Using small‐scale measurements to estimate hypolimnetic oxygen depletion in a deep lake

Abstract

Low oxygen concentrations in lakes and reservoirs are an ongoing environmental concern, particularly in light of increasing anthropogenic activity and climate change. Oxygen depletion processes in lakes are still not completely understood and a variety of models have been proposed based on limited field observations. Here, we present field measurements of oxygen depletion processes in a deep lake, Lake Geneva (Switzerland). The aim of this study was to quantify three basic processes controlling hypolimnetic oxygen depletion and their relative contribution to the total oxygen depletion (TOD) rate. Sediment oxygen uptake (SOU) and the flux of reduced substances were estimated based on oxygen microprofile measurements and sediment core data of reduced substances. Acoustic Doppler current profiler measurements and hydrodynamic modeling were used to ensure that SOU was measured under typical hydrodynamic conditions. Comparison with long‐term monitoring data allowed for an estimate of the relative importance of SOU and water column mineralization (WCM). Results show a decrease in both SOU and WCM down to mid‐depth which could not be explained by changes in hydrodynamic conditions or temperature. Below mid‐depth, TOD increased due to an enhanced sediment area to water volume ratio (α). This vertical pattern of oxygen depletion is driven by (1) lake morphometry paired with increasing α, and (2) decreasing organic matter mineralization in the water column with depth. The findings are explained by a model which separates the oxygen depletion into an exponentially decreasing component, representing the fast‐decaying fraction of the organic matter, and a constant background component.

Biogeochemical changes at the sediment–water interface during redox transitions in an acidic reservoir: exchange of protons, acidity and electron donors and acceptors

“…Diffusive oxygen uptake (DOU) rates at the sediment water interface were in the range or slightly higher than those available in the literature for acid lakes (Kühl et al 1998;Koschorreck et al 2003;Lagauzère et al 2011) and neutral lakes (Sweerts et al 1991;Maerki et al 2009;Matzinger et al 2010;Schwefel et al 2017). The instantaneous increase in O 2 concentration in the HI-OX transition probably induced an increase in the oxidation rates of organic matter and reduced compounds like Fe 2?…”

“…The effect of hypolimnetic hypoxic and anoxic conditions on degradation and preservation rates of organic matter and the regeneration and release of nutrients from lake sediments has received considerable attention (Maerki et al 2009;Matzinger et al 2010;Schwefel et al 2017). However, the number of studies dealing specifically with the effects of reversible redox oscillations on the biogeochemistry of lake sediments is scarce (Borch et al 2010;Frindte et al 2013;Torres et al 2014;Karimian et al 2017).…”

Hypolimnetic oxygen depletion rates in deep lakes: Effects of trophic state and organic matter accumulation

“…n.d., not determined. Some data were taken from the respective literature: 1 Frenzel et al (1990), 2 Span et al (1990), 3 Schwalb et al (1998), 4 Müller et al (2007), 5 Zimmermann (2008), 6 Putyrskaya et al (2009), 7 Sobek et al (2009), 8 Wirth et al (2011), 9 Bierlein et al 2017, 10 Steinsberger et al (2017), 11 Schwefel et al (2018). to SOU, while in Lake Geneva and Lake Thun, due to high loads from the catchment geology, SO 4 2− fluxes contributed about one third to SOU.…”

“…Studies of Lakes Michigan (Thomsen et al 2004), Erie (Edwards et al 2005;Smith and Matisoff 2008), and Superior (Li et al 2012) have further demonstrated the importance of SOU and/or WCM as O 2 sinks in these lakes. A study of the highly productive and deep Lake Geneva by Schwefel et al (2018) showed that, as with the Great Lakes, O 2 consumption primarily occurred in the water column rather than near or in the sediment.…”

“…In general, deep lakes such as Baikal or Superior store enough O 2 in their large hypolimnia to prevent anoxia in bottom waters, assure aerobic OM remineralization and limit the production of reduced substances (Müller et al 2005; Li et al 2012). Even in the very productive and deep Lake Geneva, which exhibits a TP concentration of ~ 24 mg P m −3 (average from 2008 to 2018) and a carbon assimilation rate of ~ 250 g C m −2 yr −1 (Anneville and Pelletier 2000; Soomets et al 2019), sediment characteristics resemble those of an oligotrophic lake with low TOC content (~ 1%), very small fluxes of CH 4 and NH 4 + from the sediment and limited O 2 consumption at the sediment–water interface (Steinsberger et al 2017; Schwefel et al 2018). The high fraction of WCM (~ 70%) on the total AHM diminishes the oxidizing capacity of the settling material on its way to the sediment.…”