Nitrogen mineralization and gaseous nitrogen losses from waterlogged and drained organic soils in a black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forest

Black alder (<i>Alnus glutinosa</i> (L.) Gaertn.) forests on peat soils have been reported to be hotspots for high nitrous oxide (N₂O) losses. High emissions may be attributed to alternating water tables of peatlands and to the incorporation of high amounts of easily decomposable nitrogen (N) into the ecosystem by symbiotic dinitrogen (N₂)-fixation of alder trees. Our study addressed the question to what extent drainage enhances the emissions of N₂O from black alder forests and how N turnover processes and physical factors influence the production of N₂O and total denitrification. The study was conducted in a drained black alder forest with variable groundwater tables at a southern German fen peatland. Fluxes of N₂O were measured using the closed chamber method at two drained sites (D-1 and D-2) and one undrained site (U). Inorganic N contents and net N mineralization rates (NNM) were determined. Additionally a laboratory incubation experiment was carried out to investigate greenhouse gas and N₂ fluxes at different temperature and soil moisture conditions. Significantly different inorganic N contents and NNM rates were observed, which however did not result in significantly different N₂O fluxes in the field but did in the laboratory experiment. N₂O fluxes measured were low for all sites, with total annual emissions of 0.51 ± 0.07 (U), 0.97 ± 0.13 (D-1) and 0.93 ± 0.08 kg N₂O–N ha⁻¹ yr^&minus;1 (D-2). Only 37% of the spatiotemporal variation in field N₂O fluxes could be explained by peat temperature and groundwater level, demonstrating the complex interlinking of the controlling factors for N₂O emissions. However, temperature was one of the key variables of N₂O fluxes in the incubation experiment conducted. Increasing soil moisture content was found to enhance total denitrification losses during the incubation experiment, whereas N₂O fluxes remained constant. At the undrained site, permanently high groundwater level was found to prevent net nitrification, resulting in a limitation of available nitrate (NO₃^&minus;) and negligible gaseous N losses. N₂O flux rates that were up to four times higher were measured in the incubation experiment. They reveal the potential of high N₂O losses under changing soil physical conditions at the drained alder sites. The high net nitrification rates observed and high NO₃^&minus; contents bear the risk of considerable NO₃^&minus; leaching at the drained sites

CO2 fluxes and ecosystem dynamics at five European treeless peatlands – merging data and process oriented modeling

The carbon dioxide (CO2) exchange of five different peatland systems across Europe with a wide gradient in land use intensity, water table depth, soil fertility and climate was simulated with the process oriented CoupModel. The aim of the study was to find out whether CO2 fluxes, measured at different sites, can be explained by common processes and parameters or to what extend a site specific configuration is needed. The model was calibrated to fit measured CO2 fluxes, soil temperature, snow depth and leaf area index (LAI) and resulting differences in model parameters were analyzed. Finding site independent model parameters would mean that differences in the measured fluxes could be explained solely by model input data: water table, meteorological data, management and soil inventory data. Seasonal variability in the major fluxes was well captured, when a site independent configuration was utilized for most of the parameters. Parameters that differed between sites included the rate of soil organic decomposition, photosynthetic efficiency, and regulation of the mobile carbon (C) pool from senescence to shooting in the next year. The largest difference between sites was the rate coefficient for heterotrophic respiration. Setting it to a common value would lead to underestimation of mean total respiration by a factor of 2.8 up to an overestimation by a factor of 4. Despite testing a wide range of different responses to soil water and temperature, rate coefficients for heterotrophic respiration were consistently the lowest on formerly drained sites and the highest on the managed sites. Substrate decomposability, pH and vegetation characteristics are possible explanations for the differences in decomposition rates. Specific parameter values for the timing of plant shooting and senescence, the photosynthesis response to temperature, litter fall and plant respiration rates, leaf morphology and allocation fractions of new assimilates, were not needed, even though the gradient in site latitude ranged from 48° N (southern Germany) to 68° N (northern Finland) differed largely in their vegetation. This was also true for common parameters defining the moisture and temperature response for decomposition, leading to the conclusion that a site specific interpretation of these processes is not necessary. In contrast, the rate of soil organic decomposition, photosynthetic efficiency, and the regulation of the mobile carbon pool need to be estimated from available information on specific soil conditions, vegetation and management of the ecosystems, to be able to describe CO2 fluxes under different condition

Klimarelevanz von Mooren und Anmooren in Deutschland: Ergebnisse aus dem Verbundprojekt "Organische Böden in der Emissionsberichterstattung"

[Projektziel] Ziel des Projekts war es, deutschlandweit aktuelle Daten zu Flächen organischer Böden, Nutzung, Wasserständen und Treibhausgasemissionen zu erheben und somit die aktuelle Treibhausgasbilanz der organischen Böden in Deutschland zu quantifizieren

Treibhausgasemissionen aus organischen Böden im deutschen Treibhausgasinventar: Methodenentwicklung und Ergebnisse

Entwässerte organische Böden sind in vielen Ländern, darunter auch in Deutschland, eine starke Quelle anthropogener Treibhausgase (THG). Daher müssen sie bei der Berichterstattung gemäß UNFCCC und Kyoto-Protokoll angemessen berücksichtigt werden. Hier beschreiben wir die Methodik, Daten und Ergebnisse der deutschen detaillierten Tier-3-Methodik zur Berichterstattung anthropogener Treibhausgasemissionen aus entwässerten organischen Böden, die für das deutsche Treibhausgasinventar entwickelt und angewandt wurden. Der Ansatz basiert auf nationalen Daten und bietet das Potenzial, Änderungen der Landnutzung und des Wassermanagements zu verfolgen, falls Zeitreihen zu relevanten Aktivitätsdaten vorliegen. Die Aktivitätsdaten umfassen hochauflösende Karten zu Klima, Landnutzung, organischen Böden und vom mittleren jährlichen Grundwasserflurabstand. Die Grundwasserkarte wurde durch ein statistisches Modell aus Daten von &gt; 1000 Standorten abgeleitet. Die THG-Emissionen beruhen auf einem einzigartigen Datensatz mit mehr als 200 THG-Bilanzen für fast alle Kombinationen von Landnutzungskategorien und Typen organischer Böden. Die Messungen wurden mit vollständig harmonisierten Protokollen durchgeführt. Nicht-lineare Funktionen beschreiben die Abhängigkeit der Kohlendioxid- und Methan-Flüsse vom mittleren jährlichen Grundwasserstand und, wenn erforderlich, von der Landnutzung. Die daraus resultierenden "angewandten Emissionsfaktoren" für jede Landnutzungskategorie berücksichtigen sowohl die Unsicherheit der nicht-linearen Funktionen als auch die Verteilung der Grundwasserstände in jeder Landnutzungskategorie. Da keine einfachen funktionellen Zusammenhänge für die Lachgasemissionen gefunden wurden, wurden die entsprechenden Emissionsfaktoren daher als Mittelwerte der Messwerte jeder Landnutzungskategorie berechnet. Für kleinere THG-Quellen wie Methanemissionen aus Gräben und Austräge von gelöstem organischem Kohlenstoff wurden IPCC-Standard-Emissionsfaktoren verwendet

The greenhouse gas balance of a drained fen peatland is mainly controlled by land-use rather than soil organic carbon content

Drained organic soils are considered to be hotspots for greenhouse gas (GHG) emissions. Arable lands and intensively used grasslands, in particular, have been regarded as the main producers of carbon dioxide (CO2) and nitrous oxide (N2O). However, GHG balances of former peatlands and associated organic soils not considered to be peatland according to the definition of the Intergovernmental Panel on Climate Change (IPCC) have not been investigated so far. Therefore, our study addressed the question to what extent the soil organic carbon (SOC) content affects the GHG release of drained organic soils under two different land-use types (arable land and intensively used grassland). Both land-use types were established on a Mollic Gleysol (labeled Cmedium) as well as on a Sapric Histosol (labeled Chigh). The two soil types differed significantly in their SOC contents in the topsoil (Cmedium: 9.4–10.9 % SOC; Chigh: 16.1–17.2 % SOC). We determined GHG fluxes over a period of 1 or 2 years in case of N2O or methane (CH4) and CO2, respectively. The daily and annual net ecosystem exchange (NEE) of CO2 was determined by measuring NEE and the ecosystem respiration (RECO) with the closed dynamic chamber technique and by modeling the RECO and the gross primary production (GPP). N2O and CH4 were measured with the static closed chamber technique. Estimated NEE of CO2 differed significantly between the two land-use types, with lower NEE values (−6 to 1707 g CO2-C m−2 yr−1) at the arable sites and higher values (1354 to 1823 g CO2-C m−2 yr−1) at the grassland sites. No effect on NEE was found regarding the SOC content. Significantly higher annual N2O exchange rates were observed at the arable sites (0.23–0.86 g N m−2 yr−1) than at the grassland sites (0.12–0.31 g N m−2 yr−1). Furthermore, N2O fluxes from the Chigh sites significantly exceeded those of the Cmedium sites. CH4 fluxes were found to be close to zero at all plots. Estimated global warming potential, calculated for a time horizon of 100 years (GWP100) revealed a very high release of GHGs from all plots ranging from 1837 to 7095 g CO2 eq. m−2 yr−1. Calculated global warming potential (GWP) values did not differ between soil types and partly exceeded the IPCC default emission factors of the Tier 1 approach by far. However, despite being subject to high uncertainties, the results clearly highlight the importance of adjusting the IPCC guidelines for organic soils not falling under the definition in order to avoid a significant underestimation of GHG emissions in the corresponding sectors of the national climate reporting. Furthermore, the present results revealed that mainly the type of land-use, including the management type, and not the SOC content is responsible for the height of GHG exchange from intensive farming on drained organic soils

Short-term effects of biogas digestate and cattle slurry application on greenhouse gas emissions affected by N availability from grasslands on drained fen peatlands and associated organic soils

A change in German energy policy has resulted in a strong increase in the number of biogas plants in Germany. As a consequence, huge amounts of nutrient-rich residues, the by-products of the fermentative process, are used as organic fertilizers. Drained peatlands are increasingly used to satisfy the huge demand for fermentative substrates (e.g., energy crops, grass silage) and the digestate is returned to the peatlands. However, drained organic soils are considered as hot spots for nitrous oxide (N2O) emissions and organic fertilization is additionally known to increase N2O emissions from managed grasslands. Our study addressed the questions (a) to what extent biogas digestate and cattle slurry application increase N2O and methane (CH4) fluxes as well as the mineral nitrogen use efficiency (NUEmin) and grass yield, and (b) how different soil organic matter contents (SOMs) and nitrogen contents promote the production of N2O. In addition NH3 volatilization was determined at one application event to obtain first clues with respect to the effects of soil and fertilizer types. The study was conducted at two sites within a grassland parcel, which differed in their soil organic carbon (SOC) and N contents. At each site (named Corg-medium and Corg-high) three plots were established: one was fertilized five times with biogas digestate, one with cattle slurry, and the third served as control plot. On each plot, fluxes of N2O and CH4 were measured on three replicates over 2 years using the closed chamber method. For NH3 measurements we used the calibrated dynamic chamber method. On an annual basis, the application of biogas digestate significantly enhanced the N2O fluxes compared to the application of cattle slurry and additionally increased the plant N-uptake and NUEmin. Furthermore, N2O fluxes from the Corg-high treatments significantly exceeded N2O fluxes from the Corg-medium treatments. Annual cumulative emissions ranged from 0.91 ± 0.49 to 3.14 ± 0.91 kg N ha−1 yr−1. Significantly different CH4 fluxes between the investigated treatments or the different soil types were not observed. Cumulative annual CH4 exchange rates varied between −0.21 ± 0.19 and −1.06 ± 0.46 kg C ha−1 yr−1. Significantly higher NH3 losses, NUEmin and grass yields from treatments fertilized with biogas digestate compared to those fertilized with cattle slurry were observed. The total NH3 losses following the splash plate application were 18.17 kg N ha−1 for the digestate treatments and 3.48 kg N ha−1 for the slurry treatments (36 and 15% of applied NH4+–N). The observed linear increase of 16 days' cumulative N2O–N exchange or annual N2O emissions, with mean groundwater level and ammonium application rate, reveals the importance of site-adapted N fertilization and the avoidance of N surpluses in Corg-rich grasslands

Leitfaden für den Abstimmungskurs im Rahmen der Inventurleitungstagung zur Waldzustandserhebung

Zum Zwecke der Qualitätssicherung der Waldzustandserhebung (WZE) findet jährlich im Rahmen der Inventurleitungstagung ein Abstimmungskurs statt. Der Kurs wird üblicherweise vom jeweiligen Gastgeberland organisiert. Im Laufe des Kurses werden dieselben Bäume von allen Teilnehmenden aus den verschiedenen Bundesländern hinsichtlich ihrer Kronenverlichtung bewertet. Das gemeinsame Ansprechen und Diskutieren von Trainingsbäumen dienen dabei zunächst dem Erfahrungsaustausch und der Standardisierung der Bewertungen. Das anschließende unabhängige Ansprechen von Testbäumen und die statistische Auswertung dieser Bewertungen dienen dazu mögliche Abweichungen einzelner Länder zu erkennen und die Bewertungskriterien wenn nötig anzupassen. Über die Ergebnisse des Abstimmungskurses wird jedes Jahr am Thünen-Institut ein umfassender Bericht verfasst. Diese Berichte belegen seit Jahren die Übereinstimmungen in den Kronenverlichtungsbewertungen zwischen den Bundesländern und über die Zeit. Für die Vergleichbarkeit der Ergebnisse über Jahre hinweg ist es wichtig, dass die Abstimmungskurse standardisiert durchgeführt werden. Dieser Leitfaden dokumentiert den Ablauf des Abstimmungskurses, die Anforderungen bezüglich der Probebäume und Parcours und die aufzuzeichnenden Daten. Der Leitfaden soll als Anleitung für die Kursvorbereitung durch die jeweils gastgebende Landesanstalt dienen.For the purpose of quality assurance of the crown condition survey, a cross-comparison course is held annually within the framework of the inventory management meeting. The course is usually organized by the respective host state. During the course, the same trees are evaluated by all participants from the different federal states with regard to their crown defoliation. The joint evaluation and discussion of training trees, at first, have the purpose of exchange of experience and the standardization of the evaluations. The subsequent independent addressing of test trees and the statistical analyses of these assessments serve to identify possible deviations of individual countries and to adjust the assessment criteria if necessary. A comprehensive report on the results of the cross-comparison course is produced each year at the Thünen Institute. For years, these reports have documented the consistency in crown condition assessments among the states and over time. For comparability of results over years, it is important that the cross-comparison courses are conducted in a standardized manner. This guide documents the cross-comparison course procedure, the requirements regarding sample trees and courses, and the data to be recorded. The guide is intended to serve as a guide for course preparation by the host state agency