99 research outputs found
Modern to millennium-old greenhouse gases emitted from ponds and lakes of the Eastern Canadian Arctic (Bylot Island, Nunavut)
Ponds and lakes are widespread across the rapidly changing permafrost
environments. Aquatic systems play an important role in global
biogeochemical cycles, especially in greenhouse gas (GHG) exchanges between
terrestrial systems and the atmosphere. The source, speciation and emission
rate
of carbon released from permafrost landscapes are strongly influenced by
local conditions, hindering pan-Arctic generalizations. This study reports
on GHG ages and emission rates from aquatic systems located on Bylot Island,
in the continuous permafrost zone of the Eastern Canadian Arctic. Dissolved
and ebullition gas samples were collected during the summer season from
different types of water bodies located in a highly dynamic periglacial
valley: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes.
The results showed strikingly different ages and fluxes depending on aquatic
system types. Polygonal ponds were net sinks of dissolved CO2, but
variable sources of dissolved CH4. They presented the highest
ebullition fluxes, 1 or 2 orders of magnitude higher than from other
ponds and lakes. Trough ponds appeared as substantial GHG sources,
especially when their edges were actively eroding. Both types of ponds
produced modern to hundreds of years old (< 550 yr BP) GHG, even if
trough ponds could contain much older carbon (> 2000 yr BP)
derived from freshly eroded peat. Lakes had small dissolved and ebullition
fluxes, however they released much older GHG, including millennium-old
CH4 (up to 3500 yr BP) from lake central areas. Acetoclastic
methanogenesis dominated at all study sites and there was minimal, if any,
methane oxidation in gas emitted through ebullition. These findings provide
new insights on GHG emissions by permafrost aquatic systems and their
potential positive feedback effect on climate
Sources of mycosporine-like amino acids in planktonic Chlorella-bearing ciliates (Ciliophora)
Mycosporine-like amino acids (MAAs) are a family of secondary metabolites known to protect organisms exposed to solar UV radiation. We tested their distribution among several planktonic ciliates bearing Chlorella isolated from an oligo-mesotrophic lake in Tyrol, Austria. In order to test the origin of these compounds, the MAAs were assessed by high performance liquid chromatography in both the ciliates and their symbiotic algae.Considering all Chlorella-bearing ciliates, we found: (i) seven different MAAs (mycosporine-glycine, palythine, asterina-330, shinorine, porphyra-334, usujirene, palythene); (ii) one to several MAAs per species and (iii) qualitative and quantitative seasonal changes in the MAAs (e.g. in Pelagodileptus trachelioides). In all species tested, concentrations of MAAs were always <1% of ciliate dry weight.Several MAAs were also identified in the Chlorella isolated from the ciliates, thus providing initial evidence for their symbiotic origin. In Uroleptus sp., however, we found evidence for a dietary source of MAAs.Our results suggest that accumulation of MAAs in Chlorella-bearing ciliates represents an additional benefit of this symbiosis and an adaptation for survival in sunlit, UV-exposed waters
High methylmercury in Arctic and subarctic ponds is related to nutrient levels in the warming eastern Canadian Arctic
Permafrost thaw ponds are ubiquitous in the eastern
Canadian Arctic, yet little information exists on their potential as
sources of methylmercury (MeHg) to freshwaters. They are
microbially active and conducive to methylation of inorganic
mercury, and are also affected by Arctic warming. This multiyear
study investigated thaw ponds in a discontinuous permafrost region
in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a
continuous permafrost region in the Arctic tundra (Bylot Island,
NU). MeHg concentrations in thaw ponds were well above levels
measured in most freshwater ecosystems in the Canadian Arctic
(>0.1 ng L−1). On Bylot, ice-wedge trough ponds showed
significantly higher MeHg (0.3−2.2 ng L−1) than polygonal
ponds (0.1−0.3 ng L−1) or lakes (<0.1 ng L−1). High MeHg was
measured in the bottom waters of Subarctic thaw ponds near
Kuujjuarapik (0.1−3.1 ng L−1). High water MeHg concentrations in thaw ponds were strongly correlated with variables
associated with high inputs of organic matter (DOC, a320, Fe), nutrients (TP, TN), and microbial activity (dissolved CO2 and
CH4). Thawing permafrost due to Arctic warming will continue to release nutrients and organic carbon into these systems and
increase ponding in some regions, likely stimulating higher water concentrations of MeHg. Greater hydrological connectivity
from permafrost thawing may potentially increase transport of MeHg from thaw ponds to neighboring aquatic ecosystems
Increase in photosynthetic efficiency as a strategy of planktonic organisms exploiting deep lake layers
Contrasting effects of ultraviolet radiation on the growth efficiency of freshwater bacteria
Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment
As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wildfire, and hydrologic carbon flux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identified water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous findings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced
Carbon dynamics in highly heterotrophic subarctic thaw ponds
Global warming has accelerated the formation of
permafrost thaw ponds in several subarctic and arctic regions.
These ponds are net heterotrophic as evidenced by
their greenhouse gas (GHG) supersaturation levels (CO2
and CH4), and generally receive large terrestrial carbon inputs
from the thawing and eroding permafrost. We measured
seasonal and vertical variations in the concentration
and type of dissolved organic matter (DOM) in five subarctic
thaw (thermokarst) ponds in northern Quebec, and explored
how environmental gradients influenced heterotrophic and
phototrophic biomass and productivity. Late winter DOM
had low aromaticity indicating reduced inputs of terrestrial
carbon, while the high concentration of dissolved organic
carbon (DOC) suggests that some production of nonchromophoric
dissolved compounds by the microbial food
web took place under the ice cover. Summer DOM had a
strong terrestrial signature, but was also characterized with
significant inputs of algal-derived carbon, especially at the
pond surface. During late winter, bacterial production was
low (maximum of 0.8 mg C m−3 d
−1
) and was largely based
on free-living bacterioplankton (58 %). Bacterial production
in summer was high (up to 58 mg C m−3 d
−1
), dominated
by particle-attached bacteria (67 %), and strongly correlated
with the amount of terrestrial carbon. Primary production
was restricted to summer surface waters due to strong light
limitation deeper in the water column or in winter. The phototrophic
biomass was equal to the heterotrophic biomass,
but as the algae were mostly composed of mixotrophic
species, most probably they used bacteria rather than solar
energy in such shaded ponds. Our results point to a strong
heterotrophic energy pathway in these thaw pond ecosystems,
where bacterioplankton dominates the production of
new carbon biomass in both summer and winter.peerReviewe
Changing Climates, Earth Systems and Society. Chapter 6: Climate and Lacustrine Ecosystems
Extremotrophs, extremophiles and broadband pigmentation strategies in a high arctic ice shelf ecosystem
Remnant ice shelves along the northern coast of Ellesmere Island, Nunavut, Canada (∼83°N) provide a habitat for cryo-tolerant microbial mat communities. Bioassays of bacterial and primary production were undertaken to quantify the short-term physiological response of the mats to changes in key variables that characterize this cryo-ecosystem (salinity, irradiance and temperature). The heterotrophic versus autotrophic community responses to these stressors differed markedly. The heterotrophic bacteria were extremophilic and specifically adapted to ambient conditions on the ice shelf, whereas the autotrophic community had broader tolerance ranges and optima outside the ambient range. This latter, extremotrophic response may be partly due to a diverse suite of pigments including oligosaccharide mycosporine-like amino acids, scytonemins, carotenoids, phycobiliproteins and chlorophylls that absorb from the near UV-B to red wavelengths. These pigments provide a comprehensive broadband strategy for coping with the multiple stressors of high irradiance, variable salinity and low temperatures in this extreme cryo-environment
- …