Performance of existing QAAs in Secchi disk depth retrieval in phytoplankton and dissolved organic matter dominated inland waters

Abstract

A semianalytical model developed to estimate the Secchi disk depth (Z SD ) was used in eutrophic-to-hypereutrophic reservoirs (Ibitinga, Ibi, and Barra Bonita, BB) placed in the cascade system of the Tietê River, Brazil. The model was evaluated using the simulated remote sensing reflectance based on the Ocean and Land Color Instrument/Sentinel-3A and the Operational Land Imager/Landsat-8 from both reservoirs. Three quasianalytical algorithm (QAA) versions (QAA v5 , QAA M14 , and QAA W16 ) were evaluated to derive the absorption and backscattering coefficients, and then used for Z SD retrieval. For BB, where the chlorophyll-a concentration exceeded 200 mg m −3 , the model based on QAA v5 showed high uncertainties while the QAA W16 , which was originally parameterized for BB showed better performance regarding the Z SD retrieval (mean absolute percentage errors-MAPE of 22%). However, QAA W16 did not perform satisfactorily for Ibi, which is dominated by colored dissolved organic matter (CDOM). For Ibi, QAA v5 provided the best result with MAPE of 34.60%, followed by QAA M14 with 34.65%. QAA-based Z SD models tend to perform poorly in waters with high concentration of chlorophyll-a possibly due to phytoplankton package effect, whereas the same models may require additional parameterization in waters dominated by CDOM. Landsat-8 data showed significant potential for Z SD retrieval in inland waters. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Remote sensing of water transparency variability in the Ibitinga reservoir during COVID-19 lockdown

“…Its transparency is affected by organic and inorganic waste and pollutants from agricultural, urban and industrial activities in the watershed; the reservoir is characterized as a turbulent and eutrophic reservoir ( Rotta et al, 2021 ). Its trophic state can also be affected by the seasonal rainfall, in which rainy seasons usually result in an intense eutrophication process through increased surface runoff and stormwater drainages ( Rodrigues et al, 2018 ).…”

“…The Ibitinga reservoir, the third largest in the Tietê River's cascade system, is an organic matter dominated water along the middle portion of the Tietê River that receives both organic and inorganic waste from agricultural, urban and industrial activities. Therefore, the water quality and the level of pollution in the reservoir is dynamic and depends largely on the hydrological inputs from the surrounding drainages from the metropolitan region near the city of São Paulo ( Rodrigues et al, 2018 ). Here we hypothesize that although the city's drainage is the major reservoir's input, as opposed to what has been reported elsewhere (e.g.…”