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Die Stickstoffimmission und -deposition in Wäldern
Abstract
The paper summarises results of nitrogen emission and deposition measurements in a spruce forest ecosystem in Solling in Central Germany.
... Open field N-deposition was highest at Solling and lowest at Zierenberg, whereas N-values in stand precipitation and total deposition were somewhat lower at Göttinger Wald than at Solling and Zierenberg. For a spruce stand at Solling, Ibrom et al. (1995) calculated by use of micro-meteorological methods a total deposition of N of 460 mmol m 2 per year, whereas total deposition at the same stand calculated with the model of Ulrich (1994) was only 285 mmol m À2 per year. Marques et al. (2001) showed that dry deposition (particulate and gaseous) contributed 75% to total deposition at the Solling spruce stand. ...
... Alternative canopy budget models are more specific with respect to nitrogen, but require independent input parameters, which are sometimes difficult to estimate (Horn et al. 1989; Draaijers and Erisman 1995 ). Independent measurements with micro-meteorological methods at a spruce stand adjacent to the Solling beech stand suggested an undestimation of N-deposition of almost 50% by the Ulrich model (Ibrom et al. 1995; Marques et al. 2001). Gauger et al. (2002) compared deposition estimates from inferential modelling with estimates from throughfall measurements and canopy budget modelling and found an underestimation of about 50% by canopy budget modelling for Level II monitoring plots in Germany stocked with spruce. ...
Element inputs by atmospheric deposition form a major contribution to a number of element fluxes of forest ecosystems. During the last few decades, inputs from the atmosphere have significantly altered the geochemical cycles of forest ecosystems especially in heavily polluted areas of Central Europe where forests have remained major sinks for air pollution. The deposition of acids such as sulphuric and nitric acids was a major environmental concern during recent decades (Galloway 1995). Acid deposition has caused the acidification of soils and freshwaters in large areas of North America and Europe (Johnson et al. 1991). The effects of soil acidification are the leaching of base cations from the soil (Matzner and Murach 1995), the release of aluminium (Al) ions and heavy metals into soil solution (Tyler 1983), reduced decomposition of soil organic matter, and reduced growth of fine roots (Godbold et al. 2003). The release of acid soil solutions to the hydrosphere is detrimental to aquatic ecosystems. During the last two decades, deposition of acids has decreased substantially in Central Europe due to improved emission controls and the closing down of industry in eastern Germany after the reunion (Meesenburg et al. 1995). However, the deposition of nitrogen (N) compounds has decreased only slightly and has become an increasingly important fraction of the total deposition of acids (Wright et al. 1995). Despite reduced deposition of free acidity, the acid load to soils is still high because of high deposition of ammonium (NH
4+). The fate of elevated N-input on forest ecosystem remains partly unknown, but besides the impact on the acid/base balance of ecosystems there are some indications of increased tree growth, reduced root/shoot ratio, nutrient imbalances, reduced frost hardiness and elevated foliage consumption by insects (Binkley and Högberg 1997; Aber et al. 1998; Meiwes et al. 1999). In N-saturated ecosystems, soils have increased susceptibility for losses of nitrate (NO
3−) to the hydrosphere and of trace gases to the atmosphere (Aber 2002).
... Für die N-Komponenten muss davon ausgegangen werden, dass die Berechnung der Gesamtdeposition nach ULRICH (1994) eine konservative Schätzung darstellt und somit die realen Eintragsraten wesentlich höher liegen ( GAUGER et al. 2002, MEESENBURG et al. 2005). In einem dem Buchenbestand im Solling benachbarten Fichtenbestand fanden IBROM et al. (1995) mittels mikrometeorologischer Methoden eine gegenüber der Kronenraumbilanzierung um 60 % höhere N-Deposition. Auch bei konservativer Schätzung liegen die N-Einträge weit über dem Bedarf der Waldbestände für den Zuwachs der Holzbiomasse von 10 bis 16 kg ha-1 a-1 (RADE MACHER et al. 2008). ...
... The ammonia concentrations in Germany ranges from approximately 1 µg/m 3 in ammonia unloaded areas to 15 µg/m 3 in highly ammonia loaded areas characterised by agricultural systems (www.umweltministerium.bayern.de/service/ umwberat/; Ibrom et al., 1994). According to KRdL (1992) a region can be characterised as nitrogen loaded when about 12 µg/m 3 are reached. ...
This paper studies the effects of high ammonia emissions and nitrogen deposition on tree growth. Wood cores of 125Norway spruces were analysed along a transect (800m) from forest edge to forest interior. The forest edge was exposed to a strong ammonia emission source (poultry farm, less than 50m). Atmospheric nitrogen bulk deposition, ammonia concentration, soil solution concentration, soil nutrient content, foliar Nconcentration and C/N ratio of the humus layer were measured at five plots along the transect. The tree growth increment of two clusters of trees close to the forest edge and forest interior was compared. The results indicate extremely high nitrogen load at the forest edge. All nitrogen variables show an `edge effect' with increasing values from forest interior to the forest edge. The growth of nitrogen-influenced spruce trees generally increases. Trees with excessive long-term nitrogen load appear to loose increment after a long-term nitrogen impact. The average gain of increment at the edge appears to be related to the amount of nitrogen emission.
... The soil is a 1-m deep dystric cambisol, with few hydromorphic areas. It has not been fertilized apart from the relatively high annual atmospheric nitrogen deposition (> 50 kg N ha –1 year –1 ) during the last 20 to 30 years (Ibrom et al. 1995). The forest has been subject to intensive ecosystem research starting almost 40 years ago with the International Biological Programme (Ellenberg 1971). ...
Gross canopy photosynthesis (P(g)) can be simulated with canopy models or retrieved from turbulent carbon dioxide (CO2) flux measurements above the forest canopy. We compare the two estimates and illustrate our findings with two case studies. We used the three-dimensional canopy model MAESTRA to simulate P(g) of two spruce forests differing in age and structure. Model parameter acquisition and model sensitivity to selected model parameters are described, and modeled results are compared with independent flux estimates. Despite higher photon fluxes at the site, an older German Norway spruce (Picea abies L. (Karst.)) canopy took up 25% less CO2 from the atmosphere than a young Scottish Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation. The average magnitudes of P(g) and the differences between the two canopies were satisfactorily represented by the model. The main reasons for the different uptake rates were a slightly smaller quantum yield and lower absorptance of the Norway spruce stand because of a more clumped canopy structure. The model did not represent the scatter in the turbulent CO2 flux densities, which was of the same order of magnitude as the non-photosynthetically-active-radiation-induced biophysical variability in the simulated P(g). Analysis of residuals identified only small systematic differences between the modeled flux estimates and turbulent flux measurements at high vapor pressure saturation deficits. The merits and limitations of comparative analysis for quality evaluation of both methods are discussed. From this analysis, we recommend use of both parameter sets and model structure as a basis for future applications and model development.
Central Europe is an ancient cultural landscape, in which not even the smallest of areas has remained in what we can call a natural state. The sharp boundaries between forest, plantations, pastures, meadows and crop fields that are so characteristic of Central Europe today (see Fig. 3.1) are all the work of man. Even the areas that appear to be ruled by the forces of nature have usually also been influenced by humans in one way or another. Many so-called primeval forests, such as the ‘Neuenburger Urwald’ near Bremen and the Białowieża Forest in eastern Poland, show traces of earlier use (see Falinski 1980; Pott and Hüppe 1991; Pott 1999). Particularly the gnarled, spreading old trees that look so primeval are actually the result of earlier grazing with cattle, horses, goats and pigs, which kept down the undergrowth and opened up the forest (see Figs. 3.2 and 3.3). Today, there are only a few small fragments left of these once widespread wood-pastures (Glaser and Hauke 2004). Since they have been put under nature conservation and grazing management stopped, shade-tolerant trees have shot upwards and quickly overshadowed the venerable wide-crowned oaks and hornbeams. In terms of tree form, the slender-stemmed, high forest of modern forestry, forced upwards by competition, probably provides a better idea of most natural Central European forests than these ‘primeval’ forests and other protected former wood-pastures.
Vielfach können wesentliche Strukturen und Prozesse in der Atmosphäre sowie in aquatischen und in terrestrischen Ökosystemen erst verstanden werden, wenn Transferwege der Energie- und Stoffhaushalte für diese Systeme bekannt sind. Der Grenzbereich zwischen Atmosphäre und Erde ist daher ein wichtiger Bereich, um Wirkungsge- füge innerhalb der Atmosphäre und an der Erdoberfläche zu verstehen. Atmosphäre und Ökosysteme sind offene Systeme, die mit ihrer Umgebung Stoffe, Energie und Informationen austauschen. Ändert sich die Umgebung von offenen Systemen, so werden sich auch die Systeme selbst ändern. Um beurteilen zu können, wie sich komplexe Systeme entwickeln, ist es oft sinnvoll, die Einwirkungen von außen auf ein System zusammenzufassen und außerdem die gemeinsamen Auswirkungen vielfältiger interner Prozesse auf die Umgebung eines Systems zu erheben. Wenn ein Ökosystem langfristig Nährstoffe an seine Umgebung durch Ernte, Austrag im Sickerwasser, Wind- und Wassererosion oder Verflüchtigung verliert, so ist fraglich, ob sich die Organismen im Ökosystem langfristig ohne Nährstoffzufuhr von außen, z.B. aus der Atmosphäre, ernähren können. In der Landwirtschaft ist diese Einschätzung seit Liebig allgemein bekannt. In der Forstwirtschaft wird dieses Prinzip der Nachhaltigkeit schon seit fast 300 Jahren vertreten (Gravenhorst et al. 1997), ohne daß dieses Prinzip gleich mit Stoffbilanzen im Wald in Verbindung gebracht worden wäre. Heute wird die ökologische Nachhaltigkeit des Waldwachstums durch sauerwirkende, stickstoffhaltige und toxische Stoffeinträge aus der Atmosphäre gefährdet. In der Evolutionsgeschichte hat sich ein dynamisches Gleichgewicht zwischen dem Angebot für lebenswichtige Stoffe und der Nachfrage nach ihnen von Organismen eingestellt. Aus der Atmosphäre werden unter naturnahen Bedingungen lebensnotwendige Stoffe, die bei der Verwitterung der Minerale nicht genügend freigesetzt werden, den Pflanzen zugeführt, so daß sich ein Gleichgewicht zwischen Eintrag und Austrag einstellen kann. Durch anthropogene Aktivitäten (z.B. intensive Nutzung fossiler Energieträger und Landnutzungsänderungen) wird dieser Gleichgewichtszustand in der Gegenwart verändert, so daß gewachsene Lebensgemeinschaften in ihrer Existenz bedroht werden können. Luftgetragene anthropogene Spurenstoffe mit spezifischen Eigenschaften in der bodennahen Grenzschicht greifen Assimilationsorgane von Pflanzen an, waschen Nährstoffe aus den Sproßorganen und dem Wurzelbereich von Pflanzen aus, setzen toxische Komponenten im Boden frei und verschlechtern das Lebensmilieu von Pflanzen, Zersetzern und Mikroorganismen im Boden und in Gewässern (Ulrich 1983, 1994; Guderian et al. 1989). Gleichzeitig werden jedoch auch Schwermetalle, chlorierte Kohlenwasserstoffe und Nährstoffe wie Phosphor und Stickstoff in terrestrische und aquatische Ökosysteme aus der Atmosphäre eingetragen (UBA 1998). Das chemische Milieu in Böden und in nachgeschalteten Fließgewässern wird daher durch Stoffeinträge aus der Atmosphäre so geändert, daß Existenzbedingungen und Konkurrenzstärken von Organismen gestört, jedoch auch verbessert werden können.
The effect of a spruce forest in the Solling-hills (Germany) on the concentration of airborne trace compounds in the atmospheric boundary layer is discussed. The discussion is based on field measurements of vertical concentration profiles and vertical fluxes of reactive trace gases and particles in and above a spruce forest and on numerical modelling. Measured SO−, O− and PAN-concentrations are 10 % to 20 % lower near the forest floor than just above the canopy. NO is emitted from the forest into the atmospheric boundary layer and NO is transported both from the atmosphere and from the forest floor into the spruce canopy air space. The net NO−flux between the atmosphere and this spruce forest can be neglected compared quantitatively to other N-fluxes. Numerical experiments using two models show that a 1000 m long spruce forest reduces the near surface concentration of an airborne trace substance with a deposition velocity of about 0.7 cm/s by up to 6 % as compared to the upwind SO−concentration. If a forest is replaced by a meadow the SO−concentration at the former downwind side of a forest increases by about 10 %.
German
Der Einfluss eines Fichtenbestandes im Mittelgebirge Solling (Deutschland) auf die Konzentration von luftgetragenen Spurenstoffen in der atmosphärischen Grenzschicht wird diskutiert. Die Diskussion basiert auf Feldmessungen von vertikalen Konzentrationsprofilen und von vertikalen Flüssen von reaktiven Gasen und von Partikeln über und innerhalb eines Fichtenbestandes und auf Ergebnissen von numerischen Modellen. Die Luftkonzentrationen von SO2, O3 und PAN sind im Stammraum etwa 10 % bis 20 % niedriger als unmittelbar über dem Kronenraum. NO2 wird vom Wald in die Atmosphäre über dem Kronenraum emittiert, und NO wird sowohl aus der Atmosphäare als auch aus dem Boden in den Kronenraum des Fichtenwaldes transportiert. Der Netto-NOx -Fluss zwischen Atmosphäre und diesem Fichtenwald kann quantitativ im Vergleich zu anderen N-Transferraten vernachlässigt werden. Ein 1 km langer Fichtenwald reduziert die bodennahe Luftkonzentration eines Spurenstoffes bei einer Depositionsgeschwindigkeit von etwa 0,7 cm/s um etwa 6 %, wenn die windabgewandte Seite mit der windzugewandten verglichen wird. Wenn der Wald durch eine Wiese ersetzt wird, erhöht sich an der ehemals windabgewandten Seite des Waldes die SO2-Konzentration um etwa 10 %.
The atmospheric deposition of air pollutants was studied by means of monitoring canopy throughfall at six forest stands. The investigation was carried out in Norway spruce (Picea abies L. Karst.) forests in Southern Bavaria with high ambient ammonia concentrations due to either adjacent intensive agriculture or poultry housing. Five monitoring plots transected the forest edges and forest interior from the edge, at 50, 150, about 400 m and about 800m to the interior. Additionally, nutrient concentration in soil solution was sampled with suction cups at each plot, and C/N ratio of the humus layer was also determined. The variation of ambient ammonia concentration between three of the six investigated sites was estimated using diffusive samplers. In order to compare the effects of atmospheric deposition on European beech (Fagus sylvatica L.) and Norway spruce additional monitoring plotswere installed under each of these species in a mixed beech and spruce stand. Bulk deposition and soil water samples were analysed for major ions (NO3
-, NH4
+, SO4
2-, Cl-, Na+, K+, Mg2+, Ca2+M).The results show a substantial increase of deposition towards the forest edges for all ions. This so called ''edge effect'' continued in most cases until a distance from 50 to 150 m from edge. For both ambient ammonia concentrations and nitrogen deposition, it can be concluded that increased dry deposition is the main reason for the edge effect. Over 76% of the nitrogen ratios in throughfall deposition between the edge and 50 m distance into the spruce forest exceed 1.0. Except for potassium, beech generally showed lower ratios than spruce.Due to high nitrogen deposition the forest floor, C/N ratios were lower at stand edges when compared to their interior. In contrast to the increase of nitrogen deposition at the edge, nitrate export below the main rooting zone was lower at the edge. Nitrate export was generally lower under beech than spruce. Nitrogen budgets of some plots were negative, indicating a reduction of total ecosystem nitrogen stock.The results show that forest edges, especially in areas with high air pollution, receive much more atmospheric deposition than the interior parts of closed forest stands. As many deposition studies in forests were conducted at field stations in the central parts of forests the estimated deposition for the whole forest may be underestimated. This may be important to consider in geo-statistical studies and models aiming to estimate spatial critical deposition values, especially with an increasing fragmentation of the forest cover.
Hypotheses about the impacts of elevated atmospheric deposition of nitrogen on the forest ecosystem include an increased sensitivity to natural stress, impacts on roots, reduced species diversity of the ground vegetation, reduced growth, and unbalanced nutritional status due to eutrophication and acidification. The impact of N deposition has gained in ecological importance during recent decades, in part due to the steady decline in S emissions. Results of throughfall and deposition measurements at 163 plots in Europe show that total deposition of S and N compounds ranged from 100 to 3000 mol ha/yr in approximately 90% of the plots, but values up to 4000-8000 mol ha/yr were also observed. Approximately 50% of the plots received N inputs, dominated byNH4, above 1000 mol ha/yr which is a deposition level at which species diversity of the ground vegetation may be at risk. Results of input-output budgets for plots concentrated in Northern and Western Europe indicate that nitrate leaching starts to occurat throughfall inputs above 10 kg ha-1 yr-1, specifically in soils with C/N ratios in the humus layer below 25. Examples are given of field evidence for impacts of elevated N deposition, including elevated N contents in foliage and soil, Al release in soil response to increased nitrate concentrations, reduced shoot/root ratios, and a reduction in species diversity. Although knowledge about the response of forest ecosystems to N inputs has increased over the last decade, there is still a lack of information on the dynamics of N accumulation and related critical N loads in a range of environmental conditions. Furthermore, a European-wide perspective of N saturation in forest ecosystems is still lacking.
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