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Model simulation of the effects of climate change and river regulation on a humic lake
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
(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: urn:nbn:se:liu:diva-79298OAI: oai:DiVA.org:liu-79298DiVA: diva2:540289
Available from: 2012-07-09 Created: 2012-07-09 Last updated: 2012-07-09Bibliographically approved
In thesis
1. Modelling organic matter dynamics in aquatic systems
Open this publication in new window or tab >>Modelling organic matter dynamics in aquatic systems
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
Vatten, Kol, Oceanografi, Hydrologi
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-32133 (URN)17993 (Local ID)91-7219-825-7 (ISBN)17993 (Archive number)17993 (OAI)
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

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Rahm, Lars

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