Project

Discipline

carbon cycle; Bayesian isotope mixing models; land use; human disturbance; radiocarbon; compound-specific isotope analysis; biogeochemistry; soil erosion

Lead
Die Flüsse von modernem (biogenem) gegenüber gealtertem (petrogenem) organischem Kohlenstoff sind bisher in erodierenden Landschaften nur schwach belegt. Jedoch konnte kürzlich gezeigt werden, dass das Alter von organischem Kohlenstoff in Flüssen mit dem Anteil an durch Menschen veränderten Landschaften innerhalb eines Wassereinzugsgebiets zunimmt.
Lay summary
Inhalt und Ziel des Forschungsprojekts Die Ziele des Projekts sind (1) die Quantifizierung der Quellen und Verhältnisse von modernem gegenüber gealtertem organischen Kohlenstoff welcher von Böden in Flusssysteme transportiert wird und (2) zu bestimmen, ob diese Quellen und Verhältnisse von der jeweiligen Landnutzung im Wassereinzugsgebiet abhängen. Dafür sollen Radiokarbon (14C) und komponentenspezifische 14C Analysen an Vegetationsmarkern in Böden unter verschiedenen Landnutzungen sowie an Flusssedimenten durchgeführt werden und die Verhältnisse von modernem gegenüber altem organischem Kohlenstoff mittel Modellierung bestimmt werden.   Gesellschaftlicher Kontext des Forschungsprojekts Das zu untersuchende Wassereinzugsgebiet mündet in das grösste Wasserreservoir von Nepal, welches von zentraler Bedeutung für die Energiesicherheit des Landes ist. Grosse Sedimentfrachten durch anthropogene Aktivitäten gefährden die Nachhaltigkeit der Energieproduktion durch Versandung des Reservoirs. Die Ergebnisse des Projekts könnten Empfehlungen an Managementbehörden der lokalen Kommunen geben, um gezielt Bodenerosion bei Landnutzungen zu vermeiden, welche als Hauptquellen für Sedimente im Wassereinzugsgebiet identifiziert werden. Das Projekt könnte zudem Informationen bereitstellen um Praktiken des Bodenschutzes effektiver zu machen, z.B. durch die Festlegung von spezifischen Standorten welche besonders zu beobachten sind. Diese wertvollen Informationen können von diversen Akteuren genutzt werden um Ressourcen gezielt für angemessene Entscheidungen im Landschaftsmanagement zu gebrauchen.

Direct link to Lay Summary

Last update: 26.09.2017

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

There is currently a lack of necessary measurements and data to fully capture the high degree of heterogeneity in organic carbon (OC) exported from eroding landscapes. The respective fluxes of modern (biospheric) and aged OC are poorly constrained, and mechanisms controlling OC export have remained elusive. Recently, the age of riverine OC was found to increase with the proportion of human-dominated landscapes within a catchment, potentially due to aged soil OC that is mobilized by human disturbance and reintroduced into the modern C cycle. Furthermore, most previous studies have focused on catchment outlets, whereas a greater within-catchment focus will undoubtedly provide further direction to pinpoint locations of aged OC export to the river, and to better constrain its impact on the C cycle and aquatic biogeochemistry. The proposed project aims (1) to quantify the sources and proportions of modern (biospheric) versus aged OC exported from soils into river systems within a catchment and (2) to investigate if theses sources and proportions of OC are dependent on the different types of land-use within a catchment. Therefore, bulk 14C and compound-specific 14C analyses of vegetation markers (fatty acids) in particle-size fractions of soils under different land-use and suspended river sediments will be performed and the proportions of modern versus aged OC determined by application of isotope mixing models. 14C measurements have provided key constraints on aged OC concentrations and fluxes and recent advances in compound-specific 14C analysis will no doubt contribute to a more refined understanding of the transport and fate of modern and aged OC in the aquatic environment.The study site is located in the mid-hill region of Nepal within two catchments that exhibit different land-uses including various types of forest and agricultural land-use. Soils were sampled over three consecutive years (2013-2015) and sediments were sampled during each subsequent monsoon season. A broad data basis is already available for the content and stable C isotopes (d13C) of bulk OC and specific vegetation markers (long-chain fatty acids). Purified lipid fractions of all samples are ready to be further prepared for compound-specific 14C analysis, which includes the collection of desired compounds in sufficient amounts by preparative gas chromatography, followed by their conversion to CO2, which will then be analyzed for 14C using accelerator mass spectrometry. Isotope mixing models that use bulk and compound-specific 13C and 14C data as input will be applied to estimate the relative contributions of modern versus aged OC to the OC transported by rivers. The proposed project will generate an extensive 14C dataset of bulk OC and specific vegetation markers in soils under different land-use and suspended river sediments to provide a within-catchment focus on the mechanisms controlling OC export from terrestrial and aquatic ecosystems. Combination with the available complementary datasets for 13C of bulk OC and specific vegetation markers will reveal the sources and proportions of modern (biospheric) versus aged OC within the catchment. This information is needed to develop accurate constraints on fluvial transfer of biospheric OC, which is of importance to predict OC fluxes quantitatively as a result of anthropogenic change. The proposed project will furthermore test whether soils under different land-use export different proportions of modern versus aged OC into river systems and therefore also determine the responds to human disturbance such as changes in soil management. In summary, the proposed study will contribute to a comprehensive understanding of the factors that control the sources, transport pathways and turnover times of terrestrial OC within river systems. It will furthermore help to improve our ability to predict the present and future contribution of the aquatic OC fluxes to the global C budget and to parameterize the various C cycle processes and their sensitivity to environmental perturbations.