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Molybdenum isotope fractionation accompanying soil development is studied across three pedogenic gradients encompassing a range of controlling factors. These factors include variable redox conditions, organic matter content, Fe and Mn oxy(hydr)oxide content, mineral composition, degree of weathering, pH, type and amount of atmospheric inputs, age, climate, and underlying rock type. Soil profiles from the island of Maui (Hawaii) along a precipitation gradient ranging from 850 to 5050 mm mean annual precipitation show a decrease in average soil δ98Mo from -0.04±0.11‰ at the driest, most oxic site, which is indistinguishable from the basalt parent material (-0.09±0.08‰), to -0.33±0.10‰ at the wettest, most reducing site. A suite of 6 Icelandic soils display a broad trend with heavier δ98Mo values (up to +1.50±0.09‰) in soil horizons that are more weathered and have higher organic matter content. Selective extractions of Mo from different soil components indicate that the association with organic matter and silicate or Ti-oxide residue dominates retention of Mo in these soils, with adsorption on Fe and Mn oxy(hydr)oxides playing a lesser role. Across all basaltic soils, δ98Mo values are lighter in soils that exhibit the most net Mo loss relative to the parent material, and δ98Mo values are heavier in soils that exhibit net Mo gains. A well-drained regolith profile in the Luquillo Mountains of Puerto Rico developed on quartz diorite shows heavier δ98Mo values than the parent material (up to +0.71±0.10‰ with an integrated profile average of +0.28±0.10‰) in soil and shallower saprolite, despite overall moderate loss of 28% of Mo relative to the bedrock. However, the deeper saprolite is unfractionated from bedrock (-0.01±0.10‰, quartz diorite bedrock) indicating that rock weathering dissolution processes and secondary clay formation do not fractionate Mo isotopes. Our data suggest that the Mo mass balance and isotope composition of soils are controlled by redox conditions, organic matter, and atmospheric inputs. In this way Mo isotopes have the potential to react to and record climate driven changes in the weathering environment. The presence of both isotopically light and heavy Mo (relative to parent material) across all sites and within individual soil profiles suggests that it is normal for multiple fractionation mechanisms to operate under the open-system conditions of soils.

Understanding the biogeochemical cycle of magnesium (Mg) is not only crucial for terrestrial ecology, as this element is a key nutrient for plants, but also for quantifying chemical weathering fluxes of Mg and associated atmospheric CO2 consumption, requiring distinction of biotic from abiotic contributions to Mg fluxes exported to the hydrosphere. Here, Mg isotope compositions are reported for parent basalt, bulk soils, clay fractions, exchangeable Mg, seasonal soil solutions, and vegetation for five types of volcanic soils in Iceland in order to improve the understanding of sources and processes controlling Mg supply to vegetation and export to the hydrosphere. Bulk soils (δ26Mg = -0.40±0.11‰) are isotopically similar to the parent basalt (δ26Mg = -0.31‰), whereas clay fractions (δ26Mg = -0.62±0.12‰), exchangeable Mg (δ26Mg = -0.75 ± 0.14 ‰), and soil solutions (δ26Mg = -0.89 ± 0.16 ‰) are all isotopically lighter than the basalt. These compositions can be explained by a combination of mixing and isotope fractionation processes on the soil exchange complex. Successive adsorption-desorption of heavy Mg isotopes leads to the preferential loss of heavy Mg from the soil profile, leaving soils with light Mg isotope compositions relative to the parent basalt. Additionally, external contributions from sea spray and organic matter decomposition result in a mixture of Mg sources on the soil exchange complex. Vegetation preferentially takes up heavy Mg from the soil exchange complex (Δ26Mgplant-exch = +0.50±0.09‰), and changes in δ26Mg in vegetation reflect changes in bioavailable Mg sources in soils. This study highlights the major role of Mg retention on the soil exchange complex amongst the factors controlling Mg isotope variations in soils and soil solutions, and demonstrates that Mg isotopes provide a valuable tool for monitoring biotic and abiotic contributions of Mg that is bioavailable for plants and is exported to the hydrosphere.

Temperature change is acknowledged to have a significant effect on soil biological processes and the corresponding sequestration of carbon and cycling of nutrients. Soils at high latitudes are likely to be particularly impacted by increases in temperature. Icelandic soils experience unusually frequent freeze and thaw cycles compare to other Arctic regions, which are increasing due to a warming climate. As a consequence these soils are frequently affected by short term temperature fluctuations. In this study, the short term response of a range of soil microbial parameters (respiration, nutrient availability, microbial biomass carbon, arylphosphatase and dehydrogenase activity) to temperature changes was measured in sub-arctic soils collected from across Iceland. Sample sites reflected two soil temperature regimes (cryic and frigid) and two land uses (pasture and arable). The soils were sampled from the field frozen, equilibrated at −20 °C and then incubated for two weeks at −10 °C, −2 °C, +2 °C and +10 °. Respiration and enzymatic activity were temperature dependent. The soil temperature regime affected the soil microbial biomass carbon sensitivity to temperatures. When soils where sampled from the cryic temperature regime a decreasing soil microbial biomass was detected when temperatures rose above the freezing point. Frigid soils, sampled from milder climatic conditions, where unaffected by difference in temperatures. Nitrogen mineralisation did not change with temperature. At −10 °C, dissolved organic carbon accounted for 88% of the fraction of labile carbon which was significantly greater than that recorded at +10 °C when dissolved organic carbon accounted for as low as 42% of the labile carbon fraction.

An evaluation of the response of an Andosol and a Cambisol to acid deposition and weathering rates was studied by using a controlled laboratory leaching experiment. Both soils where derived from mafic parent material, a Histic Andosol from Western Iceland and a Cambisol from North East Scotland. De-ionized water and water acidified with H2SO4 (pH 3) was leached through reconstructed soil columns to simulate 34 years of precipitation. Acidic input increased cation leaching and weathering rates in both soil types and reduced pH levels. The Andosol proved generally to have higher weathering rates, leaching potential, ion exchange and acid-buffering capacity as well as maintaining a relatively steady pH despite intense acidic input. This was due to differences in parent material and mineral composition. The Andosol was developed from basaltic volcanic tephra, which had higher dissolution rates due to its amorphous mineral structures. The Cambisol was developed from gabbro with more stable mineral structures.

In the frame of the Land Use/Land Cover Area Frame Survey sampling of topsoil was carried out on around 22.000 points in 25 EU Member States in 2009 and in additional 2 member States in 2012. Beside other basic soil properties soil phosphorus (P) content of the samples were also measured in a single laboratory in both years. Based on the results of the LUCAS Topsoil survey we performed an assessment of plant available P status of European croplands. Higher P levels can be observed in regions where higher crop yields can be expected and where high fertiliser P inputs are reported. Plant available phosphorus levels were determined using two selected fertilizer recommendation systems; one from Hungary and one from the United Kingdom. The fertiliser recommendation system of the UK does not recommend additional fertiliser use on croplands with highest P supply, which covers regions mostly in Belgium and the Netherlands. According to a Hungarian advisory system there is a need for fertilizer P input in all regions of the EU. We established a P fertiliser need map based on integrating results from the two systems. Based on data from 2009 and 2012, P input demand of croplands in the European Union was estimated to 3,849,873 tons(P2O5)/year. In the meanwhile we found disparities of calculated input need and reported fertiliser statistics both on local (country) scale and on EU level. The first ever uniform topsoil P survey of the EU highlights the contradictions between soil P management of different countries of the Union while also highlights the inconsistencies between reported P fertiliser consumption and advised P doses. Our analysis shows a status of a baseline period of the years 2009 and 2012, while a repeated LUCAS topsoil survey can be a useful tool to monitor future changes of nutrient levels, including P in soils of the EU., JRC.H.5-Land Resources Management

We examine the potential of trait-based parameters of taxa for linking above- and below-ground ecological networks (hereafter ‘green’ and ‘brown’ worlds) to understand and predict community dynamics. This synthesis considers carbon, nitrogen and phosphorus-related traits, the abundance of component species and their size distribution across trophic levels under different forms of management. We have analysed existing and novel databases on plants, microbes and invertebrates that combine physico-chemical and biological information from (agro)ecosystems spanning the globe. We found (1) evidence that traits from above- and below-ground systems may be integrated in the same model and (2) a much greater than expected stoichiometric plasticity of plants and microbes which has implications for the entire food-web mass–abundance scaling. Nitrogen and phosphorus are primary basal resources (hence, drivers) and more retranslocation of P than of N from leaves will lead to higher N:P in the litter and soil organic matter. Thus, under nutrient-rich conditions, higher foliar concentrations of N and P are reflected by lower N:P in the brown litter, suggesting less P retranslocated than N. This apparent stoichiometric dichotomy between green and brown could result in shifts in threshold elemental ratios critical for ecosystem functioning. It has important implications for a general food-web model, given that resource C:N:P ratios are generally assumed to reflect environmental C:N:P ratios. We also provide the first evidence for large-scale allometric changes according to the stoichiometry of agroecosystems. Finally, we discuss insights that can be gained from integrating carbon and nitrogen isotope data into trait-based approaches, and address the origin of changes in Δ 13 C and Δ 15 N fractionation values in relation to consumer–resource body-mass ratios.

Polychlorinated biphenyls (PCBs) pose a threat to the envuronment due to their high adsorption capacity to soil organic matter, stability and low reactivity, low water solubility, toxicity and ability to accumulate. With Icelandic soils, research on contamination issies has been very limited, and no data has been reported either on PCB degradation potential or rate. The goals of this research were to assess the bioavailability of aged PBCs in the soils of the old NATO facility in Keflavík, Iceland, and to find the best feasable biostimulation method to decrease the pollution. The effectiveness of different iostimulation additives at different temperatures and oxygen levels were tested. PCB bioavailability to soil fauna was assessed with earthworms (Eisenia foetia). PCBs were biovailable to earthworms, with less chlorinated congeners showing higher bioaccumulation factors than highly chlorinated congeners. Biostimulation with pine needles at 10 degrees under aerobic conditions resulted in nearly 38% degradation of total PCBs after two months incubation. Detection of aerobic PCB degrading bphA gene supports the indigenous capability of the soils to aerobically degrade PCBs., JRC.H.5-Land Resources Management

Weathering of basaltic ash in volcanic areas produces andosols, rich in allophane and ferrihydrite. Since the rate of mineral formation is very useful in climate and geochemical modelling, this study investigates Si isotope compositions of allophane as a proxy for mineral formation. Allophane formed in contrasting conditions in five Icelandic soil profiles displays silicon isotope signatures lighter than the basalt in less weathered soils (-0.64 ± 0.15‰), and heavier in more weathered organic-rich soils (+0.23 ± 0.10‰). The fate of the dissolved Si in those volcanic soils strongly depends on Al availability. In organic-rich soils, most of Al is humus-complexed, and the results support that Si precipitates as opaline silica by super-saturation, leaving an isotopically heavier dissolved Si pool to form allophane with uncomplexed Al. This study highlights that Si isotopes can be useful to record successive soil processes involved in mineral formation, which is potentially useful in environmental paleo-reconstruction. © 2011 Elsevier Ltd.

Temperature change is acknowledged to have a significance effect on soil biological processes and the corresponding sequestration of carbon and the cycling of key nutrients. Soils at high latitudes are likely to be particularly impacted by increases in temperature. In this study, the response of a range of soil microbial parameters (respiration, nutrient availability, microbial biomass carbon, arylphosphatase and dehydrogenase activity) to temperature changes was measured in sub-arctic soils collected from across Iceland. Sample sites reflected two soil temperature regimes (cryic and frigid) and two land uses (pasture and arable). The soils were sampled from the field frozen, equilibrated at −20°C and then incubated for two weeks at −10°C, −2°C, +2°C and +10°C. Respiration and enzymatic activity were temperature dependent. Microbial biomass carbon and nitrogen mineralisation did not change with temperature. The main factor controlling soil respiration at −10°C was the concentration of dissolved organic carbon. At −10°C, dissolved organic carbon accounted for 88% of the fraction of labile carbon which was significantly greater than that recorded at +10°C when dissolved organic carbon accounted for as low as 42% of the labile carbon fraction. Heterotrophic microbial activity is governed by both substrate availability and the temperature and this has been described by the Q10 factor. Elevated temperatures in the short term may have little effect on the size of the microbial biomass but will have significant impacts on the release of carbon through respiration. These results demonstrate that gradual changes in temperature across large areas at higher latitudes will have considerable impacts in relation to global soil carbon dynamics.

Summary Background In 2010 contamination by dioxins and dioxin-like PCBs was detected in milk and meat in the valley Engidalur situated at the bottom of a fjord (Skutulsfjörður) in North West Iceland. The valley is narrow and surrounded by high mountains resulting in prevailing calm weather. The contamination was traced to a small municipal waste incinerator operating in the valley. Annual agricultural production in Engidalur was modest (≈6 tons of meat and 45 tons of milk). The Icelandic Food and Veterinary Authority conducted a series of measurements examining the contamination and the results are reported in this paper. Results Earlier inspection of the waste incinerator had shown dioxin levels in fly ash of 2.1 ng I-TEQ/m3, which exceeded the EU maximum limit of 0.1 ng I-TEQ/m3. Late in 2010 routine inspection found 4.0 pg WHO-TEQ/g for PCDD/Fs and 7.4 pg total WHO-TEQ/g fat in one milk sample from a farm in Engidalur; levels exceeding the EU maximum limits of 3.0 and 6.0 pg WHO-TEQ/fat for dairy fat, respectively. These results were confirmed in an additional milk sample. Elevated levels exceeding the maximum limits were also observed in one out of two beef samples collected from the farm (4.7 pg WHO-TEQ/g for dioxins and 12.3 pg total WHO-TEQ/g fat). Elevated levels in lamb and ewe meat were also observed but concentration varied greatly, reflecting different migration routes of animals during summer grazing and different sources of hay used during winter. A composite sample of hay from Engidalur had levels of PCDD/Fs of 0.85 pg WHO-TEQ/g and 1.36 pg total WHO-TEQ/g; levels that were marginally, but not significantly, above the EU maximum limit of 0.75 pg WHO-TEQ/g and 1.25 pg WHO-TEQ/g, respectively. Conclusions Operation of a small municipal waste incinerator, not fulfilling modern standards, may lead to elevated levels of dioxins in local livestock.