Articles | Volume 14, issue 13
Research article
10 Jul 2017
Research article |  | 10 Jul 2017

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

Thomas Steinsberger, Martin Schmid, Alfred Wüest, Robert Schwefel, Bernhard Wehrli, and Beat Müller

Abstract. The flux of reduced substances, such as methane and ammonium, from the sediment to the bottom water (Fred) 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 meso- to eutrophic lakes Fred was directly proportional to the total organic carbon mass accumulation rate (TOC-MAR) of the sediments. TOC-MAR and thus Fred in eutrophic lakes decreased systematically with increasing mean hypolimnion depth (zH), 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, Fred was low in the 310 m deep meso-eutrophic Lake Geneva, with high O2 concentrations in the hypolimnion. By contrast, seasonal anoxic conditions enhanced Fred in the deep basin of oligotrophic Lake Aegeri. As TOC-MAR and zH are based on more readily available data, these relationships allow estimating the areal O2 consumption rate by reduced compounds from the sediments where no direct flux measurements are available.

Short summary
Based on a broad dataset of lake sediment analysis and porewater measurements from various Swiss lakes, this paper argues that the accumulation of organic carbon in the sediment is one of the main driving forces for the generation of reduced substances such as methane and ammonia. These substances significantly contribute to the hypolimnetic oxygen consumption. The relationships presented help to evaluate the scale of the flux of reduced substances where no direct measurements are available.
Final-revised paper