Bioavailability and bacterial degradation rates of dissolved organic matter in a temperate coastal area during an annual cycle

Lønborg, Christian; Davidson, Keith; Álvarez-Salgado, X. Antón; Miller, Axel E. J.

doi:10.1016/j.marchem.2009.02.003

Cited by 113 publications

(59 citation statements)

References 38 publications

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“…This means that the initial qualities of DOC and DON (as specified in Table 2), determined by the catchment characteristics, were the major factor defining the biodegradability of DOC and DON, which supports our main hypothesis. Bioavailability of DOM has been previously reported to have strong seasonal variation (Lønborg et al, 2009;Sintes et al, 2010). However, in the experiments presented here the season surprisingly did not have significant effect on DOC and DON degradation in spite of the seasonal changes in DOM quantity and quality in study estuaries (Fig.…”

Section: Doc and Don Degradationmentioning

confidence: 45%

Bioavailability of riverine dissolved organic matter in three Baltic Sea estuaries and the effect of catchment land use

et al. 2013

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Abstract. The microbial degradation of dissolved organic carbon and nitrogen (DOC, DON) was studied in three Finnish boreal estuaries with contrasting land use patterns (Kiiminkijoki -natural forest and peatland; Kyrönjoki -agricultural; Karjaanjoki -mixed/urban). Bioassays of 12-18 d long durations were used in 3 seasons at in situ temperatures. Besides the bulk parameters, a suite of dissolved organic matter (DOM) quality parameters were also investigated, including colored DOM (CDOM), fluorescent DOM and the molecular weight of DOM. Bioavailable DOC and DON pools varied significantly between the estuaries, from 7.9 to 10.6 % and from 5.5 to 21.9 %, respectively. DOM originating from the catchment dominated by natural forests and peatlands (Kiiminkijoki) had the lowest DOC and DON degradation rates, as well as the lowest proportions of biodegradable DOC and DON. A greater proportion of agricultural land in the catchment increased the bioavailability of DON, but not the bioavailability of DOC (Kyrönjoki). Additionally, DOM quality varied significantly between the estuaries, and DOM originating from the agricultural Kyrönjoki catchment sustained higher DOC and DON degradation rates and higher bacterial growth efficiency (BGE) compared to those of the natural forest and peat dominated Kiiminkijoki catchment. The quality of DOM, indicated by differences in CDOM, fluorescent DOM and molecular weight, varied between estuaries with differing land use and was concluded to be major driver of BGE of these systems and thereafter to the microbial CO 2 fluxes from the estuaries. The differences in BGE resulted in a 5-fold difference in the calculated daily bacterial CO 2 emissions between the study's estuaries due to bacterial activity, ranging from 40 kg C d −1 in the Karjaanjoki estuary to 200 kg C d −1 in the Kyrönjoki estuary. Lower DOC : DON ratios, smaller molecular weight and higher CDOM absorption spectral slope values of DOM resulted in higher proportion of the initial DOC and DON being transferred to microbial growth and therefore to the pelagic food web. The pristine, peatland and forest-dominated Kiiminkijoki catchment had the lowest BGE, and therefore proportionally highest CO 2 fluxes.

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Section: Doc and Don Degradationmentioning

confidence: 45%

Bioavailability of riverine dissolved organic matter in three Baltic Sea estuaries and the effect of catchment land use

et al. 2013

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“…In order to overcome methodological differences between the few available studies, we only included data where changes in DOC concentration over time had been measured at different temperatures. These include laboratory incubations using phytoplankton-derived DOC (Seiki et al, 1991), marine humic substances (Bussmann, 1999), and DOC collected in a coastal system (Lønborg et al, 2009). In one case (Bussmann, 1999), only initial DOC was measured but the time course of dissolved oxygen was followed over time.…”

Section: Determination Of Doc L and Doc Sl Decay Constants From Incubmentioning

confidence: 99%

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

et al. 2018

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More than 96% of organic carbon in the ocean is in the dissolved form, most of it with lifetimes of decades to millennia. Yet, we know very little about the temperature sensitivity of dissolved organic carbon (DOC) degradation in a warming ocean. Combining independent estimates from laboratory experiments, oceanographic cruises and a global ocean DOC cycling model, we assess the relationship between DOC decay constants and seawater temperatures. Our results show that the apparent activation energy of DOC decay (E a ) increases by three-fold from the labile (lifetime of days) and semi-labile (lifetime of months) to the semi-refractory (lifetime of decades) DOC pools, with only minor differences between the world's largest ocean basins. This translates into increasing temperature coefficients (Q 10 ) from 1.7-1.8 to 4-8, showing that the generalized assumption of a constant Q 10 of ∼2 for biological rates is not universally applicable for the microbial degradation of DOC in the ocean. Therefore, rising ocean temperatures will preferentially impact the microbial degradation of the more recalcitrant and larger of the three studied pools. Assuming a uniform 1 • C warming scenario throughout the ocean, our model predicts a global decrease of the DOC reservoir by 7 ± 1 Pg C. This represents a 15% reduction of the semi-labile + semi-refractory DOC pools.

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“…Marine and estuarine systems are biogeochemically responsive to fixed nitrogen (N), exhibiting rapid uptake of dissolved inorganic N (DIN) and dissolved organic N (DON) (Seitzinger et al, 2002;Seitzinger and Sanders, 1999). In estuaries, however, DIN accounts for only a portion of the total N inputs, while DON is often a much more important (30-80 %) component of the dissolved N pool (Berman and Bronk, 2003;Lønborg et al, 2009). In marine sediments, a large portion of particulate organic matter (POM) is recycled by bacterial hydrolysis during early sedimentary diagenesis; this results in the accumulation of dissolved organic components (DOM) in the sediment porewater.…”

Section: Introductionmentioning

confidence: 99%

“…The differential susceptibility of dissolved organic components with variable carbon-to-nitrogen (C / N) ratios to microbial degradation within the sediments, and its role with regards to ecosystem respiration and the generation of basin-scale oxygen deficits (e.g. hypoxia) has been a matter of unresolved debate (Faganeli et al, 1991;Lahajnar et al, 2005;Lønborg et al, 2009). Therefore, the identification of key reaction and transport processes that affect porewater DOC and DON distributions is critical to assessing the significance of benthic metabolism during early sedimentary diagenesis and the associated alteration of the bulk sedimentary organic matter pool.…”

Section: Introductionmentioning

confidence: 99%

Benthic fluxes of dissolved organic nitrogen in the lower St. Lawrence estuary and implications for selective organic matter degradation

et al. 2013

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Abstract. The distribution of dissolved organic nitrogen (DON) and carbon (DOC) in sediment porewaters was determined at nine locations along the St. Lawrence estuary and in the gulf of St. Lawrence. In a previous manuscript (Alkhatib et al., 2012a), we have shown that this study area is characterized by gradients in the sedimentary particulate organic matter (POM) reactivity, bottom water oxygen concentrations, and benthic respiration rates. Based on the porewater profiles, we estimated the benthic diffusive fluxes of DON and DOC in the same area. Our results show that DON fluxed out of the sediments at significant rates (110 to 430 µmol m −2 d −1 ). DON fluxes were positively correlated with sedimentary POM reactivity and varied inversely with sediment oxygen exposure time (OET), suggesting direct links between POM quality, aerobic remineralization and the release of DON to the water column. DON fluxes were on the order of 30 to 64 % of the total benthic inorganic fixed N loss due to denitrification, and often exceeded the diffusive nitrate fluxes into the sediments. Hence they represented a large fraction of the total benthic N exchange, a result that is particularly important in light of the fact that DON fluxes are usually not accounted for in estuarine and coastal zone nutrient budgets. In contrast to DON, DOC fluxes out of the sediments did not show any significant spatial variation along the Laurentian Channel (LC) between the estuary and the gulf (2100 ± 100 µmol m −2 d −1 ). The molar C / N ratio of dissolved organic matter (DOM) in porewater and the overlying bottom water varied significantly along the transect, with lowest C / N in the lower estuary (5-6) and highest C / N (> 10) in the gulf. Large differences between the C / N ratios of porewater DOM and POM are mainly attributed to a combination of selective POM hydrolysis and elemental fractionation during subsequent DOM mineralization, but selective adsorption of DOM to mineral phases could not be excluded as a potential C / N fractionating process. The extent of this C-versus N-element partitioning seems to be linked to POM reactivity and redox conditions in the sediment porewaters. Our results thus highlight the variable effects selective organic matter (OM) preservation can have on bulk sedimentary C / N ratios, decoupling the primary source C / N signatures from those in sedimentary paleoenvironmental archives. Our study further underscores that the role of estuarine sediments as efficient sinks of bioavailable nitrogen is strongly influenced by the release of DON during early diagenetic reactions, and that DON fluxes from continental margin sediments represent an important internal source of N to the ocean.

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Bioavailability and bacterial degradation rates of dissolved organic matter in a temperate coastal area during an annual cycle

Cited by 113 publications

References 38 publications

Bioavailability of riverine dissolved organic matter in three Baltic Sea estuaries and the effect of catchment land use

Bioavailability of riverine dissolved organic matter in three Baltic Sea estuaries and the effect of catchment land use

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

Benthic fluxes of dissolved organic nitrogen in the lower St. Lawrence estuary and implications for selective organic matter degradation

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