the number of numerical models offering to bridge some of these gaps is growing, the decision-making process for the modeler becomes increasingly difficult. It is the objective of this study to identify a suitable model for reproducing measured data from a laboratory flume experiment, in which oxygen was measured as a proxy for metabolic activity under changing dissolved organic carbon inflow in a hyporheic zone with varying residence times. The decision-making process for a suitable numerical model was hereby exemplified by comparing the two numerical models FEFLOW, based on the finite element method (FEM), and MIN3P, based on the finite volume method (FVM). Various aspects of both models are taken into account and evaluated from software technological, numerical or end-user point of view. These include among others the mass balance, meshing algorithm, computational effort and coupling interfaces to surface water models.}, language = {en} }