Use of absorption optical indices to assess seasonal variability of dissolved organic matter in amazon floodplain lakes

Abstract

<p><strong>Abstract.</strong> Given the importance of DOM in the carbon cycling of aquatic ecosystems, information on its seasonal variability is crucial. This study assesses the use of available absorption optical indices based on in situ data to both characterize the seasonal variability of the DOM dynamics in a highly complex environment and their viability of being used for satellite remote sensing on large scale studies. The study area comprises four lakes located at the Mamirauá Sustainable Development Reserve (MSDR). Samples for the determination of coloured dissolved organic matter (CDOM) and remote sensing reflectance (Rrs) were acquired in situ. The Rrs was applied to simulate MSI visible bands and used in the proposed models. Differences between lakes were tested regarding CDOM indices. Significant difference in the average of a<sub>CDOM</sub> (440), a<sub>CDOM</sub> spectra and S<sub>275–295</sub> were found between lakes located inside the flood forest and those near the river bank. The proposed model showed that a<sub>CDOM</sub> can be used as proxy of S<sub>275–295</sub> during rising water with good validation results, demonstrating the potential of Sentinel/MSI imagery data in large scale studies on the dynamics of DOM.</p>

Organic Molecular Signatures of the Congo River and Comparison to the Amazon

“…Autochthonous DOM is largely produced by algae and cyanobacteria (Patriarca et al., 2021), which are active in the Amazon River during low discharge (Doherty et al., 2017) and in seasonal floodplain wetlands where most of the primary production in the Amazon is thought to occur (Richey et al., 1990). Indeed, chromophoric DOM absorbance decreases in floodplain lakes around the Amazon mainstem and its tributaries during falling‐water periods while spectral slope parameters generally increase, suggesting that less aromatic DOM is delivered to the river system during this time (da Silva et al., 2020). Concurrently, the abundance of fresh, protein‐like DOM, which is likely derived from phytoplankton biomass and aquatic macrophytes, increases in floodplains during low‐ and falling‐water periods and is transported into the mainstem as the water level recedes (de Melo et al., 2020; Moreira‐Turcq et al., 2013).…”

Linking Biogeochemical and Hydrodynamic Processes to Model Methane Fluxes in Shallow, Tropical Floodplain Lakes

“…Hence, simulations of methane fluxes from lakes throughout the region will require modifying parameter values and inputs from those used for Lake Janauacá. In addition to incorporation of data from field studies, remote sensing offers approaches for estimating chlorophyll, suspended sediment and dissolved organic matter concentrations, though the optically complex waters add analytical difficulty and uncertainty (Fassoni-Andrade & Paiva, 2019;Novo et al, 2006;Sayers et al, 2015;Silva et al, 2019).…”

Amazon Hydrology From Space: Scientific Advances and Future Challenges

“…1) Estimates of sediment concentration in rivers (Bayley & Moreira, 1978; Mertes et al., 1993), chlorophyll in floodplain lakes (Novo et al., 2006), and colored dissolved organic material in lakes (M. P. da Silva et al., 2019).…”

“…M. P. da Silva et al. (2019) proposed an empirical algorithm for estimating CDOM absorption at 440 nm from Sentinel‐2/MSI images. Table 5 presents a summary of these studies.…”

“…The Amazon River exports the largest sedimentary supply to the world's ocean (1.1 × 10 9 tons per year (Armijos et al., 2020; Figure 14). Several seminal studies and algorithm developments using RS to characterize the water composition of rivers and lakes were primarily conducted in Amazon (see Table 5), such as the pioneering estimates of sediment concentration in rivers (Bayley & Moreira, 1978; Mertes et al., 1993), chlorophyll in floodplain lakes (Novo et al., 2006) and colored dissolved organic material (M. P. da Silva et al., 2019). The spatio‐temporal pattern of these components is related to SWE variations and mixing processes from different sources.…”