Abstract
Suspended particulate matter (SPM) directly affects the underwater light field and, as a consequence, changes the water clarity and can reduce the primary production. Remote sensing-based bio-optical modeling can provide efficient monitoring of the spatiotemporal dynamics of SPM in inland waters. In this paper, we present a novel and robust bio-optical model to retrieve SPM concentrations for inland waters with widely differing optical properties (the Tietê River Cascade System (TRCS) in Brazil). In this system, high levels of Chl-a concentration of up to 700 mg/m3, turbidity up to 80 NTU and high CDOM absorption highly complicate the optical characteristics of the surface water, imposing an additional challenge in retrieving SPM concentration. Since Kd is not susceptible to the saturation issue encountered when using remote sensing reflectance (Rrs), we estimate SPM concentrations via Kd. Kd was derived analytically from inherent optical properties (IOPs) retrieved through a re-parameterized quasi-analytical algorithm (QAA) that yields relevant accuracy. Our model improved the estimates of the IOPs by up to 30% when compared to other existing QAAs. Our developed bio-optical model using Kd(655) was capable of describing 74% of SPM variations in the TRCS, with average error consistently lower than 30%.
Highlights
Suspended particulate matter (SPM—see Table 1 for symbols and acronyms) is a major component of the aquatic environment, composed by organic and inorganic fractions
When we considered the errors retrieved in the Tietê River Cascade System (TRCS) (Table S3), we observed that QAA specific for the TRCS (QAATRCS) retrieved the lowest error when compared to QAAOMW; when we evaluated each fieldwork, we verified the lowest errors in QAAOMW, with the exception of BB and BAR, which are more eutrophic environments and failed the QAAOMW estimates for bb
Regarding the light attenuation caused by SPM within the water, we observed throughout our experiments that Kd, which represented the light attenuation, was a suitable single explanatory variable to estimate SPM concentrations for inland waters
Summary
Suspended particulate matter (SPM—see Table 1 for symbols and acronyms) is a major component of the aquatic environment, composed by organic and inorganic fractions. It plays an important role in the hydrophysical functioning and biogeochemical cycles of inland waters [1]. It essentially controls, through the absorption and backscattering of light and the turbidity and transparency of the water column, which can affect the total available energy for photosynthetic activities [2]. The gradient of available energy underwater largely determines the biogeochemical cycles and biodiversity of aquatic organisms [5,6,7]
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