The FLOWatch project: Measuring water,carbon dioxide and energy fluxes at the field scale

Abstract

For water, energy and CO2 fluxes in agricultural landscapes, the field scale plays a crucial role since it corresponds to the scale at which humans directly influence fluxes by managing the system for crop cultivation. This leads to a human-induced spatio-temporal variability of these fluxes at the regional scale. Consequently, the field scale is considered as the elementary scale for modelling of water, CO2 and energy fluxes. Despite intensive research in the past, there is still a lack in knowledge concerning the spatial and temporal interdependency of soil state variables (e.g. moisture, soil temperature), matter fluxes from soil and vegetation (e.g. water, carbon dioxide) as well as their variability and respective effective values at the field scale. The FLOWatch project aims to improve our understanding of the spatial and temporal variability of water, energy and carbon dynamics in the soil and their role in determining effective evapotranspiration and carbon exchange fluxes at the field scale. To this end, micrometeorological, geophysical and (ground-based) remote sensing methods will be combined with mechanistic models describing the dynamics of water, energy and CO2 in soils. Modelling of C-dynamics involves the description of the turn-over of different organic matter pools. The turnover rates depend on soil temperature, soil water content, and soil CO2 concentration amongst others. Therefore, an accurate representation of these state variables is a key issue for the predictive modelling of carbon turnover and CO2 efflux. Within the FLOWatch project, several non-invasive and soil physical methods to measure soil water content at different scales will be implemented. At the point scale, far-field ground penetrating radar (GPR), electrical resistivity tomography (ERT), and time domain reflectrometry (TDR) will be used. For plot scale estimates of soil water content, a passive L-band radiometer will be installed. To obtain a spatial representation of the energy balance components, meteorological measurements will be combined with 2D soil surface temperature images from an IR-camera. Spatial and temporal variability of CO2 fluxes will be measured with automated soil CO2 flux systems (LICOR Biosciences). Temporal variability of the CO2 flux at the plot scale will be measured using the eddy covariance method when conditions allow it. For the modelling of the water balance, the energy balance and the CO2 efflux, a model containing the following processes will be used: (I) water and heat transport in variably saturated soils, (II) organic carbon turnover based on with multiple pools with variable turnover rates, (III) multiphase CO2 transport from the soil to the atmosphere. In this presentation, the experimental setup, the modelling concept and the first results of the FLOWatch project will be presented.