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Satellite-based water quality monitoring for improved spatial and temporal retrieval of chlorophyll-a in coastal waters
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2015 (English)In: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 158, p. 417-430Article in journal (Refereed) Published
Abstract [en]

The coastal zones are the most inhabited areas of the world and are therefore strongly affected by humans, leading to undesirable environmental changes that may alter the ecosystems, such as eutrophication. In order to evaluate changes in the environment an effective water quality monitoring system for the coastal zones must be in place. The chlorophyll-a concentration is commonly used as a proxy for phytoplankton biomass and as indicator for eutrophication and it can be retrieved from ocean colour remote sensing data. Several operational monitoring systems based on remote sensing are in place to monitor the open sea and, to some extent, the coastal zones. However, evaluations of coastal monitoring systems based on satellite data are scarce. This paper compares the chlorophyll-a concentrations retrieved from an operational satellite system based on MERIS (Medium Resolution Imaging Spectrophotometer) data with ship-based monitoring for the productive seasons in 2008 and 2010, in a coastal area in the Baltic Sea. The comparisons showed that the satellite-based monitoring system is reliable and that the estimations of chlorophyll-a concentration are comparable to in situ measurements in terms of accuracy and quantitative retrieval. A very strong correlation was found between measurements from satellite-derived chlorophyll-a compared to in situ measurements taken close in time (0-3 days), with RMSE of 64% and a MNB of 17%. The comparison of the monthly means showed improved RMSE and a MNB of only 8%. Furthermore, this study shows that MERIS is better at capturing spatial dynamics and the extent of phytoplankton blooms than ship-based monitoring, since it has a synoptic view and higher temporal resolution. Satellite-based monitoring also increases the frequency of chlorophyll-a observations considerably, where the degree of improvement is dependent on the sampling frequency of the respective monitoring programme. Our results show that ocean colour remote sensing can, when combined with field sampling, provide an improved basis for more effective monitoring and management of the coastal zone. These results are important for eutrophication assessment and status classifications of water basins and can be applied to a larger extent within national and international agreements considering the coastal zones, e.g. the European Commission's Water Framework Directive.

Place, publisher, year, edition, pages
2015. Vol. 158, p. 417-430
Keyword [en]
Water quality assessment, Chlorophyll-a, Coastal zone, MERIS, Eutrophication, Monitoring, Management, Remote sensing
National Category
Earth and Related Environmental Sciences
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-115272DOI: 10.1016/j.rse.2014.11.017ISI: 000348879100030OAI: oai:DiVA.org:su-115272DiVA, id: diva2:799812
Note

AuthorCount:3;

Available from: 2015-03-31 Created: 2015-03-18 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Bio-optics, satellite remote sensing and Baltic Sea ecosystems: Applications for monitoring and management
Open this publication in new window or tab >>Bio-optics, satellite remote sensing and Baltic Sea ecosystems: Applications for monitoring and management
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Earth observation satellites cover large areas with frequent temporal repetition and provide us with new insight into ocean and coastal processes. Ocean colour measurements from satellite remote sensing are linked to the bio-optics, which refers to the light interactions with living organisms and dissolved and suspended constituents in the aquatic environment. Human pressures have changed the aquatic ecosystems, by, for example, the increased input of nutrient and organic matter leading to eutrophication. This thesis aims to study and develop the link between bio-optical data and the remote sensing method to the monitoring and management of the Baltic Sea. The results are applied to the European Union’s Water Directives, and the Baltic Sea Action Plan from the Helsinki commission. In paper I indicators for eutrophication, chlorophyll-a concentration and Secchi depth were evaluated as a link to remote sensing observations. Chlorophyll-a measurements from an operational satellite service (paper I) were compared to conventional ship-based monitoring in paper II and showed high correlations to the in situ data. The results in paper I, II and IV show that the use of remote sensing can improve both the spatial and temporal monitoring of water quality. The number of observations increased when also using satellite data, thus facilitating the assessment of the ecological and environmental status within the European Union’s water directives. The spatial patterns make it possible to study the changes of e.g. algae blooms and terrestrial input on larger scales. Furthermore, the water quality products from satellites can offer a more holistic and easily accessible view of the information to decision makers and end-users. In paper III variable relationships between in situ bio-optical parameters, such as coloured dissolved organic matter (CDOM), dissolved organic carbon, salinity and Secchi depth, were found in different parts of the Baltic Sea. In paper IV an in situ empirical model to retrieve suspended particulate matter (SPM) from turbidity was developed and applied to remote sensing data. The use of Secchi depth as an indicator for eutrophication linked to the concentrations of chlorophyll-a and SPM and CDOM absorption was investigated in paper V. The variations in Secchi depth were affected differently by the mentioned parameters in the different regions. Therefore, one must also consider those when evaluating changes in Secchi depth and for setting target levels for water bodies. This thesis shows good examples on the benefits of incorporating bio-optical and remote sensing data to a higher extent within monitoring and management of the Baltic Sea.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2015. p. 59
Keyword
Bio-optics, Remote sensing, MERIS, Eutrophication, Baltic Sea, Monitoring, Management, WFD, MSFD, HELCOM, Chlorophyll-a, Secchi depth, Coloured Dissolved Organic Matter, Suspended Particulate Matter
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-119578 (URN)978-91-7649-219-2 (ISBN)
Public defence
2015-10-02, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish National Space Board, Dnr. 165/11EU, European Research Council, SPICOSA 36992Nordic Council of Ministers, 80106 & 42041EU, FP7, Seventh Framework Programme, WaterS 251527Baltic Ecosystem Adaptive Management (BEAM), 4315403Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE, 4315403Swedish Environmental Protection Agency, WATERS
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2015-09-10 Created: 2015-08-17 Last updated: 2017-04-11Bibliographically approved

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