WP1: Process Understanding: Technical developments, observations & experiments


WP1-1 Optimization and adaptation of sensors for CO2, CH4 and O2 across the full river-ocean mixing regime

Specific objectives:  In the highly dynamic aquatic systems of the LOAC, continuous CO2, CH4, and O2 measurements are crucial for quantifying carbon and greenhouse gas fluxes and for understanding their physical and biological drivers. However, the determination of accurate pCO2 and pCH4 across the full spectrum of aquatic environments, from limnic to marine, constitutes an important technological challenge. The goal is to link a CO2 (and CH4) continuous measurement to an integrated sensor system for the standard physical parameters temperature, conductivity and O2, and to test its applicability in various environments of the river-to-coastal ocean continuum. The developments will benefit from the sensor technology already operational in open ocean waters. Best candidate sites for the deployment of the sensors are the Amazon plume (GEOMAR) and the Rhine river (ETHZ).

Expected Results: Optimized stationary and mobile measurement system for rivers, lakes, and coastal and ocean waters focusing on the key CO2 parameter

Host institution: CONTROS Secondment(s):  GEOMAR and ETHZ

Primary Supervisor: Peer Fietzek (Contros); Secondary Supervisors: Prof. Arne Körtzinger  (GEOMAR), Prof. Bernhard Wehrli (ETHZ)


WP1-2  Temporal variations of greenhouse gas fluxes (CO2, CH4, N2O) from headwaters to downstream water systems

Specific objectives: GHG outgassing from streams is highly dynamic in space and time, and can be driven not only by diurnal and seasonal factors (e.g., metabolism, temperature, discharge), but also by discrete storm events. Such dynamics have major implications for regional estimates of C fluxes. We propose to couple online measurements of streamwater CO2, CH4 and N2O in an alpine fluvial network with hydrology, dissolved organic carbon (DOC) and nitrogen biogeochemistry. Hydrology will include the hydrological regime and its relation to the gas exchange velocity, as well as fluvial network topology and surface/subsurface exchange. DOC will be measured online using optical techniques and paired with more advance mass spectrometry (Orbitrap) analyses; we will also determine the bioavailability of DOC and the biogeochemistry of nitrogen will also be determined using bioassays. The results will be used to extrapolate GHG outgassing fluxes to the level of an entire fluvial network and above all to predict their diurnal and seasonal dynamics. Findings will also help fill the important knowledge gap on C cycling in alpine streams, which are purportedly very susceptible to climate change.

Expected Results: Quantification of temporal variations of greenhouse gas fluxes from headwaters to downstream water systems

Host institution: EPFL Lausanne Secondment(s): UU and CONTROS 

Primary Supervisor: Prof. T. Battin (EPFL); Secondary Supervisors: Prof. G. Weyhenmeyer (UU), Dr. C. Frank (Contros)


WP1-3  Particulate organic carbon dynamics along the LOAC

Specific objectives: Accelerated erosion as a result of agricultural intensification and expansion is estimated to have increased the lateral flux of inorganic sediments and organic C by more than one order of magnitude in temperate environments. A large proportion of this eroded material is deposited in rapidly accreting colluvial stores and up to 50% of the soil that is exported is sequestered for a period in floodplain stores. In both colluvial and alluvial sedimentary environments, soil residence time is determined by geomorphic processes but C residence time is further controlled by mineralization/stabilization processes that are not well characterized by models developed for surface soils. Furthermore, during transport POC may be mineralised to release DOC and additional POC can be produced from DOC by flocculation in surface waters. Thus the fate of POC along the LOAC is not well understood. The aim of this task is to advance our understanding of POC dynamics along the LOAC in order to improve the representation in land surface models such as JULES. This will be achieved by database analyses, field campaigns with measurements of the lateral POC transfer including POC production and transformation processes and model development.

Expected Results: Quantification of POC erosion, sedimentation and transformation rates along the LOAC

Host institution: UNEXE Secondment(s): UU 

Primary Supervisor: Prof. Timothy Quine (UNEXE); Secondary Supervisor: Prof. Lars Tranvik (UU)


WP1-4  Influence of organic carbon quality changes on greenhouse gas emissions from inland waters

Specific objectives: Dissolved organic matter (DOM) is a key driver of GHG emission in inland waters. Since DOM changes in quantity and chemical characteristics the main goal is to assess whether CO2, CH4 and N2O emission from inland waters depend on the characteristics of DOM. The chemical composition and diversity of DOM in relation to GHG production and emission will be determined in mesocosm experiments and coupled with observations in natural waters. To determine the chemical composition and diversity of DOM, advanced mass spectrometric methods will be applied in combination with established methods such as fluorescence spectroscopy and HPLC analyses. To quantify gas emissions rates the ESR will deploy automated CO2 and N2O sensors, carry out traditional gas chamber measurements and use data from an available CO2 and CH4. Eddy Tower at a lake site. In the mesocosms DOM quality will be manipulated to assess effects on gas production and emission. This approach will allow us to evaluate the extent to which the observed ongoing DOM quality changes in natural waters might affect GHG emission rates.

Expected Results: Quantification of greenhouse gas fluxes from inland waters in relation to organic carbon quality changes

Host institution: UU Secondment(s): EPFL 

Primary Supervisor: Prof. Gesa Weyhenmeyer (UU); Secondary Supervisor: Prof. Tom Battin (EPFL)


WP1-5  Inorganic and organic carbon pathways in the Seine River system

Specific objectives: The Seine River is a eutrophic system where lateral C fluxes are strongly influenced by primary production. The main goal is to understand and quantify (i) how an excess of anthropogenic nutrients entering the Seine River system may locally enhance primary production and C sequestration and (ii) how the modification of organic C loads can influence C metabolism, i.e. induce autotrophic vs. heterotrophic conditions in rivers, estuaries, and possibly coastal waters. As in Task 1.3, transformations between the dissolved and the particulate phase of OC will be studied. Focus is on the improvement of the River Seine model, partly by analysing data from national databases on ground- and surface waters, and partly by C degradation and bioavailability laboratory experiments. After final validation of the RiverStrahler (RS) model new conditions of land-use, water flows, alternative agriculture, etc. will be explored.

Expected Results: Quantification of inorganic and organic carbon pathways in the Seine River system and improvement of the RS model

Host institution: CNRS-IPSL  Secondment(s): VE-CGE

Primary Supervisors: Dr. Josette Garnier and Dr. Vincent Thieu (CNRS-IPSL); Secondary Supervisor: Emmanuel Soyeux (VE-CGE)