Modelling nitrogen dynamics at Lochnagar, N.E. Scotland.

International audienceControls on nitrate leaching from upland moorland catchments are not yet fully understood and yet, despite agreements on emission reductions, increased surface water nitrate concentrations may affect significantly the acidity status of these waters in the future. At Lochnagar, an upland moorland catchment in N.E. Scotland, 12 years of surface water chemistry observations have identified a steady increase in nitrate concentration despite no measured change in inorganic nitrogen deposition. The MAGIC model has been applied to simulate a "best case" situation assuming nitrate in surface water represents "hydrological" contributions (direct run-off) and a ?worst case' assuming a nitrogen saturation mechanism in the catchment soil. Only the ?saturation' model is capable of matching the 12 years of observation for nitrate but both model structures match the pH and acid neutralising capacity record. Future predictions to 2040, in response to the agreed emission reductions under the Gothenburg Protocol, are markedly different. The worst case predicts continued surface water acidification whilst the best case predicts a steady recovery. Keywords: nitrogen saturation, modelling, Lochnagar, Gothenburg Protoco

Quantum healing of classical singularities in power-law spacetimes

We study a broad class of spacetimes whose metric coefficients reduce to powers of a radius r in the limit of small r. Among these four-parameter "power-law" metrics we identify those parameters for which the spacetimes have classical singularities as r approaches 0. We show that a large set of such classically singular spacetimes is nevertheless nonsingular quantum mechanically, in that the Hamiltonian operator is essentially self-adjoint, so that the evolution of quantum wave packets lacks the ambiguity associated with scattering off singularities. Using these metrics, the broadest class yet studied to compare classical with quantum singularities, we explore the physical reasons why some that are singular classically are "healed" quantum mechanically, while others are not. We show that most (but not all) of the remaining quantum-mechanically singular spacetimes can be excluded if either the weak energy condition or the dominant energy condition is invoked, and we briefly discuss the effect of this work on the strong cosmic censorship hypothesis.Comment: 14 pages, 1 figure; extensive revision

Recovery from acidification of lochs in Galloway, south-west Scotland, UK: 1979-1998

International audienceThe Galloway region of south-west Scotland has historically been subject to long-term deposition of acidic precipitation which has resulted in acidification of soils and surface waters and subsequent damage to aquatic ecology. Since the end of the 1970s, however, acidic deposition has decreased substantially. The general pattern is for a rapid decline in non-marine sulphate in rainwater over the period 1978-1988 followed by stable concentrations to the mid-1990s. Concentrations of nitrate and ammonium in deposition have remained constant between 1980 and 1998. Seven water quality surveys of 48 lochs in the Galloway region have been conducted between 1979 and 1998. During the first 10 years, from 1979, there was a major decline in regional sulphate concentrations in the lochs, which was expected to have produced a decline in base cations and an increase in the acid neutralising capacity. But sea-salt levels (as indicated by chloride concentrations) were approximately 25% higher in 1988 than in 1979 and thus short-term acidification due to sea-salts offset much of the long-term recovery trend expected in the lochs. During the next 10 years, however, the chloride concentrations returned to 1979 levels and the lochs showed large increases in acid neutralising capacity despite little change in sulphate concentrations. From the observed decline in sulphate deposition and concentrations of sulphate in the lochs, it appears that approximately 75% of the possible improvement in acid neutralising capacity has already occurred over the 20-year period (1979-1998). The role of acid deposition as a driving factor for change in water chemistry in the Galloway lochs is confounded by concurrent changes in other driving variables, most notably, factors related to episodic and year-to-year variations in climate. In addition to inputs of sea-salts, climate probably also influences other chemical signals such as peaks in regional nitrate concentrations and the sharp increase in dissolved organic carbon during the 1990s. Keywords: acidification, recovery, Galloway, sulphur, nitroge

Quantum singularity of Levi-Civita spacetimes

Quantum singularities in general relativistic spacetimes are determined by the behavior of quantum test particles. A static spacetime is quantum mechanically singular if the spatial portion of the wave operator is not essentially self-adjoint. Here Weyl's limit point-limit circle criterion is used to determine whether a wave operator is essentially self-adjoint. This test is then applied to scalar wave packets in Levi-Civita spacetimes to help elucidate the physical properties of the spacetimes in terms of their metric parameters

A two-layer application of the MAGIC model to predict the effects of land use scenarios and reductions in deposition on acid sensitive soils in the UK

International audienceA two-layer application of the catchment-based soil and surface water acidification model, MAGIC, was applied to 21 sites in the UK Acid Waters Monitoring Network (AWAMN), and the results were compared with those from a one-layer application of the model. The two-layer model represented typical soil properties more accurately by segregating the organic and mineral horizons into two separate soil compartments. Reductions in sulphur (S) emissions associated with the Second S Protocol and different forestry (land use) scenarios were modelled, and their effects on soil acidification evaluated. Soil acidification was assessed in terms of base saturation and critical loads for the molar ratio of base cations (CA2+ + MG 2+ + K+) to aluminium (Al) in soil solution. The results of the two-layer application indicate that base saturation of the organic compartment was very responsive to changes in land use and deposition compared with the mineral soil. With the two- layer model, the organic soil compartment was particularly sensitive to acid deposition, which resulted in the critical load being predicted to be exceeded at eight sites in 1997 and two sites in 2010. These results indicate that further reductions in S deposition are necessary to raise the base cation (BC):Al ratio above the threshold which is harmful to tree roots. At forested sites BC:Al ratios were generally well below the threshold designated for soil critical loads in Europe and forecasts indicate that forest replanting can adversely affect the acid status of sensitive term objectives of protecting and sustaining soil and water quality. Policy formulation must seek to protect the most sensitive environmental receptor, in this case organic soils. It is clear, therefore, that simply securing protection of surface waters, via the critical loads approach, may not ensure adequate protection of low base status organic soils from the effects of acidification

Particle Creation If a Cosmic String Snaps

We calculate the Bogolubov coefficients for a metric which describes the snapping of a cosmic string. If we insist on a matching condition for all times {\it and} a particle interpretation, we find no particle creation.Comment: 10 pages, MRC.PH.17/9

Dependence of ombrotrophic peat nitrogen on phosphorus and climate

Nitrogen (N) is a key, possibly limiting, nutrient in ombrotrophic peat ecosystems, and enrichment by pollutant N in atmospheric deposition (Ndep, g m-2 a-1) is of concern with regard to peatland damage. We collated data on the N content of surface (depth ≤ 25 cm, mean 15 cm) ombrotrophic peat (Nsp) for 215 sites in the UK and 62 other sites around the world, including boreal, temperate and tropical locations (wider global data), and found Nsp to range from 0.5 % to 4%. We examined the dependences of Nsp on surface peat phosphorus (P) content (Psp), mean annual precipitation (MAP), mean annual temperature (MAT) and Ndep. Linear regression on individual independent variables showed highly significant (p < 0.001) correlations of Nsp with Psp (r2 = 0.23) and MAP (r2 = 0.14), and significant (p < 0.01) but weaker correlations with MAT (r2 = 0.03) and Ndep (r2 = 0.03). A multiple regression model using log-transformed values explained 36% of the variance of the UK data, 84% of the variance of the wider global data, and 47% of the variance of the combined data, all with high significance (p < 0.001). In all three cases, most of the variance was explained by Psp and MAP, but in view of a positive correlation between MAP and MAT for many of the sites, a role for MAT in controlling Nsp cannot be ruled out. There is little evidence for an effect of Ndep on Nsp. The results point to a key role of P in N fixation, and thereby C fixation, in ombrotrophic peats

Instability of cosmological event horizons of non-static global cosmic strings

The stability of the cosmological event horizons found recently by Gregory [Phys. Rev. D54, 4955 (1996)] for a class of non-static global cosmic strings is studied. It is shown that they are not stable to both test particles and physical perturbations. In particular, the back reaction of the perturbations of null dust fluids will turn them into spacetime singularities. The resulted singularities are strong in the sense that the distortion of test particles diverges logarithmically when these singular hypersurfaces are approaching.Comment: Latex, no figure