Cyanobacteria detection in Guarapiranga Reservoir (São Paulo State, Brazil) using Landsat TM and ETM+ images

Igor Ogashawara,José Luiz Stech,José Galizia Tundisi,Enner Herenio De Alcântara

doi:10.4136/ambi-agua.1327

Abstract

Algae bloom is one of the major consequences of the eutrophication of aquatic systems, including algae capable of producing toxic substances. Among these are several species of cyanobacteria, also known as blue-green algae, that have the capacity to adapt themselves to changes in the water column. Thus, the horizontal distribution of cyanobacteria harmful algae blooms (CHABs) is essential, not only to the environment, but also for public health. The use of remote sensing techniques for mapping CHABs has been explored by means of bio-optical modeling of phycocyanin (PC), a unique inland waters cyanobacteria pigment. However, due to the small number of sensors with a spectral band of the PC absorption feature, it is difficult to develop semi-analytical models. This study evaluated the use of an empirical model to identify CHABs using TM and ETM+ sensors aboard Landsat 5 and 7 satellites. Five images were acquired for applying the model. Besides the images, data was also collected in the Guarapiranga Reservoir, in Sao Paulo Metropolitan Region, regarding the cyanobacteria cell count (cells/mL), which was used as an indicator of CHABs biomass. When model values were analyzed excluding calibration factors for temperate lakes, they showed a medium correlation (R2=0.81, p=0.036), while when the factors were included the model showed a high correlation (R2=0.96, p=0.003) to the cyanobacteria cell count. The empirical model analyzed proved useful as an important tool for policy makers, since it provided information regarding the horizontal distribution of CHABs which could not be acquired from traditional monitoring techniques.

Highlights

River damming is a well-known process in the neo-tropical regions mainly due to its electricity generating potential, and for its other uses such as leisure, navigation, fisheries and water supply (Tundisi et al, 2008)
It is located in the city of São Paulo, in an area that belongs to the Companhia de Saneamento Básico do Estado de São Paulo (SABESP, 2012), which is responsible for drinking water treatment and distribution in the RMSP
It is important to the water supply of RMSP, water quality is monitored at only three sample points (Figure 1) no more than three times a week by traditional methods, which is insufficient to reveal the horizontal distribution of cyanobacteria harmful algae blooms (CHABs)

Summary

Introduction

River damming is a well-known process in the neo-tropical regions mainly due to its electricity generating potential, and for its other uses such as leisure, navigation, fisheries and water supply (Tundisi et al, 2008). Because of the irresponsible uses of water, mainly in urbanized regions, issues such as deforestation, loss of green areas, increased toxicity, accelerated eutrophication and changes in biodiversity lead to the deterioration of water quality (Straskraba and Tundisi, 1999). All of these problems are consequences of the lack of an adequate system of water governance, which negatively impacts the environment and human health (Tundisi, 2008)

Methods

Results

Conclusion