Abstract
The high nutrient concentrations coming from non-point and point pollution have been linked to algae blooms, especially in hydroelectric plant reservoirs, due to higher residence time compared to rivers. The monitoring of algae is important to prevent risk of contamination by toxins in reservoirs used for drinking water supply. In this context, a physical model-based approach was adopted to retrieve chlorophyll-a (chl a) concentration, a photosynthetic pigment found in all phytoplankton species. We assumed that a semi-analytical algorithm parameterized to a eutrophic reservoir could also be applied to other eutrophic reservoirs, at least the specific inherent optical properties (SIOPs) are not similar. The parameterization was carried out based on Ocean and Land Color Instrument (OLCI) bands aboard Sentinel-3 spacecraft. In our study, the semi-analytical approach showed good performance in retrieving chl a content, with a normalized root mean square error (NRMSE) of 18.7%. The findings encourage the use of a unique semi-analytical algorithm in a reservoir cascade, where the impoundments present similar bio-optical status. The good performance of the algorithm indicates that this approach is rather useful in predicting trophic status in reservoirs.
Highlights
Rivers crossing large urban centers in developing countries receive high loads of domestic and industrial wastewater and, when dams are built in polluted stretches, the ecological impact is often severe
The semi-analytical algorithm designed in this research from data collected in a eutrophic reservoir showed good performance in estimating accurately chl a concentration in a reservoir with high trophic status
The parameterization using both the BB1 and BB2 datasets was capable of predicting a large chl a concentration range in BA
Summary
Rivers crossing large urban centers in developing countries receive high loads of domestic and industrial wastewater and, when dams are built in polluted stretches, the ecological impact is often severe. Rrs is an apparent optical property, i.e., it depends on the properties of the water column and underwater light field geometry [8] Based on this optical relationship, semi-analytical algorithms have been proposed for retrieving optically significant constituents (OSCs) [1,9,10,11,12,13,14], bathymetry [15] and Secchi disk depth, ZSD [16]. This approach considers Rrs as a function of a and bb for each OSC (phytoplankton pigments, detritus and dissolved organic matter), where a and bb are linear combinations between specific absorption and backscattering coefficients (a* and bb*, respectively) of each OSC times its concentration [17]
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