Towards more realistic estimates of DOM decay in streams: Incubation methods, light, and non-additive effects

Kelso, Julia E.; Rosi, Emma J.; Baker, Michelle A.

doi:10.1086/710218

Cited by 5 publications

(8 citation statements)

References 73 publications

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“…This trend is consistent with expectations for longitudinal DOM processing patterns in another wetland system (Pinney et al 2000 ). While laboratory incubations do not encompass all ecosystem-level DOM processing, BDOC incubations do capture general DOM cycling patterns in aquatic systems (Kelso et al 2020 ), so we are confident that the high mineralization rate of effluent DOM observed in incubations extends to the ecosystem scale, especially since this conclusion is supported by the 2021 mass balance that showed intense net DOM consumption.…”

Section: Discussionmentioning

confidence: 85%

Organic matter cycling in a model restored wetland receiving complex effluent

2022

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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.

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Section: Discussionmentioning

confidence: 85%

Organic matter cycling in a model restored wetland receiving complex effluent

2022

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“…Given the notable discrepancy between OC removal estimated using bioassays or whole‐stream metabolism, we suggest future investigators consider the context and tradeoffs of using bioassays to ecosystem OC fluxes in place of whole‐stream metabolism. Although bioassays underestimate whole‐stream OC cycling, they often allow us to isolate, control, and test how different physical (e.g., temperature, light) and biogeochemical controls (e.g., nutrient availability, stoichiometry) influence OC uptake (Kelso et al., 2020; Koehler et al., 2012) and assess the reactivity of different OC sources (Hotchkiss et al., 2014; Kelso et al., 2020) across different ecosystem types (Catalán et al., 2016). Bioassays can also provide standardized estimates of water column DOC uptake in aquatic ecosystems where sensor deployment or whole‐stream metabolism modeling methods prove challenging (e.g., high air‐water gas exchange, low GPP, or maintaining sensor deployments in remote regions; Ward et al., 2019; Wologo et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

“…When we compared previously published values of v f-OC measured using bioassays (n = 59) or whole-stream metabolism (n = 126), with the caveat that most bioassay and metabolism measurements were not made at overlapping sites, we observed a similar order of magnitude difference in v f-OC depending on the method used (Figure 2). We thus argue that whole-stream metabolism provides a more realistic estimate of in-stream OC removal because whole-stream metabolism integrates C processing in the water column as well as highly reactive benthic and hyporheic substrates (Griffiths et al, 2012;Kelso et al, 2020).…”

Section: In-stream Doc Removal Estimated From Bioassays and Whole-eco...mentioning

confidence: 99%

“…Bioassays (e.g., in vitro incubations of water samples) are often used to measure DOC biodegradability in the water column as a function of microbial DOC uptake using reproducible and standardized methods that allow for comparisons across different OC sources and ecosystem types (Guillemette & del Giorgio, 2011; Wologo et al., 2021). By measuring DOC uptake in a more controlled setting, bioassays can provide insight into how different environmental drivers such as nutrient concentrations, organic matter source, and temperature affect microbial DOC metabolism rates (Kelso et al., 2020; Mineau et al., 2016). While bioassay methods are limited in their scope and ability to represent in‐stream conditions (e.g., they exclude benthic activity and fresh OC inputs of different forms and sources), DOC uptake rates derived from bioassays are still often extrapolated and used in whole‐ecosystem assessments of C cycling, fate, and transport (e.g., Catalán et al., 2016; Kaplan et al., 2006; Raymond et al., 2016).…”

Section: Introductionmentioning

confidence: 99%

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Integrating Perspectives on Dissolved Organic Carbon Removal and Whole‐Stream Metabolism

2022

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Inland waters are active sites of carbon cycling; they process, store, and emit more than half of the carbon (C) they receive as terrestrial inputs (Battin et al., 2009;Butman et al., 2018;Cole et al., 2007). An estimated 5.1 Pg C is loaded into inland waters from terrestrial landscapes every year, which can comprise anywhere from 12% to 34% of terrestrial net ecosystem productivity when scaled to global surface area (Butman et al., 2015;Drake et al., 2018). The difference between estimates of terrestrial C loading into and export from inland waters to the ocean (0.9 Pg C yr −1 export) highlights the active role inland waters play in removing C (4.2 Pg C yr −1 stored or emitted) (Butman et al., 2015;Drake et al., 2018). Regional and global C budgets and earth system models, however, often exclude the loss of C from land to aquatic ecosystems. Including freshwater C fluxes and cycling in global C budgets requires estimates of freshwater ecosystem metabolism as well as metabolism-informed calculations of C fluxes to inland waters from the surrounding landscape (Hotchkiss et al., 2015;Vachon et al., 2021).

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“…Field experiments on biodegradation and photodegradation are often hindered by confounding factors that are di cult to control for in eld settings such as terrestrial inputs into the buried stream network (Haag and Matschonat, 2001). Mesocosm experiments are a useful alternative to eld studies by allowing much greater control over the in uencing factors acting on photodegradation and biodegradation rate (Nélieu et al, 2009;Kelso et al, 2020). Furthermore, by being able to control conditions, mesocosm experiments are extremely useful for testing potential interaction effects (e.g.…”

Section: Introductionmentioning

confidence: 99%

The impact of urban stream burial on DOM cycling: new insights from a mesocosm experiment

Croghan,

Khamis,

Bradley

et al. 2024

Preprint

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Urban landscapes can drastically alter light regimes through stream burial, and also modify water temperature patterns, both of which have profound implications for the degradation of dissolved organic matter (DOM) through photodegradation and biodegradation, respectively. Despite their likely significance, the dynamics of short-term biodegradation and photodegradation in urban environments remain poorly understood, with limited knowledge regarding the potential interplay between warming and stream burial effects. This study used a replicated flume experiment to investigate the effects of shading, warming (+ 4.5–6.6°C), and their interaction on DOM processing. We used optical techniques to characterize DOM quantity and composition, allowing us to assess photodegradation and biodegradation rates in urban stream analogues. Linear mixed effects models revealed that the degradation of the fluorescent DOM pool decreased under shaded conditions, accompanied by an increase in humic-like compounds. Additionally, shaded flumes exhibited a shift towards higher molecular weight organic matter, indicating the importance of photodegradation in DOM processing within urban rivers. Temperature effects on DOM processing rates were found to be relatively minor compared to shading, with no interaction with shading observed. Principal Component Analysis demonstrated clear distinctions between shaded and unshaded treatments. In contrast, no significant differences were observed between warmed and ambient temperature treatments. Our findings suggest that stream burial impedes DOM processing and alters DOM composition in urban headwaters by inhibiting the photodegradation of humic material. The temperature treatments examined had limited impacts on biodegradation over the relatively short timescales of this study. This study provides experimental support for daylighting interventions as a strategy to enhance DOM processing in urban streams and mitigate the flux of labile material to downstream ecosystems.

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Towards more realistic estimates of DOM decay in streams: Incubation methods, light, and non-additive effects

Cited by 5 publications

References 73 publications

Organic matter cycling in a model restored wetland receiving complex effluent

Organic matter cycling in a model restored wetland receiving complex effluent

Integrating Perspectives on Dissolved Organic Carbon Removal and Whole‐Stream Metabolism

The impact of urban stream burial on DOM cycling: new insights from a mesocosm experiment

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