Mapping portuguese Natura 2000 sites in risk of biodiversity change caused by atmospheric nitrogen pollution

In this paper, we assess and map the risk that atmospheric nitrogen (atN) pollution poses to biodiversity in Natura 2000 sites in mainland Portugal. We first review the ecological impacts of atN pollution on terrestrial ecosystems, focusing on the biodiversity of Natura 2000 sites. These nature protection sites, especially those located within the Mediterranean Basin, are under-characterized regarding the risk posed by atN pollution. We focus on ammonia (NH ) because this N form is mostly associated with agriculture, which co-occurs at or in the immediate vicinity of most areas of conservation interest in Portugal. We produce a risk map integrating NH emissions and the susceptibility of Natura 2000 sites to atN pollution, ranking habitat sensitivity to atN pollution using expert knowledge from a panel of Portuguese ecological and habitat experts. Peats, mires, bogs, and similar acidic and oligotrophic habitats within Natura 2000 sites (most located in the northern mountains) were assessed to have the highest relative risk of biodiversity change due to atN pollution, whereas Natura 2000 sites in the Atlantic and Mediterranean climate zone (coastal, tidal, and scrubland habitats) were deemed the least sensitive. Overall, results allowed us to rank all Natura 2000 sites in mainland Portugal in order of evaluated risk posed by atN pollution. The approach is of great relevance for stakeholders in different countries to help prioritize site protection and to define research priorities. This is especially relevant in countries with a lack of expertise to assess the impacts of nitrogen on biodiversity and can represent an important step up from current knowledge in such countriesinfo:eu-repo/semantics/publishedVersio

Woody stem methane emission in mature wetland alder trees

Methane (CH4) is an important greenhouse gas that is predominantly emitted to the atmosphere from anoxic wetland ecosystems. Understanding the sources and emissions of CH4 is crucially important for climate change predictions; however, there are significant discrepancies between CH4 source estimates derived via so-called bottom-up and top-down methods. Here we report CH4 emission from the stems of mature wetland alder (Alnus glutinosa) trees in the UK, a common tree of northern hemisphere floodplains and wetlands. The alder stems most likely behave as conduits for soil-produced CH4 either in the gaseous or aqueous phase, and may, therefore, help to reconcile methodological differences in the way the wetland CH4 source is estimated. Alder tree stems emitted average peak CH4 fluxes of 101 μg CH4 m−2 h−1 (on a stem area basis) in early October, a rate that is similar to that obtained from mature Japanese ash (Fraxinus mandshurica var. japonica) in Japan and amounting to approximately 20% of the measured CH4 flux from the soil surface. The finding suggests that trees, which occupy 60% of Earth's wetlands and are normally excluded from the measurement programmes that form the basis for bottom-up estimates of the global wetland source, could be important contributors to overall terrestrial ecosystem CH4 flux

Evidence for differential effects of reduced and oxidised nitrogen deposition on vegetation independent of nitrogen load

Nitrogen (N) deposition impacts natural and semi-natural ecosystems globally. The responses of vegetation to N deposition may, however, differ strongly between habitats and may be mediated by the form of N. Although much attention has been focused on the impact of total N deposition, the effects of reduced and oxidised N, independent of the total N deposition, have received less attention. In this paper, we present new analyses of national monitoring data in the UK to provide an extensive evaluation of whether there are differences in the effects of reduced and oxidised N deposition across eight habitat types (acid, calcareous and mesotrophic grasslands, upland and lowland heaths, bogs and mires, base-rich mires, woodlands). We analysed data from 6860 plots in the British Countryside Survey 2007 for effects of total N deposition and N form on species richness, Ellenberg N values and grass:forb ratio. Our results provide clear evidence that that N deposition affects species richness in all habitats except base-rich mires, after factoring out correlated explanatory variables (climate and sulphur deposition). In addition, the form of N in deposition appears important for the biodiversity of grasslands and woodlands but not mires and heaths. Ellenberg N increased more in relation to NHx deposition than NOy deposition in all but one habitat type. Relationships between species richness and N form were habitat-specific: acid and mesotrophic grasslands appear more sensitive to NHx deposition while calcareous grasslands and woodlands appeared more responsive to NOy deposition. These relationships are likely driven by the preferences of the component plant species for oxidised or reduced forms of N, rather than by soil acidification

Suppression of rice methane emission by sulfate deposition in simulated acid rain

Sulfate in acid rain is known to suppress methane (CH4) emissions from natural freshwater wetlands. Here we examine the possibility that CH4 emissions from rice agriculture may be similarly affected by acid rain, a major and increasing pollution problem in Asia. Our findings suggest that acid rain rates of SO2-4 deposition may help to reduce CH4 emissions from rice agriculture. Emissions from rice plants treated with simulated acid rain at levels of SO2-4 consistent with the range of deposition in Asia were reduced by 24% during the grain filling and ripening stage of the rice season which accounts for 50% of the overall CH4 that is normally emitted in a rice season. A single application of SO2-4 at a comparable level reduced CH4 emission by 43%. We hypothesize that the reduction in CH4 emission may be due to a combination of effects. The first mechanism is that the low rates of SO2-4 may be sufficient to boost yields of rice and, in so doing, may cause a reduction in root exudates to the rhizosphere, a key substrate source for methanogenesis. Decreasing a major substrate source for methanogens is also likely to intensify competition with sulfate-reducing microorganisms for whom prior SO2-4 limitation had been lifted by the simulated acid rain S deposition

Regional trends in soil acidification and exchangeable metal concentrations in relation to acid deposition rates

The deposition of high levels of reactive nitrogen (N) and sulphur (S), or the legacy of that deposition, remain among the world's most important environmental problems. Although regional impacts of acid deposition in aquatic ecosystems have been well documented, quantitative evidence of wide-scale impacts on terrestrial ecosystems is not common. In this study we analysed surface and subsoil chemistry of 68 acid grassland sites across the UK along a gradient of acid deposition, and statistically related the concentrations of exchangeable soil metals (1 M KCl extraction) to a range of potential drivers. The deposition of N, S or acid deposition was the primary correlate for 8 of 13 exchangeable metals measured in the topsoil and 5 of 14 exchangeable metals in the subsoil. In particular, exchangeable aluminium and lead both show increased levels above a soil pH threshold of about 4.5, strongly related to the deposition flux of acid compound

Ammonia exposure promotes algal biomass in an ombrotrophic peatland

Nitrogen pollution affects many peatlands with consequences for their biodiversity and ecosystem function. Microorganisms control nutrient cycling and constitute most of the biodiversity of peatlands but their response to nitrogen is poorly characterised and likely to depend on the form of deposition. Using a unique field experiment we show that ammonia exposure at realistic point source levels is associated with a general shift from heterotrophic (bacteria and fungi) to autotrophic (algal) dominance and an increase in total biomass. The biomass of larger testate amoebae increased, suggesting increased food supply for microbial predators. Results show the widespread impacts of N pollution and suggest the potential for microbial community-based bioindicators in these ecosystems

Microclimatological consequences for plant and microbial composition in Sphagnum-dominated peatlands

In three Scandinavian peatlands we studied to what extent plant and microbial community compositions are governed by local-scale microhabitat, with a special interest in the effect of aspect (i.e. exposition of slopes). Despite differences in solar irradiance between the south- and north-facing slopes, maximum temperature was elevated in the south-facing slopes at the most northern site only. Pore-water nutrient concentrations were not affected by aspect, yet dissolved organic carbon concentrations were higher in the south-facing microhabitats. This was likely caused by higher vascular plant biomass. Plant and microbial community composition clearly differed among sites. In all three sites, microhabitat (i.e. prevailing water-table depth) affected the plant and microbial community compositions. Aspect, however, did not affect community composition, even though microclimate significantly differed between the south- and the north-facing aspects at the northernmost site. Our results highlight the complex link between plant community composition, microbial community and environmental conditions, which deserves much more attention than currently in order to fully understand the effects of climate change on peatland ecosystem function.I

Riverine concentrations and export of dissolved silicon, and potential controls on nutrient stoichiometry, across the land–ocean continuum in Great Britain

Silicon (Si) is an essential nutrient element in freshwater and marine ecosystems, and its abundance relative to macro-nutrients (N, P) can impact phytoplankton communities in eutrophic rivers and estuaries. This study is the first national assessment examining (i) the primary sources (geological, biological, landcover) and controls (geomorphological, precipitation) on the transport of terrestrial dissolved silicon across Great Britain to the ocean, and (ii) the current extent and nature of its interactions with macro-nutrients in these catchments in relation to its potential impacts on phytoplankton community structure. It uses results from a year-long survey of 41 rivers along with historical data. Highest concentrations of dissolved Si (4–5.5 mg L-1) were found in rivers of the chalk- and sedimentary sandstone-based catchments of southern Great Britain and the hard sandstone catchments of Scotland. Catchment yield rates for dissolved Si varied between 0.2 and 2.6 t km−2 yr−1, with highest yields found in catchments with higher precipitation and runoff. Analysis of river N:P and dissolved Si:N ratios suggested that the sampled rivers were typically N enriched, and P limited with respect to dissolved Si. Molar dissolved Si:N ratios < 1, an indicator of river eutrophication, were associated with total nitrogen concentrations exceeding 1.8 mg L-1 or greater. The Indicator of Coastal Eutrophication index was used to assess the potential role of dissolved Si in the eutrophication of coastal waters. Negative values indicating limited eutrophication potential to non-siliceous algae were generally found, although some rivers had annual Indicator of Coastal Eutrophication index values exceeding 0, with values as high as 35 kg C km−2 day−1. In many eutrophic rivers, high dissolved Si concentrations derived from catchment lithology, kept the Indicator of Coastal Eutrophication index values below zero. Results have demonstrated that high N and P export have likely shifted most Great Britain rivers and coastal waters beyond the stoichiometric range where diatoms dominate production and into one where non-siliceous algae maybe increasingly present. Thus, future assessments of macro-nutrient management schemes, such as those involving wetlands should include dissolved Si routinely due to its stoichiometric importance

Dissolved inorganic carbon export from rivers of Great Britain: Spatial distribution and potential catchment-scale controls

Dissolved inorganic carbon (DIC) fluxes from the land to ocean have been quantified for many rivers globally. However, CO2 fluxes to the atmosphere from inland waters are quantitatively significant components of the global carbon cycle that are currently poorly constrained. Understanding, the relative contributions of natural and human-impacted processes on the DIC cycle within catchments may provide a basis for developing improved management strategies to mitigate free CO2 concentrations in rivers and subsequent evasion to the atmosphere. Here, a large, internally consistent dataset collected from 41 catchments across Great Britain (GB), accounting for ∼36% of land area (∼83,997 km2) and representative of national land cover, was used to investigate catchment controls on riverine dissolved inorganic carbon (DIC), bicarbonate (HCO3−) and free CO2 concentrations, fluxes to the coastal sea and annual yields per unit area of catchment. Estimated DIC flux to sea for the survey catchments was 647 kt DIC yr−1 which represented 69% of the total dissolved carbon flux from these catchments. Generally, those catchments with large proportions of carbonate and sedimentary sandstone were found to deliver greater DIC and HCO3− to the ocean. The calculated mean free CO2 yield for survey catchments (i.e. potential CO2 emission to the atmosphere) was 0.56 t C km−2 yr−1. Regression models demonstrated that whilst river DIC (R2 = 0.77) and HCO3− (R2 = 0.77) concentrations are largely explained by the geology of the landmass, along with a negative correlation to annual precipitation, free CO2 concentrations were strongly linked to catchment macronutrient status. Overall, DIC dominates dissolved C inputs to coastal waters, meaning that estuarine carbon dynamics are sensitive to underlying geology and therefore are likely to be reasonably constant. In contrast, potential losses of carbon to the atmosphere via dissolved CO2, which likely constitute a significant fraction of net terrestrial ecosystem production and hence the national carbon budget, may be amenable to greater direct management via altering patterns of land use