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  • 1.
    Vikström, Kevin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Importance of bacterial maintenance respiration and baseline respiration for development of coastal hypoxia2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Reduced oxygen concentrations and increasing hypoxic zones havebecome more common in the sea due to climate change andeutrophication. The main cause of oxygen loss in oxygenatedenvironments is respiration. Respiration rates can be estimated usingoptode methodologies which utilize dynamic luminescence quenching toestimate the oxygen concentration declines in dark incubations. Apublished optode methodology was improved by using optodes withtitanium housing instead of plastic housing plausibly trapping oxygen.Drift was highly reduced by the titanium casings leading to a higherprecision and lower detection limit of 0.97 mmol O2 m-3 d-1. 28% ofmeasurements were shown to have non-linear oxygen concentrationdeclines. The rate of oxygen change was derived with a 2nd degreepolynomial at 1 hour from the incubation start. The majority of non-lineardeclines were concave and due to carbon substrate limitation. Analyzingnon-linear trends linearly, a common practice, leads to anunderestimation of respiration by up to 64%.

    Bacterial maintenance respiration (Rm) was studied using anecophysiological model unverified in natural environments. The modelwas applicable at high productivities but a quadratic model wasdemonstrated to give a better fit. Rm was found to represent a significantpart in the sub-arctic estuary contributing to 58% of the annual specificbacterial respiration. Therefore, Rm may be more important in nature thanpreviously recognized. The ecophysiological model is driven solely by thebacterial specific growth rate (μ) where the relative influence of Rm iselevated as μ decreases. As a consequence, I hypothesize that a reductionin nutrients may not decrease the oxygen consumption but rather shiftbacterial growth based respiration to Rm as μ approaches zero.Baseline respiration (Rbl), defined as ecosystem respiration disconnectedfrom contemporary primary produced carbon, was also studied. Rbl wasshown to be largely supplied by allochthonous carbon in a coastalecosystem and had a contribution of 50% to the annual planktoncommunity respiration in the sub-arctic estuary studied. I claim that Rbland Rm are crucial to include for understanding and managingdevelopment of aquatic hypoxia in an effective and economic manner.

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  • 2.
    Vikström, Kevin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bartl, Ines
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wikner, Johan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    High influence of baseline respiration in a sub-Arctic coastal ecosystemManuscript (preprint) (Other academic)
    Abstract [en]

    Respiration is a key metabolic process in the marine environment that is usually assumed to be driven by phytoplankton production. However, respiration in the absence of contemporary phytoplankton production, termed baseline respiration, can influence the energetics of an ecosystem and its sensitivity to hypoxia. Direct studies of baseline respiration and its importance for coastal oxygen status are currently lacking. This study aims to obtain a first estimate of baseline respiration in a sub-arctic estuary, determine its contribution to annual plankton community respiration and identify the main carbon sources. The four different methods used to define baseline respiration converged on an average rate of 4.2 mmol O2 m-3 d-1 ± 0.1 (SE), corresponding to an annual contribution of 50 % of planktonic respiration on the basin scale. Respiration during the winter season (sporadic ice cover) was significant and comprised 25 % of annual pelagic respiration. No correlation between plankton respiration and phytoplankton production occurred on the intra-annual scale, while there was a weak exponential dependence on riverine total organic carbon inflow combined with phytoplankton production (i.e., major C input). Measured carbon sources could supply most (78 %) of the annual plankton respiration but only 39 % of the winter season respiration, suggesting some missing carbon sources. Nitrification had a negligible (≤ 2.4 %) effect on baseline respiration in the system. The results showed that baseline respiration could constitute a significant share of coastal plankton respiration, when allochthonous carbon sources dominate the carbon supply.

  • 3.
    Vikström, Kevin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom.
    Bartl, Ines
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wikner, Johan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Strong Influence of Baseline Respiration in an Oligotrophic Coastal Ecosystem2020In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 7, article id 572070Article in journal (Refereed)
    Abstract [en]

    Respiration is a key metabolic process in the marine environment and contemporary phytoplankton production (PhP) is commonly assumed the main driver. However, respiration in the absence of contemporary PhP, termed baseline respiration, can influence the energetics of an ecosystem and its sensitivity to hypoxia. Direct studies of baseline respiration are currently lacking. This study aims to obtain a first estimate of baseline respiration in a sub-arctic estuary and determine its contribution to plankton community respiration. Three approaches used to define baseline respiration determined the average rate to be 4.1 ± 0.1 (SE) mmol O2 m–3 d–1. A hypsographic model at the basin scale accounting for seasonal variation estimated an annual contribution of 30% baseline respiration to planktonic respiration. There was no correlation between plankton respiration and PhP, but a significant linear dependence was found with the total carbon supply from phytoplankton and riverine input. The sum of dissolved organic carbon transported by rivers, provided by both benthic and pelagic algae, could sustain 69% of the annual plankton respiration, of which as much as 25% occurred during winter. However, only 32% of the winter season respiration was explained, indicating that unknown carbon sources exist during the winter. Nitrification had a negligible (≤2.4%) effect on baseline respiration in the system. The results show that baseline respiration accounted for a significant percentage of coastal plankton respiration when allochthonous sources dominated the carbon supply, weakening the respiration-to- PhP relationship.

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  • 4.
    Vikström, Kevin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Tengberg, Anders
    Wikner, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Improved accuracy of optode‐based oxygen consumption measurements by removal of system drift and nonlinear derivation2019In: Limnology and Oceanography: Methods, E-ISSN 1541-5856, Vol. 17, no 3, p. 179-189Article in journal (Refereed)
    Abstract [en]

    This method evaluation aimed to improve the accuracy and precision of the previously published method to measure oxygen consumption using optodes with integrated temperature and salinity correction in dark incubations. Significant short‐term system drift currently requires a correction to remove the drift, thus reducing the precision of the oxygen consumption rates. Frequent nonlinear declines in oxygen concentration with time also call for improved data analysis and identification of its origin. Optodes in titanium casings (Aanderaa™ model 4330) with low oxygen binding properties showed no significant system drift in autoclaved seawater. Nonlinear oxygen dynamics fitting a quadratic polynomial occurred in 28% of 230 field samples, independent of season and water depth. Polynomial curve fit resulted in 64% higher respiration rates when derived within 1 h of the quality assured incubation, than obtained when using linear fit. Carbon substrate limitation explained the nonlinearity of oxygen decline during dark incubations. Pretreatment of the optode attached to stoppers with 0.3 mol dm−3 hydrochloric acid resulted in the most stable performance of the sensor and simultaneously provided proper cleaning of the equipment. A conservative detection limit of 0.97 μmol O2 dm−3 d−1 was calculated for the titanium optodes, matching other methods for oxygen consumption reported in the literature. Thus, we recommend the use of model 4330 optode pretreated with HCl and the derivation of initial respiration rates by a quadratic polynomial function for best accuracy and precision of oxygen consumption in oxygenated surface waters.

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  • 5.
    Vikström, Kevin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wikner, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Havets dolda andetag2019In: Havsutsikt, ISSN 1104-0513, no 2, p. 6-8Article in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Det råder syrebrist i haven. Stora pengar pumpas årligen in i åtgärder mot övergödning, i hopp om att lägre tillväxt av alger och växtplankton ska leda till att syrehalterna går upp igen. Men vår forskning visar att havssamhället inte slutar andas bara för att det växer långsammare. Snarare tvärtom.

  • 6.
    Vikström, Kevin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Wikner, Johan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Importance of Bacterial Maintenance Respiration in a Subarctic Estuary: a Proof of Concept from the Field2019In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 77, no 3, p. 574-586Article in journal (Refereed)
    Abstract [en]

    Bacterial respiration contributes to atmospheric carbon dioxide accumulation and development of hypoxia and is a critical, often overlooked, component of ecosystem function. This study investigates the concept that maintenance respiration is a significant proportion of bacterial respiration at natural nutrient levels in the field, advancing our understanding of bacterial living conditions and energy strategies. Two river-sea transects of respiration and specific growth rates were analyzed representing low- and highproductivity conditions (by in situ bacterial biomass production) in a subarctic estuary, using an established ecophysiological linear model (the Pirt model) estimating maintenance respiration. The Pirt model was applicable to field conditions during high, but not low, bacterial biomass production. However, a quadratic model provided a better fit to observed data, accounting for the maintained respiration at low μ. A first estimate of maintenance respiration was 0.58 fmol O2 day−1 cell−1 by the quadratic model. Twenty percent to nearly all of the bacterial respiration was due to maintenance respiration over the observed range of μ (0.21– 0.002 day−1 ). In the less productive condition, bacterial specific respiration was high and without dependence on μ, suggesting enhanced bacterial energy expenditure during starvation. Annual maintenance respiration accounted for 58% of the total bacterioplankton respiration based on μ from monitoring data. Phosphorus availability occasionally, but inconsistently, explained some of the remaining variation in bacterial specific respiration. Bacterial maintenance respiration can constitute a large share of pelagic respiration and merit further study to understand bacterial energetics and oxygen dynamics in the aquatic environment.

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  • 7.
    Wikner, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Haraguchi, Lumi
    Vikström, Kevin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kisand, Veljo
    Stedmon, Colin
    Carstensen, Jacob
    Coastal filter effect by microbial mineralization of riverine DOC in a sub-arctic river-estuary gradientManuscript (preprint) (Other academic)
    Abstract [en]

    The existence of a coastal filtering effect was studied in a 16 km boreal river-estuary system (RES) during contrasting low and high production conditions. Marked transformations occurred within 5 km (salinity 3) from the river mouth for many of the variables during high productive conditions. During the less productive season changes were small and occurred closer to the river mouth. Active transformation dominated the patterns detected in August (53 %), while mixing of river and coastal marine water was the dominant process in April. Bacterial community respiration was similar during both seasons averaging 2.6 μmol O2 dm-3 d-1, indicating efficient remineralization of riverine dissolved organic carbon (DOC). This was further reflected in a low and variable bacterial growth efficiency (BGE) with a mean of 12 % in the surface water at high productivity, but only 3 % at low productivity conditions. Bacterial community growth (BCG) showed strong relationship to water temperature at both seasons indicating energy limitation. Some indication of removal of nitrogen was observed, while no removal of phosphorus could be demonstrated. Phosphorus concentration showed a strong reciprocal power-function relationship to BCG, suggesting efficient assimilation of the limiting nutrient at carbon sufficiency. Marked spatial changes in diversity of phytoplankton, protozoa and bacterioplankton occurred at low salinities within 1 km from the river mouth. We conclude that this subarctic estuary acts as a coastal filter mainly by remineralizing riverine DOC to CO2.

  • 8.
    Wikner, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Larsson, Henrik
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF). Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Vikström, Kevin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Båmstedt, Ulf
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Berger, Stella A.
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
    Kyle, Mayers
    NORCE.
    Nejstgaard, Jens
    Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
    Report on boundary conditions for winter mesocosms2023Report (Other academic)
    Abstract [en]

    Ongoing climate change is projected to extend the warmer and therefore the biologically productive season, reducing ice cover, ice thickness, and quality, potentially influencing biodiversity, and productivity of aquatic ecosystems. Changed influence of dissolved organic matter is one factor that can contribute to those effects. Winter ecology is little studied, and the advancement of knowledge would benefit from controlled experiments on the mesocosm scale. To investigate the capability of mesocosm experimental infrastructures for winter ecological research, a 5-months long experiment during the sub-arctic winter in 2021/2022 was conducted in Umeå, Sweden. Simultaneously, the performance of an outdoor and indoor mesocosm facility with ice-forming capability at the same site was compared. Boundary conditions for hydrographic, chemical, and biological variables were determined.The facilities were operated successfully over winter and treatments caused similar effects in both systems, despite some differences presented below. Salinity and temperature were similar between the facilities throughout the experiment. Ice was markedly thicker on the sea compared to in the indoor facility. Further the ice inside the outdoor mesocosms, was significantly thicker than on the surrounding natural sea. Light irradiance indoors correlated with the outdoor facility, but light irradiance indoors could not reach the outside values in the lightest months of the experiment (after mid-March). Both dissolved organic carbon and dissolved nitrogen was higher in the outdoor facility, possibly caused by a pump effect increasing organic carbon and nitrogen concentrations. Most other nutrient levels remained similar. Chlorophyll-a was comparable between the facilities, while plankton respiration was twice the rate outdoors compared to indoors. Two substances were used to simulate browning, HuminFeed® (a commercially available leonardite) and soil extract, causing similar treatment effects in both facilities for 75% of measured variables. HuminFeed caused a marked increase in CDOM (coloured dissolved organic matter) and nitrite during spring. Treatment with soil extract resulted in slightly higher phosphorus concentrations.The indoor mesocosm facility was thus comparable to the outdoor facility regarding experimental effects, despite facility differences observed. The organic matter sources HuminFeed and soil extract differ in some experimental effects that need to be considered. These results should provide basic knowledge for improving experimental design in future winter mesocosm studies.

  • 9.
    Wikner, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Vikström, Kevin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Extensive prokaryotic maintenance respiration in the sea influenced by osmoregulation2023In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 10, article id 1070070Article in journal (Refereed)
    Abstract [en]

    Microbial respiration is the major process consuming oxygen in the biosphere. The relative energy demand from growth of biomass or maintenance activities determines the regulation of respiration with impact on how the development of hypoxia and CO2 emissions is controlled. This coupling is crucial for understanding the life history and associated ecological interactions of microorganisms. However, the knowledge of rate and regulating factors of maintenance respiration in the biosphere is limited. In this study, we demonstrated significant relationships in marine field samples where the prokaryotic specific growth rate predicts cell-specific respiration, in accordance with theory from culture models, over a 10-fold salinity range. This enables the first reported direct estimates of maintenance respiration in nature to show a 6-fold variation between 0.12-0.62 fmol O2 cell-1 d-1, comprising 29-72% of prokaryotic specific respiration. The lowest maintenance respiration occurred at salinity close to physiological osmolarity, suggesting osmoregulation as one of the more energy-consuming maintenance activities. A conservative global estimate of maintenance respiration accounted for 66% of the total prokaryotic respiration in the ocean´s mixed layer. This means that maintenance activities dominate the use of the energy generated by prokaryotic respiration in the sea, where osmoregulation is one significant energy consumer. Consequently, maintenance respiration and its regulation must be included in ecological and biogeochemical models to accurately project and manage the development of hypoxia and CO2 emissions from the ocean.

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  • 10.
    Wikner, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Vikström, Kevin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Ecology and Genetics, Limnology, Uppsala University, Uppsala, Sweden.
    Verma, Ashish
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Regulation of marine plankton respiration: a test of models2023In: Frontiers in Marine Science, E-ISSN 2296-7745, Vol. 10, article id 1134699Article, review/survey (Refereed)
    Abstract [en]

    Plankton respiration is a major process removing oxygen from pelagic environments and constitutes one of the largest oxygen transformations in the sea. Where the O2 supplies due to dissolution, advection and oxygenic photosynthesis are not sufficient, hypoxic, or anoxic waters may result. Coastal waters with limited water exchange are especially prone to have low oxygen levels due to eutrophication and climate change. To support marine environmental management in a period of rapid climate change, we investigated the current knowledge of regulating plankton respiration based on field and experimental studies reported in the literature. Models for regulation of plankton respiration was tested on a three-year field data set. Temperature is the most reported predictor positively influencing plankton respiration (mean r2 = 0.50, n=15). The organic carbon supply driven by primary production has a similar coefficient of determination but fewer reported relationships (mean r2 = 0.52, n=6). Riverine discharges of dissolved organic carbon can override the influence of primary production in estuaries precluding effects of nutrient reductions. The median predictions of respiration regulation produced by current models vary by a factor of 2 from the median of observed values and extreme values varied even more. Predictions by models are therefore still too uncertain for application at regional and local scales. Models with temperature as predictor showed best performance but deviated from measured values in some seasons. The combined dependence of plankton respiration on temperature, phytoplankton production and discharge of riverine organic carbon will probably lead to increased oxygen consumption and reduced oxygen levels with projected climate change. This will be especially pronounced where increased precipitation is expected to enhance riverine discharges of carbon compounds. The biologically mediated transfer of carbon for long-term storage in deeper layers will slow down. Implementation of plankton respiration measurements in long-term ecological monitoring programs at water body and basin scales is advocated, which would enable future multivariate analyses and improvements in model precision across aquatic environments.

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