Modeling rates of DOC degradation using DOM composition and hydroclimatic variables

Moody, Catherine; Worrall, Fred

doi:10.1002/2016jg003493

Cited by 25 publications

(23 citation statements)

References 69 publications

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“…Additionally, there is some evidence that some LMW compounds (such as those with carboxylic functional groups) might elute with higher molecular weight compounds with similar functional groups during size‐exclusion chromatography (Ruhl & Jekel, ). Previous studies have also reported rapid depletion of soil‐derived small molecular weight compounds, such as carboxylic acids and other high H/C and N compounds in small headwater streams (Berggren et al, ; Drake et al, ; Moody & Worrall, ), which have been suggested to fuel the bulk of microbial metabolism in these systems (Berggren et al, ). Our results would suggest that most of these soil‐derived, highly labile substrates are actually depleted at the soil‐stream interface and that only a small proportion actually reach the stream channel to fuel bacterial metabolism there.…”

Section: Resultsmentioning

confidence: 98%

The Optical, Chemical, and Molecular Dissolved Organic Matter Succession Along a Boreal Soil‐Stream‐River Continuum

et al. 2017

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Soils export large amounts of organic matter to rivers, and there are still major uncertainties concerning the composition and reactivity of this material and its fate within the fluvial network. Here we reconstructed the pattern of movement and processing of dissolved organic matter (DOM) along a soil‐stream‐river continuum under summer baseflow conditions in a boreal region of Québec (Canada), using a combination of fluorescence spectra, size exclusion chromatography and ultrahigh resolution mass spectrometry. Our results show that there is a clear sequence of selective DOM degradation along the soil‐stream‐river continuum, which results in pronounced compositional shifts downstream. The soil‐stream interface was a hot spot of DOM degradation, where biopolymers and low molecular weight (LMW) compounds were selectively removed. In contrast, processing in the stream channel was dominated by the degradation of humic‐like aromatic DOM, likely driven by photolysis, with little further degradation of either biopolymers or LMW compounds. Overall, there was a high degree of coherence between the patterns observed in DOM chemical composition, optical properties, and molecular profiles, and none of these approaches pointed to measurable production of new DOM components, suggesting that the DOM pools removed during transit were likely mineralized to CO2. Our first order estimates suggest that rates of soil‐derived DOM mineralization could potentially sustain over half of the measured CO2 emissions from this stream network, with mineralization of biopolymers and humic substances contributing roughly equally to these fluvial emissions.

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Section: Resultsmentioning

confidence: 98%

The Optical, Chemical, and Molecular Dissolved Organic Matter Succession Along a Boreal Soil‐Stream‐River Continuum

et al. 2017

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“…Here, I suggest that this could result from stream respiration alone accounting for 23% ± 11% of the annual total inputs of DOC in a first order stream, assuming implicitly that sunlight and other potential processes did not play a significant role (see below). More DOC losses will occur downstream through the whole network (Raymond et al ; Bertuzzo et al ; Moody and Worrall ). The stream efficiency to mineralize carbon will be much lower under very high flows (not part of this study) where POC losses are likely to be significant contributors to the carbon flux.…”

Section: Discussionmentioning

confidence: 99%

“…This may not be the case (e.g., Dawson et al 2001;Dawson et al 2002), but at least the metabolic rates and hydrological behaviors were found to be similar in two independent streams with significant lateral inflows and the upscaling was limited to the same stream order. Further studies should explore the downstream effects through the river network (e.g., Raymond et al 2016;Bertuzzo et al 2017;Moody and Worrall 2017;Ulseth et al 2018).…”

Section: Upscalingmentioning

confidence: 99%

Hydrological pulses and burning of dissolved organic carbon by stream respiration

Demars

2018

Limnology & Oceanography

103

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Stream metabolism plays a significant role in the global carbon cycle. Storm events can lower stream metabolic activities by removing standing biomass and river bed stock of organic matter. However, hydrological events could also stimulate stream ecosystem respiration (ER) by providing dissolved organic carbon (DOC) derived from soils. Here, I show how hydrological connectivity between land and water affects fluxes of DOC and daily whole stream bacterial respiration over an annual cycle in streams rich in DOC in north‐west Europe. The novelty of the approach resides in combining continuous whole stream metabolism with hydrological flow paths and water chemistry to quantify the in situ fate of DOC at ecosystem scale, with an estimation of all major stream carbon fluxes (land‐derived CO2, in‐stream biotic CO2, HCO3, and DOC) at catchment scale. An average 23% ± 11% of the annual DOC inputs from the land was respired away by benthic microbial metabolism within about an hour of transit time in small watersheds (about 1 km2). Stream ER was highly related to discharge and was stimulated for as long as the hydrological connectivity between land and water remained, as indicated by soil moisture continuous monitoring. In‐stream heterotrophic respiration represented 16% ± 7% of the annual total carbon fluxes (also including HCO3, land‐derived CO2, and DOC) at the catchment outlet under stable flows. This study suggests that DOC supply (soil carbon loss) will increase with rainfall, stimulating aquatic respiration, and CO2 emissions in streams.

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“…These rates of pool “turnover” may be important for peatland chemistry and peat accumulation rates (Beer & Blodau, ; Morris & Waddington, ) and for understanding aquatic carbon fluxes from peatlands with pools, particularly if the carbon processing is different between natural and artificial pool systems. Pools with longer water residence times may be subject to enhanced photochemical processing of dissolved organic carbon (e.g., Pickard, Heal, McLeod, & Dinsmore, ; all pools were ≤50 cm deep); hence, the quality of dissolved organic carbon may vary between pools, which could be important for downstream water treatment for potable supply (Moody & Worrall, ; Worrall & Burt, ). On the other hand, the slower turnover of water in some larger pools may mean that the remaining carbon is largely recalcitrant, and little further processing can occur, whereas in smaller pools, processing of carbon can continue for longer periods if the pool water volume is replaced more frequently.…”

Section: Discussionmentioning

confidence: 99%

Water‐level dynamics in natural and artificial pools in blanket peatlands

Holden

Moody

Turner

et al. 2018

Hydrological Processes

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Perennial pools are common natural features of peatlands, and their hydrological functioning and turnover may be important for carbon fluxes, aquatic ecology, and downstream water quality. Peatland restoration methods such as ditch blocking result in many new pools. However, little is known about the hydrological function of either pool type. We monitored six natural and six artificial pools on a Scottish blanket peatland. Pool water levels were more variable in all seasons in artificial pools having greater water level increases and faster recession responses to storms than natural pools. Pools overflowed by a median of 9 and 54 times pool volume per year for natural and artificial pools, respectively, but this varied widely because some large pools had small upslope catchments and vice versa. Mean peat water‐table depths were similar between natural and artificial pool sites but much more variable over time at the artificial pool site, possibly due to a lower bulk specific yield across this site. Pool levels and pool‐level fluctuations were not the same as those of local water tables in the adjacent peat. Pool‐level time series were much smoother, with more damped rainfall or recession responses than those for peat water tables. There were strong hydraulic gradients between the peat and pools, with absolute water tables often being 20–30 cm higher or lower than water levels in pools only 1–4 m away. However, as peat hydraulic conductivity was very low (median of 1.5 × 10−5 and 1.4 × 10−6 cm s−1 at 30 and 50 cm depths at the natural pool site), there was little deep subsurface flow interaction. We conclude that (a) for peat restoration projects, a larger total pool surface area is likely to result in smaller flood peaks downstream, at least during summer months, because peatland bulk specific yield will be greater; and (b) surface and near‐surface connectivity during storm events and topographic context, rather than pool size alone, must be taken into account in future peatland pool and stream chemistry studies.

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Modeling rates of DOC degradation using DOM composition and hydroclimatic variables

Cited by 25 publications

References 69 publications

The Optical, Chemical, and Molecular Dissolved Organic Matter Succession Along a Boreal Soil‐Stream‐River Continuum

The Optical, Chemical, and Molecular Dissolved Organic Matter Succession Along a Boreal Soil‐Stream‐River Continuum

Hydrological pulses and burning of dissolved organic carbon by stream respiration

Water‐level dynamics in natural and artificial pools in blanket peatlands

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