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Rain‐on‐snow (ROS) is a compound hydrometeorological extreme event that can lead to severe socioeconomic impacts and affect ecosystem function. In high‐latitude regions, the percolation of liquid precipitation through snowpack and the associated formation of ice layers can create greater potential for significant runoff and also cause hardship for wintertime ungulate foraging. In this study, we assess the characteristics of ROS events and the corresponding impacts over a large sub‐arctic river basin in northwestern Canada. We propose seven indices to assess the projected changes in both major and minor ROS events, defined as instances of 10 and 3 mm/day, respectively, of rainfall occurring on SWE greater than 5 mm, taking into account precipitation intensity and snowpack depth. We use simulations from the variable infiltration capacity hydrologic model driven by a suite of multivariate bias‐corrected global climate models from the fifth phase of the Coupled Model Intercomparison Project and assess the ROS changes under the 1.5, 2, 3 and 4°C global warming levels above the pre‐industrial period. Overall, ROS events occur more frequently in October–December and January–March (JFM) compared to other seasons. The effects of major and minor ROS events on runoff generation in JAS and OND are considerable at higher elevations, with mean runoff more than 50% greater on ROS days than non‐ROS days in many cases. Furthermore, the analyses project notable increases in the frequency of both Major and Minor ROS events in all summer and fall. However, a notable decrease in ROS frequency is present in spring, and in winter, ROS frequency has inconsistent changes. Our comprehensive assessment of ROS events, their projected changes, and associated impacts in a sub‐arctic river basin underscore these events' critical role in shaping hydrological patterns and affecting communities, infrastructure and ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Plants typically experience great losses from their reproductive potential represented by ovule production to the post-dispersal crop of viable seed. We examined seed density and viability in a founder population of mountain birch (Betula pubescens ssp. tortuosa), aiming to quantify losses at different stages and examine potential selection forces on the reproduction success of the founder generation of an isolated population. At the time of the study (2017–2020), the population had recently reached reproductive maturity, following its colonization around 1990 through long-distance dispersal onto an early successional outwash plain in southeast Iceland. Seed densities were high, but 89% of apparently intact seeds did not contain an embryo, despite being visually indistinguishable from filled seeds. Externally evident losses amounted to about 45% of the total seed crop and were mostly due to predation by the gall midge Semudobia betulae. When all losses were accounted for, 2.7% of the seed crop remained viable and germinated. Pollen limitation may partially explain the high incidence of empty seeds. Excessive flower production is compatible with the predator satiation hypothesis but cannot explain pre-dispersal losses. Another adaptation to predation, masting, appears poorly developed in Iceland. Our results suggest the presence of constraints on the reproduction potential of the new island population, that are more limiting than in neighbouring populations, and we discuss their developmental, ecological, and environmental correlates. [ABSTRACT FROM AUTHOR]

Our understanding of the environmental behavior, bioaccumulation and concentrations of chlorinated paraffins (CPs) and Dechloranes (Dec) in the Arctic environment is still limited, particularly in freshwater ecosystems. In this descriptive study, short chain (SCCPs) and medium chain (MCCPs) CPs, Dechlorane Plus (DP) and analogues, and polychlorinated biphenyls (PCBs) were measured in sediments, benthic organisms, three-spined stickleback (Gasterosteus aculeatus), Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in two Sub-Arctic lakes in Northern Norway. Takvannet (TA) is a remote lake, with no known local sources for organic contaminants, while Storvannet (ST) is situated in a populated area. SCCPs and MCCPs were detected in all sediment samples from ST with concentration of 42.26--115.29 ng/g dw and 66.18--136.69 ng/g dw for SCCPs and MCCPs, respectively. Only SCCPs were detected in TA sediments (0.4--5.28 ng/g dw). In biota samples, sticklebacks and benthic organisms showed the highest concentrations of CPs, while concentrations were low or below detection limits in both char and trout. The congener group patterns observed in both lakes showed SCCP profiles dominated by higher chlorinated congener groups while the MCCPs showed consistency in their profiles, with C14 being the most prevalent carbon chain length. Anti- and syn-DP isomers were detected in all sediment, benthic and stickleback samples with higher concentrations in ST than in TA. However, they were only present in a few char and trout samples from ST. Dec 601 and 604 were below detection limits in all samples in both lakes. Dec 603 was detected only in ST sediments, sticklebacks and 2 trout samples, while Dec 602 was the only DP analogue found in all samples from both lakes. While there were clear differences in sediment concentrations of DP and Dec 602 between ST and TA, differences between lakes decreased with increasing δ15N. This pattern was similar to the PCB behavior, suggesting the lake characteristics in ST are playing an important role in the lack of biomagnification of pollutants in this lake. Our results suggest that ST receives pollutants from local sources in addition to atmospheric transport. [ABSTRACT FROM AUTHOR]

Rapid warming at high latitudes triggers poleward shifts of species' distributions that impact marine biodiversity. In the open sea, the documented redistributions of fish lead to a borealization of Arctic fauna. A climate‐driven borealization and increased species diversity at high latitudes are also expected in coastal fish communities, but they have not been previously documented on a large, biogeographic scale. Here, we investigate the impact of temperature change over the last 25 years on fish communities along the coast of Norway. The study area, spanning different ecoclimatic zones between 62° and 71° N, harbors over 200 species of boreal and Arctic fish. Several of these fish species are harvested by coastal and indigenous communities, influencing settlement geography and livelihood. The long‐term data on coastal water temperatures and fish species were obtained from monitoring stations and scientific surveys. Water temperature measured at three fixed sampling stations distributed along the coast show increased temperatures during the study period. The fish species distribution and abundance data were obtained from the annually standardized scientific bottom trawl survey program. Fish species richness, which was highest in the south, increased with warming first in the south and then, gradually, further north, eventually affecting biodiversity in the whole study area. Fish community composition showed a distinct latitudinal pattern early in the study, with Arctic fish species confined to the north and boreal species dominating the south. The poleward shifts eventually eroded this zoogeographic pattern, resulting in more boreal fish species in the north and an increased homogenization of species composition along the Norwegian coast. The climate‐driven reorganization of fish communities affects coastal ecosystems that are exposed to fisheries, aquaculture, and other rapidly expanding human activities, stressing the urgent need for a climate adaptation of integrated coastal management. [ABSTRACT FROM AUTHOR]

This study explores the Swedish diversity of the thrips families Aeolothripidae and Melanthripidae. Currently, a total of 12 species in 2 genera of Aeolothripidae occur in Sweden, and 1 in Melanthripidae. The aims of this study include to provide an updated identification key with photographic material and an updated checklist of the country with provincial records. In this study both museum material and new material collected in understudied provinces are included, and a large number of molecular barcodes are produced. The results reveal 26 new provincial records in Sweden, predominantly in northern regions, and 11 provinces in total had new species records. New records of Rhipidothrips brunneus Williams 1913 warranted an examination of distinguishing characters compared to R. niveipennis Reuter, 1899. The original description of R. niveipennis is found to lack sufficient characters to delimit the species, and a redescription based on syntypes is presented. [ABSTRACT FROM AUTHOR]

Oxidative stress from ozone (O3) causes plants to alter their emission of biogenic volatile organic compounds (BVOC) and their photosynthetic rate. Stress reactions from O3 on birch trees can result in prohibited plant growth and lead to increased BVOC emission rates as well as changes in their compound blend to emit more monoterpenes (MT) and sesquiterpenes (SQT). BVOCs take part in atmospheric reactions such as enhancing the production of secondary organic aerosols (SOA). As the compound blend and emission rate change with O3 stress, this can influence the atmospheric conditions by affecting the production of SOA. Studying the stress responses of plants provides important information on how these reactions might change, which is vital to making better predictions of the future climate. In this study, measurements were taken to find out how the leaves of mature mountain birch trees (Betula pubescens ssp. czerepanovii) respond to different levels of elevated O3 exposure in situ depending on leaf age. We found that leaves from both early and late summers responded with induced SQT emission after exposure to 120 ppb O3. Early leaves were, however, more sensitive to increased O3 concentrations, with enhanced emission of green leaf volatiles (GLV) and tendencies of both induced leaf senescence as well as poor recovery in the photosynthetic rate between exposures. Late leaves had more stable photosynthetic rates throughout the experiment and responded less to exposure at different O3 levels. [ABSTRACT FROM AUTHOR]

Passenger travel by car currently accounts for a significant part of greenhouse gas emissions, but reducing dependency on the car in rural areas while ensuring accessibility is challenging. This study offers a user perspective on the constraints to fossil-free mobility in a remote rural area of Sweden, drawing on focus group discussions with inhabitants of six rural settlements.The study took place in Västerbotten and Norrbotten, Sweden's two northernmost regions where the climate is sub-arctic, population density low, and car dependence high.It explores constraints including the shift from personal and individual responsibility for transport to more collective solutions. Both contextual and individual aspects impact on people's ability to change, including social networks, working arrangements, socioeconomic preconditions, and personal flexibility.

Our understanding of the environmental behavior, bioaccumulation and concentrations of chlorinated paraffins (CPs) and Dechloranes (Dec) in the Arctic environment is still limited, particularly in freshwater ecosystems. In this descriptive study, short chain (SCCPs) and medium chain (MCCPs) CPs, Dechlorane Plus (DP) and analogues, and polychlorinated biphenyls (PCBs) were measured in sediments, benthic organisms, three-spined stickleback (Gasterosteus aculeatus), Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in two Sub-Arctic lakes in Northern Norway. Takvannet (TA) is a remote lake, with no known local sources for organic contaminants, while Storvannet (ST) is situated in a populated area. SCCPs and MCCPs were detected in all sediment samples from ST with concentration of 42.26–115.29 ng/g dw and 66.18–136.69 ng/g dw for SCCPs and MCCPs, respectively. Only SCCPs were detected in TA sediments (0.4–5.28 ng/g dw). In biota samples, sticklebacks and benthic organisms showed the highest concentrations of CPs, while concentrations were low or below detection limits in both char and trout. The congener group patterns observed in both lakes showed SCCP profiles dominated by higher chlorinated congener groups while the MCCPs showed consistency in their profiles, with C14 being the most prevalent carbon chain length. Anti- and syn-DP isomers were detected in all sediment, benthic and stickleback samples with higher concentrations in ST than in TA. However, they were only present in a few char and trout samples from ST. Dec 601 and 604 were below detection limits in all samples in both lakes. Dec 603 was detected only in ST sediments, sticklebacks and 2 trout samples, while Dec 602 was the only DP analogue found in all samples from both lakes. While there were clear differences in sediment concentrations of DP and Dec 602 between ST and TA, differences between lakes decreased with increasing δ15N. This pattern was similar to the PCB behavior, suggesting the lake characteristics in ST are playing an important role in the lack of biomagnification of pollutants in this lake. Our results suggest that ST receives pollutants from local sources in addition to atmospheric transport.

Abstract Oxidative stress from ozone (O3) causes plants to alter their emission of biogenic volatile organic compounds (BVOC) and their photosynthetic rate. Stress reactions from O3 on birch trees can result in prohibited plant growth and lead to increased BVOC emission rates as well as changes in their compound blend to emit more monoterpenes (MT) and sesquiterpenes (SQT). BVOCs take part in atmospheric reactions such as enhancing the production of secondary organic aerosols (SOA). As the compound blend and emission rate change with O3 stress, this can influence the atmospheric conditions by affecting the production of SOA. Studying the stress responses of plants provides important information on how these reactions might change, which is vital to making better predictions of the future climate. In this study, measurements were taken to find out how the leaves of mature mountain birch trees (Betula pubescens ssp. czerepanovii) respond to different levels of elevated O3 exposure in situ depending on leaf age. We found that leaves from both early and late summers responded with induced SQT emission after exposure to 120 ppb O3. Early leaves were, however, more sensitive to increased O3 concentrations, with enhanced emission of green leaf volatiles (GLV) and tendencies of both induced leaf senescence as well as poor recovery in the photosynthetic rate between exposures. Late leaves had more stable photosynthetic rates throughout the experiment and responded less to exposure at different O3 levels.

Study region: This study analyzed lake surface temperature (LST) trends and spatial distribution across 535 predominantly small to medium lakes across the North Slave Region (NSR) of the Northwest Territories (NWT), Canada. Study focus: The NWT is characterized by a vast number of lakes covering a significant portion of its spatial extent. However, there is limited knowledge of how LST responds to climate warming in this region. To address this, LST was analyzed in four distinct periods: open water season (OW), ice cover season (IC), and the transitional months of May (TM) and October (TO). LSTs from 1984 to 2021 were retrieved from a lake-specific satellite-derived LST dataset (North Slave LST). LST trend distribution and relationships were analyzed using the Mann-Kendall test and a multilinear regression model. New hydrological insights: The analysis revealed an overall increase in LST, with average rates (max) of 0.03 °C/year (0.05 °C/year), 0.03 °C/year (0.06 °C/year), and 0.13 °C/year (0.27 °C/year) for OW, TM, and TO, respectively accross study lakes. A faster rate of change was observed in October compared to other periods. Results indicated significant increases in LST for 411 lakes (77%) during OW, 418 lakes (78%) during TO, and 490 lakes (92%) during TM. The spatial distribution and magnitude of LST change were primarily influenced by geographical than morphometric properties. The analysis demonstrated later freeze-up (0.20 day/year) and earlier break-up (−0.17 day/year) of lake ice across the NSR.

Understanding the relative importance of different water sources that replenish soil water storage is necessary to assess the vulnerability of sub‐arctic areas to changes in climate and altered rain and snow conditions, reflected in the timing and magnitude of water infiltration. We examine spatiotemporal variability and seasonal origin of soil water at the soil‐vegetation interface in Pallas catchment, located in northern Finland. The field study was conducted from May 2019 to June 2020 over two snowmelt seasons and one summer growing season. We sampled soil cores up to a 1‐m depth and stem water of dominant tree species at four sites located in forests and forested peatlands for stable water isotopes. Seasonal rainfall variation and late snowmelt events were well identifiable in the well‐drained soils of forested areas, while this input signal is heavily attenuated in wetter, forested peatland areas. Spatiotemporal variability of soil water in two forest sites was similar, whereas soil water storage in peatland sites was controlled by the extent of hydrologic connectivity to the adjoining water pools. A mixture of both summer and winter precipitation was present in peatlands during the entire study period, while forest mineral soils showed an ephemeral response to water input and got nearly fully flushed twice during the hydrological year. Meltwater signal in forest soils was dominant after snowmelt and in early spring but became displaced by isotopically enriched rainfall during the summer. Seasonal evolution of soil water pools was not reflected in tree stem dynamics but offset between soil and stem water isotopic signals was less pronounced in forested peatlands. This field data set uncovered seasonal changes of soil water isotopic signal at high depth‐resolution, quantifying the importance of snowmelt water in replenishing and sustaining soil water storage in sub‐arctic conditions. [ABSTRACT FROM AUTHOR]

This research investigates the role air transportation plays in remote community resilience by examining air cargo delivery and flight operations in northern Ontario, Canada. Building off of the Disaster Resilience of Place (DROP) model for community resilience, we develop a high-level interdependency model that shows the interdependencies between community infrastructure systems and air transportation in the unique context of remote communities that rely on air transportation. Air transportation is the only mode of travel available year-round for the 26 remote communities studied. Alternative modes are seasonal (e.g., winter roads) and threatened by climate change. Analysing 6 years of cargo data highlights infrastructure interdependencies in energy, the built environment, and transportation systems. Flight operations data and semi-structured interviews with airline employees advance our understanding of air transportation infrastructure and operating challenges that impact flight reliability and ultimately remote community resilience. [ABSTRACT FROM AUTHOR]

A residential building which had been subjected to an energy efficiency measures study had its indoor thermal climate investigated using two software approaches to understand how each approach would predict the outcome, using the predicted percentage of dissatisfied (PPD). The computational fluid dynamics software (ANSYS CFX) and the building performance simulation (BPS) software (IDA ICE) were used to simulate the indoor thermal climate before and after the measures. The measures included additional insulation and changing the ventilation system. The results showed a difference in how the software packages handled the thermal radiation. The difference was also because CFX could calculate the indoor thermal climate of the whole interior. While the PPD values could remain similar between the CFX solutions, the area with dissatisfaction in the apartment was decreased when the building envelope was improved. These changes gave an improvement for the CFX solutions, which was not possible to predict with IDA ICE because only the central node was visible. The user should be aware of the shortcomings of BPS and building energy simulation software when evaluating the indoor thermal climate to predict changes. A coupling between BPS and CFX software should be considered when new measures or significant changes are planned. [ABSTRACT FROM AUTHOR]

The Matanuska–Susitna Borough is the fastest growing region in the State of Alaska and is impacted by a number of human activities. We conducted a multiscale assessment of the stressors facing the borough by developing and mapping the Index of Watershed Integrity (IWI) and Index of Catchment Integrity (the latter considers stressors in areas surrounding individual stream segments exclusive of upstream areas). The assessment coincided with the borough’s stormwater management planning. We adapted the list of anthropogenic stressors used in the original conterminous United States IWI application to reflect the borough’s geography, human activity, and data availability. This analysis also represents an early application of the NHDPlus High Resolution geospatial framework and the first use of the framework in an IWI study. We also explored how remediation of one important stressor, culverts, could impact watershed integrity at the catchment and watershed scales. Overall, we found that the integrity scores for the Matanuska–Susitna basin were high compared to the conterminous United States. Low integrity scores did occur in the rapidly developing Wasilla–Palmer core area. We also found that culvert remediation had a larger proportional impact in catchments with fewer stressors.

Nitrous oxide (N2O) emissions from permafrost-affected terrestrial ecosystems have received little attention, largely because they have been thought to be negligible. Recent studies, however, have shown that there are habitats in subarctic tundra emitting N2O at high rates, such as bare peat surfaces on permafrost peatlands. The processes behind N2O production in these high-emitting habitats are, however, poorly understood. In this study, we established an in situ 15N-labelling experiment with the main objectives to partition the microbial sources of N2O emitted from bare peat surfaces (BP) on permafrost peatlands and to study the fate of ammonium and nitrate in these soils and in adjacent vegetated peat surfaces (VP) showing low N2O emissions. Our results confirm the hypothesis that denitrification is mostly responsible for the high N2O emissions from BP surfaces. During the study period denitrification contributed with ~79% of the total N2O emission in BP, while the contribution of ammonia oxidation was less, about 19 %. However, nitrification is a key process for the overall N2O production in these soils with negligible external nitrogen (N) load because it is responsible for nitrite/nitrate supply for denitrification, as also supported by relatively high gross nitrification rates in BP. Generally, both gross N mineralization and gross nitrification rates were much higher in BP with high N2O emissions than in VP, where the high C/N ratio together with low water content was likely limiting N mineralization and nitrification and, consequently, N2O production. Also, competition for mineral N between plants and microbes was additionally limiting N availability for N2O production in VP. Our results show that multiple factors control N2O production in permafrost peatlands, the absence of plants being a key factor together with inter-mediate to high water content and low C/N ratio, all factors which also impact on gross N turnover rates. The intermediate to high soil water content which creates anaerobic microsites in BP is a key N2O emission driver for the prevalence of denitrification to occur. This knowledge is important for evaluating future permafrost -N feedback loops from the Arctic. [ABSTRACT FROM AUTHOR]

Phyto- and zooplankton in Arctic and sub-Arctic seas show very strong seasonal changes in diversity and biomass. Here we document the seasonal variability in the mesozooplankton community structure in a sub-Arctic fjord in Northern Norway based on monthly sampling between November 2018 and February 2020. We combined traditional morphological zooplankton identification with DNA metabarcoding of a 313 base pair fragment of the COI gene. This approach allowed us to provide the most detailed mesozooplankton species list known for this region across an entire year, including both holo- and meroplankton. The zooplankton community was dominated by small copepods throughout the sampling period both in terms of abundance and relative sequence counts. However, meroplankton was the most diverse group, especially within the phylum polychaeta. We identified four distinct periods based on the seasonal analysis of the zooplankton community composition. The pre-spring bloom period (February–March) was characterized by low abundance and biomass of zooplankton. The spring bloom (April) was characterized by the presence of Calanus young stages, cirripedia and krill eggs. The spring-summer period (May–August) was characterized by a succession of meroplankton and a relatively high abundance of copepods of the genus Calanus spp. Finally, the autumn-winter period (September–December) was characterized by a high copepod diversity and a peak in abundance of small copepods (e.g., Oithona similis, Acartia longiremis, Pseudocalanus acuspes, Pseudocalanus elongatus, Pseudocalanus moultoni, Pseudocalanus minutus). During this period, we also observed an influx of boreal warm-water species which were notably absent during the rest of the year. Both the traditional community analysis and metabarcoding were highly complementary and with a few exceptions showed similar trends in the seasonal changes of the zooplankton community structure.

Mesozooplankton research in high latitude ecosystems tends to focus on different life stages of Calanus spp. due to its biomass dominance and trophic roles. However, a complex seasonal succession of abundant smaller mesozooplankton taxa suggests that the ecological functioning of the mesozooplankton communities is more complicated. We studied the year‐round taxon‐specific biomass measurements and size distributions of mesozooplankton on a sub‐Arctic continental shelf based on formalin preserved samples. Our results confirm that Calanus spp. dominate the mesozooplankton biomass (81%). We show that commonly used length–weight relationships underestimate Calanus biomass in autumn and winter, and accordingly, a strong seasonal bias was introduced in our understanding of sub‐Arctic plankton communities. We observed two periods with considerable contribution of meroplankton, the planktonic larvae of benthic invertebrates, to the mesozooplankton biomass: (a) Cirripedia nauplii accounted for 17% of total biomass close to the coast in early April and (b) meroplankton comprised up to 12.7% of total biomass in late July. Based on these results, we suggest that meroplankton may play an ecologically important role in addition to their role in dispersal of benthic species. We conclude that the seasonal succession of the biomass of small‐sized holoplankton and meroplankton, often obscured by patterns in the Calanus biomass, should receive more attention as these smaller individuals are likely an important functional component of the pelagic food web. [ABSTRACT FROM AUTHOR]

Arctic environmental change has induced shifts in high latitude plant community composition and stature with implications for Arctic carbon cycling and energy exchange. Two major components of high latitude ecosystems undergoing change is the advancement of trees into treeless tundra and the increased abundance and size of shrubs. How future changes in key climatic and environmental drivers will affect distributions of major ecosystem types is an active area of research. Dynamic Vegetation Models (DVMs) offer a way to investigate multiple and interacting drivers of vegetation distribution and ecosystem function. We employed the LPJ-GUESS DVM over a subarctic landscape in northern Sweden, Torneträsk. Using a highly resolved climate dataset we downscaled CMIP5 climate data from three Global Climate Models and two 21st century future scenarios (RCP2.6 and RCP8.5) to investigate future impacts of climate change on these ecosystems. We also performed three model experiments where we factorially varied drivers (climate, nitrogen deposition and [CO2]) to disentangle the effects of each on ecosystem properties and functions. We found that treelines could advance by between 45 and 195 elevational meters in the landscape until the year 2100, depending on the scenario. Temperature was a strong, but not the only, driver of vegetation change. Nitrogen availability was identified as an important modulator of treeline advance. While increased CO2fertilisation drove productivity increases it did not result in any range shifts of trees. Treeline advance was realistically simulated without any temperature dependence on growth, but biomass was overestimated. As nitrogen was identified as an important modulator of treeline advance, we support the idea that accurately representing plant-soil interactions in models will be key to future predictions Arctic vegetation change. [ABSTRACT FROM AUTHOR]

Summary: Plant associated mutualists can mediate invasion success by affecting the ecological niche of nonnative plant species. Anthropogenic disturbance is also key in facilitating invasion success through changes in biotic and abiotic conditions, but the combined effect of these two factors in natural environments is understudied.To better understand this interaction, we investigated how disturbance and its interaction with mycorrhizas could impact range dynamics of nonnative plant species in the mountains of Norway. Therefore, we studied the root colonisation and community composition of arbuscular mycorrhizal (AM) fungi in disturbed vs undisturbed plots along mountain roads.We found that roadside disturbance strongly increases fungal diversity and richness while also promoting AM fungal root colonisation in an otherwise ecto‐mycorrhiza and ericoid‐mycorrhiza dominated environment. Surprisingly, AM fungi associating with nonnative plant species were present across the whole elevation gradient, even above the highest elevational limit of nonnative plants, indicating that mycorrhizal fungi are not currently limiting the upward movement of nonnative plants.We conclude that roadside disturbance has a positive effect on AM fungal colonisation and richness, possibly supporting the spread of nonnative plants, but that there is no absolute limitation of belowground mutualists, even at high elevation. See also the Commentary on this article by Bueno et al., 230: 883–885. [ABSTRACT FROM AUTHOR]

Abstract The distribution and composition of Arctic vegetation are expected to shift with ongoing climate change. Global models generally predict northward shifts in high‐latitude ecotones, and analysis of remote sensing data shows widespread greening and changes in vegetation structure across the circumpolar Arctic. However, there are still uncertainties related to the timing of these shifts and variation among different plant functional types. In this paper, we investigate disequilibrium dynamics of green alder and white spruce in the Tuktoyaktuk Coastal Plain, NWT. We used high‐resolution air photographs captured in the 1970s and 2000s to quantify changes in the distribution and abundance of alder and spruce near their northern limits. We found increases in alder and spruce stem density over time, but no change in their range limits, indicating that both species are affected by leading‐edge disequilibrium. Low stand density and temperature limitation of reproduction along the northern margin likely contributed to observed disequilibrium in both species. We also observed the greatest change in species occupancy within a burned area, suggesting that the increased frequency of fire will play a significant role in the timing and magnitude of near‐term vegetation change.

A dietary transition away from traditional foods and toward a diet of the predominantly unhealthy market is a public health and sociocultural concern throughout Indigenous communities in Canada, including those in the sub-Arctic and remote regions of Dehcho and Sahtú of the Northwest Territories, Canada. The main aim of the present study is to describe dietary intakes for macronutrients and micronutrients in traditional and market food from the Mackenzie Valley study. We also show the trends of contributions and differences of dietary intakes over time from 1994 data collected and reported by the Centre for Indigenous People’s Nutrition and Environment (CINE) in 1996. Based on 24-h dietary recall data, the study uses descriptive statistics to describe the observed dietary intake of the Dene First Nations communities in the Dehcho and Sahtú regions of the NWT. Indigenous people in Canada, like the sub-Arctic regions of Dehcho and Sahtú of the NWT, continue to consume traditional foods, although as a small percentage of their total dietary intake. The observed dietary intake calls for action to ensure that traditional food remains a staple as it is critical for the wellbeing of Dene in the Dehcho and Sahtú regions and across the territory.

In spite of the generally high interest to ecosystems of high latitudes, there is not a single mite species list for any Arctic coastal location yet. Mesostigmatic mites are diverse and abundant in invertebrate littoral communities, while in the sea wrack, they are a dominant mite group. We studied these mites in different coastal habitats in the forested tundra landscape in the vicinity of Murmansk, Kola Bay, Barents Sea (68° 55′ N, 33° 02′ E). Altogether, 31 species from 21 genera and 12 families are recorded. This species number is only half to ¾ of that of the coastal species richness within the taiga zone of the Murmansk Region, White Sea coasts. Along the vertical profile from the low littoral zone (Fucus spp.) to the supralittoral one (grass-forb meadow), both species diversity and abundance grow from 1 to 22 species and from 3 to 170–450 ind. dm−2, respectively. About 1/3 of the species show vast distributions, but 40% species are amphi-Atlantic or European. No truly Arctic species were found, an Arcto-Montane+Arcto-Boreal+Boreal fraction of the fauna was very small (19%), and half of the species demonstrating polyzonal patterns. From an ecological point of view, the fauna is rather specialized, since 29% species are halobiontic seashore residents, while 39% are common dwellers of humid meadows and bogs. Winter populations of mites belonging to the family Halolaelapidae are represented mainly by deutonymphs, but populations of Cheiroseius spp. (family Blattisocidae) include mostly females. Similarities between the coastal mite assemblages of the study transect are primarily determined by hypsometric levels, but no principal differences in the mite communities of vegetation parcels within individual levels are found. [ABSTRACT FROM AUTHOR]

In 2018 and 2019, salmonid fishes, Salmo trutta L. and Salvelinus alpinus (L.) from lakes in Iceland were assessed for trematodes during a parasitological examination. Combined morphological and molecular analyses revealed the presence of four trematode species, two of which were previously known to parasitise salmonids in Iceland, Crepidostomum farionis (Müller, 1780) and Phyllodistomum umblae (Fabricius, 1780), and the two remaining species were recognised as new to science. Morphologically and genetically, Crepidostomum brinkmanni n. sp. and C. pseudofarionis n. sp. are closely related to two European species, namely C. metoecus and C. farionis. However, C. brinkmanni n. sp. is distinct by the position of maximum body width and arrangement of vitelline follicles; C. pseudofarionis n. sp. is distinct by its stout body, position of maximum body width, size of muscular papillae relative to oral sucker and the anterior extent of vitelline follicles. The new species were previously molecularly detected in their intermediate and definitive hosts in Norway and Ukraine, but their sequences were not supplemented with any morphological characterisation. In the present study, we provide detailed morphological descriptions and molecular sequences (28S rDNA and ITS2) of the four species of trematodes detected in Iceland. The discovery of the two new species of Crepidostomum indicates that the trematode diversity in fishes in the north is higher than previously known; our finding doubles the species spectrum of fish trematodes for Iceland. The record of C. brinkmanni from Ukraine indicates that its distribution might not be limited to northern latitudes. [ABSTRACT FROM AUTHOR]

The distribution and composition of Arctic vegetation are expected to shift with ongoing climate change. Global models generally predict northward shifts in high‐latitude ecotones, and analysis of remote sensing data shows widespread greening and changes in vegetation structure across the circumpolar Arctic. However, there are still uncertainties related to the timing of these shifts and variation among different plant functional types. In this paper, we investigate disequilibrium dynamics of green alder and white spruce in the Tuktoyaktuk Coastal Plain, NWT. We used high‐resolution air photographs captured in the 1970s and 2000s to quantify changes in the distribution and abundance of alder and spruce near their northern limits. We found increases in alder and spruce stem density over time, but no change in their range limits, indicating that both species are affected by leading‐edge disequilibrium. Low stand density and temperature limitation of reproduction along the northern margin likely contributed to observed disequilibrium in both species. We also observed the greatest change in species occupancy within a burned area, suggesting that the increased frequency of fire will play a significant role in the timing and magnitude of near‐term vegetation change. [ABSTRACT FROM AUTHOR]

The Matanuska--Susitna Borough is the fastest growing region in the State of Alaska and is impacted by a number of human activities. We conducted a multiscale assessment of the stressors facing the borough by developing and mapping the Index of Watershed Integrity (IWI) and Index of Catchment Integrity (the latter considers stressors in areas surrounding individual stream segments exclusive of upstream areas). The assessment coincided with the borough's stormwater management planning. We adapted the list of anthropogenic stressors used in the original conterminous United States IWI application to reflect the borough's geography, human activity, and data availability. This analysis also represents an early application of the NHDPlus High Resolution geospatial framework and the first use of the framework in an IWI study. We also explored how remediation of one important stressor, culverts, could impact watershed integrity at the catchment and watershed scales. Overall, we found that the integrity scores for the Matanuska--Susitna basin were high compared to the conterminous United States. Low integrity scores did occur in the rapidly developing Wasilla--Palmer core area. We also found that culvert remediation had a larger proportional impact in catchments with fewer stressors. [ABSTRACT FROM AUTHOR]

• CFWs effectively remove nitrate from freshwater systems under cold climatic conditions. • Plant associated denitrification is the main nitrogen removal pathway in CFWs. • Successful application of CFWs relies on the correct choice of macrophyte species. Constructed floating wetlands (CFWs) have been tested in different climatic regions and aquatic habitat types for nitrogen (N) removal from surface water, but there is limited knowledge about their applicability for N removal in cold climate regions. Most CFWs studies are conducted at the micro- or mesocosm scale, while the application of CFWs at in situ is rare. Moreover, most CFWs studies have focused on plant N accumulation without considering macrophyte root-associated denitrification as a possible N removal pathway. Here, we study the N removal potential of CFWs through N accumulation by macrophytes and potential denitrification activity (PDA) associated with plants. At a mining area in the sub-arctic region of Sweden receiving N-rich mine effluents, we tested the concept of CFWs and evaluated the performance of six native, emerging macrophyte species planted in CFWs. The CFWs were deployed in two types of systems: in situ in the recipient lake, subjected to ambient N concentrations, and CFWs placed in water-side "eco-tanks", subjected to higher N concentrations. We showed that macrophyte establishment in CFWs is feasible under cold climatic conditions, both in situ and eco-tanks. The standing biomass of macrophytes, bulk N accumulation in plant biomass and PDA in mesocosms were 0.54–2.25 kg m−2, 7.56–24.75 mg N m−2 d−1 and 31.82–2250.77 mg N 2 O-N m−2 d−1, respectively. In the recipient, the variation was larger and the values were higher (standing biomass, 0.37–6.74 kg m−2; bulk N accumulation, 8.09–106.93 mg N m−2 d−1; PDA, 11.89–8446.15 mg N m−2 d−1). Macrophyte root-associated denitrification was the main N removal pathway in the CFWs. Given the demonstrated applicability of CFWs and the high denitrification rates that can be obtained, future studies should focus on designing CFWs to enhance denitrification as this process leads to permanent removal of N from the water phase. [ABSTRACT FROM AUTHOR]

Anadromous Arctic charr Salvelinus alpinus and sea trout Salmo trutta are commonly found in marine, estuarine and freshwater habitats across the Northern Hemisphere. The marine phase varies between populations but often involves summer foraging in nearshore waters while spawning and overwintering occur in freshwater. The dependence of anadromous salmonids on nearshore habitats makes them vulnerable to increased industrial activity, such as aquaculture developments, that may increase the risk of salmon lice Lepeophtheirus salmonis, infection. Lice infection in wild salmonids depends on farmed fish density but can also be correlated to environmental factors, including foraging ecology. In the current paper we examine niche use and trophic variation of co-occurring Arctic charr and sea trout in northwest Iceland, using stomach contents and stable isotope values of δ13C, δ15N and δ34S. We then test if these factors correlated to salmon lice infection. The salmonid species differed in niche use, for example, in time of marine foraging, with Arctic charr having a longer marine phase than was expected, and in the level of piscivory between both species. Moreover, we show that both environmental factors and individual trophic use are related to salmon lice infection in sea trout. This information may be useful in evaluating the risk and spatial management of sea farming. [ABSTRACT FROM AUTHOR]

• Fire-killed trees in NWT are an unexplored large-scale bioenergy resource; • Carbon footprint model includes previously ignored post-wildfire carbon dynamics; • Pyrogenic CCS of fire-killed trees produces carbon-negative heat; • A carbon-negative bioenergy economy is possible without harvesting live trees; • Biomass-based heating in NWT would require ∼ 2% of the annual wildfire burn. Heating buildings in Northern communities is carbon-intensive and existing low-carbon technologies are ill-suited for northern conditions. Pyrogenic carbon capture and storage (Pyro-CCS), which heats biomass anoxically to produce fuels and biochar, could provide low-carbon heat in this climate. We calculate the carbon footprint of Pyro-CCS in Northwest Territories (NWT), Canada using wood-pellets and a novel feedstock of fire-killed trees and compare these to conventional heat sources. We find that Pyro-CCS emits 40.9 g CO 2 eq. MJ-1 using wood-pellets and sequesters -10.3 g CO 2 eq. MJ-1 using fire-killed trees, compared to emissions of 59.7 g CO 2 eq. MJ-1 for wood-pellet combustion, and 79.4-89.9 g CO 2 eq. MJ-1 for fossil fuels. Scenarios suggest that widespread Pyro-CCS could allow the heating sector in NWT to achieve 1.5°C-aligned emissions reductions targets using only 121 km2 of burned forests annually (∼ 2% of annual burn in NWT). We propose five policies to promote Pyro-CCS and transform NWT into a model for northern decarbonization. [ABSTRACT FROM AUTHOR]

The fundamental niche of many species is shifting with climate change, especially in sub‐arctic ecosystems with pronounced recent warming. Ongoing warming in sub‐arctic regions should lessen environmental constraints on tree growth and reproduction, leading to increased success of trees colonising tundra. Nevertheless, variable responses of treeline ecotones have been documented in association with warming temperatures. One explanation for time lags between increasingly favourable environmental conditions and treeline ecotone movement is reproductive limitations caused by low seed availability. Our objective was to assess the reproductive constraints of the dominant tree species at the treeline ecotone in the circumpolar north. We sampled reproductive structures of trees (cones and catkins) and stand attributes across circumarctic treeline ecotones. We used generalized linear mixed models to estimate the sensitivity of seed production and the availability of viable seed to regional climate, stand structure, and species‐specific characteristics. Both seed production and viability of available seed were strongly driven by specific, sequential seasonal climatic conditions, but in different ways. Seed production was greatest when growing seasons with more growing degree days coincided with years with high precipitation. Two consecutive years with more growing degree days and low precipitation resulted in low seed production. Seasonal climate effects on the viability of available seed depended on the physical characteristics of the reproductive structures. Large‐coned and ‐seeded species take more time to develop mature embryos and were therefore more sensitive to increases in growing degree days in the year of flowering and embryo development. Our findings suggest that both moisture stress and abbreviated growing seasons can have a notable negative influence on the production and viability of available seed at treeline. Our synthesis revealed that constraints on predispersal reproduction within the treeline ecotone might create a considerable time lag for range expansion of tree populations into tundra ecosystems. [ABSTRACT FROM AUTHOR]

Highlights • During an outbreak of Epirrita autumnata , larvae shifted host choice according to host availability. • Patches with preferred shrubs mixed with other shrubs were avoided. • Reduced consumption of the preferredshrub in mixed stands took place under warming. • Elevated CO 2 had no significant effect regardless of host. • A simple Gompertz model predicts host choice and consumption. Abstract With warming climate many species are predicted to shift their distributions toward the poles. However, climate change models developed to predict species distributions do not always incorporate interactions between them. The northerly shift of the boreal forest and associated dwarf shrub communities will be directly affected by warming. But warming will also indirectly affect plant communities via impacts on the intensity and frequency of associated insect outbreaks. We present a general model exploring plant host herbivory in response to the balance between insect crowding, host consumption and climate. We examined how these factors dictate the feeding preference of Epirrita autumnata larvae during an outbreak on dwarf shrub vegetation in Sub-arctic Fennoscandia. Data were collected from an outdoor experiment investigating future climate change scenarios (elevated CO 2 and temperature) on the dwarf shrub community that included deciduous (Vaccinium myrtillus) and evergreen species (V. vitis-idaea and Empetrum nigrum). We observed that larval crowding was independent of treatment under outbreak conditions. We also tested and confirmed model predictions that larvae would prefer monospecific stands of either deciduous shrubs or its evergreen competitors. For current climate conditions, larvae had a preference to consume more deciduous shrubs in mixed stands. However, at elevated temperature bilberry consumption and herbivore pressure was lower, particularly in mixed stands. Our results show that during future warming, E. autumnata herbivory could promote the success of thermophile deciduous species and possible northward migration. Insect behaviour and preferences should therefore be considered when predicting future vegetation movements responding to warming. [ABSTRACT FROM AUTHOR]

The sub-Arctic Iceland Sea is an important feeding area for the Icelandic capelin stock with copepods as a major food item. Information on the life history of copepods in the area is limited, and therefore the major aim of the present paper is to describe the population development and ontogenetic vertical migrations of dominant copepods in the area. Depth stratified samples were collected on six cruises covering all seasons of the year from 2006 to 2008. Calanus hyperboreus dominated the biomass (~ 45% of copepods), with C. finmarchicus ranking second (~ 28%) and Metridia longa third (~ 17%). The copepods differed in their life history strategies. C. hyperboreus is unique in that it has the deepest winter distribution (~ 800-1000 m), reproduces at depth in February-March in the absence of phytoplankton food, and spends relatively short time in the surface layers during summer. C. finmarchicus also hibernates at depth, however much shallower (~  200-600 m), and the reproduction at the surface in May-June is timed to the productive period of phytoplankton. A 2- to 3-year life cycle is proposed for C. hyperboreus and a 1 year for C. finmarchicus. Pseudocalanus spp. appear to have a similar life history as C. finmarchicus, while occupying intermediate depths (~ 400-1000 m) during the overwintering period. The life history of the omnivorous species M. longa appears relatively decoupled from the phytoplankton spring bloom. The same applies to the omnivorous species Oithona spp. and Oncaea spp. The information presented adds to the comparative description and understanding of copepods in sub-Arctic areas in general. [ABSTRACT FROM AUTHOR]

Abstract While marine animals are exposed to environmental contaminants via their prey, because plastic pollution in the aquatic environment can concentrate some chemicals, ingested plastics are thought to increase the exposure of biota to contaminants. Currently, in the literature there are contradictory results relating to how higher levels of ingested plastics by birds may lead to higher levels of polychlorinated biphenyl (PCBs). To date none of these have incorporated known Toxic Equivalency Factors (TEFs) for non- ortho and mono- ortho congeners of PCB which is critical to assessing the potential effects from PCBs. We examined northern fulmars (Fulmarus glacialis) from the Labrador Sea region Canada, and the ingested plastics from these same birds for comparative PCB concentrations. We found no significant correlations between the PCB concentrations in the birds and the mass or number of retained ingested plastic pieces in the stomach, this held true when PCBs were considered by a number of different ways, including ∑ 4 PCB, ∑PCB, lower-chlorinated, high-chlorinated, non-ortho PCB, and mono- ortho congeners. PCB concentrations were lower in plastics as compared with livers. We found significant differences in congener profiles between the ingested plastics and seabird livers suggesting that while plastics do not contribute to the PCB concentrations, there may be some interactions between plastics and the chemicals that the birds are exposed to via ingested plastics. Highlights • The ingestion of plastics can lead to increased contaminant exposure. • We examined PCB concentrations in seabirds and their ingested plastics. • No significant correlations were found between PCBs and ingest plastics. • There were differences in the PCB concentrations and congener profiles in plastics and livers. • Xenobiotics, such as PCBs, may undergo metabolism in upper trophic level species. [ABSTRACT FROM AUTHOR]

Climate warming in northern high latitudes has progressed twice as fast as the global average, leading to prominent but puzzling changes in vegetation structure and functioning of tundra and boreal ecosystems. While some regions are becoming greener, others have lost or shifted vegetation condition as indicated by a browning signal. The mechanisms underlying this ‘greening or browning enigma’ remain poorly understood. Here we use multi-sourced time-series of satellite-derived vegetation indices to reveal that spectral greening is associated with reductions in surface water cover (i.e. fraction of surface water bodies), whereas spectral browning is linked to increases in surface water cover. These patterns are consistently observed from both 30 m resolution Landsat data and 250 m resolution MODIS data on the basis of grid cells sized of 1, 2 and 4 km. Our study provides, to our knowledge, the first biome-scale demonstration that interactions between vegetation condition and water cover change can explain the contrasting trajectories of ecosystem dynamics across the northern high latitudes in response to climate warming. These divergent trajectories we identified have major implications for ecosystem functioning, carbon sequestration and feedbacks to the climate system. Further unraveling the interaction between vegetation and surface water will be essential if we are to understand the fate of tundra and boreal biomes in a warming climate.

Studies of trophic interactions give valuable insights into the functioning of ecosystems and can be used to identify qualitative differences among ecosystems. Here, we use natural stable isotope concentrations (δ13C and δ15N) to study the food-web structure in four contrasting locations on the northern European continental shelf: two sub-Arctic locations in the Lofoten-Vesterålen region (fjord vs. open shelf) and two temperate locations (northern vs. southern North Sea). Phytoplankton was identified as the major primary producer in all studied ecosystems, even in the sub-Arctic fjord, where macroalgae only played a minor role in the food web. We used mixing models to determine the relative reliance on prey of benthic affinity and found that reliance on benthic prey was higher in the North Sea than in the Lofoten-Vesterålen region. Atlantic cod (Gadus morhua) was identified as the single top-predator in the North Sea, utilizing food from both benthic and pelagic trophic channels. More separate benthic and pelagic trophic channels characterize the Lofoten-Vesterålen region, where G. morhua acts as part of the pelagic food chain. Furthermore, our data indicate that the recent mesopredator outburst in the southern North Sea might have been enhanced by reduced predation pressure due to the collapse of the local cod stocks. We conclude that the resilience toward a high fishing pressure is higher in the Lofoten-Vesterålen region than in the North Sea.

As the extremity of Arctic climate lessens with global warming, the risk of invasion increases. We assess the presence of introduced plant species and their persistence (since the previous survey) in a Canadian subpolar site on the Hudson Bay with a history of human introductions from large-scale grain inputs. Widespread sampling was done to locate all introduced plant species in the Churchill, MB, Canada area. We quantified edaphic variations through soil sampling, and the effect of aspect on introduced species’ richness, cover, and height. At the regional scale, species life history traits and climate envelopes (average and variability of climate in a native range) were established to determine if persistent plant species had similar climate requirements. We found that despite statistically significant warming and increased precipitation, the number of introduced plant species in sub-Arctic Churchill declined from 80 to 36 between the 1989 and 2013 sampling periods. We found that introduced species favor locally warmer, human-disturbed sites with above average soil nutrients. The plant species that remained in Churchill since the 1989 survey compared to those that did not persist are better able to tolerate colder temperatures and have wider, more variable climate envelopes. The decline in introduced species is likely linked to changes in grain shipment inputs. Many of the introduced species recorded in 1989 may have only existed through constant seed subsidies from imports, suggesting that most species have not yet been successful in the absence of human modification. Although the number of introduced plants has decreased, we suggest that continuous disturbance is no longer required for some introduced species to persist suggesting that a climate threshold may have been crossed for some species. One introduced species (Taraxacum officinale, common dandelion) has spread to areas that have not been modified by humans and is now growing in two undisturbed locations. Its current distribution outside disturbed areas does not yet warrant the distinction of invasive at this time. The findings of this study suggest that in the Canadian Arctic, if disturbance and nutrient enrichment are reduced, the potential for introduced plants to establish and possibly become invasive is still limited but will likely change as warming continues. [ABSTRACT FROM AUTHOR]

Abstract: Agriculture is one of the primary threats to biodiversity but agricultural land can also provide key resources for many species and, in some parts of the world, agricultural land supports important populations of species of conservation concern. In these cases, it is important to understand species’ use of agricultural land before further expansion or intensification of agricultural activities occurs. Agriculture in Iceland is still relatively low in intensity and extent, and internationally important populations of several breeding bird species are abundant in farmed regions. In these high latitude landscapes, agricultural land could provide resources that help to support these species, and the consequences of future agricultural expansion will depend on the nature of these relationships. To address these issues, we conducted surveys of bird abundance at 64 farms in areas of Iceland that vary in underlying soil productivity, and quantified (a) levels of breeding bird use of farmed land managed at three differing intensities, ranging from cultivated fields to semi‐natural land and (b) changes in patterns of use throughout the breeding season, for an assemblage of species. Breeding birds use all three land management types in large numbers but, overall, bird abundance is lower in more intensively managed farmland. However, more intensively managed agricultural land supports higher densities of birds than semi‐natural habitats in areas with lower underlying productivity. This suggests that in landscapes in which agricultural land does not yet dominate, conservation and commercial production can co‐exist, especially in areas of low productivity. Areas like Iceland, in which agricultural land still supports large populations of internationally important species, are rare and this study highlights the need to protect these systems from the agricultural development that has led to widespread biodiversity loss throughout most of the world. [ABSTRACT FROM AUTHOR]

Microwave imagery has a distinct advantage over optical imagery in high-latitude areas because it allows data to be acquired independently of cloud cover and solar illumination. Synthetic aperture radar (SAR)-based monitoring has become increasingly important for understanding the state and dynamics of permafrost landscapes at the regional scale. This study presents a permafrost landscape mapping method that uses multi-temporal TerraSAR-X backscatter intensity and interferometric coherence information. The proposed method can classify permafrost landscape features and map the two most important features in sub-arctic permafrost environments: permafrost-affected areas and thermokarst ponds. First, a land cover map is generated through the combined use of object-based image analysis (OBIA) and classification and regression tree (CART) analysis. An overall accuracy of 98% is achieved when classifying rock and water bodies, and an accuracy of 79% is achieved when discriminating between different vegetation types with one year of single-polarized acquisitions. Second, the distributions of the permafrost-affected areas and thermokarst ponds are derived from the classified landscapes. Permafrost-affected areas are inferred from the relationship between vegetation cover and the existence of permafrost, and thermokarst pond distributions are directly inherited from the land cover map. The two mapped features exhibit good agreement with manually delineated references. The proposed method can produce permafrost landscape maps in complex sub-arctic environments and improve our understanding of the effects of climate change on permafrost landscapes. This classification strategy can be transferred to other time-series SAR datasets, e.g., Sentinel-1, and other heterogeneous environments. [ABSTRACT FROM AUTHOR]

Documenting distribution patterns of juvenile Pacific herring ( Clupea pallasii ) can clarify habitat preferences and provide insight into ecological factors influencing early life survival. However, few analyses relating juvenile Pacific herring density to habitat characteristics have been conducted. We sampled age-0 Pacific herring in nine bays and fjords distributed throughout Alaska's Prince William Sound during November over a 3-year period (2013–2015) and investigated associations between catch rate and habitat covariates using generalized linear mixed models. Our results indicated that the night-time distribution of age-0 Pacific herring in the pelagic environment was influenced by proximity to eelgrass ( Zostera marina ) beds, salinity, and water depth. Age-0 Pacific herring catch rate was negatively associated with tow depth, with herring favoring shallower water across the range of depths sampled (7.2–35.4 m). In addition, Pacific herring distribution was positively associated with fresher water within the sampled salinity gradient (24.1–32.3 psu) and proximity to eelgrass beds. Seasonal changes in juvenile Pacific herring distribution were investigated by sampling one bay over a seven month period (October-April). Age-0 Pacific herring tended to remain in the inner bay region throughout the seven months, while age-1 Pacific herring had shifted from the inner to the outer bay by spring (March-April). Additionally, catch rate of age-0 Pacific herring in areas where ice breakup had just occurred was higher than in open water, suggesting that age-0 herring preferentially select ice-covered habitats when available. Based on our results we recommend that habitat preferences of age-0 Pacific herring should be considered in the development of Pacific herring year-class strength indices from catch data. [ABSTRACT FROM AUTHOR]

A key question for the evolution of thermokarst wetlands and lakes in Arctic and sub-Arctic permafrost regions is how large-scale warming interacts with local landscape conditions in driving permafrost thaw and its spatial variability. To answer this question, which also relates to risks for ecology, society, and health, we perform systematic model simulations of various soil-permafrost cases combined with different surface-warming trends. Results show that both the prevalence and the thaw of permafrost depended strongly on local soil conditions and varied greatly with these for the same temperature conditions at the surface. Greater ice contents and depth extents, but also greater subsurface volumes thawing at depth under warming, are found for peat soils than other studied soil/rock formations. As such, more thaw-driven regime shifts in wetland/lake ecosystems, and associated releases of previously frozen carbon and pathogens, may be expected under the same surface warming for peatlands than other soil conditions. Such risks may also increase in fast permafrost thaw in mineral soils, with only small thaw-protection effects indicated in the present simulations for possible desertification enhancement of mineral soil covers.

Biomagnification (increase in contaminant concentrations at successively higher levels of trophic web), is a process that can transversally impair biodiversity and human health. Most research shows that biomagnification should be higher at poles with northern sites having a major tendency to biomagnify Persistent Organic Pollutants (POPs) through their marine food webs. We investigated the biomagnification degree into two marine trophic webs combining carbon and nitrogen stable isotopes and POP analyses. We showed that the Antarctic trophic web was more depleted than the sub-Arctic one and the differences highlighted for the basal part could explain the difference in length between them. Concentrations of polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), and p,p’ -DDE were of the same order of magnitude in the two polar trophic webs, with some values surprisingly higher in the Antarctic than sub-arctic organisms: PCBs ranged (average ± standard deviation) 1.10 ± 0.39–12.93 ± 7.62, HCB <0.10–7.28 ± 5.32, and p,p’ -DDE 0.52 ± 0.18–11.36 ± 5.3 ng/g wet weight (wt) in the Antarctic organisms, and 0.53–5.08, <0.10–1.48, and 0.27 ± 0.35–5.46 ± 1.73 ng/g wet wt, respectively, in the sub-Arctic ones. The contribution of tetra- and penta-CBs to the ∑PCBs was 10–65% in the Antarctic species and 15–45% in the Arctic species. The relationships between POPs and trophic levels, and the information obtained by the Trophic Magnification Factor revealed that the Antarctic trophic web had a greater tendency to biomagnify PCBs and p,p’ -DDE than its sub-Arctic counterpart. POP availability in the environment and specific ecological features may play an important role in the bioaccumulation, and biomagnification is apparently less important than bioconcentration. [ABSTRACT FROM AUTHOR]

To identify trematode diversity and life-cycles in the sub-Arctic Lake Takvatn, Norway, we characterised 120 trematode isolates from mollusc first intermediate hosts, metacercariae from second intermediate host fishes and invertebrates, and adults from fish and invertebrate definitive hosts, using molecular techniques. Phylogenies based on nuclear and/or mtDNA revealed high species richness (24 species or species-level genetic lineages) and uncovered trematode diversity (16 putative new species) from five families typical in lake ecosystems (Allocreadiidae, Diplostomidae, Plagiorchiidae, Schistosomatidae and Strigeidae). Sampling potential invertebrate hosts allowed matching of sequence data for different stages, thus achieving molecular elucidation of trematode life-cycles and exploration of host-parasite interactions. Phylogenetic analyses also helped identify three major mollusc intermediate hosts ( Radix balthica , Pisidium casertanum and Sphaerium sp.) in the lake. Our findings increase the known trematode diversity at the sub-Arctic Lake Takvatn, showing that digenean diversity is high in this otherwise depauperate sub-Arctic freshwater ecosystem and indicating that sub-Arctic and Arctic ecosystems may be characterised by unique trematode assemblages. [ABSTRACT FROM AUTHOR]

Context: 'Conserving Nature's stage' has been advanced as an important conservation principle because of known links between biodiversity and abiotic environmental diversity, especially in sensitive high-latitude environments and at the landscape scale. However these links have not been examined across gradients of human impact on the landscape. Objectives: To (1) analyze the relationships between land-use intensity and both landscape-scale biodiversity and geodiversity, and (2) assess the contributions of geodiversity, climate and spatial variables to explaining vascular plant species richness in landscapes of low, moderate and high human impact. Methods: We used generalized additive models (GAMs) to analyze relationships between land-use intensity and both geodiversity (geological, geomorphological and hydrological richness) and plant species richness in 6191 1-km grid squares across Finland. We used linear regression-based variation partitioning (VP) to assess contributions of climate, geodiversity and spatial variable groups to accounting for spatial variation in species richness. Results: In GAMs, geodiversity correlated negatively, and plant species richness positively, with land-use intensity. Both relationships were non-linear. In VP, geodiversity best accounted for species richness in areas of moderate to high human impact. These overall contributions were mainly due to variation explained jointly with climate, which dominated the models. Independent geodiversity contributions were highest in pristine environments, but low throughout. Conclusions: Human action increases biodiversity but may reduce geodiversity, at landscape scale in high-latitude environments. Better understanding of the connections between biodiversity and abiotic environment along changing land-use gradients is essential in developing sustainable measures to conserve biodiversity under global change. [ABSTRACT FROM AUTHOR]

Sub-arctic birch forests ( Betula pubescens Ehrh. ssp. czerepanovii) periodically suffer large-scale defoliation events caused by the caterpillars of the geometrid moths Epirrita autumnata and Operophtera brumata. Despite their obvious influence on ecosystem primary productivity, little is known about how the associated reduction in belowground C allocation affects soil processes. We quantified the soil response following a natural defoliation event in sub-arctic Sweden by measuring soil respiration, nitrogen availability and ectomycorrhizal fungi (EMF) hyphal production and root tip community composition. There was a reduction in soil respiration and an accumulation of soil inorganic N in defoliated plots, symptomatic of a slowdown of soil processes. This coincided with a reduction of EMF hyphal production and a shift in the EMF community to lower autotrophic C-demanding lineages (for example, /russula-lactarius). We show that microbial and nutrient cycling processes shift to a slower, less C-demanding state in response to canopy defoliation. We speculate that, amongst other factors, a reduction in the potential of EMF biomass to immobilise excess mineral nitrogen resulted in its build-up in the soil. These defoliation events are becoming more geographically widespread with climate warming, and could result in a fundamental shift in sub-arctic ecosystem processes and properties. EMF fungi may be important in mediating the response of soil cycles to defoliation and their role merits further investigation. [ABSTRACT FROM AUTHOR]

The direction of pan-Arctic ecosystem shifts in response to climate warming is relatively well understood; however, landscape-level linkages among terrestrial, wetland, and lake ecosystems significantly influence the dynamics of each, making it difficult to generalize about lake responses to warming across the Arctic, and at times difficult to interpret paleoclimate records from lake sediments. To investigate differences in lake responses to recent climate change at the boreal-tundra ecotone, we conducted a 2-year survey of diatom assemblages from lakes with varying catchment characteristics in northern Manitoba, Canada. We investigated whether catchment geomorphology and landscape, including slope and vegetative cover, result in characteristic water chemistries and hence diatom assemblage signatures, which could then be used in paleolimnological studies to infer past changes in the catchment. Forty-four lakes were sampled for water chemistry and catchment vegetation was characterized using Landsat Imagery. Lake catchments were generally small (median 702 ha) and dominated by peat ( Sphagnum) with or without lowland forest ( Picea- Larix), or open tundra, with different amounts of exposed rock/till, upland forest/woodlands, and burn recovery area. Lakes were generally nutrient-poor, with lower nutrient and DOC concentrations in tundra-dominated catchments, and higher nutrients and DOC in catchments with greater forest cover. A diatom-based transfer function for pH (R = 0.72, $$ {\text{R}}_{\text{boot}}^{2} $$ = 0.54) was developed and compared with diatom assemblage turnover and sediment geochemistry in cores from eight lakes to reconstruct limnologic conditions over the past ~200 years. Most cores showed similar increases in biogenic silica and carbon burial, beginning around AD 1880 in the tundra lakes and about 1920 in the more forested catchments, likely in response to regional warming. In contrast to lakes in other Arctic regions, our lakes showed only minor pH changes in recent decades. The shift, however, was more pronounced in higher-latitude lakes with less forest cover, suggesting small-scale watershed influence on lake response to climate, even on short time scales. Diatom assemblages did not follow previously published models of climate-linked community change seen in circum-Arctic and sub-Arctic lakes. Translating local changes detected in the paleolimnological record to the regional level requires an understanding of how different catchment properties mediate the response of lakes, and their diatom assemblages, to climate change. [ABSTRACT FROM AUTHOR]