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Anoxic degradation of organic matter in lakes: implications for carbon cycling and aquatic food webs
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Considerable evidence from laboratory studies and marine environments suggests that degradation of organic matter (OM) is restricted under anoxic conditions compared to when molecular oxygen (O2) is present. However, other studies contradict this view since they found similar OM degradation rates and bacterial growth rates under both oxic and anoxic conditions in aquatic environments. Studies from freshwater environments are rare, and have been primarily based on bacterial production estimates. Anoxic degradation of OM in lakes is commonly considered to be slow and of little importance for overall lake food webs compared to oxic degradation. The present thesis and the work it is based on challenge this view. First, the performance of a commonly used method to measure bacterial production was tested in both oxic and anoxic lake water. Then, the oxic and anoxic potentials of bacterial growth and OM mineralization were compared in lake water and sediment. In addition, I assessed the potential of carbon transfer from methane (CH4; i.e. an end-product of anoxic degradation) to pelagic food webs. Three methods for measuring water column methane oxidation were evaluated. Then, the potential transport of methane carbon into the microbial community via methane oxidation, and further -up the food web- into the zooplankton community was estimated. Results indicate 1) that OM degradation and bacterial growth may be similar in oxic and anoxic lake environments, 2) that OM characteristics may be more important for the mineralization than the O2 regime per se in the short term (daysweeks), and 3) that methane can be a significant source of carbon and energy for pelagic food webs. This suggests that the anoxic carbon metabolism may be extensive and potentially important for pelagic organisms in many lakes.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2002. , 55 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 262
Keyword [sv]
Ekonsystem i vatten
National Category
Social Sciences Interdisciplinary
Identifiers
URN: urn:nbn:se:liu:diva-29575Local ID: 14951ISBN: 91-7373-436-5 (print)OAI: oai:DiVA.org:liu-29575DiVA: diva2:250391
Public defence
2002-11-01, Sal Elysion, Hus-T, Universitetsområdet Valla, Linköping, 10:00 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-08-29Bibliographically approved
List of papers
1. The leucine incorporation method estimates bacterial growth equally well in both oxic and anoxic lake waters
Open this publication in new window or tab >>The leucine incorporation method estimates bacterial growth equally well in both oxic and anoxic lake waters
2001 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 67, no 7, 2916-2921 p.Article in journal (Refereed) Published
Abstract [en]

Bacterial biomass production is often estimated from incorporation of radioactively labeled leucine into protein, in both oxic and anoxic waters and sediments. However, the validity of the method in anoxic environments has so far not been tested. We compared the leucine incorporation of bacterial assemblages growing in oxic and anoxic waters from three lakes differing in nutrient and humic contents, The method was modified to avoid O-2 contamination by performing the incubation in syringes. Isotope saturation levels in oxic and anoxic waters were determined, and leucine incorporation rates were compared to microscopically observed bacterial growth. Finally, we evaluated the effects of O-2 contamination during incubation with leucine, as well as the potential effects of a headspace in the incubation vessel, isotope saturation occurred at a leucine concentration of above about 50 nM in both ode and anoxic waters from all three lakes. Leucine incorporation rates were linearly correlated to observed growth, and there was no significant difference between oxic and anoxic conditions. O-2 contamination of anoxic water during I-h incubations with leucine had no detectable impact on the incorporation rate, while a headspace in the incubation vessel caused leucine incorporation to increase in both anoxic and O-2-contaminated samples. The results indicate that the leucine incorporation method relates equally to bacterial growth rates under oxic and anoxic conditions and that incubation should be performed without a headspace.

National Category
Social Sciences
Identifiers
urn:nbn:se:liu:diva-49209 (URN)10.1128/​AEM.67.7.2916-2921.2001 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12Bibliographically approved
2. Similar bacterial growth on dissolved organic matter in anoxic and oxic lake water
Open this publication in new window or tab >>Similar bacterial growth on dissolved organic matter in anoxic and oxic lake water
2001 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 24, no 1, 41-49 p.Article in journal (Refereed) Published
Abstract [en]

Anoxic metabolism yields less energy per unit substrate utilized than oxic respiration. In addition, substrate availability is believed to be reduced under anoxic conditions since oxygenases cannot be used. Consequently, it is generally assumed that bacteria grow slower in anoxic environments than in oxic environments. The results of the present study challenge this view. We compared the growth of bacterial assemblages under carbon-limited conditions in lake water under anoxic and oxic conditions. Bioassay experiments were performed with water from 3 lakes differin9 in nutrient concentrations and organic matter content. Amon9 bacteria usin9 the same source of organic matter, median anoxic growth rates were 84 to 110% of oxic growth rates. The total biomass yield durin9 the experiments did not differ between anoxic and oxic treatments. We suggest that anoxic bacterial growth was regulated by substrate availability rather than by metabolic energy yield and that availability of organic matter under anoxic conditions was equal to or even greater than that in oxic treatments. This implies that anoxic decomposition rates may actually have been faster than oxic rates.

Keyword
DOC, DOM, Anaerobic degradation, Bacteria
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-31046 (URN)10.3354/ame024041 (DOI)16755 (Local ID)16755 (Archive number)16755 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13Bibliographically approved
3. Simultaneous measurements of organic carbon mineralization and bacterial production in oxic and anoxic lake sediments
Open this publication in new window or tab >>Simultaneous measurements of organic carbon mineralization and bacterial production in oxic and anoxic lake sediments
2003 (English)In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 46, no 1, 73-82 p.Article in journal (Refereed) Published
Abstract [en]

Based on work in marine sediments it can be hypothesized that (i) overall OM mineralization depends on the enzymatic capacity and is largely independent from the energy yield, (ii) similar oxic and anoxic rates are expected for fresh OM, while oxic rates should be faster for old OM that is partially degraded or adsorbed to particles, and (iii) that the thermodynamic energy yield does not regulate mineralization, but primarily determines the energy fraction allocated to bacterial production (BP). We addressed these hypotheses by simultaneous measurements of mineralization rates (MR) and BP in sediments from a eutrophic lake, along with MR measurements in sediments of a dystrophic lake. Anoxic MR were 44 and 78% of oxic MR in the eutrophic and dystrophic lake, respectively, which was always higher than expected given the theoretical energy yields. The BP:MR ratio was 0.94 and 0.24 in the oxic and anoxic treatments, respectively, in accordance with the expected energy yields. Thus, the results support all three hypotheses above. We also critically discuss BP measurements in sediments and suggest that bacterial growth efficiency values from simultaneous MR and BP measurements can be used to evaluate the reliability of BP estimates.

National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30668 (URN)10.1007/s00248-002-1061-9 (DOI)16268 (Local ID)16268 (Archive number)16268 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13Bibliographically approved
4. Measurement of methane oxidation in lakes: A comparison of methods
Open this publication in new window or tab >>Measurement of methane oxidation in lakes: A comparison of methods
2002 (English)In: Environmental Science & Technology, ISSN 0013-936X, Vol. 36, no 15, 3354-3361 p.Article in journal (Refereed) Published
Abstract [en]

Methane oxidation in lakes constrains the methane emissions to the atmosphere and simultaneously enables the transfer of methane carbon to pelagic food webs, Several different methods have been used to estimate methane oxidation, but these methods have not previously been compared. In this study, we present methane oxidation estimates from three different lakes during summer and winter, using methods based on the transformation of added (CH4)-C-14, the fractionation of natural methane C-13, and the mass balance modeling of concentration gradients, All methods yielded similar results, including similar differences between lakes and seasons. Average methane oxidation rates varied from 0.25 to 81 mg of C m(-2) d(-1) and indicate that the three methods are comparable, although they to some extent take different processes into account. Critical issues as well as drawbacks and advantages with the used methods are thoroughly discussed. We conclude that methods using the stable isotope or mass balance modeling approach represent promising alternatives, particularly for studies focusing on ecosystem-scale carbon metabolism.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2002
National Category
Physical Geography
Identifiers
urn:nbn:se:liu:diva-28226 (URN)10.1021/es010311p (DOI)000177242600043 ()2-s2.0-0036667658 (Scopus ID)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-02-09Bibliographically approved
5. Methane as a source of carbon and energy for lake pelagic food webs
Open this publication in new window or tab >>Methane as a source of carbon and energy for lake pelagic food webs
2003 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 84, no 4, 969-981 p.Article in journal (Refereed) Published
Abstract [en]

Water-column methane oxidation can represent a substantial carbon transformation pathway in lakes, and circumstantial evidence indicates that methane may be a potentially important source of carbon for pelagic food webs. We estimated methanotrophic bacterial production (MBP), methanotrophic bacterial growth efficiency (MBGE), heterotrophic bacterial production (HBP), primary production (PP), and the relative contribution of methanotrophic bacteria to overall bacterial biomass in three very different lakes during summer and winter. In addition, we measured stable carbon isotope ratios in particulate organic matter (POM), surface sediments, zooplankton, and methane. MBP corresponded to 0.3-7% of the organic C production by primary producers, and 0.5-17% of HBP during summer. During winter, MBP was 3-120% of HBP. MBP generally dominated the heterotrophic bacterial production at greater depths. Methanotrophic biomass was 3-11% of total bacterial biomass on a depth-integrated basis. Zooplankton were generally more depleted in 13C than POM. If phytoplankton d13C signatures were -35 to -30ë, such as the POM signals, observed zooplankton signatures could be explained by a fraction of 5-15% methanotrophic bacteria in their diet. The results indicate that methanotrophic bacteria can provide a significant food source for zooplankton, and that methane oxidation represents a potentially important benthic-pelagic carbon and energy link in many lakes, particularly during winter.

Keyword
aquatic food webs, bacterial growth efficiency, carbon cycling, methane, as source of C and energy in lake food webs, methane oxidation, methanotrophic bacteria, stable isotopes, Swedish lakes, zooplankton
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30671 (URN)10.1890/0012-9658(2003)084[0969:MAASOC]2.0.CO;2 (DOI)16272 (Local ID)16272 (Archive number)16272 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13Bibliographically approved

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