Decreased efficiency of sediment carbon burial in boreal lakes at warming lake water temperatures
(English)Manuscript (preprint) (Other academic)
Organic carbon (OC) burial in lake sediments is a fundamental process for aquatic carbon (C) cycling since it removes C from the active cycling pool. Here, we address the effect of lake warming on the OC burial efficiency (OCBE) of sediments in boreal humic lakes to evaluate the impact of warmer water temperatures and altered water column stratification patterns on the OCBE with respect to future climate change. Present-day water column conditions of temperature and oxygen concentration were monitored in two small (<0.1 km2) boreal lakes in central and southwestern Sweden over an annual cycle. Furthermore, OC burial, sediment OC mineralization, the OCBE, and lake CO2 and CH4 emission to the atmosphere, were quantified on a whole-basin scale and for a whole year. Then, future temperature and stratification patterns were simulated in both lakes by adjusting present-day temperature and oxygen conditions according to projected air temperature warming scenarios, in order to quantify the net effect on the OCBE. Present-day conditions were found to be similar in the two study lakes, with annual OC mineralization (~1 t C yr-1) exceeding annual OC burial (<0.5 t C yr-1) at least by a factor of two, returning whole-basin OC burial efficiencies of 28 and 25%, respectively. Also, annual CO2 and CH4 emission was found to be of similar magnitude in both study lakes (6-7 t C yr-1) surpassing sediment C fluxes by at least 5 times. The different lake warming scenarios (RCP 2.6, 4.5 and 8.5, corresponding to increase in annual mean air temperature of 1.5-4.5 °C) caused moderate decreases in the OCBE of 5-16% and 3-11% for each lake, respectively. The more pronounced decreases in OCBE were obtained for the more shallow lake, related to a higher proportion of sediments being affected by warming in the epilimnion. Our results suggest that warmer surface water temperatures in the future are likely to reduce the efficiency of the lake sediment C sink, thereby affecting the long-term C balance of the boreal forest biome.
Research subject Biology with specialization in Limnology
IdentifiersURN: urn:nbn:se:uu:diva-260668OAI: oai:DiVA.org:uu-260668DiVA: diva2:851760