Carbon flows in eutrophic Lake Rotsee: a 13C-labelling experiment

Abstract

The microbial segment of food webs plays a crucial role in lacustrine food-web functioning and carbon transfer, thereby influencing carbon storage and CO 2 emission and uptake in freshwater environments. Variability in microbial carbon processing (autotrophic and heterotrophic production and respiration based on glucose) with depth was investigated in eutrophic, methane-rich Lake Rotsee, Switzerland. In June 2011, 13 C-labelling experiments were carried out at six depth intervals in the water column under ambient light as well as dark conditions to evaluate the relative importance of (chemo)autotrophic, mixotrophic and heterotrophic production. Label incorporation rates of phospholipid-derived fatty acid (PLFA) biomarkers allowed us to differentiate between microbial producers and calculate group-specific production. We conclude that at 6 m, net primary production (NPP) rates were highest, dominated by algal photoautotrophic production. At 10 m -the base of the oxycline-a distinct low-light community was able to fix inorganic carbon, while in the hypolimnion, heterotrophic production prevailed. At 2 m depth, high label incorporation into POC could only be traced to nonspecific PLFA, which prevented definite identification, but suggests cyanobacteria as dominating organisms. There was also depth zonation in extracellular carbon release and heterotrophic bacterial growth on recently fixed carbon. Large differences were observed between concentrations and label incorporation of POC and biomarkers, with large pools of inactive biomass settling in the hypolimnion, suggesting late-/post-bloom conditions. Net primary production (115 mmol C m -2 d -1 ) reached highest values in the epilimnion and was higher than glucose-based production (3.3 mmol C m -2 d -1 , highest rates in the hypolimnion) and respiration (5.9 mmol C m -2 d -1 , highest rates in the epilimnion). Hence, eutrophic Lake Rotsee was net autotrophic during our experiments, potentially storing large amounts of carbon.

Assessing the Water Quality of Lake Hawassa Ethiopia—Trophic State and Suitability for Anthropogenic Uses—Applying Common Water Quality Indices

“…It is very probable that the increased pH values are mainly due to the consumption of dissolved carbon dioxide by the autotrophic biomass in the upper layer of the eutrophic lake. These conditions may completely change in deeper layers, where due to the absence of light heterotrophic degradation processes should be dominant [68].…”

Microbial carbon processing in oligotrophic Lake Lucerne (Switzerland): results of in situ 13C-labelling studies

“…This close coupling between bacterial production and respiration with NPP was much stronger than in the Rotsee bottle experiments, where the depth-integrated NPP rate was [ 12 times higher than the sum of glucose-based production and respiration (Lammers et al 2016). This indicates that heterotrophic producers in Lake Lucerne are well adapted to rapidly respond to an increase in primary productivity, which is in line with calculated bacterial growth efficiencies in the surface water layer.…”

“…Comparison to eutrophic Lake Rotsee A second bottle labelling experiments similar to the one in Lake Lucerne was carried out in Rotsee during the same month (Lammers et al 2016). Rotsee is a eutrophic lake north of Lake Lucerne (Fig.…”

The Depleted Carbon Isotopic Signature of Nematodes and Harpacticoids and Their Place in Carbon Processing in Fish Farm Sediments

“…About 1-2 of 13 C enrichment is mostly observed per trophic level through the marine food web (DeNiro and Epstein, 1981;Ostrom and Fry, 1993;Soreide et al, 2006). The food-labeled experiments, in contrast, focus on an exact food source, e.g., diatoms, excessively enriched in 13 C, which can be traced in the grazers, e.g., meiofauna, resulting as higher values of δ 13 C (Wyckmans et al, 2007;Franco et al, 2008;Maria et al, 2011;Lammers et al, 2016). The natural abundance of isotopes reflect the accumulation of it over a longer period of time and allows trophic level estimates.…”