Using CDOM optical properties for estimating DOC concentrations and pCO₂ in the Lower Amazon River

Abstract

Coloured dissolved organic matter (CDOM) is one of the major contributors to the absorption budget of most freshwaters and can be used as a proxy to assess non-optical carbon fractions such as dissolved organic carbon (DOC) and the partial pressure of carbon dioxide (pCO). Nevertheless, riverine studies that explore the former relationships are still relatively scarce, especially within tropical regions. Here we document the spatial-seasonal variability of CDOM, DOC and pCO, and assess the potential of CDOM absorption coefficient (a(412)) for estimating DOC concentration and pCO along the Lower Amazon River. Our results revealed differences in the dissolved organic matter (DOM) quality between clearwater (CW) tributaries and the Amazon River mainstream. A linear relationship between DOC and CDOM was observed when tributaries and mainstream are evaluated separately (Amazon River: N = 42, R = 0.74, p<0.05; CW: N = 13, R = 0.57, p<0.05). However, this linear relationship was not observed during periods of higher rainfall and river discharge, requiring a specific model for these time periods to be developed (N = 25, R = 0.58, p<0.05). A strong linear positive relation was found between a(412) and pCO(N = 69, R = 0.65, p<0.05) along the lower river. pCO was less affected by the optical difference between tributaries and mainstream waters or by the discharge conditions when compared to CDOM to DOC relationships. Including the river water temperature in the model improves our ability to estimate pCO (N = 69; R = 0.80, p<0.05). The ability to assess both DOC and pCO from CDOM optical properties opens further perspectives on the use of ocean colour remote sensing data for monitoring carbon dynamics in large running water systems worldwide.

Hydrodynamic Modeling and Simulation of Water Residence Time in the Estuary of the Lower Amazon River

“…The referred author simulated Rt behavior [84] and estimated a value close to 30 days; therefore, when Rt value was compared to results in the present research, such value was relatively close to that of the estuarine system in Santos Basin at the dry period (November); of the period presenting lower rainfall and of the period when there was greater oceanic tide influence over upstream Amazonian estuary. In other words, saltwater is potentially more influential in the estuary at this period [10].…”

“…Physical gradients controlling the water masses entering, leaving or accumulating in each unit volume are interesting highlights in these interactions -they show the dependence between currents and tidal phases ( Figures 10-12). These tidal phases get more intense as the flood period and the maximal annual water pulse approach [10,22,23]. On the other hand, some of these factors have not been taken into account in the water balance of great water bodies, such as the estuary of the Amazon River, once there is a series of the experimental barriers and high complexity of hydrodynamic modeling processes.…”

“…Both regions are located close to Macapá City. These regions are of prominent ecological-environmental interest, since their challenges demand knowledge about the extremely complex hydrodynamics in these environments [10,13,22], which are influenced by high water discharges that depend on the meso-tidal phases [23].…”

“…The geomorphological complexity and connectivity among small and mid-sized channels, lagoons and the main rivers are other factors to be taken into consideration [10,23,37]. These water bodies significantly contribute to worsening the logistical difficulties and Rt quantifications of the complex Amazonian estuarine.…”

Matéria Orgânica Dissolvida Cromófora E Não Cromófora Em Sistemas Fluviais Tropicais

“…pH, salinidade, temperatura, oxigênio dissolvido, tipo de sistema lêntico-lótico), acoplados ou não a modelagens matemáticas, representam exemplos adicionais de possibilidades de integração científica para um desenvolvimento aprofundado e relacional entre as frações cromóforas e não cromóforas da MOD no âmbito de sistemas aquáticos. Valerio et al (2018) utilizaram as propriedades ópticas da MODC para estimar as concentrações de carbono (COD e pCO 2 ) no rio Amazonas e concluíram que a aplicação da abordagem óptica utilizada permitirá uma avaliação mais ampla das margens dos rios de todo o mundo e um monitoramento mais persistente das alterações na ciclagem do carbono aquático durante as mudanças climáticas.…”