Sulfate reduction and iron-manganese cycling in intertidal surface sediments of the southern North Sea [Elektronische Ressource] / von Katja Bosselmann
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English
Documents
2007
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228
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English
Ebook
2007
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Publié par
Publié le
01 janvier 2007
Nombre de lectures
24
Langue
English
Poids de l'ouvrage
4 Mo
Publié par
Publié le
01 janvier 2007
Nombre de lectures
24
Langue
English
Poids de l'ouvrage
4 Mo
Sulfate reduction and iron-manganese cycling
in intertidal surface sediments of
the southern North Sea
Dissertation
zur Erlangung des Grades eines Doktors der Naturwissenschaften
– Dr. rer. nat. –
angenommen bei der Fakultät für Mathematik und Naturwissenschaften
der Carl von Ossietzky Universität Oldenburg
von
Katja Bosselmann
geboren am 31.07.1972 in Bremen
Gutachter:
Prof. Dr. H.-J. Brumsack
Prof. Dr. M.E. Böttcher
Prüfer:
Prof. Dr. G. Liebezeit
Eingereicht am: 12.11.2007
Disputation am: 17.12.2007
So eine Arbeit wird eigentlich nie fertig.
Man muss sie für fertig erklären, wenn man nach Zeit und Umständen
das Mögliche getan hat.
Johann Wolfgang von Goethe (1787)
Table of contents
Abstract V
Kurzfassung VIII
Chapter 1: Introduction 1
The continental shelf 2
Southern North Sea and Wadden Sea 2
Intertidal sediments 4
Transport processes in marine sediments 5
Degradation of organic matter 7
Iron and manganese in aquatic systems 8
Sedimentary manganese cycle 9 riron cycle 10
Iron and manganese reduction 11
Sedimentary sulfur cycle 13
The main objectives of this thesis 31
Overview about enclosed manuscripts 32
Chapter 2: Microbial sulfate reduction in intertidal sediments surface sediments
of the southern North Sea 35
Chapter 3: Dynamics of manganese in intertidal surface sediments. 71
Chapter 4: An in-situ 2D Photopaper Technique to monitor spatial sulfide distribution in
surface sediments 109
Chapter 5: Sources and fate of manganese in a tidal basin of the German Wadden Sea 127
Chapter 6: Nutrient release from an exposed intertidal sand flat 147
Chapter 7: Benthic photosynthesis in submerged Wadden Sea intertidal flats 167
Chapter 8: Diversity and vertical distribution of magnetotactic bacteria along chemical
gradients in freshwater microcosms 183
Chapter 9: Conclusions and outlook 197
Anhang 207
Acknowledgements - Danksagung 213
Curiculm vitae 215
Abstract
The main focus of this thesis was the investigation of factors controlling the cycle of manganese, iron
and sulfur in different types of intertidal sediments. Measurements were carried out to investigate the
seasonal dynamics of the biogeochemical reactions in the sedimentary sulfur cycle and the closely
connected element cycles of iron and manganese. The interactions of geochemical and microbial
processes with the decomposition of organic matter were compared between sand, mixed and mud
flats. Concurrent measurements of microbial sulfate reduction, dissolved and reactive iron and
manganese pools, organic stock and temperature dynamics in different sediments demonstrate the
strong effect of the activity of sulfate-reducing bacteria on metal cycling.
The main interest of the first chapter was the regulation of the overall sulfate reduction activity in
different sediment types and the formation and accumulation of reduced sulfur compounds compared
to the sulfur geochemistry. Special focus was the application of a model to estimate the response of
microbial sulfate reduction during the daily temperature variations under the influence of the tidal
dynamics. Seasonal investigations were performed to verify the influence of different factors as
temperature, availability of organic matter and metal oxides in surface sediments. Maximum activities
of sulfate reducing bacteria were detected at the sediment surface of the upper 10 cm depth at all
sites. The vertical distribution of microbial activity showed decreasing sulfate reduction rates (SRR)
accompanied by only small decline of organic carbon with depth, even at the finer grained stations (N,
D). Thus, lower SRR with depth may have been caused by the shift of the reactive to the more
refractory organic matter at depth. This indicates that besides temperature, the availability of reactive
organic matter as the main SRR-controlling factors in the investigated intertidal flats. Moreover, the
organic poor permeable sediments showed considerably high mineralization rates and point out the
important role of marine sands for carbon and sulfur cycling. The mixed and muddy stations represent
highly productive sediments where intensive sulfate reduction leads to high accumulation of reduced
sulfur. The pool size of the total reduced sulfur compounds (TRIS) and especially acid volatile sulfur
(AVS) showed a dynamic seasonal response at all investigated stations and was not permanently
trapped in the sediment. The results demonstrated that especially at the sediment surface, where the
highest activity of sulfate reducing bacteria occurred, abiotic re-oxidizing processes superimposed the
bacterial sulfide production and led to a rapid turnover of reduced sulfur compounds. The oxidative
sulfur cycling in the advection-driven sandy sediments was more dynamic compared to the diffusive
dominated mixed sediments. Furthermore, the limited availability of reactive iron phases or
intermediate sulfur species at the sandy sediments became a process limiting factor for further sulfide
fixation and prevented a permanent fixation of sulfide into the thermodynamically more stable pyrite.
The surface of intertidal sediments is characterized by the development of steep temperature
gradients. In order to examine the influence of highly dynamic temperature conditions on sulfate
reducing activity a model was applied to simulate the development of temperature-induced changes.
The model relates the measured SRR to in situ conditions under the influence of the tidal dynamics.
V
In the second study the cycles of manganese and fluxes across the sediment-water interface were
investigated in a quantitative manner in order to understand the role of the benthic biogeochemistry on
element cycling and interactions between manganese (Mn), iron (Fe), and sulfur (S) in surface
sediments (Böttcher et al., 2004; Bosselmann et al., 2003, in prep.). Water column concentrations of
dissolved manganese are elevated in the Wadden Sea compared to the open North Sea and showed
seasonality with highest Mn concentrations during summer time and low tide (Dellwig et al., 2007).
This suggests that tidal flat sediments may form a very important source for dissolved Mn. To quantify
the exchange of Mn across the sediment-water interface a combination of pore water, solid phase
data and benthic chamber incubations were arranged in different sediments types. From the pore
water profiles it becomes evident that the top 15 cm of the surface sediments are most important for
Mn cycling and are controlling the metal flux across the sediment-water interface. Gradients and
concentrations in pore water responded to the seasonal variation of microbial sulfate reduction and the
reservoir of reactive metal oxides. This considers the importance of chemical reduction of MnO by 2
-2 -1biogenic sulfide in near-surface sediments. Highest Mn release rates (up to 57-90 µmol m h ) were
2+found at the mixed and muddy sediments. The relatively low rates of Mn reduction and release (0-
-2 -155 µmol m h ) at the sandy Station S III reflects high sediment oxidation and low microbial activity
(Billerbeck et al., 2006; Walpersdorf et al., in prep). The local seepage of sulfidic pore water at station
2+S I revealed high concentrations of Mn probably due to the lateral draining of anoxic pore water
downward the sand flat which was postulated by Billerbeck et al., 2006. Furthermore, imbedded fine
2+ grained layers may function as sources for locally enhanced Mn concentrations at the low water line
of the station S I.
The sedimentary Mn and Fe hydr(oxid)e inventory reflected the different reaction kinetics of Fe and
Mn. Decline of the Mn and Fe inventory indicated that, especially during the warmer months HCl HCl
manganese escaped from the sediment by diffusion, advection and biologic
