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Tidal wetlands are a significant source of dissolved organic matter (DOM) to coastal ecosystems, which impacts nutrient cycling, light exposure, carbon dynamics, phytoplankton activity, microbial growth, and ecosystem productivity. There is a wide variety of research on the properties and sources of DOM; however, little is known about the characteristics and degradation of DOM specifically sourced from tidal wetland plants. By conducting microbial and combined UV exposure and microbial incubation experiments of leachates from fresh and senescent plants in Chesapeake Bay wetlands, it was demonstrated that senescent material leached more dissolved organic carbon (DOC) than fresh material (77.9 ± 54.3 vs 21.6 ± 11.8 mg DOC L−1, respectively). Degradation followed an exponential decay pattern, and the senescent material averaged 50.5 ± 9.45% biodegradable DOC (%BDOC), or the loss of DOC due to microbial degradation. In comparison, the fresh material averaged a greater %BDOC (72.6 ± 19.2%). Percent remaining of absorbance (83.3 ± 26.7% for fresh, 90.1 ± 10.8% for senescent) was greater than percent remaining DOC, indicating that colored DOM is less bioavailable than non-colored material. Concentrations of DOC leached, %BDOC, and SUVA280 varied between species, indicating that the species composition of the marsh likely impacts the quantity and quality of exported DOC. Comparing the UV + microbial to the microbial only incubations did not reveal any clear effects on %BDOC but UV exposure enhanced loss of absorbance during subsequent dark incubation. These results demonstrate the impacts of senescence on the quality and concentration of DOM leached from tidal wetland plants, and that microbes combined with UV impact the degradation of this DOM differently from microbes alone.
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Biogeochemical and Physical Controls on the Microbial Degradation of Dissolved Organic Matter Along a Temperate Microtidal Estuary
Abstract Dissolved organic matter (DOM) is the foundation of the microbial loop and plays an important role in estuarine water quality and ecosystem metabolism. Because estuaries are influenced by DOM with different sources and composition, changing hydrologic regimes, and diverse microbial community assemblages, the biological fate of DOM (i.e., microbial degradation) differs across spatiotemporal scales and between DOM pools. To better understand controls on DOM degradation, we characterized the biogeochemical and physical conditions of the York River Estuary (YRE), a sub-estuary of the Chesapeake Bay in southeast Virginia (USA), during October 2018 and February, April, and July 2019. We then evaluated how these conditions influenced the degradation of dissolved organic carbon (DOC) and nitrogen (DON) and chromophoric dissolved organic matter (CDOM) by conducting parallel dark incubations of surface water collected along the YRE. Compared to other sampling dates, DOC reactivity (ΔDOC (%)) was over two-fold higher in October when freshwater discharge was lower, temperatures were warmer, and autochthonous, aquatic sources of DOC dominated. ΔDOC (%) was near zero when allochthonous, terrestrial sources of DOC were more abundant and when temperatures were cooler during higher discharge periods in February when precipitation in the Chesapeake Bay region was anomalously high. DON was up to six times less reactive than DOC and was sometimes produced during the incubations whereas ΔCDOM (%) was highly variable between sampling periods. Like ΔDOC (%), spatiotemporal patterns in ΔDON (%) were controlled primarily by hydrology and DOM source and composition. Our results show that higher freshwater discharge associated with prolonged wet periods decreased estuarine flushing time and increased the delivery of allochthonous DOM derived from terrestrial sources into coastal waters, resulting in lower rates of DOM degradation especially under cool conditions. While these findings provide evidence for seasonal variation in DOM degradation, shifting environmental conditions (e.g., increasing temperatures and precipitation) due to climate change may also have interactive effects on the magnitude and composition of DOM exported to estuaries and its subsequent reactivity.
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- Award ID(s):
- 1737258
- PAR ID:
- 10579807
- Publisher / Repository:
- Estuaries and Coasts
- Date Published:
- Journal Name:
- Estuaries and Coasts
- Volume:
- 48
- Issue:
- 2
- ISSN:
- 1559-2723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Uncovering which biogeochemical processes have a critical role controlling dissolved organic matter (DOM) compositional changes in complex estuarine environments remains a challenge. In this context, the aim of this study is to characterize the dominant patterns of variability modifying the DOM composition in an estuary off the Southeastern U.S. We collected water samples during three seasons (July and October 2014 and April 2015) at both high and low tides and conducted short- (1 day) and long-term (60 days) dark incubations. Samples were analyzed for bulk DOC concentration, and optical (CDOM) and molecular (FT-ICR MS) compositions and bacterial cells were collected for metatranscriptomics. Results show that the dominant pattern of variability in DOM composition occurs at seasonal scales, likely associated with the seasonality of river discharge. After seasonal variations, long-term biodegradation was found to be comparatively more important in the fall, while tidal variability was the second most important factor correlated to DOM composition in spring, when the freshwater content in the estuary was high. Over shorter time scales, however, the influence of microbial processing was small. Microbial data revealed a similar pattern, with variability in gene expression occurring primarily at the seasonal scale and tidal influence being of secondary importance. Our analyses suggest that future changes in the seasonal delivery of freshwater to this system have the potential to significantly impact DOM composition. Changes in residence time may also be important, helping control the relative contribution of tides and long-term biodegradation to DOM compositional changes in the estuary.more » « less
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This dataset includes (1) original data from a dissolved organic carbon (DOC) incubation experiment and (2) a data synthesis of the DOC incubation experiment literature. Study component (1) was a factorial lab experiment crossing varying dissolved organic matter (DOM) sources (Suwannee River Fulvic Acid, Elliott soil leachate, Chlorella leachate) with varying microbial communities. The objective of this study component was to test the interacting effects of microbial community composition and DOM characteristics on carbon (C) biodegradation. We used a Micro-Oxymax Respirometer (Columbus Instruments, Columbus, Ohio) to measure carbon dioxide and oxygen accumulation at two hour intervals for a period of two weeks, and quantified the initial and final concentrations of dissolved organic carbon and total dissolved nitrogen of each experimental unit. To verify that the three DOM source solutions had differing chemical compositions and potential bioreactivity, we optically characterized each DOM source using mass spectra analysis and excitation-emission matrices (EEMs). Study component (2) is a synthesis of DOC concentrations from the C degradation experiment literature. The criteria for including a study in this synthesis was that (a) incubation DOM was sourced from a river, lake, marine, estuary, or marsh, and (b) that C concentrations were measured at least twice throughout the incubation in addition to an initial measurement. For each study, we extracted initial DOC values, elapsed incubation time, and reported DOC concentrations during the incubation period for each experimental treatment. This data package is completed.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1007/s12237-024-01474-0
