Organic carbon mass accumulation rate regulates the flux of reduced substances from the sediments of deep lakes

Abstract

Abstract. The flux of reduced substances, such as methane and ammonium, from the sediment to the bottom water (F red ) is one of the major factors contributing to the consumption of oxygen in the hypolimnia of lakes and thus crucial for lake oxygen management. This study presents fluxes based on sediment porewater measurements from different water depths of five deep lakes of differing trophic states. In mesoto eutrophic lakes F red was directly proportional to the total organic carbon mass accumulation rate (TOC-MAR) of the sediments. TOC-MAR and thus F red in eutrophic lakes decreased systematically with increasing mean hypolimnion depth (z H ), suggesting that high oxygen concentrations in the deep waters of lakes were essential for the extent of organic matter mineralization leaving a smaller fraction for anaerobic degradation and thus formation of reduced compounds. Consequently, F red was low in the 310 m deep mesoeutrophic Lake Geneva, with high O 2 concentrations in the hypolimnion. By contrast, seasonal anoxic conditions enhanced F red in the deep basin of oligotrophic Lake Aegeri. As TOC-MAR and z H are based on more readily available data, these relationships allow estimating the areal O 2 consumption rate by reduced compounds from the sediments where no direct flux measurements are available.

Effects of eutrophication on sedimentary organic carbon cycling in five temperate lakes

“…Standards were made using ICP-multi element standards (solution IV, MERCK, Certipur). Dissolved Fe 2+ was also determined spectrophotometrically (Plate Reader Biotek, Synergy HT) at 562 nm absorption using a ferrozine assay (Stookey, 1970;Braunschweig et al, 2012). Standards were made from FeCl 2 (Sigma, analytical quality) and verified using ICP-OES.…”

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

“…Standard deviations of all measurements were < 5%. The setup is described in detail by Torres et al (2013) and Steinsberger et al (2017).…”

“…A one-dimensional balance model originally developed by Epping and Helder (1997) for oxygen and adapted to other dissolved substances was used to estimate species fluxes. The model, a reactiondiffusion model based on the assumption of steady-state conditions in the sediment, is described in detail in M€ uller et al (2003) and Steinsberger et al (2017). The modeled fluxes of reduced substances were then converted to oxygen equivalents based on redox stoichiometry (Matzinger et al 2010) by:…”

“…DO depletion in the sediment depends on the amount of organic matter and its quality (Steinsberger et al 2017). While parts of organic material are easily degradable (i.e., labile) and decompose relatively quickly, other parts degrade over longer time scales (Kristensen and Holmer 2001;Arndt et al 2013;Bouffard and Perga 2016).…”

“…M€ uller et al (2012a) reported relative contributions of up to 80% of AHM in very shallow small-or mediumsized lakes. In Steinsberger et al (2017), a direct relationship is documented between the relative importance of reduced substances, mean hypolimnion depth, and the organic carbon content of the sediment. Deeper hypolimnia of lakes correspond to larger DO reservoirs and smaller sediment surface to water volume ratios (a).…”