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Uncertainty and sensitivity analyses of a model of dissolved organic carbon in a lake
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]

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 [en]
uncertainty analysis, sensitivity analysis, Monte Carlo simulation, lake model, dissolved organic carbon
National Category
Social Sciences Interdisciplinary
URN: urn:nbn:se:liu:diva-79297OAI: diva2:540287
Short title: Sensitivity of a Doc ModelAvailable 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.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 214
Vatten, Kol, Oceanografi, Hydrologi
National Category
Social Sciences Interdisciplinary
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)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-08-27Bibliographically approved

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