Drivers of Organic Molecular Signatures in the Amazon River

Kurek, Martin; Stubbins, Aron; Drake, Travis W.; Moura, J. M. S.; Holmes, Robert M.; Osterholz, Helena; Dittmar, Thorsten; Peucker‐Ehrenbrink, Bernhard; Mitsuya, Miyuki; Spencer, Robert G. M.

doi:10.1029/2021gb006938

Cited by 15 publications

(26 citation statements)

References 83 publications

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“…Moreover, to our knowledge, it represents the first study attempting an analysis of land use legacy effects related to secondary succession processes following the abandonment of grasslands historically used for extensive cattle raising. This study shows that mass spectrometry, an increasingly used tool believed to provide a deeper resolution of DOM composition (e.g., Wagner et al, 2019;Peter et al, 2020;Behnke et al, 2021;Kurek et al, 2021), may also be sensitive to subtle changes in DOM properties, thereby improving our ability to characterize fluvial DOM composition. Furthermore, the results demonstrate the relevance of current riparian forest cover in determining the composition of fluvial DOM.…”

Section: Discussionmentioning

confidence: 96%

When Forests Take Over After Land Abandonment: Dissolved Organic Matter Response in Headwater Mountain Streams

Estévez¹,

Álvarez‐Martínez²,

Dittmar³

et al. 2021

Front. Water

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Dissolved organic matter (DOM) represents the largest pool of organic carbon in fluvial ecosystems. The majority of DOM in rivers is of terrigenous origin—making DOM composition highly dependent on vegetation cover and soil properties. While deforestation is still a worldwide anthropogenic phenomenon, current land cover change in temperate regions is often characterized by secondary succession processes following the abandonment of agricultural activities including grazing on pasturelands. This results in (secondary) forest expansion with a consequent, time-lagged transformation of soil properties. Predicting the time scale and spatial scale (i.e., location in the catchment: riparian vs. upslope areas) at which such land cover changes affect the terrestrial-aquatic carbon linkage and concomitantly alter properties of fluvial DOM as drivers of carbon cycling in freshwater ecosystems represents a new scientific challenge. In an attempt to identify potential legacy effects of land cover, i.e., reaction delays of fluvial DOM to changes in land cover, we here investigate the influence of specific current and historic (2 decade-old) land cover types on molecularly resolved fluvial DOM composition in headwater mountain streams. Our analysis is based on a scale-sensitive approach weighing in the distance of land cover (changes) to the stream and ultrahigh-resolution mass spectrometric analyses. Results identified the dominance of terrigenous DOM, with phenolic and polyphenolic sum formulae commonly associated to lignins and tannins, in all the studied streams. DOM properties mostly reflected present-day gradients of forest cover in the riparian area. In more forested catchments, DOM had on average higher molecular weight and a greater abundance of O-rich phenols and polyphenols but less aliphatics. Besides the modulation of the DOM source, our results also point to an important influence of photodegradation associated to variation in light exposition with riparian land cover in defining fluvial DOM properties. Despite expectations, we were unable to detect an effect of historic land cover on present-day DOM composition, at least at the investigated baseflow conditions, probably because of an overriding effect of current riparian vegetation.

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Section: Discussionmentioning

confidence: 96%

When Forests Take Over After Land Abandonment: Dissolved Organic Matter Response in Headwater Mountain Streams

Estévez¹,

Álvarez‐Martínez²,

Dittmar³

et al. 2021

Front. Water

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“…Briefly, DOM formulae in the Amazon River were low in molecular weight, saturated (high H/C), poorly oxygenated (low O/C), aromatic, and consisted of mostly CHO-containing formulae (Table 1; Table S1 in Supporting Information S1). The Amazon River DOM composition also displayed consistent variations in seasonality between the peak wet and dry seasons (Kurek et al, 2021). To illustrate, average Mass, C OX , AI mod , and IOS content were all higher during the following wet seasons than in the preceding dry seasons, though there was significant variability between the two years due to the influence of the 2011-2012 La Niña event (Kurek et al, 2021).…”

Section: Dom Composition In the Congo And Amazon Rivermentioning

confidence: 91%

“…In contrast, average heteroatom (N and S) DOM content did not follow apparent trends with peak or minimum discharge (Figures 3e and 3f). The DOM composition of the Amazon River samples taken between 2011 and 2013 have been published previously (Kurek et al, 2021). Briefly, DOM formulae in the Amazon River were low in molecular weight, saturated (high H/C), poorly oxygenated (low O/C), aromatic, and consisted of mostly CHO-containing formulae (Table 1; Table S1 in Supporting Information S1).…”

Section: Dom Composition In the Congo And Amazon Rivermentioning

confidence: 99%

“…While many of these analyses have been employed to investigate seasonal trends, molecular‐level analysis via FT‐ICR MS has only been conducted on a single sample from the Congo River and therefore lack any temporal resolution (e.g., Riedel et al., 2016; Stubbins et al., 2010; Wagner et al., 2015). Thus, the objectives of this study were: (a) to characterize the molecular‐level DOM composition of the Congo River during its wet and dry seasons via FT‐ICR MS; (b) to directly compare the overall DOM composition between the Congo River and the Amazon River from existing data (Kurek et al., 2021); and (c) to identify patterns or trends in the quality of DOM exported from each river into the Atlantic Ocean and how they compare to other major world rivers. By investigating these temporal trends in DOM composition between the Amazon and Congo Rivers, we aim to provide a baseline description of the DOM properties from the two largest rivers in the world and assess the stability of their export as the rivers respond to ongoing and predicted changes in precipitation, hydrology, and land use.…”

Section: Introductionmentioning

confidence: 99%

“…Both the Amazon and Congo River Basins drain the largest areas of tropical rainforests in the world, which have become increasingly susceptible to anthropogenic land use changes (Castello & Macedo, 2016; Davidson et al., 2012; Winemiller et al., 2016), resulting in the export of impacted DOM from these watersheds from headwaters to the mainstem (Drake et al., 2019; Drake, Podgorski et al., 2020; Spencer et al., 2019). Additionally, the annual discharge of these tropical rivers is susceptible to short‐term variations in oceanic pressure and temperature anomalies, such as the El Niño Southern Oscillation (“ENSO”; Amarasekera et al., 1997; Foley et al., 2002), which has been shown to alter DOM sourcing and composition in the Amazon River (Kurek et al., 2021), as well as organic carbon signatures in the Congo (Bayon et al., 2019) and other subtropical watersheds (Qu et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

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

Kurek

Stubbins

Drake

et al. 2022

Global Biogeochemical Cycles

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The Congo and Amazon are the two largest rivers on Earth and serve as major sources of dissolved organic carbon to the ocean. We compared the dissolved organic matter (DOM) composition of both rivers using Fourier‐transform ion cyclotron resonance mass spectrometry to investigate seasonal and regional differences in DOM composition exported to the ocean. We found that over a 15‐month observational period in the Congo River, molecular aromaticity and oxygenation between the wet and dry periods varied slightly, but most of the relative abundance of DOM formulae (∼90%) were present in all samples, suggesting that Congo River DOM quality is stable across different hydrological conditions. In contrast, the multi‐year DOM composition in the Amazon River was highly susceptible to changes in hydrology, with clear differences in molecular aromaticity, oxygenation, and heteroatom (N, S, P) content between the wet and dry seasons. Overall, the DOM composition of the Congo River was more terrestrial than Amazon River DOM, which was more characteristic of aquatic DOM. Finally, we compared the relative contribution of island of stability (IOS) formulae between the rivers and found that both rivers export similar amounts of these formulae annually, more than several major rivers combined, and that the Congo is more than twice as efficient in exporting these IOS formulae. With changing precipitation and land use, the quantity and composition of exported DOM will likely reflect the mobilization of additional terrestrial and anthropogenic sources that will also be subjected to downstream land‐to‐ocean cycling.

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Influence of land use and different plant residues on isotopic carbon distribution of total and water extractable organic matter in an incubation experiment with weathered tropical soil

Silva

Spaccini²,

Rezende

et al. 2022

Land Degrad Dev

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In weathered tropical soils, the inherent pedoclimatic characteristics strengthen the role of soil organic matter (SOM) pools within the carbon cycle for both forest and agricultural ecosystems. The fast SOM turnover and the humid climate hasten the impact of land use and emphasize the importance of water extractable organic matter (WEOM) on soil organic carbon (SOC) dynamics. The goal of this study was to determine the short‐term dynamics of bulk SOM and WEOM pool in weathered Brazilian soil, as conditioned by both land use and type of plant inputs. To this aim we used the appraisal of the natural δ13C‐OC signature to follow the variation of SOC pools and to overcome the analytical issues related to low OC concentration of WEOM fractions. In a one‐year laboratory incubation, soil samples from a natural forest and an adjacent site under sugarcane monoculture were amended with either forest litter or sugarcane straw to evaluate SOM and WEOM dynamics. The bulk SOM was mainly affected by inherited conditions rather than on the organic amendments. The incorporation of sugarcane residues in the forest site produced a partial replacement of the original SOC, while the amendments to the cultivated soil promoted a stable increase in SOC. The analysis of WEOM highlighted its influence as a reactive pool in the short‐term SOM dynamics. The δ13C variation of WEOM from cultivated soil corroborated the significant ponderal rate of OC input from forest litter that accounted for 22% of total dissolved carbon. Unexpected evidence on the shift of isotopic dilution between SOC pools indicates that the evaluation of δ13C to determine the origin of the SOC fraction should be conservatively adopted. The results outline that the steady state of SOM in forest systems may undergo a rapid decline with limited counteracting effects of exogenous OM inputs. Conversely, OC depleted agricultural soils may benefit from organic amendments, thus acting as an effective sink for SOC accumulation.

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Drivers of Organic Molecular Signatures in the Amazon River

Abstract: Inland waters have been increasingly recognized as hotspots for global carbon cycling, moving away from being viewed as passive transporters and reservoirs, to being accepted as interwoven conveyers and reactors (

Cited by 15 publications

References 83 publications

When Forests Take Over After Land Abandonment: Dissolved Organic Matter Response in Headwater Mountain Streams

When Forests Take Over After Land Abandonment: Dissolved Organic Matter Response in Headwater Mountain Streams

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

Influence of land use and different plant residues on isotopic carbon distribution of total and water extractable organic matter in an incubation experiment with weathered tropical soil

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