Thomas Cummins

Atmospheric deposition and soil acidification in five coniferous forest ecosystems: a comparison of the control plots of the EXMAN sites☆

Abstract The five sites of the EXMAN project conducted in Ireland, Denmark, Netherlands, Northern and Southern Germany were compared regarding (1) the marine and anthropogenic components of deposition, (2) the acidification of soil and consequences for Al status, and (3) the nitrate load of seepage. The marine deposition decreases with decreasing rates from the coast inland. It vanishes at a distance of more than 600 km of the sea. The most part of sea salt input in conifer forests is due to dry deposition. Sea salt Mg2+ in throughfall near the coast by far exceeds the demand of trees. The anthropogenic deposition of N and S at the Irish site is about 20%; at the Danish site, about 60% of that at the inland sites. At the Irish site, the anthropogenic deposition is the two- to threefold of the preindustrial deposition. NH4+ prevails at all sites as acid component in throughfall, controlling the pH values that vary between 3.9 and 5.3. In drainage water leaving the root zone, the mean pH values vary only between 4.1 and 4.4. Proton budgets for the forest floor have shown that N turnover dominates as a proton source at the inland sites, whereas at the coastal sites the dominant source results from the production of organic acids. The main proton sink is due to H+ output. Proton budgets for the total root zone indicate that an important proton gain is caused at the most sites by proton excretion of the roots in connection with base cation uptake. In addition, at some sites, the release and output of SO42− appears to be a considerable proton source. At all sites, buffering and output of Al represent the main proton sink. The Al solubility of each layer of the EXMAN sites was compared with the solubility of a synthetic gibbsite. Al saturation exists only at the lower boundary of the main root zone. In the soil layers above, there is an undersaturation that is largest at the humus layer efflux. The relationship between Al dissolved and Al adsorbed, both expressed in cation percentages, is rather weak for the coastal sites in contrast to the inland sites. The importance of the ionic strength effect of sea salt input is discussed with respect to the deep reaching Al saturation and acidification of the soils. Moderate to strong Al stress is indicated at all sites in the mineral soil. The nitrate load of the seepage water depends on the N status of the ecosystems rather than N deposition when the throughfall exceeds 20 kg N ha−1 yr−1. An attempt was made to classify the EXMAN sites with respect to the N status with the aid of the N flux gradient by depth.

Effect of drought experiments using roof installations on acidification/nitrification of soils

Within the framework of the EU-funded EXMAN (EXperimental MANipulation of Forest Ecosystems) project drought experiments were conducted at four different European Norway Spruce (Picea abies (L.) Karst.) plantations in the year 1992–1995. The aim of the project was to investigate if there is an additional risk of soil acidification due to nitrification/acidification pulses after extended periods of summer droughts. The sites included (Ballyhooly/BH, southwest of Ireland. Klosterhede/KH, west coast of Denmark, Hoglwald/HW, northwest of Munich, and Solling/SL, central Germany) cover considerable gradients of climatic and air pollution regimes. Artificial droughts were produced by using different types of roof constructions installed below the forest canopy (non-permanent constructions in BH and HW, permanent installations in KH and SL). Each drought was started in spring time and dry conditions were maintained until the soil water tension was below a potential of −700 hPa at 70 cm depth in the mineral soil. Results given are focused on changes in the soil solution concentrations during the rewetting of severely dried out soils. No marked nitrification pulses were observed after any of the droughts carried out at any site. Only single lysimeters/sample locations showed the hypothesized reaction with increasing aluminum concentrations and decreasing pH values, but spatial heterogeneity was high during rewetting. In the first soil solution samples after the drought, occasionally distinct peaks of NH4+, DOC and K+, and partly also Norg and HPO42− appeared. For the BH site the respective potassium concentrations increased 10 to 20 times compared to the level of the control plot. Presented data indicate a certain potential for nitrification pulses at the BH and KH site, but probably due to a fast root uptake, below the rooting zone no nitrate was determined. At the HW site, the drought induced reactions in the soil solution composition were only visible in humus water samples. At SL, nitrate concentrations were generally reduced at the drought plot. During rewetting in 1992 samples from a single lysimeter indicated a clear nitrification pulse. Applied flux calculations for SL showed a significant increase of the nitrate budget but a distinct decrease of the potassium budget. It is concluded that drought phases can influence the element cycling, but there seems to be no risk that forest soils will be subjected to pronounced acidification after summer droughts.

Linking variability in soil solution dissolved organic carbon to climate, soil type, and vegetation type

Lateral transport of carbon plays an important role in linking the carbon cycles of terrestrial and aquatic ecosystems. There is, however, a lack of information on the factors controlling one of the main C sources of this lateral flux, i.e., the concentration of dissolved organic carbon (DOC) in soil solution across large spatial scales and under different soil, vegetation, and climate conditions. We compiled a database on DOC in soil solution down to 80 cm and analyzed it with the aim, first, to quantify the differences in DOC concentrations among terrestrial ecosystems, climate zones, soil, and vegetation types at global scale and second, to identify potential determinants of the site-to-site variability of DOC concentration in soil solution across European broadleaved and coniferous forests. We found that DOC concentrations were 75% lower in mineral than in organic soil, and temperate sites showed higher DOC concentrations than boreal and tropical sites. The majority of the variation (R2 = 0.67–0.99) in DOC concentrations in mineral European forest soils correlates with NH4+, C/N, Al, and Fe as the most important predictors. Overall, our results show that the magnitude (23% lower in broadleaved than in coniferous forests) and the controlling factors of DOC in soil solution differ between forest types, with site productivity being more important in broadleaved forests and water balance in coniferous stands.

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 μm laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.

Biological response of five forest ecosystems in the EXMAN project to input changes of water, nutrients and atmospheric loads

Abstract In five coniferous forest ecosystems in Europe, water and nutrient supply, as well as atmospheric loads, were manipulated for 3 or 4 years. Water supply was optimised and nutrients were added according to tree demand in optimal proportions relative to the ambient N supply. Tree growth was strongly enhanced by optimal water supply but not further enhanced by nutrient additions. The nutritional balance in trees was improved for P and K. The increased water and nutrient supply retarded needle shedding in autumn and diminished root production. To date, the manipulated decrease in N input to the soil has decreased the N content in needles in one stand. Water additions tended to lower N contents at two sites. Large applications of N increased N content in needles even though the N nutrition was already optimal. Liming with dolomite stimulated tree growth only in the nutrient-poor stand, but has generally increased Ca content in needles. The number of species and cover of understorey vegetation has increased considerably by liming and, in some cases, by water addition. Ecosystem manipulation experiments have been shown to be a useful tool for the quantification of the growth effects of traditionally limiting factors. Additionally they give indications of the effects on forest ecosystem processes of future changes in atmospheric loads.

A comparison of sites in the EXMAN project, with respect to atmospheric deposition and the chemical composition of the soil solution and foliage☆

Abstract Forest stands, throughfall and the composition of the soil solution in six coniferous forest plantations in Europe were compared as part of the EXMAN project, which was established to quantify biogeochemical cycles and the effects of atmospheric deposition on coniferous forest ecosystems. Even though the EXMAN stands and sites are broadly similar, they represent a wide range of climatic conditions and levels of pollutant deposition. The EXMAN project incorporates treatment of forest plots and in this paper the untreated control plots are compared. The results show marked differences in ionic composition of water between sites, most clearly expressed in throughfall fluxes. At the German and Dutch sites, ionic inputs demonstrate a strong human influence. Throughfall at the Danish and Irish sites is dominated by ions of marine origin. Hydrogen ions are not the most important cations in precipitation at any site, and at only one site (Solling, Germany) was the hydrogen ion flux in throughfall greater than in precipitation. The influence of atmospheric deposition on the composition of the soil water is very evident for most major ions. Exceptions to this are ammonium and nitrate, the complexity of whose behaviour demonstrates the need for greater understanding of nitrogen transformation and uptake in coniferous forest ecosystems.

Application of the SAFE model to a Norway spruce stand at Ballyhooly, Ireland

Acid rain results in qualitative and quantitative changes in terrestrial ecosystem boundary conditions. Typically these changes exceed the range of variation observed or inferred from past states. Methods of predicting future states are required, such as process-based models or experimental treatments that mimic future scenarios. The dynamic biogeochemical model SAFE was applied to Ballyhooly intensive forest monitoring plot located in southern Ireland. SAFE is a dynamic, process-oriented soil chemistry model developed with the objective of studying the effects of acid deposition on soils and groundwaters. It calculates the values of different chemical state variables as a function of time. The model requires input data on soil mineralogy, soil texture, CEC and base saturation, together with time-series data for atmospheric deposition, nutrient uptake and cycling, and hydrology. Model results indicate that the basic principles in the model are capable of describing the present soil-solution chemistry at Ballyhooly without extensive calibration. However, the gibbsite equilibrium model does not describe the observed concentrations of aluminium at Ballyhooly, and the assumption that sulphur adsorption is insignificant appears also to be incorrect. Inclusion of processes such as sulphur adsorption, aluminium complexation with organic matter, or a kinetic-based aluminium model may improve model results.

The effect of viewing angle on the spectral behavior of a Gd plasma source near 6.7 nm

We have demonstrated the effect of viewing angle on the extreme ultraviolet (EUV) emission spectra of gadolinium (Gd) near 6.7 nm. The spectra are shown to have a strong dependence on viewing angle when produced with a laser pulse duration of 10 ns, which may be attributed to absorption by low ion stages of Gd and an angular variation in the ion distribution. Absorption effects are less pronounced at a 150-ps pulse duration due to reduced opacity resulting from plasma expansion. Thus for evaluating source intensity, it is necessary to allow for variation with both viewing angle and target orientation.

Interception of seasalt by coniferous and broadleaved woodland in a maritime environment in Western Ireland

Atmospheric deposition in maritime regions is dominated by seasalt. High inputs of seasalt can induce short-term acidification in surface waters by displacement of hydrogen and aluminium from the soil exchange complex. Measurement of sodium fluxes in two forest stands, one coniferous, one broadleaved, in a maritime region of western Ireland resulted in almost equal deposition at the two stands. This is remarkable given that the broadleaved forest has a low interception of water. Weekly throughfall data emphasise the enormous fluctuation in seasalt deposition. In both stands deposition is highest in winter.

Colliding laser-produced plasmas as targets for laser-generated extreme ultraviolet sources

Colliding plasmas produced by neodymium-doped yttrium aluminium garnet (Nd:YAG) laser illumination of tin wedge targets form stagnation layers, the physical parameters of which can be controlled to optimise coupling with a carbon dioxide (CO2) heating laser pulse and subsequent extreme ultraviolet (EUV) production. The conversion efficiency (CE) of total laser energy into EUV emission at 13.5 nm ± 1% was 3.6%. Neglecting both the energy required to form the stagnation layer and the EUV light produced before the CO2 laser pulse is incident results in a CE of 5.1% of the CO2 laser energy into EUV light.