Spatiotemporal and seasonal dynamics in the microbial communities of a landfill-leachate contaminated aquifer.

The microbiome of an aquifer contaminated by landfill leachate and undergoing intrinsic remediation was characterised using 16S rRNA metabarcoding. The archaeal/bacterial V3-V4 hypervariable region of the 16S rRNA gene was sequenced using Illumina MiSeq, and multivariate statistics were applied to make inferences. Results indicate that the aquifer recharge and aquifer sediment samples harbour different microbial communities compared to the groundwater samples. While Proteobacteria dominated both the recharge and groundwater samples, Acidobacteria dominated the aquifer sediment. The most abundant genera detected from the contaminated aquifer were Polynucleobacter, Rhodoferax, Pedobacter, Brevundimonas, Pseudomonas, Undibacterium, Sulfurifustis, Janthinobacterium, Rhodanobacter, Methylobacter and Aquabacterium. The result also shows that the microbial communities of the groundwater varied spatially, seasonally and interannually, although the interannual variation was significant for only one of the wells. Variation partitioning analysis indicates that water chemistry and well distance are intercorrelated and they jointly accounted for most of the variation in microbial composition. This implies that the species composition and water chemistry characteristics have a similar spatial structuring, presumably caused by the landfill leachate plume. The study improves our understanding of the dynamics in subsurface microbial communities in space and time.

Bioclimatic gradients and soil property trends from northernmost mainland Norway to the Svalbard archipelago. Does the arctic biome extend into mainland Norway?

The boundary between the boreal and arctic biomes in northwest Europe has been a matter of debate for many years. Some authors consider that the boundary is marked by the northern limit of tree growth in the northernmost Norwegian mainland. In this study we have collected air and soil temperature data from 37 heath stands from northern Finnmark (71°N), the northernmost part of the Norwegian mainland, through Bear Island (74°N) in the Barents sea, to Adventsdalen (78)°N (in Spitsbergen) in Svalbard archipelago. In Finnmark, plots both south and north of the treeline were investigated. Vegetation and soil chemistry analyses were performed on the plots in Finnmark and Svalbard. Significant decreasing south-north trends in air and soil temperatures were observed from Finnmark to Spitsbergen. Soils in Finnmark were acidic and rich in organic matter, while those on Adventsdalen were basic and poor in organic matter. Vegetational analysis identified five communities: three in Finnmark and two on Adventsdalen. The communities in Finnmark had marked mutual similarities but were very different from those on Adventsdalen. No significant ecological differences between heaths south and north of the treeline in Finnmark were observed. Air and soil temperature variables in Finnmark were outside the recognized range for the arctic biome and inconsistent with the presence of permafrost both south and north of the treeline. A major difference between Finnmark and Spitsbergen was amount of soil frost and length of the growing season. Our results suggest that the boreal biome extends all the way to the north coast of mainland Norway; and previously used division of heaths in Finnmark into boreal, alpine and arctic biomes is not justified.

Manipulation of snow in small headwater catchments at Storgama, Norway: effects on leaching of total organic carbon and total organic nitrogen.

Projected increases in winter temperature due to future climate change may cause decreased snow accumulation at lower and intermediate altitudes in northern temperate regions. The resulting changes in soil temperature and water regime may affect the leaching of total organic carbon (TOC) and total organic nitrogen (TON). We manipulated the snow cover of small headwater catchments in a montane heathland area of southern Norway to quantify its effect on concentrations and fluxes of TOC and TON in runoff. Manipulations included snow removal, to promote soil frost, and insulation, to prevent soil frost. Snow removal resulted in increased TOC and TON concentrations, but decreased fluxes. Insulation caused a slight decrease in concentrations and fluxes of TOC. Our experiments show that a change in snow depth, and thus soil temperature, is not likely to have serious effects on TOC and TON leaching in the montane heathland area studied.

Manipulation of snow in small headwater catchments at Storgama, Norway: effects on leaching of inorganic nitrogen.

We have manipulated the winter-time soil temperature regime of small headwater catchments in a montane heathland area of southern Norway to study the possible effects on concentrations and fluxes of inorganic nitrogen in runoff. The experiments included extra insulation of soils in two catchments to prevent subzero temperatures during winter, and removal of snow in two other catchments to promote soil frost. Increased soil temperatures during winter increased the springtime concentrations and fluxes of ammonium (NH4) and nitrate (NO3) in runoff. By contrast, snow removal with development of significant soil frost showed no systematic effects on mean concentrations or fluxes of inorganic N. The results from our experiments suggest that warmer soils during winter caused by exceptionally mild winters, or alternatively a heavy snowpack, imply a greater risk for inorganic N leaching in this region than a possible increase of soil frost events because of reduced snow cover.

Manipulation of precipitation in small headwater catchments at Storgama, Norway: effects on leaching of organic carbon and nitrogen species.

Projected changes in climate in Southern Norway include increases in summer and autumn precipitation. This may affect leaching of dissolved organic matter (DOM) from soils. Effects of experimentally added extra precipitation (10 mm week) during the growing season of 3 years (2004-2006) to small headwater catchments at Storgama (59 degrees 0'N, 550-600 m a.s.l.) on leaching of total organic carbon (TOC) and total organic nitrogen (TON) were assessed. Extra precipitation did not have a significant effect on average TOC and TON concentrations in runoff. Thus, fluxes of TOC and TON increased nearly proportionally with water fluxes. This suggests that a store of adsorbed and potentially mobile TOC and TON in catchment soils buffers the concentration of DOM in runoff. The size and dynamics of the pool of TOC and TON depends on the balance between production and leaching rates. Infrequent short droughts had only small effects on TOC and TON fluxes in runoff from the reference catchments.