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Abstract. Fluxes of the three main greenhouse gases (GHG) CO 2 , CH 4 and N 2 O from peat and other soils with high organic carbon contents are strongly controlled by water table depth. Information about the spatial distribution of water level is thus a crucial input parameter when upscaling GHG emissions to large scales. Here, we investigate the potential of statistical modeling for the regionalization of water levels in organic soils when data covers only a small fraction of the peatlands of the final map. Our study area is Germany. Phreatic water level data from 53 peatlands in Germany were compiled in a new data set comprising 1094 dip wells and 7155 years of data. For each dip well, numerous possible predictor variables were determined using nationally available data sources, which included information about land cover, ditch network, protected areas, topography, peatland characteristics and climatic boundary conditions. We applied boosted regression trees to identify dependencies between predictor variables and dip-well-specific long-term annual mean water level (WL) as well as a transformed form (WL t ). The latter was obtained by assuming a hypothetical GHG transfer function and is linearly related to GHG emissions. Our results demonstrate that model calibration on WL t is superior. It increases the explained variance of the water level in the sensitive range for GHG emissions and avoids model bias in subsequent GHG upscaling. The final model explained 45 % of WL t variance and was built on nine predictor variables that are based on information about land cover, peatland characteristics, drainage network, topography and climatic boundary conditions. Their individual effects on WL t and the observed parameter interactions provide insight into natural and anthropogenic boundary conditions that control water levels in organic soils. Our study also demonstrates that a large fraction of the observed WL t variance cannot be explained by nationally available predictor variables and that predictors with stronger WL t indication, relying, for example, on detailed water management maps and remote sensing products, are needed to substantially improve model predictive performance.

Wetlands are characterized by frequent saturated conditions, dense vegetation growth and thus high evapotranspiration (ET) rates. Understanding wetland processes and water resource implications of wetland management and restoration requires estimates of ET rates. The analysis of diurnal groundwater fluctuations (DGFs) for estimating ET has been established for nearly 80 years, yet the method is not yet well utilized in practice due to inherent limitations. This paper assesses contemporary updates to the method to define a consistent tool and applies this to two contrasting riparian zones, in southeast England and northeast Germany. The method's accuracy is compared to reference ET evaluation methods and its utility for wetland hydrological management is assessed. Finally, practical guidance on how to apply the tool is provided, with a view to providing robust estimation of ET loss at wetland sites.

A supplementary comparison, COOMET.M.FF-S2, in the field of water flow was organized by the COOMET Technical Committee (TC) 1.4 Flow Measurement. The goal of the comparison was to confirm the calibration and measurement capabilities (CMC) of the participating national metrology institutes (NMIs) in the flow ranges between 0.5 m3/h and 5.0 m3/h, and, respectively, between 20.0 m3/h and 100.0 m3/h. This is the first comparison in the field of fluid flow which has been done by the COOMET TC Flow Measurement. This report describes the comparison results of the following water flow facilities (NMIs): PTB (Braunschweig, Germany), National standards Centre of the Republic of Uzbekistan (Tashkent, Republic of Uzbekistan), LEI (Kaunas, Lithuania), SMU (Bratislava, Slovakia), BelGIM (Minsk, Belarus), VNIIR (Kazan, Russia). The PTB was designated as the pilot lab of this comparison, due to the low measurement uncertainty of its water flow primary standard, in comparison to all participants, and because of its experience in leading and participating in previous international flow comparisons. In order to cover a large flowrate range, two transfer standard packages were delivered to all involved NMIs of the inter-laboratory comparison. For low flowrate range and nominal diameter of 25 mm a turbine meter and an electromagnetic flowmeter were used as transfer standards. For upper flow rates two turbine meters with a nominal diameter of 80 mm were used. All calibrations were made during March 2009 until May 2012. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).