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Long-term phytoplankton trends in the Belgian North Sea (2002-2015): patterns and potential causes
Labatt, C.K. (2016). Long-term phytoplankton trends in the Belgian North Sea (2002-2015): patterns and potential causes. MSc Thesis. Oceans & Lakes, Interuniversity Master in Marine and Lacustrine Science and Management: Antwerpen, Gent and Brussel. 59 pp.

Thesis info:

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Document type: Dissertation

Keywords
    Salinity; Seasonality; Marine
Author keywords
    Belgian coastal zone (BCZ); Chlorophyll a; Generalized additive mixed model (GAMM) ; long-term trend

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  • Labatt, C.K.

Abstract
    A dataset provided by the Flanders Marine Institute (VLIZ, 2015) from the LifeWatch marine observatory data on nutrients, pigments and suspended matter in the Belgian Part of the North Sea was analyzed. The time series spanning the period 2002-2015 was modeled using a non-parametric generalized additive mixed model (GAMM) suited for non-normal and non-linear data. The main objectives of the study was: i) to come up with the best GAMM model for predicting Chlorophyll a (CHLa) in the Belgian coastal zone (BCZ), that could explain the seasonal cycle and long-term trend by utilizing the fewest number of predictors (environmental variables); ii) to investigate whether the seasonal cycle for blooms differed between different locations in the BCZ; iii) To determine the long-term trend and see if the management strategies in the BCZ were effective or required modifications in the reduction of harmful algal blooms (HABs) that recur annually. The Chlorophyll a pigment was elucidated by smooth functions for the long-term trend, seasonal cycle per zone, SPM, salinity and silicate concentration. The GAMM simulated seasonal trends for the southwest (SW), middle and northeast (NE) zones and showed that the shape for all the zones differed in magnitude, timing and duration (p<0.001). Silicate was strongly correlated to other nutrients, while salinity was found to increase with oceanic influences as reflected in the water transparency and light availability. SPM indicated the influence of freshwater runoff. The long-term trends indicate consistent reduction in nutrient levels for the period of 2002-2015 with the blooms condition producing more distinctive peaks than before but the mean value had remained steady since 2010. Changes in the seasonal patterns are probably an indication that either the community structure is shifting towards less silicified diatoms or non-siliceous forms that are impacting on the biomass. Missing data greatly hindered modeling process and interpretation. It was recommended that phytoplankton community structure.

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