Annual dynamics of pelagic carbon fluxes in a tidal lagoon [Elektronische Ressource] / vorgelegt von Martina Löbl

Mloebl

Sujets

• Biologie

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2005
• Nombre de lectures: 98
• Poids de l'ouvrage: 1 Mo

Extrait

Annual Dynamics of Pelagic Carbon
Fluxes in a Tidal Lagoon






Dissertation zur Erlangung eines
Doktorgrades in den Naturwissenschaften


-Dr. rer. nat.-


dem Fachbereich Biologie/Chemie
der Universität Bremen
vorgelegt von



Martina Löbl

im Dezember 2005







1. Gutachter: Herr Prof. Dr. Victor Smetacek
2. Gutachter: Herr Prof. Dr. Karsten Reise

CONTENT




SUMMARY .................................................................................................................3
ZUSAMMENFASSUNG ....................................................................................................7


CHAPTER 1 INTRODUCTION.....................................................................................11

CHAPTER 2 PELAGIC PRIMARY PRODUCTION IN THE NORTHERN WADDEN SEA -
NO QUANTITATIVE CHANGES SINCE THE MID 1980’S? ......................................29

CHAPTER 3 IMPACT OF ZOOPLANKTON GRAZING ON PHYTOPLANKTON DYNAMICS IN SHALLOW
COASTAL WATERS...............................................................................57

CHAPTER 4 SEASONAL DYNAMICS OF PELAGIC RESPIRATION IN A SHALLOW TIDAL LAGOON.....79

CHAPTER 5 MODELLING ATTEMPT ON CARBON/ NUTRIENT PROCESSES
IN A TIDAL LAGOON TO DIRECT FUTURE RESEARCH.....................................97

CHAPTER 6 GENERAL DISCUSSION........................................................................... 111


DANKSAGUNG.......................................................................................................................................127

CURRICULUM VITAE................................................................................................. 129

2 SUMMARY

The Wadden Sea is a coastal ecosystem under high anthropogenic impact. Evaluation of
man-made changes and impacts -e.g. eutrophication and fishery- require a detailed
understanding of the ecosystem functioning; especially in terms of carbon fluxes
through the ecosystem. Only little is known on annual dynamics of pelagic carbon
turnover in the Wadden Sea and its linking to the benthic system.
In aquatic ecosystems, phytoplankton primary production, zooplankton grazing, and
pelagic respiration are important processes of carbon dynamics. The aim of this study is
to quantify the annual dynamics of pelagic primary production, zooplankton grazing,
and respiration in a shallow coastal system and to investigate possible benthic impacts.
Pelagic primary production, zooplankton grazing, and respiration were investigated as
weekly/monthly time series over a one year period in the northern Wadden Sea. Studies
were related to the Sylt long term time series, providing data on temperature, salinity,
inorganic and organic nutrients, chlorophyll a and suspended matter concentrations (e.g.
MARTENS & ELBRÄCHTER 1998). This study was conducted in the framework of the
European Research Project COSA (Coastal Sands as Biocatalytical Filters) to relate the
temporal dynamics of pelagic carbon dynamics with benthic processes.

Primary production measurements showed that:
-2 -1 • Annual pelagic primary production was 210 g C m y .
• Highest production rates occurred during a Phaeocystis globosa bloom.
The impact of suspended matter (SPM) on the water column light field and primary
production was estimated:
• A doubling of SPM reduces ~20-50 % of primary production, with highest
impact in autumn, winter and spring.
Suspended matter concentrations decreased significantly within the past twenty years.
The impact of this decrease on primary production was tested. Primary production was
calculated for the years 1984-1990 and for 2000-2004 on the basis of measured P/I-
curves and hourly irradiance of 2004 and chlorophyll a and suspended matter
concentrations of the respective years.
3• The annual primary production from 1984-2004 varied between ~160-300 g C
-2 -1
m y ; No change in primary production since the mid 1980’s could be
observed.

Zooplankton grazing impact on phytoplankton biomass was measured during a
sequence of nine dilution experiments from March until October.
• During a diatom spring bloom no grazing occurred.
-1• The grazing impact during a Phaeocystis globosa bloom was ~60 % d of the
-1
standing stock; during the subseqent summer ~ 100% d of the standing stock
was grazed;
• during these periods presumably more phytoplankton biomass was maintained
within in the pelagic than lost to the benthic food web.
The applicability of data from dilution experiments on natural processes is still under
debate in literature and has not been shown before. Phytoplankton growth rates of
dilution experiments were compared to in-situ measured growth rates. For this
comparison a conversion factor regarding decreasing light intensities throughout the
water column was introduced.
• Experimental growth rates were in a good fit with in-situ measured growth rates;
• The overestimation of biomass by experimental results is in a good fit to benthic
assimilation of phytoplankton biomass reported by other studies.

Pelagic respiration measurements were carried out in two parallel time series, one at in-
situ temperature and one at 10° C to exclude temperature effects. The possible impact of
suspended matter concentrations, dissolved and particulate organic phosphorus and
temperature was tested. Size fractionated measurements were conducted to estimate the
share of the < 1μm fraction to pelagic respiration
-2 -1
• Annual pelagic respiration was 38 g C m y ;
• Approximately 50% of the annual respiration occurred during a Phaeocystis
bloom;
• Dissolved organic material seemed to have a high share (20-70%) in bacterial
degradation: The <1μm fraction contributes to 20-60% of the overall respiration;
2
A significant linear regression (r = 0.7) between respiration and dissolved
organic phosphorus was observed during winter and late spring.
4 • No linear relation between suspended matter concentrations and pelagic
respiration rates could be found.
• High respiration rates in winter (measured in the 10°C time series) together with
high sediment suspension indicates that resuspension of organic matter increases
pelagic respiration as a non-linear background signal during winter.
• The water column is predominantly autotrophic during most time of the year.

The development of a mathematical NPZD-box model on the basis of experimental
results from this study showed, that pelagic processes can be simulated only if benthic
processes were included in detail.
In terms of the benthopelagic coupling in the List tidal basin, this study shows that
during autumn, winter, and early spring, pelagic carbon dynamics were closely coupled
to the benthic system, due to an assumed biomass loss to the benthic compartment and
due to high sediment resuspension, transferring organic matter as well as nutrients into
the pelagic system. In late spring and summer large amounts of the pelagic
carbon/nutrient turnover proceed under low benthic influences.



5 6 ZUSAMMENFASSUNG


Das Wattenmeer ist ein Küstenökosystem unter hohem anthropogenem Einfluß. Um die
Effekte anthropogener Veränderungen –z.B. Eutrophierung und Fischerei- einschätzen
zu können, ist ein detailliertes Wissen über die Funktionsweise des Ökosystems
notwendig; besonders im Hinblick auf den Transport von Nährstoffen und Biomasse in
Form von Kohlenstoff durch das System.
Phytoplankton Primärproduktion, Grazing durch Zooplankton und pelagische
Respiration sind wichtige Prozesse der Kohlenstoffdynamik aquatischer Ökosysteme.
Über die Jahresdynamik der pelagischen Kohlenstoffumsätze im Wattenmeer und seiner
Vernetzung mit dem benthischen System ist bisher wenig bekannt. Ziel dieser Studie
war es, die jährliche Dynamik von pelagischer Primärproduktion, Zooplankton Grazing
und Respiration im Lister Tidebecken zu quantifizieren. Weiterhin sollten die
Beziehungen zwischen diesen Prozessen sowie der mögliche Einfluß des Benthos auf
das Pelagial u.a. durch Schwebstoffaufwirbelungen untersucht werden. Phytoplankton
Primärproduktion, Grazing durch Zooplankton und Respiration wurden über den
Zeitraum von einem Jahr als wöchentlich/monatliche Zeitreihe in einem flachen
Tidebecken des nördlichen Wattenmeeres untersucht. Diese Untersuchungen waren an
Messungen der Sylter Langzeitreihe gekoppelt, die Daten über Wassertemperatur,
Salzgehalt, organische und anorganische Nährstoffe, sowie Chlorophyll a und
Schwebstoffmengen liefert. Diese Arbeit wurde im Rahmen des europäischen
Forschungsprojektes COSA (Coastal Sands as Biocatalytical Filters) durchgeführt, um
pelagische Hintergrundinformationen für Untersuchungen über benthische Prozesse zur
Verfügung zu stellen.

Pelagische Primä