Search

The exact cause of population dieback in nature is often challenging to identify retrospectively. Plant research in northern regions has in recent decades been largely focussed on the opposite trend, namely increasing populations and higher productivity. However, a recent unexpected decline in remotely-sensed estimates of terrestrial Arctic primary productivity suggests that warmer northern lands do not necessarily result in higher productivity. As large-scale plant dieback may become more frequent at high northern latitudes with increasing frequency of extreme events, understanding the drivers of plant dieback is especially urgent. Here, we report on recent extensive damage to dominant, short, perennial heath and tundra plant populations in boreal and Arctic Norway, and assess the potential drivers of this damage. In the High-Arctic archipelago of Svalbard, we recorded that 8-50% of Cassiope tetragona and Dryas octopetala shoots were dead, and that the ratios of dead shoots increased from 2014 to 2015. In boreal Norway, 38-63% of Calluna vulgaris shoots were dead, while Vaccinium myrtillus had damage to 91% of shoots in forested sites, but was healthy in non-forested sites. Analyses of numerous sources of environmental information clearly point towards a winter climate-related reason for damage to three of these four species. In Svalbard, the winters of 2011/12 and 2014/15 were documented to be unusually severe, i.e. insulation from ambient temperature fluctuation by snow was largely absent, and ground-ice enforced additional stress. In boreal Norway, the 2013/14 winter had a long period with very little snow combined with extremely low precipitation rates, something which resulted in frost drought of uncovered Calluna plants. However, extensive outbreaks of a leaf-defoliating geometrid moth were identified as the driver of Vaccinium mortality. These results suggest that weather and biotic extreme events potentially have strong impacts on the vegetation state of northern lands.

19 páginas, 8 tablas, 4 figuras., Despite the importance of atmospheric methane as a potent greenhouse gas and the significant contribution from ruminant enteric fermentation on methane emissions at a global scale, little effort has been made to consider the influence that different plant-based natural diets have on methane emissions in grazing systems. Heathland is an ericaceous dwarf-shrub-dominated habitat widespread across the northern hemisphere, in Europe, provides valuable ecosystem services in areas with poor soils, such as water flow regulation, land-based carbon skin, energy reservoir and habitat of key game species. We (i) measured methane emissions from red deer (Cervus elaphus) and sheep (Ovis aries) fed mixed diets of natural grass plus ericaceous species (either Calluna vulgaris or Vaccinium myrtillus) using open-circuit respiration chambers; and (ii) modelled the results to estimate methane emissions from red deer and sheep populations inhabiting heathland habitats across Europe under different scenarios of grass-based mixed diets with varying proportions of ericaceous species. Our results indicated that methane emissions per unit of digestible organic matter intake decreased as the proportion of ericaceous species in diet increased, but this relationship was complex because of the significant interaction between the proportion of ericaceous species in the diet and digestible organic matter intake. According to our estimates red deer and sheep populations across European heathlands produce 129.7 kt·y methane (se = 1.79) based on a hypothetical grass-ericaceous species mixed diet containing 30% of ericaceous species; this is 0.5% of total methane emissions from human activity across Europe (24,755 kt·y), and a reduction in methane emissions of 63.8 kt·y against the same deer and sheep populations, if assumed to consume a grass-only diet. We suggest the implementation of carbon credits as a measure to value the relevance of heathland systems to promote biodiversity and its potential contribution to reduce methane emissions in ruminant grazing systems., Rural Affairs Food and the Environment Strategic Research of the Scottish Government

It has been shown in many habitats worldwide, that a shift in vegetation composition between woody shrub and graminoid dominance can influence carbon (C) cycling. Due to land management practices and environmental change, UK upland heath vegetation has historically undergone shifts in dominance from the woody dwarf shrub Calluna vulgaris (Calluna) to species poor graminoid swards. The consequences of this for C sequestration are unknown. We compared annual net ecosystem exchange (NEE) of carbon dioxide (CO₂) between building phase Calluna- and grass-dominated communities within three upland heaths in Scotland, measuring c. monthly over a year. Light and temperature response curves were generated, and the parameters derived were applied to continuous light and temperature data to extrapolate CO₂ fluxes over the full year and generate estimates of annual CO₂ sequestration for each vegetation type. Grass-dominated communities had higher ecosystem respiration rates than Calluna-dominated communities, attributed to graminoids having greater metabolic demands and producing more labile litter which decomposes readily. Both communities had similar gross primary productivity over the year; the net result being higher NEE within the Calluna-dominated than the grass-dominated community (-2.36 ± 0.23 and -1.78 ± 0.18 μmol CO₂m(-2)s(-1) respectively). Modelled CO₂ fluxes over a year showed both communities to be CO₂ sinks. The Calluna-dominated community sequesters -3.45 ± 0.96 t C ha(-1)yr(-1), double that sequestered by the grass-dominated community at 1.61 ± 0.57 t C ha(-1)yr(-1). Potential rate of C sequestration by upland heath is comparable to that of woodland and the increase in total sequestration that could be gained from habitat restoration may equate to c. 60% of the annual UK C sink attributed to forest land management. National C sequestration by heathlands is also more than double that by peatlands. Management of graminoid-dominated upland heath should promote Calluna re-establishment, thus providing a C benefit in addition to benefits to biodiversity, grazing and sporting interests.

Estimates of the greenhouse gas (GHG) fluxes resulting from sheep grazing upon upland peat soils have never been fully quantified. Previous studies have been limited to individual flux pathways or to comparing the presence to the absence of sheep grazing. Therefore, this study combines a model of the physical impact of grazing with models of: biomass production; energy usage in sheep; and peat accumulation. These combined modelling approaches enabled this study to consider the indirect and direct impacts of sheep upon the carbon and greenhouse gas balance of a peatland at different grazing intensities as well as the changes between grazing intensities. The study considered four vegetation scenarios ( Calluna sp., Molinia sp.; reseeded grasses, and Agrostis-Festuca grassland) and a mixed vegetation scenario based upon the vegetation typical of upland peat ecosystems in northern England. Each scenario was considered for altitudes between 350 and 900 m above sea level and for grazing intensities between 0.1 and 2 ewes/ha. The study can show that the total GHG flux at the vegetative carrying capacity tended to decline with increasing altitude for all vegetation scenarios considered except for Molinia sp. The average total GHG flux for all scenarios was 1505 kg CO 2 eq/ha/yr/(ewe/ha), and on average 89% of the fluxes were directly from the sheep and not from the soil, and are therefore not unique to a peat soil environment. The study suggests that emission factors for upland sheep have been greatly underestimated. By comparing the total flux due to grazers to the flux to or from the soil that allows the study to define a GHG carry capacity, i.e. the grazing intensity at which the flux due to grazing is equal to the sink represented by the peat soils, this GHG carrying capacity varies between 0.2 and 1.7 ewes/ha with this capacity declining with increasing altitude for all model scenarios.

Arsenic accumulation and speciation in different plant species growing in two polluted sites were examined, in addition to arsenic transfer from soils to plants. The studied areas were two abandoned mercury mines in Northern Spain, La Soterrana and Los Rueldos. Plants accumulated extremely high amounts of arsenic in their tissues. Accumulation rates depend on both the grade of pollution of the site and on the plant species itself. Total arsenic concentrations varied depending on the part of the plant, with roots accumulating the most arsenic in all the studied plants (up to 1400 mg·kg − 1 ). A suitable extraction method for arsenic speciation in the studied samples was developed and optimized using 0.3 M orthophosphoric acid as the extracting agent in a graphite block digestion system at 90 °C for 1 h. Extraction efficiencies were above 80% and speciation was not altered, since recoveries of the spiked arsenic species (As(III), As(V), DMA (dimethylarsonic acid) and MMA (monomethylarsonic acid)) were between 94 and 102%. Speciation studies were performed on the parts of each plant species by means of HPLC-ICP-MS with the results indicating no significant differences in the speciation between parts of the plants. As(V) was always the predominant species, although a non-negligible amount of As(III) was found for all samples. Little amounts of MMA and DMA occurred in certain samples. Arsenic uptake by plants depends on the plant available arsenic fraction in soils, here considered as the sum of water-soluble and phosphate-extractable fractions. Although soils from La Soterrana were less polluted, arsenic bioavailability was much higher than in Los Rueldos. Soil-to-plant transfer factors, based on total and available arsenic in soils, were evaluated for the studied plants. Dryopteris filix-mas and Calluna vulgaris (L.) Hull , from La Soterrana and Los Rueldos respectively, were the plants with the highest abilities to extract arsenic from their corresponding soils.

Acid atmospheric emissions within Europe and North America have decreased strongly since 1985 and most recent acidification studies have focused on the changes occurring within ecosystems as a result of this decreased deposition. This current study documents a soil acidification trend under ambient N deposition conditions over a 13 year period, suggesting that acidification continues to be a process of concern at this Calluna vulgaris dominated heathland with an acidic sandy soil. The annual manipulation of climatic conditions on this heathland simulated the predicted summer rainfall reduction (drought) and resulted in a long term retardation of the soil acidification trend. The pH of the soil solution significantly decreased over the course of the trial for both treatments, however, in the final two years the decline continued only in the Control treatment. This retardation is primarily associated with the reduction in rainfall leading to lower drainage rates, reduced loss of cations and therefore reduced lowering of the soil acid neutralizing capacity (ANC). However, a change in the underlying mechanisms also indicated that N transformations became less important in the Drought treatment. This change corresponded to an increase in groundcover of an air-pollution tolerant moss species and it is hypothesized that this increasing moss cover filtered an increasing quantity of deposited N, thus reducing the N available for transformation. A soil acidification lag time is expected to increase between the two treatments due to the cumulative disparity in cation retention and rates of proton formation. To the authors knowledge, this is the first study in which such acidification trends have been demonstrated in a field-scale climate manipulation experiment.

Leg and foot bones of adult and juvenile red grouse (Lagopus lagopus scoticus) were collected from hunter-shot birds on two Scottish estates (Glendye and Invermark) and one Yorkshire estate in September, 2003. The lead content of bones was measured by atomic absorption spectrophotometry, and corresponding stable lead isotopes (Pb(204, 206, 207, 208)) by inductively coupled plasma mass spectrometry. At the Glendye (N=111) and Invermark (N=85) estates, relatively few birds (5.4% and 3.5%, respectively) had highly elevated bone lead concentrations (20 microg/g dry weight). In bones of these highly exposed birds, a combination of Pb(206):Pb(207) and Pb(208):Pb(207)ratios was consistent with ingestion of lead gunshot available in Europe. By contrast, Yorkshire grouse experienced a high incidence (65.8%) of bone lead20 microg/g. The Pb(206):Pb(207) and Pb(208):Pb(207)ratios in bones of these highly exposed birds were consistent with a combined exposure to ingested lead gunshot and lead from galena mining in the region. Lead isotope ratios also indicated that lead from UK gasoline combustion and fallout from atmospheric particles was not a likely source of elevated lead in bones of either Scottish or Yorkshire grouse. Suggested management options for the three moors include adopting nontoxic shot for all game shooting on the estates, allowing heather (Calluna vulgaris) vegetation to grow tall in lead shot fall-out zones to reduce physical access to high densities of lead shot already present, and provision of calcareous grit across moors to reduce lead assimilation from all ingested sources of lead.

Peatlands are long term carbon catchments that sink atmospheric carbon dioxide (CO(2)) and source methane (CH(4)). In the uplands of the United Kingdom ombrotrophic blanket peatlands commonly exist within Calluna vulgaris (L.) dominated moorland ecosystems. These landscapes contain a range of topographical features that influence local hydrology, climate and plant community composition. In this study we examined the variation in ecosystem CO(2) respiration and net CH(4) fluxes from typical plant-soil systems in dendritic drainage gullies and adjacent blanket peat during the growing season. Typically, Eriophorum spp., Sphagnum spp. and mixed grasses occupied gullies while C. vulgaris dominated in adjacent blanket peat. Gross CO(2) respiration was highest in the areas of Eriophorum spp. (650+/-140 mg CO(2) m(-2) h(-1)) compared to those with Sphagnum spp. (338+/-49 mg CO(2) m(-2) h(-1)), mixed grasses (342+/-91 mg CO(2) m(-2) h(-1)) and C. vulgaris (174+/-63 mg CO(2) m(-2) h(-1)). Measurements of the net CH(4) flux showed higher fluxes from the Eriophorum spp (2.2+/-0.6 mg CH(4) m(-2) h(-1)) locations compared to the Sphagnum spp. (0.6+/-0.4 mg CH(4) m(-2) h(-1)), mixed grasses (0.1+/-0.1 mg CH(4) m(-2) h(-1)) and a negligible flux detected from C. vulgaris (0.0+/-0.0 mg CH(4) m(-2) h(-1)) locations. A GIS approach was applied to calculate the contribution of gullies to landscape scale greenhouse gas fluxes. Findings from the Moor House National Nature Reserve in the UK showed that although gullies occupied only 9.3% of the total land surface, gullies accounted for 95.8% and 21.6% of the peatland net CH(4) and CO(2) respiratory fluxes, respectively. The implication of these findings is that the relative contribution of characteristic gully systems need to be considered in estimates of landscape scale peatland greenhouse gas fluxes.

The concentration of nitrogen (N), particularly as nitrate (NO3-N), in upland streams, lakes and rivers is frequently used as a diagnostic of the vulnerability of upland ecosystems to increased atmospheric nitrogen deposition and N saturation. The N content of running waters, however, is generally assessed on the basis of sampling at a limited number of points in space and time within the catchment under investigation. The current study was conducted at Trout Beck, an 11.5 km2 blanket peat-dominated catchment in the North Pennine uplands of the UK. Results from sampling at 33 sites within this catchment demonstrated that the concentrations of all dissolved N species were highly variable, even over short distances. Statistical relationships between the concentrations of NO3-N and dissolved organic nitrogen (DON) and percentage catchment cover of Calluna/Eriophorum and Eriophorum vegetation were found. However, it was also noted that in catchments containing limestone outcrops, NO3-N concentration was much higher than in catchments where runoff was sourced directly from the blanket peat surface. It is possible that NH4-N and DON leached from the blanket peat are mineralised and nitrified, providing a source for the NO3-N found in the river channels. Overall, the current study suggests that interpretations of N-saturation based on river water chemistry measurements at a single point must be treated cautiously, and that the influence of catchment-scale physical factors, such as vegetation and geology cover on the concentration of dissolved N species in upland river waters should not be ignored.

This research addresses the occurrence, detection and possible fate of tungsten in the vicinity of an abandoned mine in the English Lake District. Aqua regia extraction and subsequent analysis of spoil and vegetation confirmed the presence of tungsten and other heavy metals. Spoil samples examined were last worked almost 100 years ago and the concentrations of copper, zinc, tungsten and arsenic detected demonstrate the environmental persistence of these metals in an area of relatively high rainfall. The bioaccumulation of tungsten by two species of plants is indicated and partitioning within different tissues of Calluna vulgaris is demonstrated. Mechanisms relating to mobility and speciation of the metals present were explored using sequential and single stage extraction systems. Tungsten appears to be relatively immobile when subjected to sequential extraction but increased bioavailability is indicated when single stage extraction using EDTA is employed.

Migration of 137Cs in the podsol soil and transfer of 137Cs, 134Cs and potassium from the soil to mushrooms and vascular plants in the mixed forest at the Kampinos National Park near Warsaw, Poland, was studied in 1994 at locations lying about 6 km apart. In the soil at both locations, up to about 40% of 137Cs was present in the Of horizon and slightly less in the mixed organic/mineral OhAh horizon. The data indicate a slow vertical migration of radiocesium. Total content of 137Cs in the soils was ∼ 3000 Bq m−2. The enrichment of the Of horizon in 137Cs from the decomposing mushroom fruitbodies was evaluated and it was shown that it can significantly contribute to the horizontal displacement of radiocesium. Transfer factors (TF) for mushrooms and Calluna were calculated using the concentrations of 137Cs in the Of horizons, whereas for grass, Vaccinium myrtillus and Polypodium vulgare TF were calculated using a weighted mean concentration of 137Cs in the nutritive horizons with organic matter as a weight.

Composite samples of L/F/H horizons from Calluna moorland peaty podzol profiles, derived from granites or granitic tills, have been collected from all over Scotland on a 20-km grid basis. The sites were all in the altitude range 200–500 m with a slope from 5–45°. At low to moderate total N and NH 4 + deposition (i.e. ≤ 9 and ≤ 4 kg ha −1 year −1 , respectively), total soil N and soil C:N ratio increased almost linearly with atmospheric N deposition. The N accumulation appears to be related to N deposition and to the effect of acidification upon organic matter accumulation rate, with C accumulating relatively much faster than N, to increase the C:N ratio at sites with low to moderate N deposition. At total N or NH 4 + deposition values > 9 and 4.0 kg ha −1 year −1 , respectively, the C:N ratio declined with increasing N deposition.

Soil samples have been collected from major horizons of Scottish upland Calluna moorland podzols derived from granites. The soil was subjected to routine chemical and mineralogical analysis. The PROFILE model was then used to calculate soil weathering rates, and hence critical loads and exceedance for sulphur depositon. Soil pH was found to be significantly correlated with marine base cation deposition. It is shown that this probably reflects the greater size of marine-derived base cation deposition fluxes compared with weathering-derived base cation fluxes estimated using PROFILE. Only when total wet deposited base cation inputs are used in addition to weathering rates as a basis for assessing critical loads and exceedance values are strong correlations found between soil pH values and exceedance for these sensitive soils. If modelled divalent base cations to aluminium ratios in soil solution are to be used as a basis for quantifying soil damage, all base cation input effects need to be considered, and not just non-marine inputs.

Large intact moorland oligotrophic peat microcosms, complete with associated Calluna vulgaris- or mixed grass-dominated vegetation, have been subjected to realistically simulated precipitation with or without enhanced N. The control ‘rainfall’ solute composition was appropriate for the site of microcosm collection. In addition, N treatments were applied by adding to this basic mixture two or six times the ambient N deposition for the site, as either (NH4)2SO4 or HNO3. For both Calluna-dominated and grass-dominated microcosms, the treatments over 12 months resulted in significant falls in peat C:N ratio, associated with substantial increases in exchangeable NH4+. The accumulation of NH4+-N in peat was greater under Calluna than under grass for all N treatments. Peat KCl-extractable NH4+ concentration increased significantly with increasing (NH4)2SO4 treatments under both types of vegetation. However, peat total N concentration was only increased significantly by both NH4+ treatments under Calluna and by the highest NH4+ treatment under grass. The results show that peat-based ecosystems respond rapidly to enhanced N deposition, with NH4+-N deposition resulting in greater soil N accumulation than the corresponding amount of NO3−-N deposition.