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Details for article 3 of 146 found articles
| Title: |
Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements |
| Author: |
C. Milford M. R. Theobald E. Nemitz K. J. Hargreaves L. Horvath J. Raso U. Dämmgen A. Neftel S. K. Jones A. Hensen B. Loubet P. Cellier M. A. Sutton |
| Appeared in: |
Biogeosciences discussions |
| Paging: | Volume 5 (2008) nr. 6 pages 4699-4744 |
| Year: |
2008 |
| Contents: |
Quantification of ammonia (NH3) land-atmosphere exchange is required for atmospheric modelling and assessment of nitrogen deposition, yet flux measurement methods remain highly uncertain. To address this issue, a major inter-comparison of ammonia fluxes over intensively managed grassland was conducted during the GRAMINAE Integrated Experiment held in Braunschweig, Germany. In order to provide a robust dataset of ammonia exchange with the vegetation, four independent continuous flux gradient systems were operated. Three independently operated continuous wet denuders systems (AMANDA) were compared with a Wet Effluent Diffusion Denuder (mini-WEDD) system. Measurements were made at two distances from an adjacent livestock farm, allowing effects of advection to be quantified in a real landscape setting. Data treatment included filtering for instrument failure, disturbed wind sectors and unsuitable micrometeorological conditions, with corrections made for storage and advection errors. <br><br> The inter-comparison demonstrated good agreement in measured ammonia concentrations and fluxes (<20% difference) for some periods, although the performance of the ammonia analyzers was variable, with much poorer agreement on particular days. However, by using four systems, the inter-comparison was able to provide a robust mean estimate of continuous ammonia fluxes through the experiment. The observed fluxes were: a) small bi-directional fluxes prior to cutting (−64 to 42 ng NH3 m<sup>−2 s<sup>−1), b) larger diurnally-varying emissions following cutting (−49 to 703 ng NH3 m<sup>−2 s<sup>−1) and c) much larger emissions following fertilizer application (0 to 3820 ng NH3 m<sup>−2 s<sup>−1). The results are a salutary reminder of the uncertainty in unreplicated ammonia flux measurements, while the replication of the present study provides a uniquely robust dataset for the evaluation of ammonia exchange processes. It is clear that consistently reliable determination of ammonia concentrations remains the major measurement challenge. |
| Publisher: |
Copernicus GmbH (provided by DOAJ) |
| Source file: |
Elektronische Wetenschappelijke Tijdschriften |
Details for article 3 of 146 found articles
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