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Abstract River organic matter transformations impact the cycling of energy, carbon, and nutrients. The delivery of distinct dissolved organic matter (DOM) sources can alter aquatic DOM cycling and associated biogeochemical processes. Yet DOM source and reactivity are not well‐defined for many river systems, including in western Canada. Here, we explore DOM cycling in the mainstem of the Oldman River (stream order 6–7), a heavily regulated river network in southern Alberta (Canada). We compared seasonal river DOM content, composition, and bioavailability with nine endmember leachates from the river valley using optical properties and incubations to estimate biodegradable dissolved organic carbon (BDOC). River DOM composition was most similar to terrestrial soil leachates, followed by autochthonous DOM leachates. River DOM bioavailability was low (BDOC = 0%–16.6%, mean of 7.1%). Endmember leachate bioavailability increased from soils (BDOC = 23.9%–53.7%), to autochthonous sources (fish excretion, macrophytes, biofilm; BDOC = 49.9%–80.0%), to terrestrial vegetation (leaves, shrubs, grass; BDOC > 80%), scaling positively with protein‐like DOM content and amount of leachable dissolved organic carbon (DOC), and negatively with aromaticity. Seasonally, DOC concentrations changed little despite >15‐fold increases in discharge during spring. River DOM composition shifted modestly toward soil‐like endmembers in spring and more bioavailable autochthonous end members in autumn and winter. Low DOM bioavailability in the river mainstem and low DOC yields shown in previous work point to limited internal processing of DOM and limited bioavailable DOM delivery to downstream habitats, possibly due to upstream flow regulation. Our observations provide important insights into the functioning of western Canadian aquatic networks.
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C Concentrations and Characterization Data from DOM Incubation Assay Experiments
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.
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- Award ID(s):
- 2141535
- PAR ID:
- 10580058
- Publisher / Repository:
- Environmental Data Initiative
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 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.more » « less
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