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Nitrogen fixation in the Baltic proper: An empirical study
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.
Department of Systems Ecology, Stockholm University, Stockholm, Sweden.
2000 (English)In: Journal of Marine Systems, ISSN 0924-7963, Vol. 25, no 3-4, 239-248 p.Article in journal (Refereed) Published
Abstract [en]

Nitrogen as the limiting nutrient for primary production in the eutrophic Baltic proper has been under debate. Based on only a limited number of actual measurements, nitrogen fixation has been assumed to be the only significant internal nitrogen source. It is then assumed that about one fifth of the net nitrogen load to the Baltic proper comes from nitrogen fixation by cyanobacteria. An alternative or additional source is utilisation of dissolved organic nitrogen (DON).

In the present study, we hypothesise that nitrogen fixation is the only internal source for inorganic nitrogen. This was done in order to investigate its potential to maintain net primary production during summer. If inorganic nitrogen is depleted after the spring bloom and if inorganic phosphorus still remains in significant concentrations, then a continuous decrease in phosphorus may be coupled to the net nitrogen fixation rate by cyanobacteria. The estimated phosphorus consumption is adjusted for external and internal inputs. An estimate of the assumed net annual nitrogen fixation based on the proper Redfield ratio in the surface layer down to the seasonal thermocline is calculated for a number of monitoring stations in the Baltic proper. Typical values of nitrogen fixation are in the range 10–130 μmol m−3 day−1. A simple integration over the Baltic proper gives an internal load in the range 30–260×103 ton N year−1. Another result is an east–west gradient in fixation rate that may reflect the nitrogen load.

Place, publisher, year, edition, pages
2000. Vol. 25, no 3-4, 239-248 p.
Keyword [en]
nitrogen fixation, cyanobacteria, Baltic proper, eutrophication
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-13423DOI: 10.1016/S0924-7963(00)00018-XOAI: oai:DiVA.org:liu-13423DiVA: diva2:20698
Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2009-05-29
In thesis
1. Model Studies of Surface Waves and Sediment Resuspension in the Baltic Sea
Open this publication in new window or tab >>Model Studies of Surface Waves and Sediment Resuspension in the Baltic Sea
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wave heights and periods of surface waves in the Baltic Sea have been modelled for a two-year period (1999-2000) with the wave model Hypas on an 11x11-km grid scale. There is a clear seasonal variation with higher waves during winter and lower during summer. This is mainly a reflection of the wind climate in the area where the winters are windier than the summers. The largest waves are found in the Skagerrak and over the deeper, eastern areas in the Baltic Proper.

In the Baltic Sea, the surface waves influence the bottom sediment by initiating resuspension down to 80 m depths. This process is dependent not only on the waves but also on the varying grain size diameters. Fine and medium sand resuspend more often than other sediment types, and these sediments cover together about 25% of the Baltic Proper area. On average sediment is here resuspended 4-5 times per month with a duration for each event of 22 hours. The highest resuspension frequencies are found on the eastern and southern side of the Baltic Proper.

During resuspension sediment grains are lifted up into the water mass and matters earlier bound in the sediment can be released. This may stimulate both production and degradation of organic matter.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2005. 49 p.
Series
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 332
Keyword
Surface waves, Wave model, Wave friction velocity, Resuspension, Sediment dynamics, Nitrogen fixation, Baltic Sea, Havsvågor, Östersjön, Oceanografi, Sediment
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:liu:diva-4680 (URN)91-85299-94-4 (ISBN)
Public defence
2005-09-23, Elysion, Hus T, Campus Valla, Linköpings universitet, Linköping, 10:00 (English)
Opponent
Supervisors
Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2014-09-22Bibliographically approved
2. The Baltic Sea Wave Field: Impacts on the Sediment and Biogeochemistry
Open this publication in new window or tab >>The Baltic Sea Wave Field: Impacts on the Sediment and Biogeochemistry
2002 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The wave field in the Baltic Sea has been modelled for a two-year period with the spectral wave model HYPAS. There is a large seasonal variation in the field and a minor annual one, both reflect the wind variation in the area. Since the Baltic Sea is fetch limited, the dominant wind direction is important for the maximum wave heights.

By studying the modelled wave energy density in combination with bottom type maps, the effect of the wave field on the sediment surface is examined. Up to half the bottoms in the Baltic Sea are affected ~25% of the time. A statistical relation between wave energy density and bottom types is found for the Gulf of Riga, but in the rest of the area the sediment maps were to coarse. It is, due to this, not possible to say if the result is valid for the whole area or if it is site specific.

During resuspension events the remineralisation is increased since deposited organic material is reintroduced into the watermass and there exposed to higher levels of oxygen. This process could act as an increased regional source of nitrogen in nutrient budgets and thus influence the conditions for nitrogen fixation and perhaps explain some of the geographical differences in the nitrogen fixation rates.

Place, publisher, year, edition, pages
Tema vatten i natur och samhälle, 2002. 23 p.
Series
Tema V report (online), ISSN 1652-4268 ; 27
Keyword
Hydraulic engineering, HYPAS; Wave modelling; Significant wave height; Wave energy, Vattenteknik
National Category
Water Engineering
Identifiers
urn:nbn:se:liu:diva-5565 (URN)91-7373-249-4 (ISBN)
Presentation
2002-01-21, 00:00 (English)
Available from: 2004-02-16 Created: 2004-02-16 Last updated: 2009-03-02

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Rahm, LarsJönsson, Anette

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