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Dive into the research topics where Rachael Y. Dyda is active.

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Featured researches published by Rachael Y. Dyda.


Journal of Geophysical Research | 2009

Photochemical degradation of dissolved organic matter and dissolved lignin phenols from the Congo River

Robert G. M. Spencer; Aron Stubbins; Peter J. Hernes; Andy Baker; Kenneth Mopper; Anthony K. Aufdenkampe; Rachael Y. Dyda; Vincent L. Mwamba; Arthur M. Mangangu; Jose N. Wabakanghanzi; Johan Six

[1] Photochemical degradation of Congo River dissolved organic matter (DOM) was investigated to examine the fate of terrigenous DOM derived from tropical ecosystems. Tropical riverine DOM receives greater exposure to solar radiation, particularly in large river plumes discharging directly into the open ocean. Initial Congo River DOM exhibited dissolved organic carbon (DOC) concentration and compositional characteristics typical of organic rich blackwater systems. During a 57 day irradiation experiment, Congo River DOM was shown to be highly photoreactive with a decrease in DOC, chromophoric DOM (CDOM), lignin phenol concentrations (S8) and carbon-normalized yields (L8), equivalent to losses of � 45, 85–95, >95 and >95% of initial values, respectively, and a +3.1 % enrichment of the d 13 C-DOC signature. The loss of L8 and enrichment of d 13 C-DOC during irradiation was strongly correlated (r = 0.99, p < 0.01) indicating tight coupling between these biomarkers. Furthermore, the loss of CDOM absorbance was correlated to the loss of L8 (e.g., a355 versus L8; r = 0.98, p < 0.01) and d 13 C-DOC (e.g., a355 versus d 13 C; r = 0.97, p < 0.01), highlighting the potential of CDOM absorbance measurements for delineating the photochemical degradation of lignin and thus terrigenous DOM. It is apparent that these commonly used measurements for examination of terrigenous DOM in the oceans have a higher rate of photochemical decay than the bulk DOC pool. Further process-based studies are required to determine the selective removal rates of these biomarkers for advancement of our understanding of the fate of this material in the ocean.


Environmental Science & Technology | 2013

Molecular Trickery in Soil Organic Matter: Hidden Lignin

Peter J. Hernes; Klaus Kaiser; Rachael Y. Dyda; C. Cerli

Binding to minerals is one mechanism crucial toward the accumulation and stabilization of organic matter (OM) in soils. Of the various biochemicals produced by plants, lignin-derived phenols are among the most surface-reactive compounds. However, it is not known to what extent mineral-bound lignin-derived phenols can be analytically assessed by alkaline CuO oxidation. We tested the potential irreversible binding of lignin from three litters (blue oak, foothill pine, annual grasses) to five minerals (ferrihydrite, goethite, kaolinite, illite, montmorillonite) using the CuO-oxidation technique, along with bulk organic carbon (OC) sorption. Up to 56% of sorbed lignin could not be extracted from the minerals with the CuO-oxidation technique. The composition of the irreversibly bound lignin component differed markedly between minerals and from that of the parent litter leachates, indicating different bonding strengths related to individual monomers and conformations. The difference in extractability of individual phenols suggests that abiotic processes, such as sorption/desorption, should be taken into account when using CuO oxidation data for assessing lignin turnover in mineral matrixes. However, given the apparent relationship between aromaticity as indicated by carbon-specific UV absorbance (SUVA) and bulk OC sorption, it is likely that irreversible sorption is a concern for any technique that addresses the broad class of aromatic/phenolic compounds in soils and sediments.


Frontiers of Earth Science in China | 2016

Pan-arctic trends in terrestrial dissolved organic matter from optical measurements

Paul J. Mann; Robert G. M. Spencer; Peter J. Hernes; Johan Six; George R. Aiken; Suzanne E. Tank; James W. McClelland; Kenna D. Butler; Rachael Y. Dyda; Robert M. Holmes

Climate change is causing extensive warming across arctic regions resulting in permafrost degradation, alterations to regional hydrology, and shifting amounts and composition of dissolved organic matter (DOM) transported by streams and rivers. Here, we characterize the DOM composition and optical properties of the six largest arctic rivers draining into the Arctic Ocean to examine the ability of optical measurements to provide meaningful insights into terrigenous carbon export patterns and biogeochemical cycling. The chemical composition of aquatic DOM varied with season, spring months were typified by highest lignin phenol and dissolved organic carbon (DOC) concentrations with greater hydrophobic acid content, and lower proportions of hydrophilic compounds, relative to summer and winter months. Chromophoric DOM (CDOM) spectral slope (S275-295) tracked seasonal shifts in DOM composition across river basins. Fluorescence and parallel factor analysis identified seven components across the six Arctic rivers. The ratios of ‘terrestrial humic-like’ versus ‘marine humic-like’ fluorescent components co-varied with lignin monomer ratios over summer and winter months, suggesting fluorescence may provide information on the age and degradation state of riverine DOM. CDOM absorbance (a350) proved a sensitive proxy for lignin phenol concentrations across all six river basins and over the hydrograph, enabling for the first time the development of a single pan-arctic relationship between a350 and terrigenous DOC (R2 = 0.93). Combining this lignin proxy with high-resolution monitoring of a350, pan-arctic estimates of annual lignin flux were calculated to range from 156 to 185 Gg, resulting in shorter and more constrained estimates of terrigenous DOM residence times in the Arctic Ocean (spanning 7 months to 2½ years). Furthermore, multiple linear regression models incorporating both absorbance and fluorescence variables proved capable of explaining much of the variability in lignin composition across rivers and seasons. Our findings suggest that synoptic, high-resolution optical measurements can provide improved understanding of northern high-latitude organic matter cycling and flux, and prove an important technique for capturing future climate-driven changes.


Frontiers of Earth Science in China | 2017

The Genesis and Exodus of Vascular Plant DOM from an Oak Woodland Landscape

Peter J. Hernes; Robert G. M. Spencer; Rachael Y. Dyda; Anthony T. O'Geen; Randy A. Dahlgren

Evaluating the collective impact of small source inputs to larger rivers is a constant challenge in riverine biogeochemistry. In this study, we investigated the generation of dissolved organic matter (DOM) in a small oak woodland catchment in the foothills of northern California, the subsequent transformation in lignin biomarkers and chromophoric DOM (CDOM) parameters during transport through the landscape to an exporting stream, and finally the overall compositional impact on the larger receiving stream and river. Our study included a natural leaching experiment in which precipitation passing through oak, pine, and grass litter and duff samples was collected after each of a series of storms. Also included were soil trench samples to capture subsurface flow, stream samples along with point-source reservoir inputs, and samples of canopy throughfall, stemflow, and gopher hole (bypass) flow. The litter/duff leaching study demonstrated changing DOM fractionation patterns throughout the season, as evidenced by changing lignin compositions in the leachates with each successive storm. This adds a necessary seasonal component to interpreting lignin compositions in streams, as the source signatures are constantly changing. Released DOM from leaching was modified extensively during transit through the subsurface to the stream, with preferential increases in aromaticity as evidenced by increases in carbon-normalized absorbance at 254 nm, yet preferential decreases in lignin phenols, as evidence by carbon-normalized lignin yields in the headwater stream that was less than half that of the litter/duff leachates. Our extensive number of lignin measurements for source materials reveals a much more complex perspective on using lignin as a source indicator, as many riverine values for syringyl:vanillyl and cinnamyl:vanillyl ratios that have previously been interpreted as degraded lignin signatures are also possible as unmodified source signatures. Finally, this study demonstrated that the impact of numerous small headwater streams can significantly overprint the DOM signatures of much larger rivers over relatively short distances spanning several to tens of kilometers. This finding in particular challenges the assumption that river studies can be adequately conducted by focusing only on the main tributaries.


Journal of Geophysical Research | 2010

Temporal controls on dissolved organic matter and lignin biogeochemistry in a pristine tropical river, Democratic Republic of Congo

Robert G. M. Spencer; Peter J. Hernes; Rosmarie Ruf; Andy Baker; Rachael Y. Dyda; Aron Stubbins; Johan Six


Geochimica et Cosmochimica Acta | 2008

The role of hydrologic regimes on dissolved organic carbon composition in an agricultural watershed

Peter J. Hernes; Robert G. M. Spencer; Rachael Y. Dyda; Brian A. Pellerin; Philip A.M. Bachand; Brian A. Bergamaschi


Geochimica et Cosmochimica Acta | 2012

An initial investigation into the organic matter biogeochemistry of the Congo River

Robert G. M. Spencer; Peter J. Hernes; Anthony K. Aufdenkampe; Andy Baker; Pauline Gulliver; Aron Stubbins; George R. Aiken; Rachael Y. Dyda; Kenna D. Butler; Vincent L. Mwamba; Arthur M. Mangangu; Jose N. Wabakanghanzi; Johan Six


Organic Geochemistry | 2010

Comparison of XAD with other dissolved lignin isolation techniques and a compilation of analytical improvements for the analysis of lignin in aquatic settings

Robert G. M. Spencer; George R. Aiken; Rachael Y. Dyda; Kenna D. Butler; Brian A. Bergamaschi; Peter J. Hernes


Soil Biology & Biochemistry | 2012

Biochemical changes across a carbon saturation gradient: Lignin, cutin, and suberin decomposition and stabilization in fractionated carbon pools

Elizabeth M. Carrington; Peter J. Hernes; Rachael Y. Dyda; Alain F. Plante; Johan Six


Aquatic Microbial Ecology | 2006

Impact of DOM composition on bacterial lipids and community structure in estuaries

H. Rodger Harvey; Rachael Y. Dyda; David L. Kirchman

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Brian A. Bergamaschi

United States Geological Survey

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Andy Baker

University of New South Wales

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Aron Stubbins

Skidaway Institute of Oceanography

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Brian A. Pellerin

United States Geological Survey

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George R. Aiken

United States Geological Survey

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Kenna D. Butler

United States Geological Survey

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