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Dominant Hydro-Climatic Drivers of Water Temperature, Salinity, and Flow Variability for the Large-Scale System of the Baltic Coastal Wetlands
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
Stockholm Univ, Bolin Ctr Climate Res, Dept Phys Geog, S-10691 Stockholm, Sweden..
Stockholm Univ, Bolin Ctr Climate Res, Dept Phys Geog, S-10691 Stockholm, Sweden..
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
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2019 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 11, no 3, article id 552Article in journal (Refereed) Published
Abstract [en]

For the large-scale coastal wetland system of the Baltic Sea, this study develops a methodology for investigating if and to what degree the variability and changes in certain hydro-climatic drivers control key coastal-marine physical conditions. The studied physical conditions include: (a) water temperature, (b) water salinity, and (c) flow structures (magnitudes and directions of flows between marine basins and the associated coastal zones and wetlands). We use numerical simulations of three hydro-climatically distinct cases to investigate the variations in hydro-climatic drivers and the resulting physical conditions (a-c) among the cases. The studied hydro-climatic forcing variables are: net surface heat flux, wind conditions, saltwater influx from the North Sea, and freshwater runoff from land. For these variables, the available observation-based data show that the total runoff from land is significantly and positively correlated with precipitation on the sea itself, and negatively correlated with saltwater influx from the North Sea to the Baltic Sea. Overall, the physical condition (a-c) variability in the Baltic Sea and its coastal zones is found to be pairwise well-explained by simulation case differences as follows: (a) Net heat flux is a main control of sea water temperature. (b) Runoff from land, along with the correlated salt water influx from the North Sea, controls average sea salinity; with the variability of local river discharges shifting some coastal zones to deviate from the average sea condition. (c) Wind variability and change control the Baltic Sea flow structure, primarily in terms of flow magnitude and less so in terms of flow direction. For specific coastal wetland zones, considerable salinity differences from average Baltic Sea conditions (due to variability in local river discharges) are found for the coasts of Finland and Estonia, while the coastal wetland zones of south-eastern Sweden, and of Estonia and Latvia, emerge as particularly sensitive to wind shifts.

Place, publisher, year, edition, pages
MDPI , 2019. Vol. 11, no 3, article id 552
Keywords [en]
coastal wetlands, Baltic sea, hydro-climatic variability and change, physical sea changes, FVCOM
National Category
Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-251352DOI: 10.3390/w11030552ISI: 000464534200002Scopus ID: 2-s2.0-85065024420OAI: oai:DiVA.org:kth-251352DiVA, id: diva2:1316804
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2020-02-18Bibliographically approved
In thesis
1. Land-Sea Interactions in the Coastal-Marine System of the Baltic Sea under Hydro-Climatic Variability
Open this publication in new window or tab >>Land-Sea Interactions in the Coastal-Marine System of the Baltic Sea under Hydro-Climatic Variability
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates a few important component processes for understanding and quantifying eutrophication in the Baltic Sea, that include characterization of nutrient loadings from land, water flow in the sea under changing climate conditions and transport of solutes originating from different locations along the coast. Furthermore, this study aims to improve our understanding on how processes from land (the nutrient loading conditions) and the sea (transport dynamics and water quality) couple to determine the fate of nutrients in the sea and the water quality in a selected localized coastal area, the Himmerfjärden Bay.

Comprehensive data are compiled as a basis for numerical simulations. An open source tool for oceanographic studies FVCOM is used to simulate flow and transport processes in the Baltic Sea. Hydrodynamic simulations are verified in terms of temperature, salinity and water level for the year 2005. Results show that most of the investigated Swedish watersheds along the coastline are dominated by subsurface legacy sources, the loads of which are positively and linearly correlated with river discharges. Moreover, subsurface legacy sources are less likely to decrease over time compared with the current surface sources. The Baltic Sea has a stable flow structure considering flux directions between basins, while the flux magnitudes between basins are mainly determined by different wind conditions. The spreading patterns in the sea with solute released from different coastal areas are similar when the released amounts are comparable, even though different cases have different source input and water flow conditions. The overall spreading patterns in the sea are generally dominated by the total mass of released solute. Local transport dynamics and patterns around the coast differ greatly for different cases and are determined by the local flow conditions. Different water quality indicators are influenced by different land-based or sea-based measures for water quality improvement. The dry-cold hydro-climatic condition is the most favorable for improving the water quality and elevating the ecological status in the Himmerfjärden Bay.

Based on this investigation, varying hydro-climatic factors impose important influence on the different component processes of nutrient loading from land to the sea. For example, the change of river discharges from land in the future would influence the total load into the sea from subsurface legacy sources, and finally influence the general spreading patterns of nutrients in the sea. The change of wind conditions would affect the flow and transport dynamics at local scale and flow fluxes magnitudes between marine basins at the sea scale. Change towards a dry-cold condition would be beneficial for the water quality and lead to improvement of coastal water quality, while the change towards a wet-warm condition will be generally unfavorable for improving the water quality. Clearly more comprehensive studies are needed based on the component processes considered in this thesis, for mapping water quality and eutrophication long-term trends in the Baltic Sea with confidence that is sufficient for effective mitigation measures and policies. 

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2020. p. 45
Series
TRITA-ABE-DLT ; 204
Keywords
Baltic Sea, nutrient loads, hydro-climatic variability, hydrodynamics, solute transport, water quality.
National Category
Oceanography, Hydrology and Water Resources Water Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-268361 (URN)978-91-7873-458-0 (ISBN)
Public defence
2020-03-16, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2020-02-21 Created: 2020-02-18 Last updated: 2020-02-21Bibliographically approved

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Chen, YuanyingCvetkovic, Vladimir

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