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Optimizing the Use of Secchi Depth as a Proxy for Euphotic Depth in Coastal Waters: An Empirical Study from the Baltic Sea
Department of Geography and Geology, University of Turku, Turku FI-20014, Finland
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Received: 30 September 2013; in revised form: 5 November 2013 / Accepted: 26 November 2013 / Published: 9 December 2013
(This article belongs to the Special Issue Coastal GIS
Abstract: Potential zone for photosynthesis in natural waters is restricted to a relatively thin illuminated surface water layer. The thickness of this layer is often indirectly estimated by measuring the depth in which 1% of the photosynthetically active radiation entering the water remains. This depth is referred to as the euphotic depth. A coarser way to evaluate the underwater light penetration is to measure the Secchi depth, which is a visual measure of water transparency. The numerical relationship between these two optical parameters, i.e., conversion coefficient m, varies according to the changes in the optical properties of water, especially in transitional coastal waters. The aim of our study is to assess which is the most suitable criterion to base these coefficients on. We tested nine methods, seven of which were locally calibrated with our own in situ data from the optically heterogeneous Baltic Sea archipelago coast of SW Finland. We managed to significantly improve the accuracy of modeling euphotic depths from Secchi depths by using scalable and locally calibrated methods instead of a single fixed coefficient. The best results were achieved by using methods, either continuous functions or series of constants, which are based on water transparency values.
Keywords: Secchi depth; euphotic depth; method optimization; modeling accuracy; coastal waters; Baltic Sea
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MDPI and ACS Style
Luhtala, H.; Tolvanen, H. Optimizing the Use of Secchi Depth as a Proxy for Euphotic Depth in Coastal Waters: An Empirical Study from the Baltic Sea. ISPRS Int. J. Geo-Inf. 2013, 2, 1153-1168.
Luhtala H, Tolvanen H. Optimizing the Use of Secchi Depth as a Proxy for Euphotic Depth in Coastal Waters: An Empirical Study from the Baltic Sea. ISPRS International Journal of Geo-Information. 2013; 2(4):1153-1168.
Luhtala, Hanna; Tolvanen, Harri. 2013. "Optimizing the Use of Secchi Depth as a Proxy for Euphotic Depth in Coastal Waters: An Empirical Study from the Baltic Sea." ISPRS Int. J. Geo-Inf. 2, no. 4: 1153-1168.