Litter decomposition represents a major path for atmospheric carbon influx into Arctic soils, thereby controlling below-ground carbon accumulation. Yet, little is known about how tundra litter decomposition varies with microenvironmental conditions, hindering accurate projections of tundra soil carbon dynamics with future climate change. Over 14 months, we measured landscape-scale decomposition of two contrasting standard litter types (Green tea and Rooibos tea) in 90 plots covering gradients of micro-climate and -topography, vegetation cover and traits, and soil characteristics in Western Greenland. We used the tea bag index (TBI) protocol to estimate relative variation in litter mass loss, decomposition rate (k) and stabilisation factor (S) across space, and structural equation modelling (SEM) to identify relationships among environmental factors and decomposition. Contrasting our expectations, microenvironmental factors explained little of the observed variation in both litter mass loss, as well as k and S, suggesting that the variables included in our study were not the major controls of decomposer activity in the soil across the studied tundra landscape. We use these unexpected findings of our study combined with findings from the current literature to discuss future avenues for improving our understanding of the drivers of tundra decomposition and, ultimately, carbon cycling across the warming Arctic.

Changes in food availability may act as a major mechanism by which global change impacts populations of birds, especially in seasonal environments at high elevations or latitudes. Systematic sampling of invertebrates, which constitute the diet of many bird species during the breeding season, is however largely missing in mountain ecosystems and is overall very rare for soil-dwelling species or stages. Here, we repeatedly sampled earthworms (Lumbricidae), the staple prey of the Ring Ouzel Turdus torquatus, over a whole breeding season in a study area in the Swiss Alps. Our main goal was to finely characterise spatio-temporal patterns of food availability for this declining bird species, in relation to elevation, habitat type and snowmelt stage. In 24 sampling plots, we extracted two soil cores every week for 6-10 weeks and hand-sorted soil invertebrates separately for two 5-cm soil layers. We then analysed the abundance of earthworms in those two layers in relation to various environmental parameters. We show that within our study area, edaphic and topographical parameters are poor predictors of the mean abundance of earthworms over the breeding season. Ground vegetation cover and soil moisture, however, are suitable predictors for the number of earthworms within the soil profile at each sampling time, i.e., of their availability for Ring Ouzels. Moreover, we provide evidence for a clear seasonal peak in earthworm availability, which was more pronounced in open grasslands compared to forested areas and happened later in the season where snow lingered. This study, by improving our understanding of the factors driving food availability for a mountain bird species, provides insights into how shifts in land-use and climate might lead to altered predator-prey interactions.

Microplastic pollution in the environment has become a source of concern in recent years. The transport and deposition of suspended atmospheric microplastics play an important role in the global linkage of microplastic sources and sinks. In this review, we summarized recent research progress on sampling devices, pretreatments, and identification methods for atmospheric microplastics. The total suspended particles and atmospheric deposition, including dust, rainfall, and snow samples, arc the environmental carriers for atmospheric microplastic studies. There arc active and passive sampling methods. Pretreatment depends on sample types and identification methods and includes sieving, digestion, density separation, filtration, and drying. The measured features for atmospheric microplastics include particle size distributions, shapes, colors, surface morphology, and polymer compositions, using stereomicroscopes, Fourier transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, and liquid chromatography-tandem mass spectrometry. laser direct infrared spectroscopy and thermochemical methods coupled with mass spectrometry arc potential methods for identifying atmospheric microplastics. Currently, models for estimating the fluxes of atmospheric microplastic emission, transport, and deposition arc in the initial stages of development; their implementation will enhance our understanding of the microplastic cycle globally based on simulated and observed data.

Prior to development of the Circumpolar Active Layer Monitoring (CALM) programme, little attention was paid to formal spatial sampling designs for measuring active-layer thickness (ALT). This omission made the accuracy of many data-sets questionable, in part because spatial periodicities caused by landscape features such as ice-wedge polygons and thaw lakes can significantly influence the depth of thaw. Early in the development of CALM's protocols, ALT was sampled in the continuous permafrost zone in northern Alaska and simulated by computer, to determine how ALT could be measured accurately. The simulated and field data-sets were analysed by comparing the means, variances and frequency distributions obtained using four spatial sampling designs (random, systematic, systematic random and systematic stratified unaligned). By a small margin, systematic stratified unaligned sampling provided the most accurate results. Systematic designs can, however, provide adequate estimates of the statistical moments of ALT with significant savings in cost, time and ease of implementation. Based on these results, the CALM programme recommended use of 10 x 10, 100 x 100 or 1000 x 1000m grids, with sampling intervals of 1, 10 and 100m, respectively. Most probed CALM sites now employ this strategy, except in terrain with unusual landscape elements or other special constraints. Copyright (c) 2016 John Wiley & Sons, Ltd.