Deposition of fixed atmospheric nitrogen and foliar nitrogen content of bryophytes and Calluna vulgaris (L.) Hull

Atmospheric deposition of fixed nitrogen as nitrate and ammonium in rain and by dry deposition of nitrogen dioxide, nitric acid and ammonia has increased throughout Europe during the last two decades, from 2-6 kg N ha(-1) year(-1) to 15-60 kg N ha(-1) year(-1). The nitrogen contents of bryophytes and the ericaceous shrub Calluna vulgaris have been measured at a range of sites, with the objective of showing the degree to which nitrogen deposition is reflected in foliar plant nitrogen. Tissue nitrogen concentrations of herbarium bryophyte samples and current samples of the same species collected from the same sites were compared. No significant change in tissue nitrogen was recorded at a remote site in north-west Scotland where nitrogen inputs are small (< 6 kg N ha(-1) year(-1)). Significant increases in tissue N occurred at four sites ranging from 38% in central Scotland to 63% in Cumbria where nitrogen inputs range from 15 to 30 kg N ha(-1) year(-1). The relationships found between the estimated input of atmospheric nitrogen and the tissue nitrogen content of the selected bryophytes and Calluna at the sites investigated were found to be generally linear and fitted the form N(tissue) = 0.62 + 0.022 N(dep) for bryophytes and N(tissue) = 0.83 + 0.045 N(dep) for Calluna. There was thus an increase in total tissue nitrogen of 0.02 mg g(-1) dry weight for bryophytes and 0.045 mg g(-1) dry weight for Calluna for an increase in atmospheric nitrogen deposition of 1 kg ha(-1) year(-1). The lowest concentrations were found in north-west Scotland and the highest in Cumbria and the Breckland heaths of East Anglia, both areas of high atmospheric nitrogen deposition (30-40 kg N ha(-1) year(-1)). The implications of increased tissue nitrogen content in terms of vegetation change are discussed. Changes in atmospheric nitrogen deposition with time were also examined using measured values and values inferred from tissue nitrogen content of mosses. The rate of increase in nitrogen deposition is not linear over the 90-year period, and the increases were negligible over the period 1880-1915. However, during the period 1950 to 1990 the data suggest an increase in nitrogen deposition of 2 kg N ha(-1) every 10 years.     

Atmospheric nitrogen deposition on the east coast of Spain: relevance of dry deposition in semi-arid Mediterranean regions

Bulk deposition composition and pine branch washing were measured from April 1999 to March 2000 on the east coast of Spain. The main objective was to characterise N deposition patterns with special emphasis on dry deposition. Bulk deposition in the region is dominated by neutralisation processes by Ca2+ and HCO3-, ClNa of marine origin and a high correlation between NO3- and SO4(2-). SO4(2-) concentrations show a decrease with respect to previous studies in the region in agreement with generalized sulfur emission decreases while the remaining ions, including NO3-, are higher due to their general increase as well as to the inclusion of dry deposition in bulk collectors in the present study. An enrichment in NO3- has been observed in dry deposition composition branch washing) with respect to bulk deposition, while an impoverishment has been observed in the case of NH4+. Annual bulk deposition varies between 7.22-3.1 and 3.5-1.8 Kg ha(-1) year(-1) for S- SO4(2-) and N- NO3-, respectively. N total deposition goes from 9.78 to 6.8 Kg ha(-1) year(-1) at most stations, with the lowest deposition at the control station and Alcoi. The relative dry deposition with respect to the total was over 40% at most stations, going up to 75% at the southern station. N-deposition is expected to be higher considering that N-NH4+ deposition has been underestimated in this study.     

The contribution of ammonia emissions from agriculture to the deposition of acidifying and eutrophying compounds onto forests

In the vicinity of a large ammonia emission area, dry and wet deposition of acidifying and eutrophying compounds onto Douglas Fir forests was studied by sampling throughfall, stemflow and bulk precipitation. Deposition amounts of NH(4)(+) and SO(4)(2-) were recognised to be among the highest of Central Europe, resulting in extremely high inputs of (potential) acid to the forest soils (13.1 kEq ha(-1) year(-1)). The contribution of NH(3) emissions from agriculture to the total acid deposition to the forests was 52%. The total nitrogen deposition amounted to 115.0 kg ha(-1) year(-1), 83% originating from NH(3) emissions and 17% from NO(x) emissions. Calculated mean dry deposition velocities of NH(3) and SO(2) were much larger than reported in the literature. A synergistic effect between NH(3) and SO(2) in the process of dry deposition is suggested and evidence for this effect is discussed. When deposition models do not take this interaction into account, they will underestimate NH(3) and SO(2) deposition amounts in areas with intensive animal husbandry.     

The dynamics of dissolved nitrogen in a blanket peat dominated catchment

Precipitation, soil solution and drainage water were collected from a blanket peat catchment at Moor House National Nature Reserve in the Northern Pennine Uplands, UK, an area of moderately high N deposition. Two tributaries of the main stream were also sampled. Between 1993 and 1995 samples were analysed for NH4+ and NO3- and for part of the period for organic N. Inputs of N in precipitation exceeded outputs in stream water. Organic N represented a small proportion of N inputs while inputs of inorganic N averaged 10.2 kg ha(-1) a(-1). Soil solution from 10 cm depth in the peat was dominated by organic N whereas at 50 cm NH4+ slightly exceeded organic N. NO3- was rarely detected at either depth except during a period of exceptionally warm and dry weather in 1995. Output fluxes in stream water of organic N (5.7 to 6.5 kg ha(-1) a(-1)) were much greater than those of inorganic N (0.6 to 2.2 kg ha(-1) a(-1)). Inorganic N in streams was predominantly NO3- except in the smallest stream which had the largest concentrations of NH4+. This suggests that N transformations, particularly nitrification, may be taking place in the mineral soils adjacent to the streams or within the stream channel of the larger catchment.     

Dissolved inorganic nitrogen budget for a forested catchment at Beddgelert, North Wales

An input-output budget for dissolved inorganic-N in a small forested catchment in North Wales is presented. From 1982 to 1990, bulk precipitation inputs averaged 10.3 kg ha(-1) year(-1), whereas throughfall inputs in 1983-1984 were 20.3 kg ha(-1) year(-1). Streamwater outputs were consistently larger than bulk precipitation inputs, averaging 14.6 kg ha(-1) year(-1). Inorganic-N in the forest stream was predominantly nitrate and concentrations were substantially higher than in a nearby moorland stream. Both streams showed seasonal trends in nitrate concentration, with highest concentrations occurring in summer in the forest stream but in winter in the moorland stream. Nitrate concentration in the forest stream increased with increasing soil temperature up to approximately 7 degrees C and decreased at higher temperatures. Nitrification is thought to be responsible for nitrate production at temperatures both below and above 7 degrees C, but root uptake becomes significant only at the higher temperatures. In the forest, dry deposition and cloudwater inputs of inorganic-N are responsible for increased nitrogen fluxes in throughfall compared with wet deposition. Mineralization and nitrification in excess of plant needs causes the organic soil horizons to act as a net source of dissolved inorganic-N. Nitrogen transformations in the soil lead to soil acidification at a rate of 1.0 keq ha(-1) year(-1).     

Nitrate in waters from sewage-sludge amended lysimeters

Nitrate nitrogen was measured in runoff and tile-drainage during two years of operation of instrumented, large-scale lysimeters planted to corn (Zea mays L.) and amended with sewage sludge which was applied at rates supplying total N amounting to 2292 kg ha(-) in 1972 and 3286 kg ha(-1) in 1973. Other lysimeters were amended with inorganic fertiliser at the rate of 336 kg N ha(-1) year(-1). Annual losses in runoff and tile-drainage from sludge treatments were 0.9 and 5.1 and 371 and 663 kg NO(3)(-)-N ha(-1). Losses from lysimeters treated with inorganic fertiliser were 1.1 and 3.3 kg NO(3)(-)-N ha(-1) year(-1) in runoff and 31 and 79 kg NO(3)(-)-N ha(-1) year(-1) in tile-drainage. Given the nitrogen inputs accounted for in the study design, unaccounted for losses of 1800 to 2400 kg ha(-1) year(-1) were calculated for sludge and 277 kg ha(-1) year(-1) for inorganic fertiliser treatments. For one year there was a 300 kg ha(-1) increase in N in the lysimeters receiving inorganic fertiliser. Median NO(3)(-)-N concentrations ranged from 8.9 to 14.0 mg litre(-1) in runoff from sludge-treated lysimeters and 3.6 to 5.9 mg litre(-1) in runoff from lysimeters receiving inorganic fertiliser. In tile-drainage the median NO(3)(-)-N concentrations were 148 to 223 mg litre(-1) and 24 to 44 mg litre(-1) for sludge and inorganic fertiliser treatments, respectively. Highest runoff levels occurred in early summer storms, whereas highest tile-drainage concentrations occurred in late winter and early spring.     

Investigation into atmospheric deposition through precipitation studies at New Delhi (India)

Rain water samples were collected during the monsoon of 1994, using automatic wet-only and manual bulk collectors at a height of 30 m above the ground at the National Physical Laboratory, New Delhi. The average pH of the rain water was 5.7 and its chemical composition was dominated by NH₄ and SO₄. The free acidity of the rain water was found to be due to S04 rather than N03 and it was mainly neutralized by NH₄ and Ca. Calculation of sea salt fraction and enrichment factor revealed that this site is free for marine influence. On an average the bulk samples had 13% higher concentration than that of wet-only samples which may be due to the deposition of soil-derived particles during the 24 h period of exposure. The higher neutralization factors of Ca and Mg in bulk samples and highest dry deposition rates for Ca in comparison to other components, indicated the positive interference of dust particles in neutralization.     

Nitrogen deposition in California forests: a review

Atmospheric concentrations and deposition of the major nitrogenous (N) compounds and their biological effects in California forests are reviewed. Climatic characteristics of California are summarized in light of their effects on pollutant accumulation and transport. Over large areas of the state dry deposition is of greater magnitude than wet deposition due to the arid climate. However, fog deposition can also be significant in areas where seasonal fogs and N pollution sources coincide. The dominance of dry deposition is magnified in airsheds with frequent temperature inversions such as occur in the Los Angeles Air Basin. Most of the deposition in such areas occurs in summer as a result of surface deposition of nitric acid vapor (HNO3) as well as particulate nitrate (NO3-) and ammonium (NH4+). Internal uptake of gaseous N pollutants such as nitrogen dioxide (NO2), nitric oxide (NO), HNO3, peroxyacetyl nitrate (PAN), ammonia (NH3), and others provides additional N to forests. However, summer drought and subsequent lower stomatal conductance of plants tend to limit plant utilization of gaseous N. Nitrogen deposition is much greater than S deposition in California. In locations close to photochemical smog source areas, concentrations of oxidized forms of N (NO2, HNO3, PAN) dominate, while in areas near agricultural activities the importance of reduced N forms (NH3, NH4+) significantly increases. Little data from California forests are available for most of the gaseous N pollutants. Total inorganic N deposition in the most highly-exposed forests in the Los Angeles Air Basin may be as high as 25-45 kg ha(-1) year(-1). Nitrogen deposition in these highly-exposed areas has led to N saturation of chaparral and mixed conifer stands. In N saturated forests high concentrations of NO3- are found in streamwater, soil solution, and in foliage. Nitric oxide emissions from soil and foliar N:P ratios are also high in N saturated sites. Further research is needed to determine the ecological effects of chronic N deposition, and to develop appropriate management options for protecting water quality and managing plant nutrient resources in ecosystems which no longer retain excess N.     

Atmospheric deposition inputs and effects on lichen chemistry and indicator species in the Columbia River Gorge, USA

Topographic and meteorological conditions make the Columbia River Gorge (CRG) an 'exhaust pipe' for air pollutants generated by the Portland-Vancouver metropolis and Columbia Basin. We sampled fog, bulk precipitation, throughfall, airborne particulates, lichen thalli, and nitrophytic lichen distribution. Throughfall N and S deposition were high, 11.5-25.4 and 3.4-6.7 kg ha(-1) over 4.5 months at all 9 and 4/9 sites, respectively. Deposition and lichen thallus N were highest at eastern- and western-most sites, implicating both agricultural and urban sources. Fog and precipitation pH were frequently as low as 3.7-5.0. Peak NO(x), NH(3), and SO(2) concentrations in the eastern CRG were low, suggesting enhanced N and S inputs were largely from particulate deposition. Lichens indicating nitrogen-enriched environments were abundant and lichen N and S concentrations were 2x higher in the CRG than surrounding national forests. The atmospheric deposition levels detected likely threaten Gorge ecosystems and cultural resources.     

Fluxes of oxidised and reduced nitrogen above a mixed coniferous forest exposed to various nitrogen emission sources

Concentrations of nitrogen gases (NH(3), NO(2), NO, HONO and HNO(3)) and particles (pNH(4) and pNO(3)) were measured over a mixed coniferous forest impacted by high nitrogen loads. Nitrogen dioxide (NO(2)) represented the main nitrogen form, followed by nitric oxide (NO) and ammonia (NH(3)). A combination of gradient method (NH(3) and NO(x)) and resistance modelling techniques (HNO(3), HONO, pNH(4) and pNO(3)) was used to calculate dry deposition of nitrogen compounds. Net flux of NH(3) amounted to -64 ng N m(-2) s(-1) over the measuring period. Net fluxes of NO(x) were upward (8.5 ng N m(-2) s(-1)) with highest emission in the morning. Fluxes of other gases or aerosols substantially contributed to dry deposition. Total nitrogen deposition was estimated at -48 kg N ha(-1) yr(-1) and consisted for almost 80% of NH(x). Comparison of throughfall nitrogen with total deposition suggested substantial uptake of reduced N (+/-15 kg N ha(-1) yr(-1)) within the canopy.     

Atmospheric nitrogen deposition in south-east Scotland: Quantification of the organic nitrogen fraction in wet,dry and bulk deposition

Water soluble organic nitrogen (WSON) compounds are ubiquitous in precipitation and in the planetary boundary layer, and therefore are a potential source of bioavailable reactive nitrogen. This paper examines weekly rain data over a period of 22 months from June 2005 to March 2007 collected in 2 types of rain collector (bulk deposition and “dry + wet” deposition) located in a semi-rural area 15 km southwest of Edinburgh, UK (N55°51′44″, W3°12′19″). Bulk deposition collectors are denoted in this paper as “standard rain gauges”, and they are the design used in the UK national network for monitoring precipitation composition. “Dry + wet” deposition collectors are flushing rain gauges and they are equipped with a rain detector (conductivity array), a spray nozzle, a 2-way valve and two independent bottles to collect funnel washings (dry deposition) and true wet deposition. On average, for the 27 weekly samples with 3 valid replicates for the 2 types of collectors, dissolved organic nitrogen (DON) represented 23% of the total dissolved nitrogen (TDN) in bulk deposition. Dry deposition of particles and gas on the funnel surface, rather than rain, contributed over half of all N-containing species (inorganic and organic). Some discrepancies were found between bulk rain gauges and flushing rain gauges, for deposition of both TDN and DON, suggesting biological conversion and loss of inorganic N in the flushing samplers.     

Ecosystem effects of atmospheric deposition of nitrogen in The Netherlands

Atmospheric deposition of inorganic N, mainly ammonium volatilized from manure produced in intensive stockbreeding, on sensitive terrestrial and aquatic ecosystems in The Netherlands is in the order of 40 to 80 kg ha(-1) year(-1). Proven effects of this deposition are (i) eutrophication with N, leading to floristic changes (ii) acidification of base-poor sandy soils and of moorland pools, leading to higher concentrations of dissolved, potentially toxic metals such as Al3+, and (iii) increased levels of nitrate in groundwater below woodlands. In acid forest soils, but not in soils under heathland, nitrification and leaching of nitrate is common. However, in very poor sandy forest soils and at very high ammonium inputs, nitrification may be too slow to prevent the development of high concentrations of ammonium. Both excessive acidification and excessive levels of ammonium probably play an important role in the general forest decline, which is most severe in the southern and central parts of the country, where ammonium inputs are highest.     

Sulphur and seasalt deposition as reflected by throughfall and runoff chemistry in forested catchments

At forested catchments at Lake G?rdsj?n on the Swedish west coast the deposition and runoff chemistry has been followed during the period 1979-1990 by throughfall and runoff measurements as well as by measurements of atmospheric concentrations. The 10-year means in throughfall and runoff are very similar for sulphur and the main seasalt ions sodium and chloride; for sulphur 26.1 and 27.6 kg ha(-1) yr(-1), for sodium 49 and 52 kg ha(-1) yr(-1) and for chloride 96 kg ha(-1) yr(-1) and 93 kg ha(-1) yr(-1), respectively. The actual flows are 100-200% higher than the wet deposition as collected in open bulk precipitation collectors indicating a very large input by dry deposition. One important question is to what extent the throughfall and runoff values can be used as measures of total deposition. We present results from studies at different experimental catchments illustrating the possibilities of using throughfall and runoff data as measures of atmospheric deposition of sulphur and seasalt.     

Analyses of NOx and wet depositions at Mühleggerköpfl,North Tyrolean Limestone Alps

The intensive investigation site ‘Mühleggerköpfl’ in the North Tyrolean Limestone Alps can be classified as a clean-air area site. The mean concentrations of NO_x are far below the effect-related limit value of the WHO (30 μg NO_x m⁻³). The gravitational depositions in the open field (bulk deposition) ranged from 10.8 to 14.7 kg N ha⁻¹ a⁻¹ (throughfall: 11.3 to 12.3 kg N ha⁻¹ a⁻¹) in the measuring years 1998 to 2000. Compared to these data, depositions in other forested areas of the Austrian Alps amounted to up to 30 kg N ha⁻¹ a⁻¹. The gravitational depositions (bulk deposition) alone - without considering dry and occult deposition - slightly exceeded the lower limit of Critical Loads for coniferous and deciduous forests (> 10 kg N ha⁻¹ a⁻¹), but were below the Critical Loads for calcareous forests (15–20 kg N ha⁻¹ a⁻¹).

     

Deposition of nitrogen-containing compounds to an extensively managed grassland in central Switzerland

During four intensive observation periods in 1992 and 1993, dry deposition of nitrogen dioxide (NO(2)) and ammonia (NH(3)), and wet deposition of nitrogen (N) were determined. The measurements were carried out in a small, extensively managed litter meadow surrounded by intensively managed agricultural land. Dry deposition of NH(3) was estimated by the gradient method, whereas eddy correlation was used for NO(2). Rates of dry deposition of total nitrate (= nitric acid (HNO(3)) + nitrate (NO(3)(-))), total nitrite (= nitrous acid (HONO) + nitrite (NO(2)(-))) and aerosol-bound ammonium (NH(4)(+)) were estimated using deposition velocities from the literature and measured concentrations. Both wet N deposition and the vertical NH(3) gradient were measured on a weekly basis during one year. Dry deposition was between 15 and 25 kg N ha(-1) y(-1), and net wet deposition was about 9.0 kg N ha(-1) y(-1). Daily average NO(2) deposition velocity varied from 0.11 to 0.24 cm s(-1). Deposition velocity of NH(3), was between 0.13 and 1.4 cm s(-1), and a compensation point between 3 and 6 ppbV NH(3) (ppb = 10(-9)) was found. Between 60 and 70% of dry deposition originated from NH(3) emitted by farms in the neighbourhood. It is concluded that total N deposition is exceeding the critical load for litter meadows, is highly correlated to local NH(3) emissions, and that NH(3) is of utmost importance with respect to possible strategies to reduce N deposition in rural regions.     

Atmospheric deposition and canopy exchange processes in heathland ecosystems

The aims of the present study were to determine canopy exchange processes and to quantify total atmospheric deposition of sulphur and nitrogen in heathland. The study was carried out in dry inland heath vegetation, dominated by Calluna vulgaris, in two nature reserves in the eastern part of the Netherlands. Atmospheric deposition was determined with throughfall-stemflow measurements, adapted for low vegetation. Throughflow measurements (sum of throughfall and stemflow) in artificial Calluna canopies showed co-deposition of SOx and NHy upon heathland vegetation. In the real Calluna canopy, a significant part of the deposited ammonia/ammonium was directly assimilated by the Calluna shoots, especially in wet periods. The concentrations of potassium, calcium and magnesium in throughflow, after passage through the Calluna canopy, increased significantly compared with bulk precipitation. The amount of cations lost from the canopy were in good agreement with the observed ammonium uptake by the Calluna. A field experiment demonstrated that losses of the above-mentioned cations can be doubled by application of ammonium sulphate. It was shown that interception deposition is an important component of the atmospheric deposition of sulphur and nitrogen upon Calluna heathland; bulk precipitation amounted to only c. 35-40% of total atmospheric input. Total atmospheric deposition of sulphur and nitrogen in the investigated heathlands was 1.5-2.1 (27-33 kg S ha(-1) yr(-1)) and 2.1-3.1 kmolc ha(-1) yr(-1) (30-45 kg N ha(-1) yr(-1)), respectively. It is concluded that the present atmospheric nitrogen deposition is a continuous threat for the existence of heathlands in Western Europe.     

Nitrogen deposition and the biodiversity of boreal forests: implications for the nitrogen critical load

The critical load concept is used to establish the deposition levels which ecosystems can tolerate without significant harmful effects. Here we summarize work within the Swedish research program Abatement Strategies for Transboundary Air Pollution (ASTA) assessing the critical load of N for boreal forests. Results from both field experiments in an area with low background N deposition in northern Sweden, and from a large-scale monitoring study, show that important vegetational changes start to take place when adding low N doses and that recovery of the vegetation after ceasing N input is a very slow process. The data presented indicate that changes in key ecosystem components occur even at a lower rate of N input than the present recommended empirical critical load for boreal forest understorey vegetation of 10-15 kg N ha(-1) yr(-1). Based on the data presented, we suggest that the critical load should be lowered to 6 kg N ha(-1) yr(-1).     

Empirical and simulated critical loads for nitrogen deposition in California mixed conifer forests

Empirical critical loads (CL) for N deposition were determined from changes in epiphytic lichen communities, elevated NO(3)(-) leaching in streamwater, and reduced fine root biomass in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at sites with varying N deposition. The CL for lichen community impacts of 3.1kg ha(-1) year(-1) is expected to protect all components of the forest ecosystem from the adverse effects of N deposition. Much of the western Sierra Nevada is above the lichen-based CL, showing significant changes in lichen indicator groups. The empirical N deposition threshold and that simulated by the DayCent model for enhanced NO(3)(-)leaching were 17kg N ha(-1) year(-1). DayCent estimated that elevated NO(3)(-) leaching in the San Bernardino Mountains began in the late 1950s. Critical values for litter C:N (34.1), ponderosa pine foliar N (1.1%), and N concentrations (1.0%) in the lichen Letharia vulpina ((L.) Hue) are indicative of CL exceedance.     

Dry deposition of particles and canopy exchange: Comparison of wet,bulk and throughfall deposition at five forest sites in Italy

The contribution of dry deposition to the total atmospheric input of acidifying compounds and base cations is of overwhelming importance. Throughfall measurements provide an estimate of the total deposition to forest soils, including dry deposition, but some uncertainties, related to the canopy interaction processes, affect this approach. We compared the concentrations and the fluxes of the main ions determined in wet-only, bulk and throughfall samples collected at five forest sites in Italy. The contribution of coarse particles deposited onto the bulk samplers was of prime importance for base cations, representing on average from 16% to 46% of the bulk deposition. The extent of this dry deposition depended on some geographical features of the sites, such as the distance from the sea and the annual rainfall. The possibility of applying specific bulk/wet ratios to estimate the wet deposition proved to be limited by the temporal variability of these ratios, which must be considered together with the spatial variability. A direct comparison of the dry contribution deriving from the bulk–wet and the throughfall–wet demonstrated that an extensive natural surface (forest canopy) performs better than a small synthetic surface (funnel of the bulk sampler) in collecting dry deposition of SO₄²⁻, NO₃⁻ and Na⁺. The canopy exchange model was applied to both bulk and wet data to estimate the contribution of dry deposition to the total input of base cations, and the uncertainty associated to the model discussed. The exclusive use of bulk data led to a considerable underestimation of base cation dry deposition, which varies among the study sites.     

Diagnostic indicators of elevated nitrogen deposition

Tissue N content of mosses, which has been shown to be an indicator of enhanced N, was studied at a range of locations dominated either by wet or dry deposited and oxidised and reduced forms of N. Tissue N responded differently to wet and dry deposited N. For a 1 kg ha(-1) y(-1) increase in N deposition, tissue N increased by 0.01% at wet deposition sites but by 0.03% at sites dominated by dry deposited NH3. Tissue N at wet deposition sites responded more to concentrations of NO3- and NH4+ in precipitation (r(2) 0.63) than to total N deposition (r(2) 0.27), concentration explaining 66% of the variation in tissue N, wet deposition 33%. The study clearly concludes that tissue N concentration in mosses provides a good indication of N deposition at sites where deposition is dominated by NH3, and is also valuable in identifying vegetation exposed to large concentrations of NH4+ or NO3-, in wet deposition dominated areas, such as hilltops and wind exposed woodland edges.