Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean

Vallières, Catherine; Retamal, Leira; Ramlal, Patricia; Osburn, Christopher L.; Vincent, Warwick F.

doi:10.1016/j.jmarsys.2007.12.002

Cited by 86 publications

(71 citation statements)

References 67 publications

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“…6); however, our estimates in these cases were similar to those found during prior studies. For example, BA in surface water averaged 67 × 10 4 cells mL −1 along a 300 km transect from the Mackenzie River into the Beaufort Sea (Vallières et al 2008), and fluctuated from 10 to 100 × 10 4 cells mL −1 in Franklin Bay (Garneau et al 2008) and on the Mackenzie Shelf (Matsuoka et al 2015).…”

Section: Photoreactivity Of Mackenzie River Freshet Dommentioning

confidence: 99%

“…Heterotrophic grazers subsequently consume bacteria, which shunts otherwise unavailable carbon, organic matter, and energy back into the aquatic food web via the microbial loop (Azam et al 1983). This is a critical process that mobilizes otherwise unavailable DOM molecules in high-latitude aquatic environments (Cole 1999;Cory et al 2014) via bacteria, contributing to overall food web production in Mackenzie Delta lakes (Spears and Lesack 2006;Tank et al 2011), the Mackenzie River (Vallières et al 2008), and the nearshore Beaufort Sea (Garneau et al 2008;Bell et al 2016). Because DOM is an important component of carbon budgets in aquatic ecosystems, an understanding of how photodegradation alters DOM bioavailability is critical to understand carbon fluxes through the landscape.…”

Section: Introductionmentioning

confidence: 99%

“…BEAU community: Freshwater discharged from the Mackenzie Delta mixes with seawater in the Beaufort basin, altering the DOM composition and reducing C concentrations offshore (Emmerton et al 2008;Vallières et al 2008). The BEAU bacterial community was collected from the nearshore Beaufort shortly before ice out, and had a salinity of 0.95 ppt, suggesting that mixing with ocean water was restricted by ice cover and that the community largely originated in the Mackenzie River plume.…”

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Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

Gareis

Lesack

2018

Arctic Science

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Lake-rich Arctic river deltas are recharged with terrigenous dissolved organic matter (DOM) during the yearly peak water period corresponding with the solstice (24 h day −1 solar irradiance). Bacteria-free DOM collected during peak Mackenzie River discharge was exposed to sunlight for up to 14 days in June 2010. As solar exposure increased, carbon and lignin concentrations declined (10% and 42%, respectively, after 14 days), as did DOM absorptivity (62% after 14 days), aromaticity, and molecular weight. Photochemical changes were on par with those normally observed in Mackenzie Delta lakes over the entire open-water season. When irradiated freshet DOM was provided as a substrate, no significant differences were observed in community-level metabolism among five bacterial communities from representative delta habitats. However, bacterial abundance was significantly greater when nonirradiated (0 day) rather than irradiated DOM (7 or 14 days) was provided, while cell-specific metabolic measures revealed that per-cell bacterial production and growth efficiency were significantly greater when communities were provided irradiated substrate. This complex response to rapid DOM photodegradation may result from the production of inhibitory reactive oxygen species (ROS), along with shifts in bacterial community composition to species that are better able to tolerate ROS, or metabolize the labile photodegraded DOM.Key words: circumpolar river delta, photodegradation, dissolved organic matter, bacterial metabolism, Mackenzie River.Résumé : Les deltas arctiques riches en lacs sont rechargés en matière organique dissoute (MOD) terrigène pendant la période annuelle de crue maximale correspondant au solstice (irradiance solaire 24 h jour −1 ). De la MOD sans bactéries collectée durant la pointe de crue du fleuve Mackenzie a été exposée à la lumière du soleil pendant 14 jours en juin 2010. À mesure que l'exposition solaire se prolongeait, les concentrations de carbone et lignine diminuaient (10 % et 42 % respectivement, après 14 jours), tout comme le pouvoir d'absorption de la MOD (62 % après 14 jours), son aromaticité et son poids moléculaire. Les changements photochimiques correspondaient à ceux normalement observés dans les lacs du delta du Mackenzie sur l'ensemble de la saison des eaux libres. Lorsque de la MOD de crue irradiée fut utilisée comme substrat, aucune différence significative n'a été observée quant au métabolisme au niveau de la communauté en comparant cinq communautés bactériennes issues d'habitats représentatifs du delta. Néanmoins, l'abondance de bactéries était considérablement plus grande lorsque de la For personal use only.MOD non irradiée (0 jour) a été fournie au lieu de la MOD irradiée (7 ou 14 jours), tandis que les mesures de l'activité métabolique spécifique aux cellules ont révélé que la production bactérienne par cellule et le rendement de croissance étaient considér-ablement plus élevés lorsque les communautés avaient accès au substrat irradié. Cette réaction complexe à la photodégradation...

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Section: Photoreactivity Of Mackenzie River Freshet Dommentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

Gareis

Lesack

2018

Arctic Science

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“…Decomposition processes in aquatic ecosystems are mediated by bacterial communities that can be separated into two ecological groups: (1) free-living bacteria, in which solitary cells are suspended in the medium and break down dissolved organic matter; and (2) particle-attached bacteria, in which the communities are associated with various size-fractions of particles and break down this particulate organic material, as well as accessing dissolved materials (Kirchman and Mitchell, 1982;Vallières et al, 2008). In both cases, these activities result in consumption of oxygen, production of carbon dioxide, and the mineralization of organic materials.…”

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confidence: 99%

“…A study of seven freshwater ecosystems including two marsh-systems showed that a small proportion of particle-attached bacteria (< 10 %) was associated with > 40 % of the bacterial community activity, and it was hypothesized that lake size may influence the presence of particulate matter for colonization via interactions between sediments and the water column (Kirchman and Mitchell, 1982). In the turbid waters of the Mackenzie River, which are strongly influenced by permafrost as well as fluvial erosion, more than 90 % of the total bacterial production was associated with particles > 3 µm (Vallières et al, 2008). Similarly, in the coastal waters of the Beaufort Sea, the > 3 µm sizefraction often accounted for > 50 % of total bacterial production (Garneau et al, 2006;Galand et al, 2008).…”

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Bacterial production in subarctic peatland lakes enriched by thawing permafrost

et al. 2016

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Abstract. Peatlands extend over vast areas of the northern landscape. Within some of these areas, lakes and ponds are changing in size as a result of permafrost thawing and erosion, resulting in mobilization of the carbon-rich peatland soils. Our aims in the present study were to characterize the particle, carbon and nutrient regime of a set of thermokarst (thaw) lakes and their adjacent peatland permafrost soils in a rapidly degrading landscape in subarctic Québec, Canada, and by way of fluorescence microscopy, flow cytometry, production measurements and an in situ enrichment experiment, determine the bacterial characteristics of these waters relative to other thaw lakes and rock-basin lakes in the region. The soil active layer in a degrading palsa (peatland permafrost mound) adjacent to one of the lakes contained an elevated carbon content (51 % of dry weight), high C : N ratios (17 : 1 by mass), and large stocks of other elements including N (3 % of dry weight), Fe (0.6 %), S (0.5 %), Ca (0.5 %) and P (0.05 %). Two permafrost cores were obtained to a depth of 2.77 m in the palsa, and computerized tomography scans of the cores confirmed that they contained high concentrations (> 80 %) of ice. Upon thawing, the cores released nitrate and dissolved organic carbon (from all core depths sampled), and soluble reactive phosphorus (from bottom depths), at concentrations well above those in the adjacent lake waters. The active layer soil showed a range of particle sizes with a peak at 229 µm, and this was similar to the distribution of particles in the upper permafrost cores. The particle spectrum for the lake water overlapped with those for the soil, but extended to larger (surface water) or finer (bottom water) particles. On average, more than 50 % of the bacterial cells and bacterial production was associated with particles > 3 µm. This relatively low contribution of free-living cells (operationally defined as the < 1 µm fraction) to bacterial production was a general feature of all of the northern lakes sampled, including other thaw lakes and shallow rock-basin lakes (average ± SE of 25 ± 6 %). However, a distinguishing feature of the peatland thaw lakes was significantly higher bacterial specific growth rates, which averaged 4 to 7 times higher values than in the other lake types. The in situ enrichment experiment showed no difference between organic carbon or phosphorus enrichment treatments at day 5 relative to the control, however there was an apparent increase in bacterial growth rates between days 1 and 5 in the soil and the carbon plus phosphorus enrichments. Collectively these results indicate that particles, nutrients and carbon are released by degrading permafrost peatland soils into their associated thermokarst lakes, creating favorable conditions for production by particle-based as well as free-living aquatic bacterial communities. The reduced bacterial concentrations despite high cellular growth rates imply that there is control of their population size by loss-related factors such as grazing and vira...

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Transitions in Arctic ecosystems: Ecological implications of a changing hydrological regime

et al. 2016

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Numerous international scientific assessments and related articles have, during the last decade, described the observed and potential impacts of climate change as well as other related environmental stressors on Arctic ecosystems. There is increasing recognition that observed and projected changes in freshwater sources, fluxes, and storage will have profound implications for the physical, biogeochemical, biological, and ecological processes and properties of Arctic terrestrial and freshwater ecosystems. However, a significant level of uncertainty remains in relation to forecasting the impacts of an intensified hydrological regime and related cryospheric change on ecosystem structure and function. As the terrestrial and freshwater ecology component of the Arctic Freshwater Synthesis, we review these uncertainties and recommend enhanced coordinated circumpolar research and monitoring efforts to improve quantification and prediction of how an altered hydrological regime influences local, regional, and circumpolar-level responses in terrestrial and freshwater systems. Specifically, we evaluate (i) changes in ecosystem productivity; (ii) alterations in ecosystem-level biogeochemical cycling and chemical transport; (iii) altered landscapes, successional trajectories, and creation of new habitats; (iv) altered seasonality and phenological mismatches; and (v) gains or losses of species and associated trophic interactions. We emphasize the need for developing a process-based understanding of interecosystem interactions, along with improved predictive models. We recommend enhanced use of the catchment scale as an integrated unit of study, thereby more explicitly considering the physical, chemical, and ecological processes and fluxes across a full freshwater continuum in a geographic region and spatial range of hydroecological units (e.g., stream-pond-lake-river-near shore marine environments).

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Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean

Cited by 86 publications

References 67 publications

Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

Bacterial production in subarctic peatland lakes enriched by thawing permafrost

Transitions in Arctic ecosystems: Ecological implications of a changing hydrological regime

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