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Physical control of primary production in a sub-arctic reservoir
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The first paper (Paper I) in this thesis treats autumn cooling in the Swedish lake Väsman. The water temperature is simulated using a one-dimensional lake model where the vertical mixing is calculated by a k - ɛ turbulence model. The heat exchange between the atmosphere and the lake is formulated in terms of heat fluxes. A great advantage with the actual heat flux formulation is that it requires only standard meteorological variables, which makes it possible to apply the model to arbitrary lakes. After the autumn cooling comes the winter season, which is described in Paper II. A simple ice model describing ice formation, growth and decay is incorporated into the lake model. Equations are derived for the insolation through snow and ice cover. Both ice and temperature during winter are simulated in a small lake with good results.

One-dimensional lake models may include the effect of horizontal pressure gradients, which changes the vertical velocity profile and thus the rate of vertical mixing. Equations describing the horizontal pressure gradients due to wind set-up in both homogeneous and two-layered lakes (Paper ill) are derived and verified against wind-induced entrainment in laboratory experiments and the water temperature development in lake Velen. Further studies of deeper lakes show that the deep water mixing, based only on the k - ɛ turbulence model, is too small. This is especially true during summer when thermal stratification inhibits the wind induced mixing to penetrate down into deeper layers. An empirical eddy viscosity, based on the buoyancy frequency N, is therefore incorporated into the model.

In Paper IV the model is applied to the Akkajaure reservoir, which has a maximum depth of 92m and a maximum surface area of 266 km2. The model is capable of simulating the seasonal water temperature cycle using standard meteorological data. Continuous simulations have been performed during the years 1998-2002 where the water temperature and ice data are verified against measurements. In the upper 40-50m the discrepancy is only 0.5-1.0 °C between measured and calculated water temperature. However in the bottom water it is not possible to verify the empirical eddy viscosity term because the temperature measurementsdid not cover this layer. From measurements and simulations Akkajaure is found to be more or less vertically homogeneous throughout the whole year, only a weak stratification exists during one to two summer weeks.

A Lagrangian particle dispersion model, coupled to the lake model, is used to explore the effects of vertical mixing on the primary production in the Akkajaure reservoir (Paper V). The particle model is used to describe the vertical movements of phytoplankton in the entire water column. The primary production of each phytoplankton cell is assumed to be a function of the ambient light (no nutrient limitations). A light model is describing the photosynthesis of each individual phytoplankton. The simulation of net production in Akkajaure is performed under realistic conditions during four different growth seasons. The main result is that the turbulence intensity controls the primary production in this sub-arctic reservoir and that the production during summertime increases as the turbulence intensity increases. This means that the primary production is larger in a relatively cold summer with a weak stratification (strong, deep reaching turbulence) compared to a warm, more stratified, summer with weak turbulence.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet , 2004. , 72 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 292
National Category
Social Sciences Interdisciplinary
Identifiers
URN: urn:nbn:se:liu:diva-29537Local ID: 14904ISBN: 91-7373-949-9 (print)OAI: oai:DiVA.org:liu-29537DiVA: diva2:250352
Public defence
2004-06-04, Sal Elysion, Hus-T, Universitetsområdet Valla, Linköping, 10:00 (Swedish)
Supervisors
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2014-09-03Bibliographically approved
List of papers
1. A Hydrodynamical Model for Calculating the Vertical Temperature Profile in Lakes During Cooling
Open this publication in new window or tab >>A Hydrodynamical Model for Calculating the Vertical Temperature Profile in Lakes During Cooling
1983 (English)In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 14, no 4, 239-254 p.Article in journal (Refereed) Published
Abstract [en]

A one-dimensional hydrodynamical model is used for simulating the vertical temperature profile in a lake during cooling conditions. The vertical mixing rate is calculated by solving the equations for turbulent kinetic energy, k, and dissipation of energy, ε. The heat exchange between the water and atmosphere consists of the radiation fluxes, sensible and latent heat flux. Temperature measurements from Lake Väsman during November-December, 1981, were used in the verification study. The agreement between calculated and measured temperature profiles is very good. This indicates that both the mixing processes and the net heat flux are well described in the model.

National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-78951 (URN)10.2166/nh.1983.019 (DOI)
Available from: 2012-06-26 Created: 2012-06-26 Last updated: 2017-12-07Bibliographically approved
2. Modelling the thermal regime of a lake during the winter season
Open this publication in new window or tab >>Modelling the thermal regime of a lake during the winter season
1988 (English)In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 15, no 2, 151-159 p.Article in journal (Refereed) Published
Abstract [en]

The thermal regime of a lake is investigated using both measured and numerically simulated data. The temperature measurements clearly demonstrate the importance of knowing the amount of short wave radiation that penetrates the ice-cover and the sediment heat flux from the lake bottom. However, the sediment/water coupling will not be treated in this study. In the numerical simulations a one-dimensional model is used, where the vertical exchange coefficient is calculated by a two-equation turbulence model. The meteorological forcing, which enters the model through the surface boundary conditions, is calculated on the basis of synoptic meterological observations every third hour. These boundary conditions are strongly affected by ice formation at the surface. Therefore, parameterizations of the initial ice formation and break-up and the ice growth and melting are included in the model. The amount of short wave radiation that reaches the ice/water interface is modelled in the following three steps: first, there is the snow or ice surface albedo, second, an absorption occurs in the upper 0.1 m of the ice and/or snow-cover, and third, the remaining radiation decays exponentially down to the ice/water interface.

The modelled initial ice formation and break-up together with the ice growth and melting are verified against measurements with satisfactory results. Also the calculated water temperature increase and its vertical structure are well described by the model.

National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-78950 (URN)10.1016/0165-232X(88)90061-4 (DOI)
Available from: 2012-06-26 Created: 2012-06-26 Last updated: 2017-12-07Bibliographically approved
3. Formulae for Pressure Gradients in One-Dimensional Lake Models
Open this publication in new window or tab >>Formulae for Pressure Gradients in One-Dimensional Lake Models
1989 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 94, no C4, 4939-4946 p.Article in journal (Refereed) Published
Abstract [en]

Formulae for barotropic and baroclinic pressure gradients, suitable for one-dimensional lake models, are derived and explored. The derivation is based on the equation for free standing oscillations and a continuity relation. The formulae, which are easy to derive and use, give the correct external and internal seiche frequencies for nonrotating, rectangular one- or two-layered basins of constant depth. When applied to situations with continuous stratification, further assumptions need to be introduced. These are discussed in the paper. Applications to a laboratory experiment, dealing with wind-induced entrainment, show that pressure gradients for the entrainment process are significant and that the pressure formulae derived capture this effect. The formulae are also used in combination with a one-dimensional lake model. Comparisons with field measurements of the seasonal stratification show that the inclusion of pressure gradients improves the predictive capabilities of the lake model.

National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-78949 (URN)10.1029/JC094iC04p04939 (DOI)
Available from: 2012-06-26 Created: 2012-06-26 Last updated: 2017-12-07Bibliographically approved
4. Physical modelling of the Akkajaure reservoir
Open this publication in new window or tab >>Physical modelling of the Akkajaure reservoir
2003 (English)In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 7, no 3, 268-282 p.Article in journal (Refereed) Published
Abstract [en]

This paper describes the seasonal temperature development in the Akkajaure reservoir, one of the largest Swedish reservoirs. It lies in the headwaters of the river Luleiilven in northern Sweden; it is 60 km long and 5 km wide with a maximum depth of 92 m. The maximum allowed variation in surface water level is 30 m. The temperature field in the reservoir is important for many biochemical processes. A one-dimensional lake model of the Akkajaure reservoir is developed from a lake model by Sahlberg (1983 and 1988). The dynamic eddy viscosity is calculated by a two equation turbulence model, a k-ε model and the hypolimnic eddy diffusivity formulation which is a function of the stability frequency (Hond o et al., 1993). A comparison between calculated and measured temperature profiles showed a maximum discrepancy of 0.5-1.0oC over the period 1999-2002. Except for a few days in summer, the water temperature is vertically homogeneous. Over that period of years, a weak stratification of temperature occurred on only one to two weeks a year on different dates in July and August. This will have biological consequences.

Keyword
temperature profile, reservoir, 1-D lake model, stratification. Sweden
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-78923 (URN)10.5194/hess-7-268-2003 (DOI)
Available from: 2012-06-25 Created: 2012-06-25 Last updated: 2017-12-07Bibliographically approved
5. Light limitation of primary production in high latitude reservoirs
Open this publication in new window or tab >>Light limitation of primary production in high latitude reservoirs
2005 (English)In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 9, no 6, 707-720 p.Article in journal (Refereed) Published
Abstract [en]

To explore the effects of vertical mixing on the primary production in a northern reservoir, a Lagrangian particle dispersion model was coupled to a 1-D reservoir model where the vertical mixing was calculated using a k - ε model together with an empirically-based deep-water eddy viscosity. The primary production of each phytoplankton cell is assumed to be a function of the ambient light and not to be nutrient limited. The photoadaption follows first-order kinetics where the photoadaptive variables, α, β, and Pm, describe the coefficients of the photosynthesis-irradiance curve. The model is applied to the northern reservoir Akkajaure, which is strongly regulated with a mean and maximum depth of 30 m and 100 m respectively. Based on the release of 1000 particles (plankton), the model calculated the mean primary production of each plankton, during four different growing seasons. Vertical mixing has a substantial effect on the vertical distribution of phytoplankton and, thus, on the primary production in a reservoir. It was found that primary production was greater in a cold summer with weak stratification than in a warm summer when the reservoir was more stratified. © EGU.

Keyword
photosynthesis, particle dispersion, mixing model, physical control, reservoir
National Category
Social Sciences Interdisciplinary
Identifiers
urn:nbn:se:liu:diva-30558 (URN)10.5194/hess-9-707-2005 (DOI)16146 (Local ID)16146 (Archive number)16146 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13Bibliographically approved

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