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Modelling organic matter dynamics in aquatic systems
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
2000 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic matter is a small but active part of the global carbon cycle. About one third is stored in the oceans where it has a relatively short residence time. The rest is found in the terrestrial biomass and in the soil. Aquatic systems exchange C02 with the atmosphere. Autotrophic organisms fix C02 into their biomass, while heterotrophic organisms respire C02 when utilising organic matter. Systems with large supply of organic matter by inflow can be net heterotrophic, which thus release more C02 than what they fix.

Two systems are studied, the Lake Ortrasket in northern Sweden and the Baltic Sea. In the Baltic primary production is the main source of organic matter, while in the lake dissolved organic matter from inflow dominates. Other characteristics of the Baltic Sea are that it is brackish and has a long residence time compared to the freshwater lake. These systems are studied with different types of models.

For the Baltic proper deep water, an inverse model of the water, salt and heat fluxes was used to estimate an oxygen budget including oxygen consumption. The oxygen levels in the Baltic proper deep water are critical due to the low supply and large consumption. The oxygen consumption is mainly due to organic matter degradation. The low oxygen and salinity levels in the Baltic have consequences for, among other things, the cod spawning success.

The lake model is a mechanistic model of dissolved organic carbon based on a Lagrangian fluid particle model and a one-dimensional physical model. The results show that Lake Ortrasket is a net heterotrophic system. In spite of the differences between the systems, both seems to have similar organic matter degradation rates, ~50 g C m-2 yr-1.

To supplement, time series of phosphate concentration were studied in the Baltic proper surface layer. These show seasonal variations coupled to the primary production, and this time dependence was modelled. The main purpose of the model is to complete corrupt observation time series, which is useful for environmental model studies.

Place, publisher, year, edition, pages
Motala: Kanaltryckeriet , 2000. , 77 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 214
Keyword [sv]
Vatten, Kol, Oceanografi, Hydrologi
National Category
Social Sciences Interdisciplinary
Identifiers
URN: urn:nbn:se:liu:diva-32133Local ID: 17993ISBN: 91-7219-825-7 (print)OAI: oai:DiVA.org:liu-32133DiVA: diva2:252955
Public defence
2000-09-22, Hörsal Planck, Fysikhuset, Universitetsområdet Valla, Linköping, 10:00 (Swedish)
Supervisors
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-08-27Bibliographically approved
List of papers
1. Statistical modelling of the phosphate variations in the Baltic proper
Open this publication in new window or tab >>Statistical modelling of the phosphate variations in the Baltic proper
1997 (English)In: Boreal environment research, ISSN 1239-6095, Vol. 2, no 3, 303-315 p.Article in journal (Refereed) Published
Abstract [en]

A statistical model of the variation of phosphate concentration in the upper layers of the Baltic proper was formed, with the aim of studying the magnitude of this variation and to be able to adjust corrupted time series. The large variation observed is only partially explained by seasonal variations and geographical structures. Despite inclusion of longterm trends and annual variations, the residuals showed a substantial correlation within and between the time series.

Keyword
statistical modelling, phosphate, Baltic Sea
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30633 (URN)16227 (Local ID)16227 (Archive number)16227 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-07-09Bibliographically approved
2. Changes in apparent oxygen removal in the Baltic proper deep water
Open this publication in new window or tab >>Changes in apparent oxygen removal in the Baltic proper deep water
2000 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 25, no 3-4, 421-429 p.Article in journal (Refereed) Published
Abstract [en]

By developing a steady state diagnostic model for a stratified deep-water mass, one is able to quantify both the mass flows and apparent oxygen removal in the Baltic proper deep water. The model is based on continuity of the assumed conservative observable volume, salinity and temperature. Second degree polynomials are fitted to observed vertical profiles of temperature as well as oxygen concentration to give a functional correspondence with the used spatial variable salinity. These relations are used in the model that calculate the water flows, oxygen flows and oxygen removal during four periods between 1959 and 1997. The model forms a boundary value problem, which is solved with a finite difference scheme. The model seems to give reasonable estimates of the flows. The oxygen removal is mainly balanced by inflow of oxygen with incoming water. The oxygen consumption is 4-8 ╡1 O2 1-1 day -1, which corresponds to a degradation of organic matter in the range 30-60 g C m-2 year-1. (C) 2000 Elsevier Science B.V.

Keyword
oxygen, modelling, Baltic Sea
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30618 (URN)10.1016/S0924-7963(00)00031-2 (DOI)16210 (Local ID)16210 (Archive number)16210 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-07-09Bibliographically approved
3. Long term changes in spawning volume for Baltic Sea cod (Gadus morhua)
Open this publication in new window or tab >>Long term changes in spawning volume for Baltic Sea cod (Gadus morhua)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In the brackish Baltic Sea, cod (Gadus morhua) can reproduce only in a few deep areas, of which the Eastern Gotland basin and the Bornholm basin are the most important ones. Successful spawning requires oxygen concentrations larger than 2 ml r-1 and salinity larger than 11. The water domain that meets these requirements is referred to as the cod spawning volume. Salinity and oxygen data were collected during the period 1905-1997 and 1923-1997 from the Eastern Gotland basin and the Bornholm basin respectively. They have been analysed for changes in spawning volume over time. For each sampling occasion the spawning volume was calculated based on depth specific vertical distribution of salinity and oxygen concentration, combined with bathymetric data. The Bornholm basin constitutes a stable but limited spawning area for cod, contrary to the Eastern Gotland basin where the spawning volume is more uncertain but can be much larger. The estimated spawning volume decreased over time in the Eastern Gotland basin. This change is probably caused by increased deepwater oxygen demand due to increased organic material load from primary production. The latter is an effect of the ongoing eutrophication.

Keyword
cod, spawning volume, Baltic Sea
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-79296 (URN)
Available from: 2012-07-09 Created: 2012-07-09 Last updated: 2012-07-09Bibliographically approved
4. Modelling dissolved organic carbon turnover in humic Lake Örträsket, Sweden.
Open this publication in new window or tab >>Modelling dissolved organic carbon turnover in humic Lake Örträsket, Sweden.
Show others...
2001 (English)In: Environmental Monitoring & Assessment, ISSN 0167-6369, E-ISSN 1573-2959, Vol. 6, no 3, 159-172 p.Article in journal (Refereed) Published
Abstract [en]

The organic carbon balance of a lake with high input of allochthonous organic carbon is modelled integrating physical, chemical and biological processes. The physical model captures the behaviour of real thermal stratification in the lake for different flow situations during the period 1993–1997. The dissolved organic carbon model is based on simulated trajectories of water parcels. By tracking parcels, account is kept of environmental factors such as temperature and radiation as well as DOC quality for each parcel. The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the lake amounts to 1.5–2.5 mg C l–1 yr–1, where photooxidation is responsible for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclusion is that the model with the selected parameterisations of the degradation processes reasonably well describes the DOC dynamics in a forest lake.

Keyword
humic substances, modelling
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30604 (URN)10.1023/A:1011953730983 (DOI)16195 (Local ID)16195 (Archive number)16195 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-07-09Bibliographically approved
5. Uncertainty and sensitivity analyses of a model of dissolved organic carbon in a lake
Open this publication in new window or tab >>Uncertainty and sensitivity analyses of a model of dissolved organic carbon in a lake
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Uncertainty and sensitivity analyses have been performed on a lake model describing the dissolved organic carbon (DOC) turnover in a humic lake. The DOC model is based on a Lagrangian dispersion model where trajectories of fluid particles, representing DOC containing water parcels, are simulated. Thus the history of the individual parcel influences its present degradation and DOC concentration. Together the parcels describe the DOC concentration of the lake. A Monte Carlo simulation based on a random sampling of DOC input parameters was used for the analyses. The results were studied one day a monthbetween May 1993 and December 1997. The mean DOC concentration (9-13 mg C L"1) has a range of about 2 mg C L-1 and a coefficient of variation (CV) of 2-4%. That is rather large, but still less than the variability of the input parameters. The daily mean degradation variables (bacterial degradation and photooxidation) had larger variability (CV approx. 20%). Different methods were combined to give multiple views of the sensitivity: scatter plots, the chosen parameters in stepwise regression, and the parameters in multiple linear regression with high partial correlation coefficient and/or high standardised coefficient. In addition, both ordinary and rank based multiple linear regression were used. The combined methods show that the mean DOC concentration in the lake is most sensitive to primary production and bacterial degradation rate, while bacterial degradation and photooxidation are most sensitive to bacterialdegradation rate and the attenuation rate of light respectively. Both seasonal and annual variations in sensitivity indices were found for mean DOC concentration revealing a flow dependence of the crucial parameters. Overall, the DOC model would benefit most from a better estimation of bacterial degradation rate, a better model for primary production, and a better determination of DOC concentration of inflow.

Keyword
uncertainty analysis, sensitivity analysis, Monte Carlo simulation, lake model, dissolved organic carbon
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-79297 (URN)
Note
Short title: Sensitivity of a Doc ModelAvailable from: 2012-07-09 Created: 2012-07-09 Last updated: 2012-07-09Bibliographically approved
6. Model simulation of the effects of climate change and river regulation on a humic lake
Open this publication in new window or tab >>Model simulation of the effects of climate change and river regulation on a humic lake
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Allochthonous dissolved organic matter (DOM) plays an important role in the food web of boreal lakes in the temperate zone by providing energy and nutrients (Tranvik, 1992). It also governs environmental conditions like light attenuation of the water mass (Schindler et al., 1996). Allochthonous DOM is together with primary production the primary carbon source of the food web in these lakes. In some lakes rich in humic substances (HS), DOM is more important than the primary production for the microbial production (e.g. Jansson et al., 1999).

However, our knowledge about fate and kinetics of the terrestrial DOM and thus TOC (total organic carbon) is poor. In spite of this, it has important implications for the terrestrial and marine ecosystems as well as the global carbon cycle. The role of rivers and lakes in this degradation process has been studied in the past and one result is that only those systems with long hydraulic residence time may significantly alter the TOC composition and concentration (Curtis, 1998; Pers et al., 2000). In fact, peat and sediments in lakes and coastal waters represent the only significant long-term carbon sinks in the ecosystem of northern Scandinavia (Erikssson, 1991 ). The riverine organic matter that escapes these systems will be most likely degraded in the marine environment. In fact, of the annual sedimentation of roughly 20 g C m·' yr·' in the Bothnian Bay, up to 90% may be remineralised, the carbon is probably released as COz, and only about 2 g C m·' yr'1 is assumed to be sequestered (Eimgren, 1984). These figures support a rapid decomposition of terrestrial humic substances in the marine environment. Also, Carlsson and Graneli (1993) have shown that organic bound nitrogen in humic substances may enhance marine phytoplanktongrowth. Thus the humic substances support the marine production in this Bay.

National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-79298 (URN)
Available from: 2012-07-09 Created: 2012-07-09 Last updated: 2012-07-09Bibliographically approved

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