Soil biogenic emissions of nitric oxide from arid and semi-arid ecosystems [Elektronische Ressource] / Gregor Timothy Feig

Gregor Perko

Sujets

• Social work
• Biologie

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2009
• Nombre de lectures: 15
• Langue: English
• Poids de l'ouvrage: 13 Mo

Extrait

Soil Biogenic Emissions of Nitric
Oxide from Arid and Semi-Arid
Ecosystems



Dissertation
Zur Erlangung des Grades
“Doktor der Naturwissenschaften”
Im Promotionsfach Geographie


am Fachbereich Chemie, Pharmazie und
Geowissenschaften
der Johannes Gutenberg-Universität Mainz



Gregor Timothy Feig



geboren am 24.06.1979 in Dubai, Vereinigte
Arabische Emirate










































Tag der mündlichen Prüfung: 12 Februar 2009i Abstract
____________________________________________________________________________
Abstract
Nitric oxide (NO) has an important influence on a number of environmental processes including the production
of ozone in the troposphere, the cycling of the hydroxyl radical and the production of nitric acid. The biogenic
production of NO in the soil accounts for between 10% and 40% of the global total. A large degree of the
uncertainty in the estimation of the biogenic emissions stems from a shortage of measurements in arid regions,
which comprise a substantial proportion of the earth’s land surface area, but have been neglected from many of
the major atmospheric chemical models. This study examined the emission of NO from three ecosystems in
southern Africa which cover an aridity gradient from semi-arid savannas in South Africa through arid Kalahari
savannas in Botswana and the hyper-arid Namib Desert in Namibia. A laboratory method was used to determine
the release of NO as a function of the soil moisture and the soil temperature. Various methods were used to up-
scale the net potential NO emissions determined in the laboratory to the vegetation patch, landscape or regional
level. The importance of landscape, vegetation and climatic characteristics is emphasized. In addition NO
measurements were made in other regions such as in Israel, in the Amazon and in European temperate forests
and pastures; these measurements did not form a major part of this PhD but are included in the discussion.
The first study occurred in a semi-arid savanna region in South Africa, where soils were sampled from 4
different landscape positions along a catenal sequence in the Kruger National Park. The maximum NO emission
occurred at soil moisture contents of between 10% and 20% water filled pore space (WFPS). The highest net
potential NO emissions came from the low lying Footslope landscape positions, which have the largest nitrogen
(N) stocks and the largest input of N into the soil, the net potential NO emissions from the Midslope and Crest
landscape positions were considerably lower. Net potential NO fluxes obtained in the laboratory were converted
in field fluxes for the period 2003-2005, for the four landscape positions, using soil moisture and temperature
-1data obtained in situ at the Kruger National Park Flux Tower Site. The NO emissions ranged from 1.5-8.5 kg ha
-1
a with the highest emissions occurring in the Footslope positions. The field fluxes were up-scaled to a regional
basis using geographic information system (GIS) based techniques, this indicated that the highest NO emissions
occurred from the Midslope positions due to their large geographical extent in the considered research area.
3 3Total emissions ranged from 20 x 10 kg in 2004 to 34x10 kg in 2003 for the 56000 ha Skukuza land type.
The second study occurred in an arid savanna ecosystem in the Kalahari, near the town of Tsabong, Botswana. In
this study we collected soils from four differing vegetation patch types including: Pan, Annual Grassland,
Perennial Grassland and Bush Encroached patches. The maximum net potential NO fluxes determined in the
-2 -1 -2 -1laboratory ranged from 0.27 ng m s in the Pan patches to 2.95 ng m s in the Perennial Grassland patches.
The net potential NO emissions were up-scaled for the year December 2005-November 2006 and a region
185km x 185km in the southern Kalahari. This was done using 1) the net potential NO emissions determined in
the laboratory, 2) the vegetation patch distribution obtained from LANDSAT NDVI measurements 3) estimated
soil moisture contents obtained from ENVISAT ASAR measurements and 4) soil surface temperature
measurements using MODIS 8 day land surface temperature measurements. This up-scaling procedure gave NO
-1 -1 -1 -1fluxes which ranged from 1.8 g ha month in the austral winter months (June and July) to 323 g ha month in
the austral summer months (January-March). Differences occurred between the vegetation patches where the
highest NO fluxes occurred in the Perennial Grassland patches and the lowest in the Pan patches. Over the
-1 -1
course of the year the mean up-scaled NO emission for the studied region was 0.54 kg ha a this is within the
range of pyrogenic NO emissions in African savannas and accounts for a loss of approximately 7.4% of the
estimated N input to the region through atmospheric deposition and biological N fixation. The biogenic loss of
NO is therefore a potentially important loss mechanism for N within this region.
The third study occurred in the hyper-arid Namib Desert in Namibia. Soils were sampled from three ecosystems;
Dunes, Gravel Plains and the Riparian zone of the Kuiseb River. The net potential NO flux measured in the
laboratory was used to estimate the NO flux for the whole of the Namib Desert for the year 2006 using modelled
soil moisture and temperature data from the European Centre for Medium Range Weather Forecasts (ECMWF)
operational model on a 36km x 35km spatial resolution. The maximum net potential NO production occurred at
low soil moisture contents (<10%WFPS) and the optimal temperature was 25°C in the Dune and Riparian
ecosystems and 35°C in the Gravel Plain Ecosystems. The maximum net potential NO fluxes ranged from 3.0 ng
-2 -1 -2 -1
m s in the Riparian ecosystem to 6.2 ng m s in the Gravel Plains ecosystem. Up-scaling the net potential
-1 -1NO flux to the whole of the Namib desert gave NO fluxes of up to 0.062 kg ha a in the Dune ecosystem and
-1 -10.544 kg h a in the Gravel Plain ecosystem for 2006.
From these studies it is shown that NO is emitted ubiquitously from terrestrial ecosystems from hyper-arid
regions such as the Namib Desert to topical forests, as such the NO emission potential from deserts and
scrublands should be taken into account in the global NO models. The emission of NO is influenced by various
factors such as landscape, vegetation and climate. This study looks at the potential emissions from certain arid
and semi-arid environments in southern Africa and other parts of the world and discusses some of the important
factors controlling the emission of NO from the soil. ii Deutsche Zusammenfassung
____________________________________________________________________________
Deutsche Zusammenfassung
Die biogene NO Produktion im Boden ist am global totalen NO Freisetzung zu 10-40% beteiligt. Die
überwiegend Ungewissheit der Schätzungen stammt aus mangelnden Messungen in den ariden Regionen, welche
40% der gesamten Landfläche der Erde ausmacht. Die vorliegende Arbeit hat zum Ziel, die NO Freisetzung aus
den drei Ökosystemen in südlichen Teil von Afrika, welche eine Ariditätsstufe von Semiarid Savanne in
Südafrika bis extrem arid Namib Wüste in Namibia beschreibt, zu untersuchen. In dieser Arbeit wurde
Laborexperiment vorgenommen, aus denen die Abhängigkeit der NO Freisetzung von Bodenfeuchte und
Bodentemperatur abgleitet wurde. Es wurde unterschiedliche Methoden benutzt, um die Vegetationstypen,
Landschaftsebene sowie Regionalebene bedingten Unterschiede von NO Freisetzung bezogen auf den Standort
Punktmessdaten im Labor zu regionalisieren und die wichtige Bedeutung von Vegetationstypen,
Landschaftsebene und Klimaverhältnisse wurde hervorgehoben.
In der ersten Studie wurde semiarid Savanne in Südafrika als Untersuchungsgebiet ausgewählt und dazu sind
Bodenproben vier unterschiedlicher Landschaftsebene von Kruger National Park im Labor untersucht. Der
optimale Feuchtezustand, bei dem die NO-Freisetzung ein Maximum erreicht, sind 10-40%. Hier wird die
höchste NO-Freisetzung bei der tief gelegenen Landschaft beobachtet, in der die höchste Stickstoffbestände -
und Zufuhr haben. Die im Labor gemessene Netto-Freisetzungsrate wurde für den Zeitraum 2003-2006 in den
NO-Fluß im Feld umgewandelt, die in Verbindung mit den gemessenen Bodenfeuchten und Temperaturen für
vier Standort von Kruger National Park erfolgt wurde. Es zeigt sich eine Kurvenbereich der jährlichen
-1
Freisetzungsraten von 1,5 bis 8,5 kg ha . Es wurde punkthaft geschätzter NO-Fluß im Feld durch die
Verwendung eines Geographischen Informationssystems (GIS) auf die Fläche des Untersuchungsgebiets -
Skukuza übertragen und die Maximum NO wird von Mittelhang freigesetzt. Die gesamte Emission schwankt
3 3von 20x10 kg in 2004 bis 34x10 kg in 2003 für Skukuza Landschaft (56000 ha).
Das zweite Untersuchungsgebiet befindet sich im ariden Ökosystem Savanne – Kalahari (Botswana). Die
Bodenprobe