A Multivariate Analysis Framework to Detect Key Environmental Factors Affecting Spatiotemporal Variability of Chlorophyll-a in a Tropical Productive Estuarine-Lagoon System

David Motta Marques,Paulo Medeiros,Regina Lins,Carlos Fragoso Júnior,Jean-Michel Martinez,José Cirilo

doi:10.3390/rs10060853

Abstract

Here, we demonstrate how a combination of three multivariate statistic techniques can identify key environmental factors affecting the seasonal and spatial variability of chlorophyll-a (Chl-a) in a productive tropical estuarine-lagoon system. Remote estimation of Chl-a was carried out using a NIR-Red model based on MODIS bands, which is highly consistent with the in situ measurement of Chl-a with root mean square error (RMSE) of 15.24 mg m−3 and 13.43 mg m−3 for two independent datasets used for the model’s calibration and validation, respectively. Our findings suggest that the river discharges and hydraulic residence time of the lagoons promote a stronger effect on the spatial variability of Chl-a in the coastal lagoons, while wind, solar radiation and temperature have a secondary importance. The results also indicate a slight seasonal variability of Chl-a in Mundaú lagoon, which are different the from Manguaba lagoon. The multivariate approach was able to fully understand the relative importance of key environmental factors on the spatiotemporal variability of Chl-a of the aquatic ecosystem, providing a powerful tool for reducing dimensionality and analyzing large amounts of satellite-derived Chl-a data.

Highlights

Coastal lagoons are transitional ecosystems that exhibit large spatial variability and seasonality controlled by both continental and oceanic drives, such as river discharge, salinity, water temperature, and hydrodynamics [1,2]
The studied lagoons show different optical characteristics, it was found that an unique bio-optical model based on MODIS bands might be applied to estimate Chl-a concentrations for both lagoons, which may be used for time-series reconstruction of Chl-a concentrations
The higher Chl-a values found in Manguaba lagoon better fit the upper part of the model, while the lower Chl-a concentrations with a high interference of turbidity in Mundaú lagoon better fit the lower part of the model

Summary

Introduction

Coastal lagoons are transitional ecosystems that exhibit large spatial variability and seasonality controlled by both continental and oceanic drives, such as river discharge, salinity, water temperature, and hydrodynamics [1,2]. The low water exchange rates makes these water bodies vulnerable to eutrophication and contamination This degradation process usually results in an increase of water turbidity due to blooms of cyanobacteria or green algae, affecting the entire trophic structure [4]. Spatiotemporal variability of phytoplankton in coastal lagoons is strongly influenced by various environmental factors [8], most notably: (a) water temperature and light intensity; (b) patterns of river discharge that bring nutrients and organic matter from continental runoff; (c) tide- and wind-induced currents, which can influence nutrient and phytoplankton transport; and (d) biological factors such as grazing by aggregated zooplankton and other organisms, which influence phytoplankton growth through top-down control by herbivores

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Conclusion