University of Twente Student Theses


Remote Sensing of Wastewater Contamination in Coastal Areas: A Case Study of Conceição Lagoon, Brazil

Liz Arcari, Amanda de (2022) Remote Sensing of Wastewater Contamination in Coastal Areas: A Case Study of Conceição Lagoon, Brazil.

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Abstract:This study investigated the utility of optical remote sensing in detecting wastewater spills in Conceição Lagoon, a coastal lagoon in Southern Brazil that suffers from recurrent problems of wastewater contamination. Inherent Optical Properties (IOPs) derived from Sentinel-2 MSI imagery using the 2SeaColor model were used to characterize a representative wastewater plume. Modal analysis was applied to capture the spatial dynamic of the plume with respect to the background water, whereas the temporal features were captured by temporal standardization. This combination allowed the formulation of a novel Wastewater Contamination Index (WCI). The WCI consists of the standardized anomalies of a linear combination of IOPSs, namely: diffuse attenuation coefficient of photosynthesis available radiation, k_d (PAR) (a quasi-IOP), the absorption coefficient of phytoplankton green pigment Chlorophyll-a, a_chla (440), the absorption coefficient of detritus and coloured dissolved organic matter, a_dg (440), and backscattering of suspended particulate matter, 〖b_b〗_spm (440). The weigths of the linear combination are constructed from the eigenvectors of the IOPs Spatial Principal Component Analysis (PCA) during a wastewater outfall event. Results showed that wastewater optical signal is mostly characterized by 〖b_b〗_spm (440) and k_d (PAR), with a relative importance of approximately 40% each to the WCI. This can be associated to the elevated concentration of suspended solids in wastewater and its effect on water transparency. Despite dissolved organic matter being also characteristic of wastewater, a_dg (440) showed a secondary role in the description of the wastewater plume, with a weight of 15%. The lowest influence on WCI came from a_chla (440), with 8%. This was expected, as algal blooms would be a post-effect following nutrient enrichment from wastewater and depending on other environmental conditions. The WCI was applied to 139 Sentinel-2 images from 2019 to 2021 to detect specific outfall events and examine their spatio-temporal patterns. With the aid of photographic records, meteorological, water quality and hydrodynamics data, it was possible to find agreement between high WCI values and four wastewater outfalls in Conceição Lagoon. The spatio-temporal analysis of WCI did not indicate significant recurrent patterns of wastewater pollution in the area, highlighting the irregular nature and unpredictability of wastewater outfalls.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:02 science and culture in general, 38 earth sciences, 43 environmental science
Programme:Geoinformation Science and Earth Observation MSc (75014)
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