Late Pleistocene Stratigraphy and Fluvial History of the Dinkel Basin (Twente, Eastern Netherlands)

Das glaziale Dinkelbecken ist erfüllt mit einer Sequenz von fluviatilen und äolischen Ablagerungen. Die Spätpleistozän-Stratigraphie und Paläomorphologie würde mit Hilfe von neuen Aufschlüssen, Bohrungen und geo-elektrischen Sondierungen erforscht. Besondere Beachtung galt der Verfeinerung in der Lithostratigraphie des Dinkeltals, des Typusgebietes der Twente-Formation, und einer Rekonstruktion des Ablagerungsmilieus in den verschiedenen Perioden der Weichseleiszeit. Die Talauffüllung besteht aus Sanden mit Lehm-, Ton- und Torfschichten. Drei wichtige Leithorizonte wurden innerhalb der Twente-Formation gefunden. Diese drei Horizonte sind von erosiven Bildungen begleitet. Einige charakteristische Einheiten sind unterschieden, jede Einheit entspricht spezifischen fluviatilen und äolischen Verhältnissen. Während der Eemzeit und der Früh-Weichseleiszeit gab es Flüsse mit hoher Sinuosität in einem sumpfigen alluvialen Tiefland, mit lokal lakustrischen Verhältnissen. Das Untere Pleniglazial ist charakterisiert durch einen tiefen fluviatilen Einschnitt. Darauf folgt fluviatile Zuschüttung während des Mittleren Pleniglazials, hauptsächlich durch mäandrierende Flüsse. Während des Oberen Pleniglazials lösten sich die Flüsse in sich überkreuzende Flußarme auf. Äolische Ablagerung nahm allmählich zu. Die Entwicklung der Beuningen-Steinsohle und die Ablagerung von Flugdecksanden zeigen zunächst die Dominanz von äolischen Prozessen im Tal. Erneute fluviatile Aktivität fing mit Einschneidung im Spätglazial an, gefolgt von der Ablagerung von Sedimenten mäandrierender Flüsse.researc

The full greenhouse gas balance of an abandoned peat meadow

International audienceGlobally, peat lands are considered to be a sink of CO2, but a source when drained. Additionally, wet peat lands are thought to emit considerable amounts of CH4 and N2O. Hitherto, reliable and integrated estimates of emissions and emission factors for this type of area have been lacking and the effects of wetland restoration on methane emissions have been poorly quantified. In this paper we estimate the full GHG balance of a restored natural peat land by determining the fluxes of CO2, CH4 and N2O through atmosphere and water, while accounting for the different GWP's. This site is an abandoned agricultural peat meadow, which has been converted into a wetland nature reserve ten years ago by raising the water level. GHG fluxes were measured continuously with an eddy-correlation system (CO2) and flux chamber measurements (CH4 and N2O). Meteorological and hydrological measurements were done as well. With growing seasons of respectively 192 and 155 days, the net annual CO2 uptake was 276±61 g C m?2 for 2004 and 311±58 g C m?2 for 2005. Ecosystem respiration was estimated as 887±668 g C m?2 for 2004 and 866±666 g C m?2 for 2005. CH4 fluxes from water, saturated land and relatively dry land varied: total annual CH4 fluxes are 10.4±19.2 g C m?2 yr?1, 101 g C m?2 yr?1±30 and 37.3±10.9 g C m?2 yr?1, respectively, and a annual weighed total CH4 emission of 31.27±20.44 g C m?2 yr?1. N2O fluxes were too low to be of significance. The carbon-balance consists for the largest part of CO2 uptake, CO2 respiration and CH4 emission from wet land and water. CO2 emission has decreased significantly as result of the raised water table, while CH4 fluxes have increased. In global warming potentials the area is a very small sink of 71 g CO2-equiv m?2 (over a 100-year period)

Sensitivity analysis of a wetland methane emission model based on temperate and arctic wetland sites

Modelling of wetland CH<sub>4</sub> fluxes using wetland soil emission models is used to determine the size of this natural source of CH<sub>4</sub> emission on local to global scale. Most process models of CH<sub>4</sub> formation and soil-atmosphere CH<sub>4</sub> transport processes operate on a plot scale. For large scale emission modelling (regional to global scale) upscaling of this type of model requires thorough analysis of the sensitivity of these models to parameter uncertainty. We applied the GLUE (Generalized Likelihood Uncertainty Analysis) methodology to a well-known CH<sub>4</sub> emission model, the Walter-Heimann model, as implemented in the PEATLAND-VU model. The model is tested using data from two temperate wetland sites and one arctic site. The tests include experiments with different objective functions, which quantify the fit of the model results to the data. <br><br> The results indicate that the model 1) in most cases is capable of estimating CH<sub>4</sub> fluxes better than an estimate based on the data avarage, but does not clearly outcompete a regression model based on local data; 2) is capable of reproducing larger scale (seasonal) temporal variability in the data, but not the small-scale (daily) temporal variability; 3) is not strongly sensitive to soil parameters, 4) is sensitive to parameters determining CH<sub>4</sub> transport and oxidation in vegetation, and the temperature sensitivity of the microbial population. The GLUE method also allowed testing of several smaller modifications of the original model. <br><br> We conclude that upscaling of this plot-based wetland CH<sub>4</sub> emission model is feasible, but considerable improvements of wetland CH<sub>4</sub> modelling will result from improvement of wetland vegetation data

A compact and stable eddy covariance set-up for methane measurements using off-axis integrated cavity output spectroscopy

A Fast Methane Analyzer (FMA) is assessed for its applicability in a closed path eddy covariance field set-up in a peat meadow. The FMA uses off-axis integrated cavity output spectroscopy combined with a highly specific narrow band laser for the detection of CH<sub>4</sub> and strongly reflective mirrors to obtain a laser path length of 2–20×10<sup>3</sup> m. Statistical testing and a calibration experiment showed high precision (7.8×10<sup>−3</sup> ppb) and accuracy (<0.30%) of the instrument, while no drift was observed. The instrument response time was determined to be 0.10 s. In the field set-up, the FMA is attached to a scroll pump and combined with a 3-axis ultrasonic anemometer and an open path infrared gas analyzer for measurements of carbon dioxide and water vapour. The power-spectra and co-spectra of the instruments were satisfactory for 10 Hz sampling rates. <br><br> Due to erroneous measurements, spikes and periods of low turbulence the data series consisted for 26% of gaps. Observed CH<sub>4</sub> fluxes consisted mainly of emission, showed a diurnal cycle, but were rather variable over. The average CH<sub>4</sub> emission was 29.7 nmol m<sup>−2</sup> s<sup>−1</sup>, while the typical maximum CH<sub>4</sub> emission was approximately 80.0 nmol m<sup>−2</sup> s<sup>−1</sup> and the typical minimum flux was approximately 0.0 nmol m<sup>−2</sup> s<sup>−1</sup>. The correspondence of the measurements with flux chamber measurements in the footprint was good and the observed CH<sub>4</sub> emission rates were comparable with eddy covariance CH<sub>4</sub> measurements in other peat areas. <br><br> Additionally, three measurement techniques with lower sampling frequencies were simulated, which might give the possibility to measure CH<sub>4</sub> fluxes without an external pump and save energy. Disjunct eddy covariance appeared to be the most reliable substitute for 10 Hz eddy covariance, while relaxed eddy accumulation gave reliable estimates of the fluxes over periods in the order of days or weeks

Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra

With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arcti