An official website of the United States government
Abstract Wetlands have been used to treat anthropogenic effluents for decades due to their intense biogeochemical processes that transform and uptake nutrients, organic matter, and toxins. Despite these known functions, we lack generalizable knowledge of effluent-derived dissolved organic matter (DOM) cycling in wetlands. Here, we quantify the cycling of DOM in one of Canada’s more economically important wetland complexes (Frank Lake, Alberta), restored to hydrologic permanence in the 1980s using urban and agro-industrial effluents. Optical analyses and PARAFAC (parallel factor analysis) modelling showed a clear compositional change from more bioavailable and protein-like DOM at effluent input sites to more aromatic and humic-like at the wetland outflow, likely due to DOM processing and inputs from marsh plants and wetland soils. Microbial incubations showed that effluent DOM was rapidly consumed, with the half-life of DOM increasing from as low as 35 days for effluent, to 462 days at the outflow, as a function of compositional shifts toward aromatic, humic-like material. Long-term averaged dissolved organic carbon (DOC) export was low compared to many wetlands (10.3 ± 2.0 g C m−2 yr−1). Consistent with predictions based on water residence time, our mass balance showed Frank Lake was a net source of DOM across all measured years, but shifted from a source to sink among wet and drought years that respectively shortened or lengthened the water residence and DOM processing times. Overall, Frank Lake processes and transforms effluent DOM, despite being a longer-term net source of DOM to downstream environments.
more »
« less
Biodegradation and Photodegradation of Vegetation-Derived Dissolved Organic Matter in Tidal Marsh Ecosystems
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
- Award ID(s):
- 1950656
- PAR ID:
- 10306104
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Estuaries and Coasts
- Volume:
- 45
- Issue:
- 5
- ISSN:
- 1559-2723
- Page Range / eLocation ID:
- p. 1324-1342
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Microbes and sunlight convert terrigenous dissolved organic matter (DOM) in surface waters to greenhouse gases. Prior studies show contrasting results about how biological and photochemical processes interact to contribute to the degradation of DOM. In this study, DOM leached from the organic layer of tundra soil was exposed to natural sunlight or kept in the dark, incubated in the dark with the natural microbial community, and analyzed for gene expression and DOM chemical composition. Microbial gene expression (metatranscriptomics) in light and dark treatments diverged substantially after 4 hours. Gene expression suggested that sunlight exposure of DOM initially stimulated microbial growth by (a) replacing the function of enzymes that degrade higher molecular weight DOM such as enzymes for aromatic carbon degradation, oxygenation, and decarboxylation, and (b) releasing low molecular weight compounds and inorganic nutrients from DOM. However, growth stimulation following sunlight exposure of DOM came at a cost. Sunlight depleted the pool of aromatic compounds that supported microbial growth in the dark treatment, ultimately causing slower growth in the light treatment over 5 days. These first measurements of microbial metatranscriptomic responses to photo-alteration of DOM provide a mechanistic explanation for how sunlight exposure of terrigenous DOM alters microbial processing and respiration of DOM.more » « less
-
Summary Microbes and sunlight convert terrigenous dissolved organic matter (DOM) in surface waters to greenhouse gases. Prior studies show contrasting results about how biological and photochemical processes interact to contribute to the degradation of DOM. In this study, DOM leached from the organic layer of tundra soil was exposed to natural sunlight or kept in the dark, incubated in the dark with the natural microbial community, and analysed for gene expression and DOM chemical composition. Microbial gene expression (metatranscriptomics) in light and dark treatments diverged substantially after 4 h. Gene expression suggested that sunlight exposure of DOM initially stimulated microbial growth by (i) replacing the function of enzymes that degrade higher molecular weight DOM such as enzymes for aromatic carbon degradation, oxygenation, and decarboxylation, and (ii) releasing low molecular weight compounds and inorganic nutrients from DOM. However, growth stimulation following sunlight exposure of DOM came at a cost. Sunlight depleted the pool of aromatic compounds that supported microbial growth in the dark treatment, ultimately causing slower growth in the light treatment over 5 days. These first measurements of microbial metatranscriptomic responses to photo‐alteration of DOM provide a mechanistic explanation for how sunlight exposure of terrigenous DOM alters microbial processing and respiration of DOM.more » « less
-
Dissolved organic matter (DOM) drives biogeochemical processes in aquatic ecosystems. Yet, how hydrologic restoration in nutrient‐enriched ecosystems changes DOM and the consequences of those changes for the carbon cycle remain unclear. To predict the consequences of hydrologic restoration on carbon cycling in restored wetlands, we need to understand how local environmental factors influence production, processing, and transport of DOM. We collected surface water samples along transects in restored peat (organic‐rich, macrophyte‐dominated) and marl (carbonate, periphyton‐dominated) freshwater marshes in the Everglades (Florida, U.S.A.) that varied in environmental factors (water depth, phosphorus [P] concentrations [water, macrophytes, periphyton, and soil], and primary producer biomass) to understand drivers of dissolved organic carbon (DOC) concentrations and DOM composition. Higher water depths led to a “greening” of DOM, due to increasing algal contributions, with decreasing concentrations of DOC in peat wetlands, and a “browning” of DOM, due to increasing humic contributions, with increasing DOC concentrations in marl wetlands. Soil total P was positively correlated with DOC concentrations and microbial contributions to DOM in peat wetlands, and periphyton total P was positively correlated with algal contributions to DOM in marl wetlands. Despite large variations in both vegetation biomass and periphyton biovolume across transects and sites, neither were predictors of DOC concentrations or DOM composition. Hydrologic restoration differentially alters DOM in peat and marl marshes and interacts with nutrient enrichment to shift proportions of green and brown contributions to surface water chemistry, which has the potential to modify wetland food webs, as well as the processing of carbon by micro‐organisms.more » « less
-
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
