Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    N2O emission from tropical forest soils of Australia
    ( 2000)
    Breuer, L.
    ;
    Papen, H.
    ;
    Butterbach-Bahl, K.
    Three different tropical rain forest sites (Kauri Creek, Lake Eacham, and Massey Creek) on the Atherton Tablelands, Queensland, Australia, were investigated for the magnitude of N2O emission from soils during different seasons, that is, wet season, dry season, and transition periods. Highest mean N2O emission rates were observed for soils derived from granite at the Kauri Creek site with 74.5 + 25.2 µg N2O-N m high -2 h high -1, whereas for soils derived from Metamorphics (Lake Eacham site) mean N2O emission rates were much lower (13.1 + 1.1 µg N2O-N m high -2 h high -1). For the Massey Creek site, with soils derived from Rhyolite, a mean annual N2O emission rate of 46.2 + 1.1 µg N2O-N m high -2 h high -1 was calculated. The mean annual N2O emission rate calculated for all three sites over the entire observation period was 39.0 µg N2O-N m high -2 h high -1 and thus at the high end of reports from tropical rain forest soils. N2O emission rates showed at all sites pronounced temporal as well as spatial variability. The magnitude of N2O emissions was strongly linked to rainfall events; that is, N2O emissions strongly increased approximately 6-8 hours after precipitation. Correlation analysis confirmed the strong dependency of N2O emissions on changes in soil moisture, whereas changes in soil temperature did not mediate considerable changes in N2O fluxes. Spatial variability of N2O fluxes on a site scale could be explained best by differences in water-filled pore space, CO2 emission, and C/N ratio of the soil. On the basis of all published N2O flux rates from tropical rain forest soils we recalculated the contribution of such forests to the global atmospheric N2O budget and come up with a figure of 3.55 Tg N2O-N yr high -1, which is approximately 50 % higher than reported by others.
  • Publication
    A process-oriented model of N2O and NO emissions from forest soils: 1. Model development
    ( 2000)
    Li, C.
    ;
    Aber, J.
    ;
    Stange, F.
    ;
    Butterbach-Bahl, K.
    ;
    Papen, H.
    To predict emissions of nitrous oxide (N2O) and nitric oxide (NO) from forest soils, we have developed a process-oriented model by integrating several new features with three existing models, PnET, Denitrification-Decomposition (DNDC), and a nitrification model. In the new model, two components were established to predict (1) the effects of ecological drivers (e. g., climate, soil, vegetation, and anthropogenic activity) on soil environmental factors (e. g., temperature, moisture, pH, redox potential, and substrates concentrations), and (2) effects of the soil environmental factors on the biochemical or geochemical reactions which govern NO and N2O production and consumption. The first component consists of three submodels for predicting soil climate, forest growth, and turnover of soil organic matter. The second component contains two submodels for nitrification and denitrification. A kinetic scheme, a so-called "anaerobic balloon," was developed to calculate the anaerobic status of the soil and divide the soil into aerobic and anaerobic fractions. Nitrification is only allowed to occur in the aerobic fraction, while denitrification occurs only in the anaerobic fraction. The size of the anaerobic balloon is defined by the simulated oxygen partial pressure which is calculated based on oxygen diffusion and consumption rates in the soil. As the balloon swells or shrinks, the model dynamically allocates substrates (e. g., dissolved organic carbon, ammonium, nitrate, etc.) into the aerobic and anaerobic fractions. With this approach, the model is able to predict both nitrification and denitrification in the same soil at the same time. This feature is important for soils where aerobic and anaerobic microsites often exist simultaneously. With the kinetic framework as well as its interacting functions, the PnET-N-DNDC model links ecological drivers to trace gas emissions. Tests for validating the new model are published in a companion paper.
  • Publication
    A process-oriented model of N2O and NO emissions from forest soils. 1. Model development
    ( 2000)
    Li, C.S.
    ;
    Aber, J.
    ;
    Stange, F.
    ;
    Butterbach-Bahl, K.
    ;
    Papen, H.
  • Publication
    A process-oriented model of N2O and NO emissions from forest soils. 2. Sensitivity analysis and validation
    ( 2000)
    Stange, F.
    ;
    Butterbach-Bahl, K.
    ;
    Papen, H.
    ;
    Zechmeister-Boltenstern, S.
    ;
    Li, C.
    ;
    Aber, J.
    The process-oriented model PnET-N-DNDC describing biogeochemical cycling of C-and N and N-trace gas fluxes (N sub 2 O and NO) in forest ecosystems was tested for its sensitivity to changes in environmental factors (e. g., temperature, precipitation, solar radiation, atmospheric N-deposition, soil characterstics). Sensitivity analyses revealed that predicted N-cycling and N-trace gas emissions varied within measured ranges. For model validation, data sets of N-trace gas emissions from seven different temperate forest ecosystems in the United States, Denmark, Austria, and Germany were used. Simulations of N sub 2 O emissions revealed that field observations and model predictions agreed well for both flux magnitude and its seasonal pattern. Differences between predicted and measured mean N sub 2 O fluxes were smaller than 27 %. An exception to this was the N-limited pine stand at Harvard Forest, where predictions of fluxes deviated by 380 % form field measurements. This difference is most likely due to a missing mechanism in PnET-N-DNDC describing uptake of atmospheric N sub 2 O by soils. PnET-N-DNDC was also validated for its capability to predict NO emission from soils. Predicted and measured mean NO fluxes at three different field sites agreed within a range of plus/minus 13 %. The correlation between modeled and predicted NO emissions from the spruce and beech stand at the Höglwald Forest was r high 2 is equal 0.24 (spruce) and r high 2 is equal 0.35 (beech), respectively. The results obtained from both sensitivity analyses and validations with field data from temperate forest soils indicate that PnET-N-DNDC can be successfully used to predict N sub 2 O and NO emissions from a broad range of temperate forest sites.
  • Publication
    A 3-year continuous record of nitrogen trace gas fluxes from untreated and limed soil of a N-saturated spruce and beech forest ecosystem in Germany. Part 2: NO and NO2 fluxes
    ( 1999)
    Gasche, R.
    ;
    Papen, H.
    For 3 years we followed the complete annual cycles of NO and NO2 flux rates from soil of a spruce control site, a limed spruce site, and a beech site at the Höglwald Forest, Bavaria, Germany, with high temporal resolution in order to gain detailed information about (1) the impacts of forest type, liming, and atmospheric N input by wet deposition on the magnitude of NO and NO2 flux rates and (2) the microbial processes involved in NO production and emission. In addition to identification of seasonal variations of flux rates the huge database allowed calculation of annual mean NO and N02 fluxes with high accuracy and identification of interannual variations of fluxes. The long-term annual mean NO., emission was 61.7 mu m NOx N m(exp - 2) h(exp - 1 ) for the spruce control site, 17.3 mu m NOx N m(exp -2) h(exp -1) for the limed spruce site, and 4.0 mu m NOx N m(exp -2) h(exp -1) for the beech site. These extremely high soil NOx emissions from a temperate forest most likely reflect the status of N saturation of the Höglwald Forest as a consequence of year-long heavy atmospheric N input. Multiple regression analyses revealed the following sequence of importance of environmental factors on NO flux: soil temperature to water-filled pore space to soil NO3(exp -) concentrations to soil NH4(exp +) concentrations. Nitrification was the dominating biotic modulator of NO emission at all sites: >60% of the variation of NO emission rates were associated with variations of net nitrification rates. There was a strong positive correlation between amount of in situ N input by wet deposition and magnitude of in situ NO flux rates. Approximately 15% and 7% of the actual N input was lost as NO from the soil stocked with spruce and beech, respectively. Liming resulted in 49% reduction of NO emissions as compared to an unlimed spruce control site. The results indicate that the reduction in NO emission was due to an increase in NO consumption within the limed soil. In contrast to NO flux, NO2 flux was modulated by physico-chemical rather than biological factors. Using the data of this study, we estimate that the contribution of N-affected temperate coniferous and deciduous forests to the global NOx release is 0.3 Tg NOx N yr(exp -1).
  • Publication
    A 3-year continuous record of nitrogen trace gas fluxes from untreated and limed soil of a N-saturated spruce and beech forest ecosystem in Germany. Part 1: N2O emissions
    ( 1999)
    Papen, H.
    ;
    Butterbach-Bahl, K.
    For 3 years we followed the complete annual cycles of N2O emission rates with 2-hour resolution in spruce and beech plantations of the Höglwald Forest, Bavaria, Germany, in order to gain detailed information about seasonal and interannual variations of N2O emissions. In addition, microbiological process studies were performed for identification of differences in N turnover rates in the soil of a spruce and a beech site and for estimation of the contribution of nitrification and denitrification to the actual N2O emission. Both pronounced seasonal and extreme interannual variations of N2O emissions were identified. During long-term frost periods, while the soil was frozen, and during soil thawing, extremely high N2O emissions occurred, contributing up to 73% to the total annual N2O loss. The enormous N2O releases during the long-term frost period were due to high microbial N turnover rates (tight coupling of ammonification, nitrification, denitrification) in small unfrozen water films of the frozen soil at high concentrations of easily degradable substrates derived from the enormous pool of dead microbial biomass produced during the long-term frost period. Liming of a spruce site resulted in a significant increase in ammonification, nitrification, and N2O emissions as compared with an untreated spruce control site. The beech control site exhibited 4-5 times higher N2O emissions than the spruce control site, indicating that forest type itself is an important modulator of N2O release from soil. At all sites, nitrification contributed -70% to the N2O flux, whereas denitrification contributed markedly less (~30%). There was a significant positive correlation between amount of in situ N input by wet deposition and magnitude of in situ N2O emissions. At the beech site, 10% of the actual N input was released from the soil in form of N2O, whereas at the spruce site the fraction was 0.5%. N2O emission rates were positively correlated with net nitrification rates. The results demonstrate the need for long-term measurements over several years for more precise estimates of annual N2O losses from forest ecosystems. On the basis of our results we conclude that the importance of temperate and boreal forests for the global N2O source strength may have been significantly underestimated in the past and that these forests contribute most likely >>1.0 Tg N2O N.
  • Publication
    Temporal patterns of methane emissions from wetland rice fields treated by different modes of N application
    ( 1994)
    Wassmann, R.
    ;
    Neue, H.U.
    ;
    Lantin, R.S.
    ;
    Aduna, J.B.
    ;
    Alberto, M.C.R.
    ;
    Andales, M.J.
    ;
    Tan, M.J.
    ;
    Denier Van der Gon, H.A.C.
    ;
    Hoffmann, H.
    ;
    Papen, H.
    ;
    Rennenberg, H.
    ;
    Seiler, W.
    Methane emission rates from wetland rice fields were determined in Los Banos (Philippines) using an automatic system that allows continuous measurements over time. Methane emission was monitored in an irrigated Aquandic Epiaqualf planted to rice cultivar IR72. Urea fertilizer was applied using four modes: (1) broadcast 10 days after transplanting, (2) broadcast at transplanting, (3) broadcast and incorporated at final harrowing, and (4) deep placement as sulfur-coated granules. The treatments were laid out in a randomized complete block design with four replicates. Measurements were done in the 1991 wet season, 1992 dry season (four treatments), and the 1992 wet season (only treatment 3). Methane emission rates from the experimental plots showed pronounced seasonal and diel variations. The diel pattern of methane emission rates followed a consistent pattern, with highest rates observed in the early afternoon and lowest rates in the early morning. Methane emission rate was generally hig hest at the ripening stage. The average methane emission rate during the 1992 dry season (190 mg CH4 m(-2) d(-1)) exceeded the average flux rates of the 1992 wet season (79 mg CH4 m(-2) d(- 1)) by a factor of 2.4. The total methane emitted from these flooded rice fields amounted to 19 g CH4 m(-2) in the dry season with rice yields of 5.2-6.3 t ha(-1) and 7 g CH4 m(-2) in the wet season with rice yields of 2.4-3.3 t ha(-1) regardless of the mode of N application. Significant amounts corresponding to 20 per cent of the methane released under waterlogged conditions were released when the soil was drained after harvest. Emission rates increased sharply when the floodwater receded and macropores started to drain. Emission of methane stopped only when the soil became fully aerated.
  • Publication
    First records of a field experiment on fertilizer effects on methane emission from rice fields in Hunan-Province (PR China)
    ( 1993)
    Wassmann, R.
    ;
    Wang, M.X.
    ;
    Shangguan, X.J.
    ;
    Xie, X.L.
    ;
    Shen, R.X.
    ;
    Wang, Y.S.
    ;
    Papen, H.
    ;
    Rennenberg, H.