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Projekt Druckansicht

Treibhausgasemissionen aus Flüssen und Bächen entlang eines steilen Gradienten von biogeochemischen Einflüssen und Landnutzung

Fachliche Zuordnung Hydrogeologie, Hydrologie, Limnologie, Siedlungswasserwirtschaft, Wasserchemie, Integrierte Wasserressourcen-Bewirtschaftung
Förderung Förderung von 2013 bis 2018
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 242560981
 
Erstellungsjahr 2017

Zusammenfassung der Projektergebnisse

Inland waters play a vital role in regional to global carbon cycling. Among the latest and least understood aspects in this context is the amount of carbon emitted from inland waters into the atmosphere as carbon dioxide (CO2) and as methane (CH4). While recent research effort focused mainly on lakes and reservoirs as sources of both greenhouse gases (GHG), major research gaps exist in respect to emissions from small streams and headwater systems, as well as in respect to the contribution of CH4 to the total GHG potential of emitted gases. In this project, we investigated carbon dynamics in, and GHG emissions from, small streams at a broad range of spatial scales. At the catchment scale, we analyzed the relationship between terrestrial net primary production (NPP) and the rate at which carbon is exported from the catchments in a temperate stream network. We found that on average 2.7 % of terrestrial NPP were exported from the catchments by streams and rivers, in which both CO2 evasion and downstream transport contributed about equally to this flux. In combination with published data from a wide range of climatic zones, we found that the carbon export per catchment area varies in a surprisingly narrow range, despite a broad range of different spatial scales and hydrological characteristics of different regions. In addition to carbon imported from the catchments, we also studied anthropogenic sources of organic and inorganic carbon in streams and rivers. We demonstrated that effluent water from municipal wastewater treatment plants (WWTPs), which is discharged into the surrounding aquatic ecosystems, can be a significant source of carbon and GHG. Downstream of WWTPs, we found that the atmospheric fluxes of CO2 and CH4 increased by a factor of 1.2 and 8.6, respectively. The CH4 concentration in the effluent water was linearly related to the organic load of the treated wastewater, which provides an empirical basis for future attempts to add WWTPs inputs to regional-scale models for inland water−carbon fluxes. To elucidate the drivers of in-stream CH4 production at the catchment scale, we investigated potential methane production (PMP) and oxidation (PMO) in stream sediments. The most important predictors of PMP and PMO at catchment scale were related to sediment characteristic and included fine sediment fraction and sediment organic carbon content. Hence, at catchment scale, fine sediment deposition is a key controlling factor for the magnitude of CH4 production in small streams. Since these systems represent the largest water surface area of the global stream network, enhanced deposition of fine sediments through global change, e.g., land use change, soil erosion, extreme rainfall events, and reduced dry weather flow, may have a significant amplifying effect on CH4 production in, and consequently, emissions from running waters. The former finding was particularly surprising, as we found that CH4 fluxes from streams in the temperate zone can be as high as those from tropical aquatic systems, though being strongly variable in space and time. In contrast to lakes, methanotrophy seems to a less important source of carbon in stream food webs. At the smallest scales, we linked the diffusive gas exchange at stream surfaces to small-scale turbulence. We found that gas exchange velocities are related to energy dissipation rates and surface flow types and we introduced new methods for assessing these quantities in small streams. Further methodological advances could be achieved by improving existing approaches for measuring gas fluxes in small streams and by optimizing analytical procedures for measuring CH4 and CO2 concentrations and potential production rates in aquatic sediments.

Projektbezogene Publikationen (Auswahl)

 
 

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