Uso do sensoriamento remoto para estimar a concentração de componentes opticamente ativos na Lagoa da Pampulha - MG

Abstract

The Lagoa da Pampulha is an urban dam located in the municipality of Belo Horizonte - MG and considered a recreational center. However, anthropogenic pressures exerted in the region such as diffuse pollution and discharge of sanitary sewers carry excess nutrients to the lagoon which causes eutrophication of the water body. Laboratory monitoring methods for surface water limnological parameters present disadvantages in relation to spatial and temporal coverage and are sometimes not representative. In this sense, traditional methods can be complemented by an approach that uses the optical properties of components present in the water body and their spectral responses to estimate the concentration of these elements. The present study makes use of remote sensing to estimate the concentration of optical active components in Pampulha Lake. The methodology consists of the construction of an empirical model to relate the reflectance band ratios to the Chlorophyll-a concentration and turbidity. We also analysed the data of the historical series of monitoring of water in the Lagoon conducted by Minas Gerais Water Management Institute - IGAM as well as the limnological data collected in the field. For the chlorophyll model we chose to divide the data into two groups (1 and 2) and to use differentiated algorithms for each group of data considering the separation caused by the sediment retention curtain in the Pampulha Lagoon. The best correlation was observed with Normalized Difference Chlorophyll Index - NDCI (R2 = 0.6799 for group 1 and R2 = 0.5671 for group 2). However, there was a large deviation between observed and predicted values with RMSE = 110.07 for group 1 and 6.38 for group 2. The turbidity models presented a good correlation with the simulated bands, with the band simulated in green (B3) with the best R2 = 0.743 and RMSE = 0.037. In the validation step, it was verified that only turbidity values of up to 7NTU (turbidity unit) showed a good correlation with the model, underestimating the predicted values. The calculated errors for each of the three bands (RMSE (B3) = 3.714, RMSE (B4) = 4.014 and RMSE (B5) = 4.142) show that the model shows a deviation between observed and predicted values. of greater occurrence of chlorophyll a and turbidity in the Pampulha Lagoon and the areas with critical pollution spots. The sites with the highest occurrence of chlorophyll a and turbidity in the Pampulha Lagoon are located near the entrance of the Ressaca and Sarandi streams and in the vicinity of the garbage retention curtain indicating that they are these are the most critical areas of pollution. As practical implications the use of remote sensing for water quality assessment in Lagoa da Pampulha enables decision-making bodies to be more secure and quick to make decisions about the management of the waters of the lagoon. This thesis is original and logically involves because it combines the study of water quality in the study region with remote sensing applications. The work meets the needs highlighted by CAPES Committee on Environmental Sciences by promoting research and the social insertion of research in regions with a high index of environmental vulnerability.