Long-Term Series of Chlorophyll-a Concentration in Brazilian Semiarid Lakes from Modis Imagery

Dhalton Luiz Tosetto Ventura,Jean-Michel Martinez,Eduardo Sávio Passos Rodrigues Martins,José Luiz De Attayde,Luciane Silva Moreira,Nilva Brandini

doi:10.3390/w14030400

Dhalton Luiz Tosetto Ventura, Jean-Michel Martinez + Show 4 more

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https://doi.org/10.3390/w14030400

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Abstract

By monitoring the chlorophyll a concentration (chla), it is possible to keep track of the eutrophication status of a lake and to describe the temporal dynamics of the phytoplankton biomass. Such monitoring must be both extensive and intensive to account for the short- and long-term biomass variations. This may be achieved by the remote estimation of chla through an orbital sensor with high temporal resolution. In this study, we used MODIS imagery to produce 21-year time series of chla for three strategic lakes of the Brazilian semi-arid region: Eng. Armando Ribeiro Gonçalves, Castanhão, and Orós. We used data collected in 13 lakes of the region to test new and published regression models for chla estimation. The selected model was validated and applied to daily MODIS images for the three largest lakes. The resulting chla time series revealed that the temporal dynamics of the phytoplankton biomass is associated with the hydraulic regime of the lakes, with chla plummeting upon intense water renewal and keeping high during persistent dry periods. The intense rainy season of 2004 reduced the phytoplankton biomass and its effects even extended to the subsequent years. Our results encourage the exploration of the MODIS archived imagery in limnological studies.

Highlights

The lakes differed in their limnological properties, such as their contents of chlorophyll a—some were mesotrophic, such as Santa Cruz do Apodi, and others were clearly eutrophic, such as Eng
Armando Ribeiro Gonçalves (EARG)—and inorganic suspended solids (ISS), which varied among the lakes and sampling sites
As most reflectance spectra (Figure S1) featured a conspicuous cavity around 680 nm followed by a peak around nm, we used the difference in the seston absorption coefficients at 680 and 700 nm as an indicator of the chlorophyll a concentration

Summary

Introduction

Eutrophication has affected lakes all over the world, with several negative consequences in the ecological, economical, and sanitary areas, such as shifts in the phytoplankton composition, higher treatment costs for drinking water, and the frequent growth of potentially toxic cyanobacteria [1,2]. These consequences are associated with an exaggerated increase in the phytoplankton biomass, for which a common and reliable proxy is the chlorophyll a concentration (chla) [3]. By monitoring chla it is possible to keep track of the eutrophication status of a water body and to describe the temporal dynamics of the phytoplankton biomass

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Conclusion