Microsensors; Reduced sediment substances flux; Lakes and reservoirs; Diffusive boundary layer; Hydrodynamic modelling of currents; Bottom boundary layer; Hypolimnetic oxygen depletion
Schwefel Robert, Steinsberger Thomas, Bouffard Damien, Bryant Lee D., Müller Beat, Wüest Alfred (2018), Using small-scale measurements to estimate hypolimnetic oxygen depletion in a deep lakeOxygen depletion in a deep lake, in Limnology and Oceanography
, 63(S1), S54-S67.
Gaudard Adrien, Schwefel Robert, Vinnå Love Råman, Schmid Martin, Wüest Alfred, Bouffard Damien (2017), Optimizing the parameterization of deep mixing and internal seiches in one-dimensional hydrodynamic models: a case study with Simstrat v1.3, in Geoscientific Model Development
, 10(9), 3411-3423.
Steinsberger Thomas, Schmid Martin, Wüest Alfred, Schwefel Robert, Wehrli Bernhard, Müller Beat (2017), Organic carbon mass accumulation rate regulates the flux of reduced substances from the sediments of deep lakes, in Biogeosciences
, 14(13), 3275-3285.
Schwefel Robert, Hondzo Miki, Wüest Alfred, Bouffard Damien (2017), Scaling oxygen microprofiles at the sediment interface of deep stratified watersScaling Oxygen Microprofiles, in Geophysical Research Letters
, 44(3), 1340-1349.
Schwefel Robert, Gaudard Adrien, Wüest Alfred, Bouffard Damien (2016), Effects of climate change on deepwater oxygen and winter mixing in a deep lake (Lake Geneva): Comparing observational findings and modelingCLIMATE CHANGE EFFECTS IN A DEEP LAKE, in Water Resources Research
, 52(11), 8811-8826.
SUMMARY A two year prolongation (“Verlängerung”) of the project “Oxygen depletion in a deep perialpine lake (200021-146652)” is proposed. The original project started on 1 July 2013 and will last thru the end of June 2016. This project brought new insights into the deep-water dissolved oxygen (O2) dynamics and O2 budget of a perialpine lake which experienced, on one hand, a pronounced eutrophication but, on the other hand, never entirely lost O2 within the deep regions.The original project aims to study bottom boundary layer (BBL) O2 dynamics and to develop an O2 depletion model for a large-sized deep perialpine lake as a function of the O2 level in the BBL (and its relation to seasonal deep mixing) and the hydrodynamic (meteorological) forcing. The practical goal of this project is to explain the high O2 depletion rate in Lake Geneva. With the requested prolongation, we want to not only complete the specific (Lake Geneva) study but also to expand the results to various lakes of different sizes. First results reveal that the high rate of O2 depletion in Lake Geneva (~1.3 gO2 m-2 d-1; Task A completed) is only in small part caused by the reduced substances diffusing out of the sediment. The nature of the larger component of O2 depletion still needs to be clarified, as we find less than expected O2 diffusion into the sediment. The variation in the hypolimnetic O2 level in Lake Geneva, monitored over decades, is almost entirely due to deep seasonal mixing and not due to variations in O2 depletion, which was surprisingly not altered during the period of eutrophication. The three-dimensional (3D) Delft3D model is running (http://aphyspc1.epfl.ch/) and producing realistic BBL currents (uBBL), which we need for extrapolating the flux measurements (Tasks B/C) laterally over the entire sediment surface as well as temporally over the entire season (see outstanding Tasks D/E/F below). Also the highly-resolved BBL model (GETM) is now running but results have not yet been analysed. The objectives for the prolongation build on those achievements, the acquired data and the preliminary analysis. We set the following specific and concrete goals for two years of prolongation (the numbering of the tasks is the same as in the original proposal): (i) Completing the field measurements, consisting of O2 profiles in BBLs and O2 microprofiling through diffusive boundary layers (Task B) as well as additional sediment-to-water fluxes of reduced substance (Task C).(ii) Modelling of large-scale current patterns using Delft3D and local BBL-currents using GETM (Task D) as well as up-scaling the observed O2 fluxes by the modelled BBL-currents (Task E). (iii) Finalizing the PhD thesis of Robert Schwefel and passing the exam (formal education and credits are already completed) late Spring / early Summer 2017. (iv) Expanding the improved model - developed in (ii) - to other lakes for validation. The results will be published as one-dimensional model web-tools, which provide the vertical oxygen profiles by continuous analysis and forecasting (Task F).(v) Publishing the research outcome in peer-reviewed journals (Task G). This project will make a significant contribution to the understanding of O2 depletion in stratified freshwaters. The results will support the definition of acceptable nutrient loads to standing waters (lakes, reservoirs, ponds, etc.). We ultimately want to understand the differences in the ability of lake sediments to provide habitat for natural reproduction of whitefish, which is also of high socio-cultural value. The results will also allow environmental engineers to better (i) estimate O2 consumption in waters and (ii) design aeration / oxygenation systems for lakes and reservoirs.