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

The development of algorithms for remote sensing of water quality (RSWQ) requires a large amount of in situ data to account for the bio-geo-optical diversity of inland and coastal waters. The GLObal Reflectance community dataset for Imaging and optical sensing of Aquatic environments (GLORIA) includes 7,572 curated hyperspectral remote sensing reflectance measurements at 1 nm intervals within the 350 to 900 nm wavelength range. In addition, at least one co-located water quality measurement of chlorophyll a, total suspended solids, absorption by dissolved substances, and Secchi depth, is provided. The data were contributed by researchers affiliated with 59 institutions worldwide and come from 450 different water bodies, making GLORIA the de-facto state of knowledge of in situ coastal and inland aquatic optical diversity. Each measurement is documented with comprehensive methodological details, allowing users to evaluate fitness-for-purpose, and providing a reference for practitioners planning similar measurements. We provide open and free access to this dataset with the goal of enabling scientific and technological advancement towards operational regional and global RSWQ monitoring.

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“…Instruments: TriOS RAMSES Approach: Mobley45 ; Mobley63 Applications: Maciel et al64 ; Cairo et al65 ; da Silva et al66 8. L…”

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confidence: 99%

GLORIA - A globally representative hyperspectral in situ dataset for optical sensing of water quality

Lehmann

Gurlin²,

Pahlevan³

et al. 2023

Sci Data

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“…In contrast, high NO 3 − and NO 2 − concentrations ( Figure 6 ) are quite near the guideline values for drinking-water quality (maximum admissible concentrations) and might apply, for instance, to a surface water body receiving inputs from contaminated groundwater [ 36 ]. Moreover, increasing A o and decreasing S mean that CDOM is more aromatic and has higher molecular mass [ 37 ]. These circumstances favour sunlight absorption by CDOM (higher A CDOM values).…”

Section: Resultsmentioning

confidence: 99%

“…In environmental waters, CDOM photobleaching destroys chromophores (lower A o ) and causes molecular fragmentation (higher S ), thereby decreasing CDOM absorbance [ 34 , 37 ]. The steady-state [ 3 CDOM*] would be decreased as a consequence, while [ • OH] and [CO 3 •− ] would decrease when nitrate and nitrite are low (the main effect being the inhibition of CDOM photochemistry) or increase when nitrate and nitrite are high (the main effect being enhanced photochemistry of NO 3 − and NO 2 − , due to lower sunlight screening by CDOM).…”

Section: Discussionmentioning

confidence: 99%

Photochemical Implications of Changes in the Spectral Properties of Chromophoric Dissolved Organic Matter: A Model Assessment for Surface Waters

Altare

Vione

2023

Molecules

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Chromophoric dissolved organic matter (CDOM) is the main sunlight absorber in surface waters and a very important photosensitiser towards the generation of photochemically produced reactive intermediates (PPRIs), which take part in pollutant degradation. The absorption spectrum of CDOM (ACDOM(λ), unitless) can be described by an exponential function that decays with increasing wavelength: ACDOM(λ) = 100 d DOC Ao e− Sλ, where d [m] is water depth, DOC [mgC L−1] is dissolved organic carbon, Ao [L mgC−1 cm−1] is a pre-exponential factor, and S [nm−1] is the spectral slope. Sunlight absorption by CDOM is higher when Ao and DOC are higher and S is lower, and vice versa. By the use of models, here we investigate the impact of changes in CDOM spectral parameters (Ao and S) on the steady-state concentrations of three PPRIs: the hydroxyl radical (•OH), the carbonate radical (CO3•−), and CDOM excited triplet states (3CDOM*). A first finding is that variations in both Ao and S have impacts comparable to DOC variations on the photochemistry of CDOM, when reasonable parameter values are considered. Therefore, natural variability of the spectral parameters or their modifications cannot be neglected. In the natural environment, spectral parameters could, for instance, change because of photobleaching (prolonged exposure of CDOM to sunlight, which decreases Ao and increases S) or of the complex and still poorly predictable effects of climate change. A second finding is that, while the steady-state [3CDOM*] would increase with increasing ACDOM (increasing Ao, decreasing S), the effect of spectral parameters on [•OH] and [CO3•−] depends on the relative roles of CDOM vs. NO3− and NO2− as photochemical •OH sources.

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“…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).…”

Section: Discussionmentioning

confidence: 99%

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

Guo,

Melack,

Zhou

et al. 2023

J Adv Model Earth Syst

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Floodplains lakes are abundant in the Amazon basin and are important methane sources to the atmosphere. Existing biogeochemical models require modifications and inclusion of hydrodynamic processes operative in shallow, warm waters to be applied to these aquatic ecosystems. We modified a 1‐dimensional process‐based, lake biogeochemical model and combined a 3‐dimensional hydrodynamic model to suit Amazon floodplains. We evaluated the combined model's performance simulating methane concentrations and fluxes and several related processes in the open lake and an embayment of a well‐studied Amazon lake. Parameters for calibration were selected through sensitivity tests using a machine learning‐based algorithm, classification, and regression trees. Comparison between simulated and measured fluxes indicate generally good agreement in seasonal patterns and magnitudes. Comparisons of near‐surface concentrations varied with no clear patterns. Simulations of methane concentrations at near‐surface and near‐bottom, and diffusive emissions are most sensitive to carbon mineralization rate, Q10 factors for methanogenesis and oxidation, and methane oxidation potential. Modeled rates of planktonic photosynthesis were generally lower than measurements, though simulated planktonic respiration was often similar to measurements. Simulated rates of methane oxidation were considerably lower, with a few exceptions, than measurements of methane oxidation in oxic water of the lake. Improvements of results of the linked hydrodynamic‐biogeochemical model will result from inclusion of advective transport, use of parameter values appropriate for tropical waters, especially for methane oxidation and photosynthesis, and addition of changes in hydrostatic pressure to model of ebullition.

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

Cited by 14 publications

References 41 publications

GLORIA - A globally representative hyperspectral in situ dataset for optical sensing of water quality

GLORIA - A globally representative hyperspectral in situ dataset for optical sensing of water quality

Photochemical Implications of Changes in the Spectral Properties of Chromophoric Dissolved Organic Matter: A Model Assessment for Surface Waters

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

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