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Reliable predictions of the environmental fate and risk of engineered nanomaterials (ENMs) require a better understanding of ENM reactivity in complex, biologically active systems for chronic low-concentration exposure scenarios. Here, simulated freshwater wetland mesocosms were dosed with ENMs to assess how their reactivity and seasonal changes in environmental parameters influence ENM fate in aquatic systems. Copper-based ENMs (Kocide), known to dissolve in water, and gold nanoparticles (AuNPs), stable against dissolution in the absence of specific ligands, were added weekly to mesocosm waters for 9 months. Metal accumulation and speciation changes in the different environmental compartments were assessed over time. Copper from Kocide rapidly dissolved likely associating with organic matter in the water column, transported to terrestrial soils and deeper sediment where it became associated with organic or sulfide phases. In contrast, Au accumulated on/in the macrophytes where it oxidized and transferred over time to surficial sediment. A dynamic seasonal accumulation and metal redox cycling were found between the macrophyte and the surficial sediment for AuNPs. These results demonstrate the need for experimental quantification of how the biological and chemical complexity of the environment, combined with their seasonal variations, drive the fate of metastable ENMs.

Peatlands store one-third of global soil carbon. Drought/drainage coupled with climate warming present the main threat to these stores. Hence, understanding drought effects and inherent feedbacks related to peat decomposition has been a primary global challenge. However, widely divergent results concerning drought in recent studies challenge the accepted paradigm that waterlogging and associated anoxia are the overarching controls locking up carbon stored in peat. Here, by linking field and microcosm experiments, we show how previously unrecognized mechanisms regulate the build-up of phenolics, which protects stored carbon directly by reducing phenol oxidase activity during short-term drought and, indirectly, through a shift from low-phenolic Sphagnum/herbs to high-phenolic shrubs after long-term moderate drought. We demonstrate that shrub expansion induced by drought/warming in boreal peatlands might be a long-term self-adaptive mechanism not only increasing carbon sequestration but also potentially protecting historic soil carbon. We therefore propose that the projected ‘positive feedback loop’ between carbon emission and drought in peatlands may not occur in the long term.

Soils in the Antarctic Dry Valleys have been significantly influenced by soil formation factors such as parent material, climate, and topography. Factors common in more temperate zones, including chemical weathering and leaching of minerals, occur to a much lesser extent in these cold arid soils, leading to an accumulation of salts and bases, which will likely affect the distribution of soil biota. Since the intensity of these factors may vary with topography, this study examined the soil properties and soil invertebrate communities along an elevational gradient in Taylor Valley, Antarctica. We sampled from two spatial scales (1 × 1 m and 10 × 10 m) at three sites (83, 121, and 188 m a.s.l) on the south side of Lake Hoare in Taylor Valley, and examined soil moisture, nitrogen, carbon, pH, and electrical conductivity (which provides an estimation of soil salinity), as well as the distribution and community structure of soil invertebrates. We found significant differences in soil properties with elevation, along with associated differences in soil communities. Biodiversity was greatest at the lowest elevation, closest to the shore of Lake Hoare, where soil moisture, carbon, and nitrogen were highest, and salinity was lowest. Scottnema lindsayaedominated the nematode communities found at all sites. Electrical conductivity was higher and carbon and nitrogen contents were lower at the upper elevations. The distribution of both Eudorylaimusand Plectusappeared to be influenced by soil moisture; electrical conductivity affected the mortality of all three nematode genera found. Soil properties did differ with sampling scale, suggesting that changes in microhabitats not detected at sampling intervals of a meter or more may be more reliably detected by sampling at a smaller scale.