A Remote Sensing Approach for Monitoring Seasonal Variations in the Water Quality of Lake Guaiba, Southern Brazil

Abstract

Freshwater resources in the tropics are subjected to high rate of pollution due to algal blooms during the summer and due to particulate and organic waste discharge from urban areas during spring. Landsat TM images were used to calculate biochemical oxygen demand and turbidity of Lake Guaiba in Southern Brazil during 2010–2011. The results obtained were compared with the values derived from a yearlong sampling data which were analyzed in a laboratory by the municipal department of water and sewage. It is seen that both the in situ and remote sensing approach give comparable results. The remote sensing method was extended to the last 10 years to understand how water quality parameters have been changed. It is found that BOD and turbidity levels were higher during the beginning of summer months compared to the end. The possible causes of changes in the pollution levels, whether due to blooms or suspended sediments, were also investigated in this study. It is hypothesized that major causative agent of reduction in water quality was urban waste itself during the rainy season and not due to the accumulation of poisonous substances due to algal blooms in summer. Effective methods to separate particulates of various sizes before reaching the drainage systems are yet to be developed to reduce the discharge of particulates to this freshwater source.
Keywords: Lake Guaiba,, biochemical oxygen demand, landsat, pollution monitoring, algal blooms, turbidity