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Culp J.M.,University of New Brunswick | Lento J.,University of New Brunswick | Goedkoop W.,Swedish University of Agricultural Sciences | Power M.,University of Waterloo | And 7 more authors.

Arctic freshwater ecosystems are facing unique challenges through the interaction of natural and human-induced stressors such as climate change and industrial development. Much is unknown about the biodiversity of Arctic freshwaters, although it is believed to have already been affected by climate change. A pan-Arctic monitoring strategy is critically needed to improve abilities to detect and understand ongoing and future changes in Arctic freshwater ecosystems. The challenging issues that Arctic freshwater monitoring must address include: the large diversity of Arctic freshwater ecosystems, varying levels of stressor impacts across the Arctic, lack of historical baseline research and monitoring coordination, and poor among-country standardization of sampling protocols. In response, the Arctic Council's Freshwater Expert Monitoring Group of the Circumpolar Biodiversity Monitoring Program (Conservation of Arctic Flora and Fauna) is developing a framework for monitoring Arctic freshwater biodiversity that will lead to regular reviews of the state of freshwater ecosystems across the circumpolar Arctic. The parameters of primary focus for the monitoring framework are classified by focal ecosystem components (FECs), which are biotic or abiotic factors that are ecologically pivotal, charismatic and/or sensitive to changes in biodiversity. FECs are placed in the context of expected ecosystem change through the development of testable impact hypotheses (or predictions) that outline a cause-effect framework regarding how change in environmental and anthropogenic stressors is expected to affect FECs. These prediction statements provide both guidelines for future scientific data collection and a focus for management decision-making. Here we discuss the design of a proposed monitoring framework and the development of impact hypotheses that focus on climate change effects. We emphasise the connectivity between science, monitoring and management necessary to implement the framework across the Arctic. © 2012 Copyright Taylor and Francis Group, LLC. Source

Bokhorst S.,Swedish University of Agricultural Sciences | Huiskes A.,Netherlands Institute of Ecology | Aerts R.,VU University Amsterdam | Convey P.,British Antarctic Survey | And 12 more authors.
Global Change Biology

Environmental manipulation studies are integral to determining biological consequences of climate warming. Open Top Chambers (OTCs) have been widely used to assess summer warming effects on terrestrial biota, with their effects during other seasons normally being given less attention even though chambers are often deployed year-round. In addition, their effects on temperature extremes and freeze-thaw events are poorly documented. To provide robust documentation of the microclimatic influences of OTCs throughout the year, we analysed temperature data from 20 studies distributed across polar and alpine regions. The effects of OTCs on mean temperature showed a large range (-0.9 to 2.1 °C) throughout the year, but did not differ significantly between studies. Increases in mean monthly and diurnal temperature were strongly related (R2 = 0.70) with irradiance, indicating that PAR can be used to predict the mean warming effect of OTCs. Deeper snow trapped in OTCs also induced higher temperatures at soil/vegetation level. OTC-induced changes in the frequency of freeze-thaw events included an increase in autumn and decreases in spring and summer. Frequency of high-temperature events in OTCs increased in spring, summer and autumn compared with non-manipulated control plots. Frequency of low-temperature events was reduced by deeper snow accumulation and higher mean temperatures. The strong interactions identified between aspects of ambient environmental conditions and effects of OTCs suggest that a detailed knowledge of snow depth, temperature and irradiance levels enables us to predict how OTCs will modify the microclimate at a particular site and season. Such predictive power allows a better mechanistic understanding of observed biotic response to experimental warming studies and for more informed design of future experiments. However, a need remains to quantify OTC effects on water availability and wind speed (affecting, for example, drying rates and water stress) in combination with microclimate measurements at organism level. © 2012 Blackwell Publishing Ltd. Source

Wehn S.,Norwegian University of Science and Technology | Olsson G.,Gothenburg University | Olsson G.,Norwegian University of Science and Technology | Hanssen S.,Directorate for Nature Management | Hanssen S.,Norwegian University of Science and Technology
Norsk Geografisk Tidsskrift

Mountain treelines can be seen as boundaries between two vegetation zones -the alpine and subalpine zones -and function as an indicator of ecosystem change. Interpreting factors leading to changes in mountains includes disturbance from human resource use and climate as important factors. The article shows that forest line changes in eastern Jotunheimen, a mountain region in southern Norway, can be related to changes in livestock grazing pressure between the 1960s and 2002. In contrast to other European mountain regions, highly relevant climate variables such as the triterm (the summer months) have not changed in the studied region. Therefore, land-use change is considered the main driver for the forest line shifts observed in the region. However, the predicted climate warming, together with continued trends of decreasing and abandoned free-range grazing of livestock will cause further forest expansion above the present forest lines also in the eastern Jotunheimen mountain range. © 2012 Copyright Norwegian Geographical Society. Source

Larsson P.,University of Bergen | Hansen H.,Directorate for Nature Management | Helland L.K.B.,Torshovgata 37

Data from the International Biological Programme (IBP) and subsequent studies have been re-analysed to test the two hypotheses which previously have been suggested concerning the zooplankton in the mountain lake, Øvre Heimdalsvatn: (1) the average temperature in June, more than other summer months, is affecting the growth rate and population densities of zooplankton in the lake, (2) the invasion of the European minnow (Phoxinus phoxinus) has caused changes in the zooplankton community. The analyses have demonstrated that the June temperature strongly affects the growth rate of all the zooplankton species, but that there is no relationship with the population maxima. The species composition in the crustacean zooplankton has not changed between 1969 and 1999, and any direct impact of the minnows on the zooplankton community could not be detected. Indirectly, the minnows may have reduced the density of invertebrate predators, and thus caused an increase in juvenile survival and increased summer maximum density of Bosmina longispina. The variation in density of the copepod, Cyclops scutifer, was correlated with the density of Heterocope saliens, most likely the result of predator-prey interactions. © 2010 Springer Science+Business Media B.V. Source

Heggenes J.,University of Oslo | Heggenes J.,Telemark University College | Bremset G.,Directorate for Nature Management | Brabrand A.,University of Oslo
Freshwater Biology

The hyporheic zone may be a habitat for fish, depending on habitat patch characteristics and interactions with fish behaviour, such as movements. Theory highlights the vertical connection and potentially significant functional role of the hyporheic zone, but actual use of the hyporheic zone by fish is understudied. In replicated factorial field experiments, we investigated movements of (i) young Atlantic salmon of various size (Salmo salar, mean total lengths, 28.3, 51.7, 52.1 and 84.6 mm) through substrata of (ii) different particle size (16-22, 24-60 mm) and (iii) thickness (20, 40, 60 cm), depending on (iv) current direction (horizontal up- to downstream, vertical 'upwelling') and (v) temperature/season (summer/autumn). In nine experiments, each with different treatments, three replicated 14-cm-diameter translucent PVC tubes were used as a proxy for the hyporheic zone and placed in parallel on the bottom in a natural salmon stream. Each tube consisted of five separable 20-cm segments, with a no-substratum segment in each end and three midsegments filled with substratum. Young salmon were placed in the upstream or/and downstream free segment, localised by a snorkeler every 15 min, and after 135 min, the segments were separated and the fish per segment counted. Results indicated that (i) a significant number of fish moved into the substratum, (ii) small Atlantic salmon (28 mm) in June rapidly moved into, and even 60 cm through, both substratum particle sizes regardless of flow direction, but fewer fish into the fine substratum, and (iii) significant numbers of larger fish (52 mm, 85 mm) in September and November also moved into the 24-60 mm substratum, but not so far and relatively fewer remained in the substratum. Horizontal or vertical flow did not affect results. We conclude that young Atlantic salmon can easily move into and through the interstitial spaces in the substratum, depending on fish size and substratum coarseness. The active use by Atlantic salmon of the substratum as part of their habitat remains to be studied, but is likely to be more prevalent than commonly assumed. © 2013 John Wiley & Sons Ltd. Source

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