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
Multicompartment and multiscale long‐term observation and research are important prerequisites to tackling the scientific challenges resulting from climate and global change. Long‐term monitoring programs are cost intensive and require high analytical standards, however, and the gain of knowledge often requires longer observation times. Nevertheless, several environmental research networks have been established in recent years, focusing on the impact of climate and land use change on terrestrial ecosystems. From 2008 onward, a network of Terrestrial Environmental Observatories (TERENO) has been established in Germany as an interdisciplinary research program that aims to observe and explore the long‐term ecological, social, and economic impacts of global change at the regional level. State‐of‐the‐art methods from the field of environmental monitoring, geophysics, and remote sensing will be used to record and analyze states and fluxes for different environmental compartments from groundwater through the vadose zone, surface water, and biosphere, up to the lower atmosphere.
Abstract. For 3 years we followed the complete annual cycles of N20 emission rates with 2-hour resolution in spruce and beech plantations of the H6glwald Forest, Bavaria, Germany, in order to gain detailed information about seasonal and interannual variations of N20 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 N20 emission. Both pronounced seasonal and extreme interannual variations of N20 emissions were identified. During long-term frost periods, while the soil was frozen, and during soil thawing, extremely high N20 emissions occurred, contributing up to 73% to the total annual N20 loss. The enormous N20 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 N20 emissions as compared with an untreated spruce control site. The beech control site exhibited 4-5 times higher N20 emissions than the spruce control site, indicating that forest type itself is an important modulator of N20 release from soil. At all sites, nitrification contributed ---70% to the N20 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 N20 emissions. At the beech site, 10% of the actual N input was released from the soil in form of N20, whereas at the spruce site the fraction was 0.5%. N20 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 N20 losses from forest ecosystems. On the basis of our results we conclude that the importance of temperate and boreal forests for the global N20 source strength may have been significantly underestimated in the past and that these forests contribute most likely >> 1.0 Tg N20 N.
In order to overcome the problem of low measurement frequency, we developed a highly mobile automatic measuring system which allows the determination of N20 emissions from soils at high temporal resolution under the extreme conditions of tropical climate. This measuring system was used during different seasons to quantify N20 emissions from notogean (Australia) tropical rain forests at the Atherton Tablelands in northeastern Australia for the first time. Methods Site DescriptionField studies for the determination of N20 flux rates from tropical forest soils were conducted at three different sites on the Atherton Tablelands, Queensland, Australia (Figure 1 and Table 1
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