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Significant climate risks are associated with a positive carbon-temperature feedback in northern latitude carbon-rich ecosystems, making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on simultaneous and quasi-continuous ecosystem observations of CO 2 and CH 4 fluxes. Experimental areas are located both in natural and in managed wetlands and cover a wide range of climatic regions, ecosystem types, and management practices. Based on direct observations we predict that sustained CH 4 emissions in natural ecosystems are in the long term (i.e., several centuries) typically offset by CO 2 uptake, although with large spatiotemporal variability. Using a space-for-time analogy across ecological and climatic gradients, we represent the chronosequence from natural to managed conditions to quantify the "cost" of CH 4 emissions for the benefit of net carbon sequestration. With a sustained pulseresponse radiative forcing model, we found a significant increase in atmospheric forcing due to land management, in particular for wetland converted to cropland. Our results quantify the role of human activities on the climate footprint of northern wetlands and call for development of active mitigation strategies for managed wetlands and new guidelines of the Intergovernmental Panel on Climate Change (IPCC) accounting for both sustained CH 4 emissions and cumulative CO 2 exchange.wetland conversion | methane | radiative forcing | carbon dioxide F or their ability to simultaneously sequester CO 2 and emit CH 4 , wetlands are unique ecosystems that may potentially generate large negative climate feedbacks over centuries to millennia (1) and positive feedbacks over years to several centuries (2). Wetlands are among the major biogenic sources of CH 4 , contributing to about 30% of the global CH 4 total emissions (3), and are presumed to be a primary driver of interannual variations in the atmospheric CH 4 growth rate (4, 5). Meanwhile, peatlands, the main subclass of wetland ecosystems, cover 3% of the Earth's surface and are known to store large quantities of carbon

Abstract. Since 1992 semi-continuous in-situ observations of greenhouse gas concentrations have been performed at the tall tower of Cabauw (4.927 • E, 51.971 • N, −0.7 m a.s.l.). Through 1992 up to now, the measurement system has been gradually extended and improved in precision, starting with CO 2 and CH 4 concentrations from 200 m a.g.l. in 1992 to vertical gradients at 4 levels of the gases CO 2 , CH 4 , SF 6 , N 2 O, H 2 , CO and gradients at 2 levels for 222 Rn. In this paper the measurement systems and measurement results are described for the main greenhouse gases and CO, for the whole period. The automatic measurement system now provides half-hourly concentration gradients with a precision better than or close to the WMO recommendations.The observations at Cabauw show a complex pattern caused by the influence of sources and sinks from a large area around the tower with significant contributions of sources and sinks at distances up to 500-700 km. The concentration footprint area of Cabauw is one the most intensive and complex source areas of greenhouse gases in the world. Despite this, annual mean trends for the most important greenhouse gases, compatible with the values derived using the global network, can be reproduced from the measured concentrations at Cabauw over the entire measurement period, with a measured increase in the period 2000-2009 for CO 2 of 1.90 ± 0.1 ppm yr −1 , for CH 4 of 4.4 ± 0.6 ppb yr −1 , for N 2 O of 0.86 ± 0.04 ppb yr −1 , and for SF 6 of 0.27 ± 0.01 ppt yr −1 ; for CO no significant trend could be detected.The influences of strong local sources and sinks are reflected in the amplitude of the mean seasonal cycles observed at Cabauw, that are larger than the mean Northern Hemisphere average; Cabauw mean seasonal amplitude for CO 2 is 25-30 ppm (higher value for lower sampling levels). The observed CH 4 seasonal amplitude is 50-110 ppb. All gasesCorrespondence to: A. T. Vermeulen (a.vermeulen@ecn.nl) except N 2 O show highest concentrations in winter and lower concentrations in summer, N 2 O observations show two additional concentration maxima in early summer and in autumn.Seasonal cycles of the day-time mean concentrations show that surface concentrations or high elevation concentrations alone do not give a representative value for the boundary layer concentrations, especially in winter time, but that the vertical profile data along the mast can be used to construct a useful boundary layer mean value. The variability at Cabauw in the atmospheric concentrations of CO 2 on time scales of minutes to hours is several ppm and is much larger than the precision of the measurements (0.1 ppm). The diurnal and synoptical variability of the concentrations at Cabauw carry information on the sources and sinks in the footprint area of the mast, that will be useful in combination with inverse atmospheric transport model to verify emission estimates and improve ecosystem models. For this purpose a network of tall tower stations like Cabauw forms a very useful addition to the existing glob...

Abstract.A quantum cascade laser spectrometer was evaluated for eddy covariance flux measurements of CH 4 and N 2 O using three months of continuous measurements at a field site. The required criteria for eddy covariance flux measurements including continuity, sampling frequency, precision and stationarity were examined. The system operated continuously at a dairy farm on peat grassland in the Netherlands from 17 August to 6 November 2006. An automatic liquid nitrogen filling system for the infrared detector was employed to provide unattended operation of the system. The electronic sampling frequency was 10 Hz, however, the flow response time was 0.08 s, which corresponds to a bandwidth of 2 Hz. A precision of 2.9 and 0.5 ppb Hz −1/2 was obtained for CH 4 and N 2 O, respectively. Accuracy was assured by frequent calibrations using low and high standard additions. Drifts in the system were compensated by using a 120 s running mean filter. The average CH 4 and N 2 O exchange was 512 ngC m −2 s −1 (2.46 mg m −2 hr −1 ) and 52 ngN m −2 s −1 (0.29 mg m −2 hr −1 ). Given that 40% of the total N 2 O emission was due to a fertilizing event.

A B S T R A C TFluxes of methane (CH 4 ) and carbon dioxide (CO 2 ) estimated by empirical models based on small-scale chamber measurements were compared to large-scale eddy covariance (EC) measurements for CH 4 and to a combination of EC measurements and EC-based models for CO 2 . The experimental area was a flat peat meadow in the Netherlands with heterogeneous source strengths for both greenhouse gases. Two scenarios were used to assess the importance of stratifying the landscape into landscape elements before up-scaling the fluxes measured by chambers to landscape scale: one took the main landscape elements into account (field, ditch edge ditch), the other took only the field into account. Non-linear regression models were used to up-scale the chamber measurements to field emission estimates. EC CO 2 respiration consisted of measured night time EC fluxes and modeled day time fluxes using the Arrhenius model. EC CH 4 flux estimate was based on daily averages and the remaining data gaps were filled by linear interpolation. The EC and chamber-based estimates agreed well when the three landscape elements were taken into account with 16.5% and 13.0% difference for CO 2 respiration and CH 4 , respectively. However, both methods differed 31.0% and 55.1% for CO 2 respiration and CH 4 when only field emissions were taken into account when up-scaling chamber measurements to landscape scale. This emphasizes the importance of stratifying the landscape into landscape elements. The conclusion is that small-scale chamber measurements can be used to estimate fluxes of CO 2 and CH 4 at landscape scale if fluxes are scaled by different landscape elements. ß

Agricultural emissions in Europe are important to several atmospheric transport-related environmental issues. These include local and regional air quality problems, such as PM exposure, eutrophication and acidification, toxics and contribution to greenhouse gas emissions, resulting in a number of environmental impacts. Over Europe, agricultural emissions are variable in space and time and the contribution to the different issues are variable. Most important are ammonia (90%), PM (20%) and methane and nitrous oxide (both 5%). Policies have been developed to combat some of the emissions with success in some countries. However, future, national and European policies are necessary to successfully decrease emissions and its related problems. Current research issues include the quantification of non-point sources, the atmosphere-biosphere exchange of ammonia, the quantification of landscape processes and the primary and secondary emissions of PM. r