Processing of humic-rich riverine dissolved organic matter by estuarine bacteria: effects of predegradation and inorganic nutrients

Asmala, Eero; Autio, Riitta; Kaartokallio, Hermanni; Stedmon, Colin A.; Thomas, David N.

doi:10.1007/s00027-014-0346-7

Cited by 68 publications

(54 citation statements)

References 75 publications

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“…Consequently, it may only be during high-flow events that untransformed peat-derived DOC enters the estuary, where it is susceptible to flocculation and other removal processes. The untransformed DOC delivered by high flow events may also be relatively enriched in nutrients and therefore potentially more bioavailable (Asmala et al 2014a). Additional high-flow estuary surveys would clearly be needed to confirm this interpretation and quantify the relative contributions of flocculation and microbial degradation to DOC loss.…”

Section: Discussionmentioning

confidence: 99%

“…In peatland streams, nutrient levels are low, so biological processing may be slow relative to in-stream residence times. For catchments with varying proportions of peat cover in northern Finland, potential DOC biodegradation rates in laboratory incubations (nutrients were added to prevent nutrient limitation) ranged from 4.1 to 17.9 % (Hulatt et al 2014) and averaged 8.89 % (Asmala et al 2014a) during incubations lasting 55 and 39 days, respectively. In a batch experiment Stutter et al (2013) found that similar to other northern rivers, a maximum 19 % of DOM isolated from a Scottish moorland stream was biodegradable during 41-days incubation, and that the proportion of DOM decomposed could be predicted by DOM quality and 15 N content.…”

Section: Introductionmentioning

confidence: 99%

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Sporadic hotspots for physico-chemical retention of aquatic organic carbon: from peatland headwater source to sea

et al. 2015

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Few studies have quantified the role of instream processes on net dissolved and particulate organic carbon (DOC and POC, respectively) export from peatland catchments, and those that have offer conflicting evidence. In this study, we evaluated evidence for active organic matter processing under field conditions, via a coordinated campaign across four UK catchments with peatland headwaters, targeted on potential 'hotspots' and 'hot moments' of physico-chemical carbon cycling. We hypothesised that specific hotspots and hot moments would occur where waters enriched with DOC and POC sourced from headwaters are exposed to: (1) mixing with freshwaters of different pH, conductivity and metal concentrations; and (2) mixing with seawater during autumn when DOC concentrations were at their highest. We observed instances of POC removal in headwaters, and potential for rapid conversion between dissolved and particulate carbon forms and for net removal of peat-derived carbon at confluences further downstream (where observed, on the order of 52-75 % for POC, and 5-44 % for DOC). Estuary transect surveys indicated that up to 30 % of fluvial DOC can be removed under high flow conditions. However, in the majority of cases concentrations remained within the range that would be expected based on conservative transport. These findings indicate that rapid (e.g. solubility-related) processes within the river system may be important but sporadic, thus are unlikely to provide major removal pathways for peat-derived organic carbon.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sporadic hotspots for physico-chemical retention of aquatic organic carbon: from peatland headwater source to sea

et al. 2015

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“…Some studies have reported relative losses of colored DOC across lake basins with increasing theoretical residence times (Köhler et al, 2013;Curtis and Schindler, 1997), while other studies have found preferential loss of noncolored DOC in laboratory biodegradation experiments (Hansen et al, 2016) and in time series analyses of brown headwater lakes (Berggren et al, 2009). Although bacteria do consume colored humic substances at low rates (Tranvik, 1988), the biological degradation of DOC is unlikely a mechanism leading to selective color loss because bacteria tend to mainly consume noncolored DOC (Asmala et al, 2014;Hansen et al, 2016). An exception is the apparent preferential use of organo-ferric colloids by bacteria, whereby the removed color comes from iron, not DOC (Oleinikova et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Quality transformation of dissolved organic carbon during water transit through lakes: contrasting controls by photochemical and biological processes

et al. 2018

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Abstract. Dissolved organic carbon (DOC) may be removed, transformed, or added during water transit through lakes, resulting in changes in DOC composition and pigmentation (color). However, the process-based understanding of these changes is incomplete, especially for headwater lakes. We hypothesized that because heterotrophic bacteria preferentially consume noncolored DOC, while photochemical processing removes colored fractions, the overall changes in DOC color upon water passage through a lake depend on the relative importance of these two processes, accordingly. To test this hypothesis we combined laboratory experiments with field studies in nine boreal lakes, assessing both the relative importance of different DOC decay processes (biological or photochemical) and the loss of color during water transit time (WTT) through the lakes. We found that influence from photo-decay dominated changes in DOC quality in the epilimnia of relatively clear headwater lakes, resulting in systematic and selective net losses of colored DOC. However, in highly pigmented brown-water lakes (absorbance at 420 nm > 7 m −1 ) biological processes dominated, and there was no systematic relationship between color loss and WTT. Moreover, in situ data and dark experiments supported our hypothesis on the selective microbial removal of nonpigmented DOC, mainly of low molecular weight, leading to persistent water color in these highly colored lakes. Our study shows that brown headwater lakes may not conform to the commonly reported pattern of the selective removal of colored constituents in freshwaters, as DOC can show a sustained degree of pigmentation upon transit through these lakes.

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“…Terrestrial DOC is considered to consist of a larger‐part semilabile and refractory DOC than marine‐produced DOC and has been estimated to be removed on time scales of 10 to 100 years from the oceans [ Opsahl and Benner , ; Manizza et al , ]. Only a minor part of the DOC ter seems to be removed on time scales of days to months [ Wikner et al , ; Asmala et al , , ].…”

Section: Introductionmentioning

confidence: 99%

Tracing terrestrial DOC in the Baltic Sea—A 3‐D model study

Fransner

Nycander

Mörth

et al. 2016

Global Biogeochemical Cycles

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The fate of terrestrial organic matter brought to the coastal seas by rivers and its role in the global carbon cycle are still not very well known. Here the degradation rate of terrestrial dissolved organic carbon (DOCter) is studied in the Baltic Sea, a subarctic semienclosed sea, by releasing it as a tracer in a 3‐D circulation model and applying linear decay constants. A good agreement with available observational data is obtained by parameterizing the degradation in two rather different ways: one by applying a decay time on the order of 10 years to the whole pool of DOCter and one by dividing the DOCter into one refractory pool and one pool subject to a decay time on the order of 1 year. The choice of parameterization has a significant effect on where in the Baltic Sea the removal takes place, which can be of importance when modeling the full carbon cycle and the CO2 exchange with the atmosphere. In both cases the biogeochemical decay operates on time scales less than the water residence time. Therefore, only a minor fraction of the DOCter reaches the North Sea, whereas approximately 80% is removed by internal sinks within the Baltic Sea. This further implies that DOCter mineralization is an important link in land‐sea‐atmosphere cycling of carbon in coastal and shelf seas that are heavily influenced by riverine DOC.

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Processing of humic-rich riverine dissolved organic matter by estuarine bacteria: effects of predegradation and inorganic nutrients

Cited by 68 publications

References 75 publications

Sporadic hotspots for physico-chemical retention of aquatic organic carbon: from peatland headwater source to sea

Sporadic hotspots for physico-chemical retention of aquatic organic carbon: from peatland headwater source to sea

Quality transformation of dissolved organic carbon during water transit through lakes: contrasting controls by photochemical and biological processes

Tracing terrestrial DOC in the Baltic Sea—A 3‐D model study

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