We re‐evaluated mid‐ and late Holocene fire records at three bog sites in southern Finland and Estonia through quantitative and qualitative analysis of sedimentary charcoal records. Our analysis ...suggests synchrony amongst the Kontolanrahka, Männikjärve and Lakkasuo bog records. Over the last 5000 years, three episodes of elevated fire occurrence were evident in these bog records, taking place from 4500 to 4000, 3500 to 2000 and 1000 to 500 cal. a BP. These episodes were probably influenced primarily by climate, but also possibly by expansion/retreat of (pre)historic human populations. Although previous studies have proposed that during the late Holocene only weak fire−climate linkages exist, the presented analysis suggests millennial‐ and centennial‐scale synchronous burning episodes.
The impact climate and land-use changes have on the hydrological conditions in peat bogs and lakes is often complex, but of great importance for the carbon budget and biodiversity in these ...ecosystems. Links and feedbacks between raised bog water table depth, lake level, net precipitation, hydrometeorological indices, and radial tree growth have been studied and identified in the Rėkyva wetland complex, Lithuania. Moreover, several statistically significant correlations between raised bog water table depths, lake level, local river runoff, and tree growth were observed. The changes of raised bog water table, lake level, and tree growth show synchronous trends despite variations in the absolute values. Our results show decreasing water table in the Rėkyva wetland complex over the last 100 years, especially in the middle of the 20th century. This study also shows a potential for reconstructing water table fluctuations in wetland complexes using multi-indicator approaches. Our observations and reconstruction show consistency with several regional studies and reconstructions of moisture variations in Baltic raised bogs, at least for periods without strong anthropogenic influences.
•Hydrological conditions in wetlands are reconstructed with a multi-proxy approach.•Runoff data from local rivers are a suitable indicator of water storage in wetlands.•Ring widths of wetland pines depend on hydrological site conditions.•Driest conditions in the studied wetland were in the middle of the 20th century.
We have developed a new approach to quantitatively reconstruct past changes in evaporation based on compound-specific hydrogen isotope ratios of vascular plant and
Sphagnum biomarkers in ombrotrophic ...peatland sediments. We show that the contrast in H isotopic ratios of water available to living
Sphagnum (top 20
cm) and in the rooting zone of peatland vascular plants can be used to estimate “ƒ”—the fraction of water remaining after evaporation. Vascular plant leaf waxes record H isotopic ratios of acrotelm water, which carries the D/H ratio signature of precipitation and is little affected by evaporation, whereas the
Sphagnum biomarker, C
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n-alkane, records H isotopic ratios of the water inside its cells and between its leaves, which is strongly affected by evaporation at the bog surface. Evaporation changes can then be deduced by comparing H isotopic ratios of the two types of biomarkers. We calibrated D/H ratios of C
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n-alkane to source water with lab-grown
Sphagnum. We also tested our isotopic model using modern surface samples from 18 ombrotrophic peatlands in the Midwestern United States. Finally, we generated a 3000-year downcore reconstruction from Minden Bog, Michigan, USA. Our new record is consistent with records of other parameters from the same peatland derived from different proxies and allows us to differentiate precipitation supply and evaporative loss.
Climate warming in high‐latitude regions is thawing carbon‐rich permafrost soils, which can release carbon to the atmosphere and enhance climate warming. Using a coupled model of long‐term peatland ...dynamics (Holocene Peat Model, HPM‐Arctic), we quantify the potential loss of carbon with future climate warming for six sites with differing climates and permafrost histories in Northwestern Canada. We compared the net carbon balance at 2100 CE resulting from new productivity and the decomposition of active layer and newly thawed permafrost peats under RCP8.5 as a high‐end constraint. Modeled net carbon losses ranged from −3.0 kg C m−2 (net loss) to +0.1 kg C m−2 (net gain) between 2015 and 2100. Losses of newly thawed permafrost peat comprised 0.2%–25% (median: 1.6%) of “old” C loss, which were related to the residence time of peat in the active layer before being incorporated into the permafrost, peat temperature, and presence of permafrost. The largest C loss was from the permafrost‐free site, not from permafrost sites. C losses were greatest from depths of 0.2–1.0 m. New C added to the profile through net primary productivity between 2015 and 2100 offset ∼40% to >100% of old C losses across the sites. Differences between modeled active layer deepening and flooding following permafrost thaw resulted in very small differences in net C loss by 2100, illustrating the important role of present‐day conditions and permafrost aggradation history in controlling net C loss.
Plain Language Summary
The thawing of permafrost in tundra, fen, bog, and other peatland wetlands can enhance climate change through releasing carbon from the soil. Using a model for six sites in western Canada, we estimate how much carbon will be lost by 2100 under a high‐end emissions scenario. While these peatlands continue to accumulate carbon in the surface soil layers through enhanced vegetation growth, more carbon is lost from slightly deeper in the soil profile. As a result, most sites were projected to lose relatively small amounts of carbon compared to how much they contain (<5%). Little of the carbon lost was from newly thawed permafrost, while the largest carbon losses were from the permafrost‐free site. In sites where permafrost thawed, the carbon losses were related to peatland and permafrost history.
Key Points
Simulated carbon balance in peatlands with and without permafrost using process‐based model from 8000 BP to 2100 CE
Modeled decomposition losses from active layer peat (0.2–1.0 m) were the predominant carbon source, not deeper peat or newly thawed permafrost
Modeled new peat accumulation offset a large fraction of C losses but future changes in vegetation productivity are poorly understood
The Hudson Bay Lowlands (HBL) is a vast contiguous peatland extending over >370,000 km2 in Canada's boreal-subarctic, and is the traditional land of the Omushkego Cree. It is currently undergoing ...climatic warming alongside other anthropogenic stressors, and contains a large below-ground carbon pool. Understanding how climate variability and multiple stressors impact peat accumulation in this region is critical to discerning how northern peatlands will respond to future climate and land-use changes. Pollen- and macrofossil-based paleoecological reconstructions, and analyses of aluminum (Al) and titanium (Ti) fluxes in a Holocene-aged peat core (VM375) taken from a bog in the Attawapiskat watershed were conducted to link ecosystem changes with hydroclimate and long-term carbon storage. Peat initiation is dated to 5780 cal yr B.P., coincident with land emergence driven by glacial isostatic adjustment. From 4500 to 4200 cal yr B.P., apparent rate of carbon accumulation increased, and was linked to more rapid rates of peat accretion and increases in minerotrophic indicators in the pollen record. This increase in peat accretion and shift in vegetation composition co-occur with higher rates of mineral influx as shown by Ti and Al concentrations, which may have supplied nutrients. A fen to bog transition takes place ~3300 cal yr B.P., with increases in Sphagnum spores and macrofossils, and a decline in the apparent rate of carbon accumulation relative to the earlier half of the record, where paleoecological proxies indicate treed wetland and fen stages. Since peat inception, the total carbon stock of the 260-cm peat column is 110 kg C m−2. This multi-proxy record shows an association between changing peat types and variability in apparent rates of carbon accumulation, and supports the hypothesis that mineral nutrients either supplied by surface hydrology or by eolian deposition played a role in Holocene peat carbon accumulation in eastern North American boreal peatlands.
•Large soil carbon stocks accumulated during the Holocene in the Hudson Bay Lowlands.•A boreal bog core accumulated a carbon stock of 110 kg C m−2 since 5780 years ago.•Enhanced fluxes of mineral nutrients correlate to higher peat vertical accretion.•High rates of peat carbon accumulation are associated with minerotrophic fen stages.•Peat carbon stocks are vulnerable as hydroclimate and mineral nutrients change.
ABSTRACT
Tephra shards for electron probe microanalysis are most efficiently extracted from peat using acid digestion, which removes organic material that hinders density separation methods. However, ...strong acids are known to alter glass chemical compositions, and several studies have examined how acid digestion affects rhyolitic volcanic glass. The focus on rhyolitic tephra in these studies leaves considerable uncertainty, as the dissolution rates of natural glasses (including tephra) are determined by the chemical composition and surface area/volume ratio, both of which vary in tephra deposits. Here, we use duplicate samples of basaltic, trachydacitic and rhyolitic tephra to examine physical and geochemical alteration following acid digestion. Scanning electron microscope imagery reveals no discernible degradation of glass surfaces, and electron probe microanalysis results from duplicate samples are statistically indistinguishable. These findings suggest the acid digestion protocol for organic peats does not significantly alter glass geochemistry regardless of shard morphologies or geochemical compositions.
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•A BOG reliquefaction system using liquid air was developed.•Mathematical optimization was performed to minimize annual expenses.•Techno-economic analysis was conducted for three ...different voyage duration scenarios.•The proposed system can reduce both onboard energy consumption and capital investment.
The boil-off gas (BOG) reliquefaction of cryogenic liquefied natural gas (LNG) for its intercontinental transport is challenging. This paper proposes a novel BOG reliquefaction system using liquid air and two different process designs: (i) low-pressure liquid air (LPLA) and (ii) high-pressure liquid air (HPLA). In the proposed system, an open refrigeration system using liquid air reliquefies BOG, thereby replacing the current commercial closed refrigeration cycle. As the temperature of liquid air is in the cryogenic range, the energy consumption to reliquefy BOG onboard approaches zero. However, the additional total weight of the ship is required to store liquid air, thus necessitating increased propulsion energy. Nevertheless, the reduction in energy needed for BOG reliquefaction exceeds the energy requirement for the added engine load. Thus, the LPLA shows a massive energy reduction from 4,913.07 to 642.67 kW compared to the commercial BOG reliquefaction process involving the nitrogen expander cycle. The HPLA process shows further improved results of 436.34 kW by expanding the vaporized high-pressure air. In addition, the proposed HPLA design exhibits an exergy efficiency of 77.4 %, which is 37.6 % higher than that of the commercial nitrogen expander process. A techno-economic analysis, including the purchase and transport cost of liquid air, is conducted to reflect an effort on on-shore liquid air production and transportation. Despite the additional liquid air tanks, the overall process configuration is much simpler than that of the current commercial BOG reliquefaction system. Thus, the proposed HPLA process is more economical than commercial processes for all representative voyage duration scenarios (8, 13, and 21 days).
Abstract Studies on the effects of fish presence on lake ecosystems are widespread but only a few have been conducted in pristine aquatic environments. We employed Ecopath model for assessing food ...web structure in two fish-inhabited and one fishless lake in a pristine bog area. We hypothesized that: (a) fish absence will raise trophic positions of macroinvertebrate predators; (b) fish predation will lead to higher overall predation rates on zooplankton; (c) fish predation on large bodied zooplankton will result in top-down cascading effect, increasing phytoplankton biomasses. We found that fish have direct and indirect effects on zoobenthic communities. Chironomid biomass was greater and predatory macroinvertebrate groups had a higher trophic level in the fishless lake than in fish-inhabited lakes. Consumption rates of the benthic consumer fraction were greater than that of the planktonic fraction in the fishless lake; the opposite was found in the two lakes with fish. No effects of fish presence on zooplankton were found and we explain this partly by the low water transparency masking the impact of fish. Terrestrial insects constituted a crucial part of adult fish diet and we conclude that terrestrial secondary production contributes to the trophic support of fish communities in pristine bog lakes.
Peat bog pools are rare and fragmented in the Western Balkans. Thus, aquatic macroinvertebrate diversity and the implications for microhabitat loss in these ecosystems are poorly known. Aquatic ...oligochaetes, widely used as indicators, were sampled using a benthos net in the largest and oldest Croatian bog, in four main water body types: a pond, a deep pool, a shallow pool and a ditch. As these microhabitats lack spatial replication both in the studied bog and in the region, we applied a nested study design with replicates sampled over time. We found a species‐rich aquatic oligochaete fauna, with 11 taxa recorded. Oligochaete communities were strongly affected by vegetation complexity and the morphology of bog water bodies, namely, their size and depth. As revealed by generalised linear mixed models (GLMMs), taxon richness and abundance were significantly higher in the ditch than in other water body types. This could be attributed to the vegetation complexity, supporting many different niches and providing allochthonous food supplies for oligochaetes. The various bog pools contribute to regional biodiversity and promote distinct patterns in the spatial distribution of oligochaetes. However, the predominance of ubiquitous oligochaetes, with high taxon richness, might indicate the degradation of the studied peat bog. This was further confirmed by the spread of vascular plants to the bog area and higher pH water values. All these warning signals suggest that hydro‐ecological conditions should be urgently improved in order to preserve communities in the bog studied.
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