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

Abstract. The flux of reduced substances 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 sediment porewater measurements at different water depths from five deep lakes of differing trophic states. Fred was directly proportional to the total organic carbon mass accumulation rate (TOC-MAR) measured in the sediments. In eutrophic lakes Fred decreased systematically with increasing mean hypolimnion depth (zH). In Lake Baldegg, both TOC-MAR and Fred increased with depth due to sediment focusing. Temporarily anoxic conditions increased Fred even in the oligotrophic Lake Aegeri, while Fred was surprisingly low in the 310 m deep but eutrophic Lake Geneva. As TOC-MAR and zH are based on more commonly available data sets, these relationships provide an estimate for the O2 consumption by Fred, where no direct flux measurements are available.