The Age of Buried Carbon Changes the Greenhouse Gas Budget of a Dam

Abstract

AbstractDams are a globally relevant source of greenhouse gases (GHG), which impairs their function as a source of green energy. High burial rates of organic carbon (OC) in dam sediments may partly or fully offset the emissions. We argue that only the burial of carbon fixed in the timespan of dam operation changes the GHG balance. Here, we took sediment cores from a temperate dam. We analyzed radiocarbon age and OC molecular composition by laser desorption ionization mass spectrometry in the bulk OC and in four chemical extract fractions. The bulk samples contained modern OC, fixed after 1950. However, the extracted OC was of different ages (modern to 1900 years BP). Fractions with OC measured as old (>960 years BP) accounted for 57% of total sediment OC. Correlations of molecular composition with extract age suggest that these older fractions contained insignificant amounts of modern OC. We conclude that a substantial proportion of buried carbon did not originate from the contemporary atmosphere and cannot be offset against recent GHG emissions.