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Coastal microbial respiration in a climate change perspective
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (EcoChange)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In a climate change perspective increased precipitation and temperature are expected which should influence the coastal microbial food web. Precipitation will have a strong impact on river flow and thereby increase the carbon input to the coastal zone as well as lowering the marine salinity by dilution with freshwater. Simultaneously temperature may increase by 2-5 °C, potentially influencing e.g. metabolic processes. Consequences of this have been evaluated in this thesis with focus on microbial respiration in paper II and IV. A temperature increase of 3 °C will have a marked effect on microbial respiration rates in the coastal zone. The effect of temperature on microbial respiration showed a median Q10 value of 25 with markedly higher values during winter conditions (around 0°C). These Q10 values are several-fold higher than found in oceanic environments. The conclusion was in accordance with a consistent temperature limitation of microbial respiration during an annual field study, however, shifting to DOC limitation at the elevated temperature. Neither bacterial production nor phytoplankton production showed a consistent temperature effect, suggesting that the biomass production at the base of the food web is less sensitive to a temperature increase. Results from both a field study and a fully factorial microcosm experiment supported the conclusion. Our results suggested that areas dealing with hypoxia today will most likely expand in the future, due to increased respiration caused by higher temperatures and larger riverine output of dissolved organic carbon. 

Pelagic respiration measurements in the sea are relatively scarce in the literature, mainly due to the lack of sufficiently good and user friendly techniques. New methods such as the dynamic luminescence quenching technique for oxygen concentration have been developed. This makes it possible to obtain continuous measurements of oxygen in an enclosed vial. Two different commercially available systems based on the dynamic luminescence quenching technique were evaluated from the aspect of precision, accuracy and detection limit when applied to respiration measurements in natural pelagic samples. The Optode setup in paper III showed a practical detection limit of 0.30 mmol m-3 d-1, which can be applied to measure respiration in productive coastal waters (used in paper IV). This included development of a stopper where the sensor was attached, stringent temperature control, proper stirring and compensation for an observed system drift. For controlled laboratory experiments with organisms smaller than 1 µm the Sensor Dish Reader (paper I) has sufficient detection limit of (4.8 mmol m-3 d-1). This required a stringent temperature control and manual temperature correction. The Sensor Dish Reader gives the opportunity to perform multiple treatments at low cost (used in paper II), but the precision is too low for field studies due to the between ampule variation.

Abstract [sv]

Östersjön är ett brackvatten hav som sträcker sig från Bottenviken i norr till de danska sunden i söder och omsluts av en landmassa som representeras av nio länder. Denna miljö är på många sett unik genom stor sötvattenpåverkan och litet utbyte med världshaven (30 års omsättningstid). Östersjön utsätts framförallt för tillförsel av ämnen från såväl naturliga som antropogena aktiviteter. Något som ofta uppmärksammas är problem med syrefria områden och döda havsbottnar. Detta anses påverkas av både klimatförändringar och övergödning. En av de biologiska prosesser som påverkar syresituationen i haven är respiration, syreförbrukning, som utförs av de flesta levande organismerna i Östersjön. Den här avhandlingen presenterar resultat på hur bakteriers syreförbrukning påverkas av de förändringar vi förväntar oss i vårt klimat i framtiden. Det är framförallt ökad temperatur och ökat vattenflöde i våra floder som i sin tur leder till snabbare omsättning och tillförsel av näring åt bakteriesamhället. Resultaten från artiklarna II och IV visar att den potentiella temperaturökningen som väntas skulle öka syreförbrukningen i kustnära områden. Den blir extra stor i kustområden, troligen på grund av stor tillgång på organiskt material från älvarna. Även den högre tillförseln av näringsämnen kan ökan syreförbrukningen enligt artikel II. De områden som idag är syrefattiga kommer på grund av detta att expandera, framförallt längs kusterna där nya områden kan uppstå. Eventuellt kan det vara en förklaring till den ökande ytan av syrefria bottnar i i Östersjön och världshaven.

För att kunna utföra mätningar av syreförbrukning krävs väldigt precisa och gärna användarvänliga metoder som lätt kan tillämpas i fält. I avhandlingen presenteras hur två olika mätmetoder optimeras för att göra tillförlitliga förbrukningsmätningar av syre. Ny teknik gör att syrehalten kan mätas med en ljusbaserad metod som skiljer sig från dagens kemiska bl.a. genom att resultaten kan följas löpande på en dator. De båda metoderna kräver en väldigt precis temperaturkontroll. Optod uppsättningen presenterad i artikel III innefattaer en volym på 1 liter och organismer upp till en storlek på 50 μm omfattas i den uppmäta syreföbrukningen. Denna metod rekommenderas fö fätmäningar, och anvädes föfätmäningar i Artikel IV. I utvecklingen ingick utformning av en kork fö att montera optod-sensorn i. I artikel I presenteras en utrustning som baseras påen mindre volym (5 ml) vilket innebä att endast mäningar påbakterier och organismer mindre ä 1 μm kan anses tillfölitliga. Detta i kombination med viss variation mellan mäflaskor gö att den framföallt rekomenderas fö anvädning i laboratoriemiljö Det systemet anvädes fö mäningarna av syreföbrukning i laboratorieexperimentet som presenteras i artikel II.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2012. , 18 p.
National Category
Ecology
Research subject
biology
Identifiers
URN: urn:nbn:se:umu:diva-62734ISBN: 978-91-7459-517-8 (print)OAI: oai:DiVA.org:umu-62734DiVA: diva2:577726
Public defence
2013-01-24, KBC-huset, KB3A9, Umeå Universitet, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2012-12-20 Created: 2012-12-16 Last updated: 2017-09-01Bibliographically approved
List of papers
1. Precise microbial respiration rate in coastal waters by a contiuous multi-sample sensor
Open this publication in new window or tab >>Precise microbial respiration rate in coastal waters by a contiuous multi-sample sensor
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-62729 (URN)
Available from: 2012-12-16 Created: 2012-12-16 Last updated: 2012-12-17
2. Increased microbial activity in a warmer and wetter climate enhances the risk of coastal hypoxia
Open this publication in new window or tab >>Increased microbial activity in a warmer and wetter climate enhances the risk of coastal hypoxia
2013 (English)In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 85, no 2, 338-347 p.Article in journal (Other academic) Published
Abstract [en]

The coastal zone is the most productive area of the marine environment and the area that is most exposed to environmental drivers associated with human pressures in a watershed. In dark bottle incubation experiments, we investigated the short-term interactive effects of changes in salinity, temperature and riverine dissolved organic matter (rDOM) on microbial respiration, growth and abundance in an estuarine community. An interaction effect was found for bacterial growth, where the assimilation of rDOM increased at higher salinities. A 3 °C rise in the temperature had a positive effect on microbial respiration. A higher concentration of DOM consistently enhanced respiration and bacterial abundance, while an increase in temperature reduced bacterial abundance. The latter result was most likely caused by a positive interaction effect of temperature, salinity and rDOM on the abundance of bacterivorous flagellates. Elevated temperature and precipitation, causing increased discharges of rDOM and an associated lowered salinity, will therefore primarily promote bacterial respiration, growth and bacterivore abundance. Our results suggest a positive net outcome for microbial activity under the projected climate change, driven by different, partially interacting environmental factors. Thus, hypoxia in coastal zones may increase due to enhanced respiration caused by higher temperatures and rDOM discharge acting synergistically.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013
Keyword
bacterioplankton, protozoa, phytoplankton, marine, Baltic Sea
National Category
Microbiology
Research subject
biology
Identifiers
urn:nbn:se:umu:diva-62730 (URN)10.1111/1574-6941.12123 (DOI)
Available from: 2012-12-16 Created: 2012-12-16 Last updated: 2017-10-24Bibliographically approved
3. Precise continuous measurements of pelagic respiration in coastal waters with Oxygen Optodes
Open this publication in new window or tab >>Precise continuous measurements of pelagic respiration in coastal waters with Oxygen Optodes
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2013 (English)In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 11, 1-15 p.Article in journal (Refereed) Published
Abstract [en]

An analytical setup for respiration rate measurements was developed and evaluated in pelagic water samples using a commercially available optical oxygen sensor (Optode (TM)). This setup required the development of a gas tight stopper to connect the sensors to a 1 dm(3) glass sample bottle, precise temperature control (+/- 0.05 degrees C), and proper stirring of samples. The detection limit and precision of the method was 0.3 mmol O-2 m(-3) d(-1). This was similar to the detection limit for the high-precision Winkler titration method reported in field studies. When compared with the Winkler method, the Optode sensor enabled operator-independent, high temporal resolution measurement of respiration, better coverage of plankton groups and detection of non-linear oxygen decline, without the need for wet chemistry. Respiration rates measured by the Optodes showed good accuracy when compared with measurements made with the Winkler titration method (3% deviation), followed the expected temperature response (Q(10) = 3.0), were correlated with chlorophyll a and were congruent with earlier reported values in the literature. The main source of uncertainty was a necessary correction for system drift during the incubation period, due to oxygen release from the plastic components. Additionally, less stringent temperature control on board research vessels during rough seas reduced the precision. We conclude that the developed Optode system can be used to measure respiration in productive coastal waters. Samples from cold or deep waters were, however, often below the detection limit.

Place, publisher, year, edition, pages
Association for the Sciences of Limnology and Oceanography, 2013
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-62731 (URN)10.4319/lom.2013.11.1 (DOI)000317920600001 ()
Available from: 2012-12-16 Created: 2012-12-16 Last updated: 2017-12-06Bibliographically approved
4. Strong seasonal effect of moderate experimental warming on plankton respiration in a temperate estuarine plankton community
Open this publication in new window or tab >>Strong seasonal effect of moderate experimental warming on plankton respiration in a temperate estuarine plankton community
2013 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 136, 269-279 p.Article in journal (Refereed) Published
Abstract [en]

Climate change projections forecast a 1.1-6.4 °C global increase in surface water temperature and a 3 °C increase for the Baltic Sea. This study examined the short-term interactive effects of a realistic future temperature increase (3 °C) on pelagic respiration and bacterioplankton growth and phytoplanktonphotosynthesis in situ. This study was undertaken throughout a full seasonal cycle in the northern Baltic Sea. We found marked positive short-term effects of temperature on plankton respiration but no significant effect on bacterioplankton growth or phytoplankton photosynthesis. Absolute respiration rates remained similar to other comparable environments at the in situ temperature. With the 3 °C temperature increase, respiration rates in situ increased up to 5-fold during the winter and 2-fold during the summer. A maximum seasonal Q10 value of 332 was observed for respiration during the cold winter months (twater z 0 C), and summer Q10 values were comparatively high (9.1). Q10 values exhibited a significant inverse relationship to water temperature during winter. Our results thereby suggest that plankton respiration in this coastal zone is more temperature sensitive than previously reported. In addition, field data indicated that plankton respiration switched from being temperature limited to being limited by dissolved organic carbon (DOC) after the simulated temperature increase. Assuming that our observations are relevant over longer time scales, climate change may worsen hypoxia, increase CO2 emissions and create a more heterotrophic food web in coastal zones with a high load of riverine DOC.

Place, publisher, year, edition, pages
Academia Press, 2013
Keyword
respiration, bacteria, phytoplankton, Q10, seasonal variations, climate, Sweden, Baltic sea, Bothnian sea, Ore estuary, 63.552222, 19.777451, 63.500492, 19.732819, 63.467078, 19.867401, 63.527440, 19.870148 (DD.dddddd degree decimals)
National Category
Ecology Oceanography, Hydrology, Water Resources Microbiology
Research subject
Microbiology
Identifiers
urn:nbn:se:umu:diva-84436 (URN)10.1016/j.ecss.2013.10.029 (DOI)
Funder
Swedish Environmental Protection Agency
Note

Manuscript included in thesis with the title: Strong seasonal effect on plankton respiration by moderate experimental warming in a temperate estuarine plankton community

Available from: 2014-01-07 Created: 2014-01-07 Last updated: 2017-10-24Bibliographically approved

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