Evaluation of the changes in regional wintertime deposition in Finland during 1976–1993

Snowpack quality has been systematically monitored in Finland since winter 1975/1976 by the Finnish Environment Agency. Snow samples have been taken at the 53 groundwater observation stations in nearly natural state areas, where the impacts of local emission sources have been negligible. Thus the concentrations of impurities in snow can be considered as background levels. Samples were analyzed for conductivity, pH, major ions and trace metals (Cd, Cu, Pb, Ni, Zn and Hg). The regional variation of the chemical composition of major ions in the snowpack was outlined by cluster analysis. Sampling sites were divided into six clusters by average linkage clustering method. The largest cluster — considered as the ‘mean cluster’ — was located in central and northern Finland. The lowest levels of the total amount of dissolved impurities occurred in the cluster formed by the most northern observation site exclusively. Highest rates of the acidifying components, sulphate (SO₄), nitrate (NO₃), ammonium (NH₄) and hydrogen ions (H⁺), were encountered in southern Finland. Sampling locations of southern Finland were divided into three clusters. The acidity of snow varies among these clusters that in addition of deposition of SO₄ and NO₃ is considerably controlled by alkaline deposition. The results of chemical analyses of snow were converted to mean monthly depositions using the water equivalent of snow and the time of deposition. Deposition of SO₄ during 1985–1993 was 32% lower compared with the period 1976–1984, which presumably results from 70% reduction of sulphur emissions in Finland since the beginning of the 1980s. The deposition level of NO₃-N seemed to stay relatively stable during the whole 18 year period while the deposition of NH₄-N has decreased 18%.     

Rainfall,Stemflow, and Throughfall Chemistry at Urban- and Mountain-facing Sites at Mt. Gokurakuji,Hiroshima, Western Japan

Rainfall, stemflow, and throughfall were collected from 1996 to 1999 at two types of forest sites: (1) forests near the traffic roads and urban areas and (2) forests away from the urban areas at Mt. Gokurakuji, Hiroshima, western Japan in order to estimatethe effects of anthropogenic activities on atmospheric deposition. Rainfall deposition for major ions showed small differences between the sites. The NO₃ ^- and SO₄ ^2-concentrations in stemflow were higher at the urban-facing slope than at the mountain-facing slope. Throughfall deposition of NO₃ ^- and SO₄ ^2- was also higher at urban-facing slopes. Net throughfall (NTF) deposition (throughfall minus rainfall) of NO₃ ^- and SO₄ ^2- accounted for 77 and50% of the total throughfall deposition on urban-facing slopes, respectively, while it accounted for 44 and 23% on themountain-facing slopes, respectively. These results indicated a higher contribution from dry deposition on urban-facing slopes compared to mountain-facing slopes. Atmospheric N (NO₃ ^- +NH₄ ⁺) deposition from throughfall was estimated to be around 17–26 kg N ha^-1 yr^-1 on urban-facing slopes, which was greater than the threshold of N deposition that could cause nitrogen leaching in Europe and the United States. The highload of atmospheric N deposition may be one of the factors bringing about the decline of pine forests on urban-facing slopesof Mt. Gokurakuji.     

Intercomparison of snow Sampling and Analysis Within the Alpine-Wide Snowpack Investigation (SNOSP)

In order to investigate the seasonal and geographical distribution of snow concentrations anddeposition fluxes of environmentally relevant ionic species in the Alps, the international programSNOSP was initiated. In the framework of this program, intercomparisons of snow samplingtechniques and analytical methods to determine the ionic species C1^-, NO ₃ ^- ,SO ₄ ^2- , K⁺, Na⁺, NH4 ⁺, Mg²⁺, and Ca²⁺, as well as the pH and the specificconductivity were performed. The concentrations of these species in the snow samples collectedin the SNOSP program varied by orders of magnitude with, e.g., concentrations of NO ₃ ^- , SO ₄ ^2- , and NH4 ⁺ ranging from 0.2-60, 0.2-90, and 0.1-60 µeq L^-1,respectively. The intercomparisons revealed a reasonable agreement of the determinations of thespecies Cl^-, NO ₃ ^- , SO ₄ ^2- , Na⁺, and NH4 ⁺ in snow. Results were less satisfactory for K⁺, Mg²⁺, Ca²⁺,and H⁺, mainly due to the very low concentrations. In conclusion, recommendations areformulated for the reliable derivation of chemical inventories from snow packs.     

Long-Term Annual and Seasonal Patterns of Acidic Deposition and Stream Water Quality in a Great Smoky Mountains High-Elevation Watershed

The recovery potential of stream acidification from years of acidic deposition is dependent on biogeochemical processes and varies among different acid-sensitive regions. Studies that investigate long-term trends and seasonal variability of stream chemistry in the context of atmospheric deposition and watershed setting provide crucial assessments on governing biogeochemical processes. In this study, water chemistries were investigated in Noland Divide watershed (NDW), a high-elevation watershed in the Great Smoky Mountains National Park (GRSM) of the southern Appalachian region. Monitoring data from 1991 to 2007 for deposition and stream water chemistries were statistically analyzed for long-term trends and seasonal patterns by using Seasonal Kendall Tau tests. Precipitation declined over this study period, where throughfall (TF) declined significantly by 5.76?cm?year^?1. Precipitation patterns play a key role in the fate and transport of acid pollutants. On a monthly volume-weighted basis, pH of TF and wet deposition, and stream water did not significantly change over time remaining around 4.3, 4.7, and 5.8, respectively. Per NDW area, TF SO₄ ^2- flux declined 356.16?eq?year^?1 and SO₄ ^2- concentrations did not change significantly over time. Stream SO₄ ^2- remained about 30???eq L^?1 exhibiting no long-term trends or seasonal patterns. SO₄ ^2- retention was generally greater during drier months. TF monthly volume-weighted NH₄ ⁺ and NO₃ ^- concentrations significantly increased by 0.80???eq L^?1?year^?1 and 1.24???eq L^?1?year^?1, respectively. TF NH₄ ⁺ fluxes increased by 95.76?eq?year^?1. Most of NH₄ ⁺ was retained in the watershed, and NO₃ ^- retention was much lower than NH₄ ⁺. Stream monthly volume-weighted NO₃ ^- concentrations and fluxes significantly declined by 0.56???eq L^?1?year^?1 and 139.56?eq?year^?1, respectively. Overall, in NDW, inorganic nitrogen was exported before 1999 and retained since then, presumably from forest regrowth after Frazer fir die-off in the 1970s from balsam wooly adelgid infestation. Stream export of NO₃ ^- was greater during winter than summer months. During the period from 1999 to 2007, stream base cations did not exhibit significant changes, apparently regulated by soil supply. Statistical models predicting stream pH, ANC, SO₄ ^2-, and NO₃ ^- concentrations were largely correlated with stream discharge and number of dry days between precipitation events and SO₄ ^2- deposition. Dependent on precipitation, governing biogeochemical processes in NDW appear to be SO₄ ^2- adsorption, nitrification, and NO₃ ^- forest uptake. This study provided essential information to aid the GRSM management for developing predictive models of the future water quality and potential impacts from climate change.     

Long term trends in atmospheric deposition and seepage output in northwest German forest ecosystems

Long term trends of element fluxes in atmospheric deposition and of concentrations in seepage output of seven coniferous and deciduous forest stands in northwestern Germany have been evaluated for the period 1981 – 1994. Decreasing deposition rates of SO₄ (50 – 70%) and H⁺ (60 – 80%) occured at all sites concomitant with the decline of SO₂ emission rates in the former Federal Republic of Germany. Deposition of Ca, Mg, and K decreased at the Soiling and Göttinger Wald stands. During this period no consistent trends in the flux rates of NH₄ and NO₃ were apparent. Sulfate concentrations in soil solution decreased at the Soiling and Göttinger Wald stands, whereas an increase occured at Lange Bramke south slope. As a consequence of reduced deposition and mobile anion concentrations a decrease of Ca, Mg, K, Al, and Mn in soil solution has been observed at the Soiling stands. At the other stands trends of cations in soil solution are not consistent. Nitrate concentrations in soil solution decreased at the Göttinger Wald. A rising tendency with great fluctuations of NO₃ concentrations occured at the Soiling spruce stand.     

Throughfall and canopy buffering in three sitka spruce stands in Denmark

Throughfall was studied in three even-aged sitka spruce stands in Denmark during the years 1989 to 1994. Deposition of sea salts dominated the fluxes of substances in varying degrees between years and sites. During the study period, non-marine S deposition did not change substantially. At the site most affected by animal husbandry, fluxes of NH₄ ⁺ and NO₃ ^? increased over the years. Elevated fluxes of TOC, K⁺, and PO₄ ^3? occurred in the growing season due to canopy leaching caused by attacks by the green spruce aphid. Fluxes of Cl^?, SO₄ ^2?, Na⁺, Ca²⁺, and Mg²⁺ were highest in the dormant season. Buffering of. pH was affected by the nitrogen dynamics in the canopy, and also, at least during the summer, by elevated levels of organic compounds.     

Dry Deposition to the Forest Canopy and Surrogate Surfaces in Two Mediterranean Holm Oak Forests in Montseny (NE Spain)

The fluxes recovered from washing branches and surrogatesurfaces were compared for two holm oak (Quercus ilex L.)forests in the Montseny mountains (NE Spain) differentiallyexposed to pollution. For 5 periods in May and June 1996 afterexposures ranging between 68–189 hr, 6 metacrylate plates and 8branches were extracted with distilled water. Also, a sequentialwashing of branches was undertaken, with 5 min separationsbetween the 3 initial washes, one hour between the 3rd and the4th, and 6 hr between the 4th and the last one. The compositionwas analysed for PO₄ ^3-, SO₄ ^2-,NO₃ ^-, Cl, F, NH₄ ⁺,Ca²⁺, Mg²⁺, Na⁺, K⁺, Cu, Pb, Mn, Co, Ni and Zn. The applied techniques were consistent in that dry deposition would accountfor the throughfall fluxes of NO₃ ^-, Cl^-,Cu and Zn. Potassium and Mn would derive mostly from leaching and their fluxes were strongly related with the holm oak flower growth. ForMg²⁺ and SO₄ ^2- either leaching or impaction of small particles or gases (for SO₄ ^2-) could account forthe recovered fluxes. Also for Na⁺ and Ca²⁺ the experiments did not produce conclusive results. Ammonium, F, Pb,Co, and Na were under the detection limit of analyticaltechniques in the plate-wash. The exposed site presented higherleaf-wash and plate-wash fluxes for all elements. This wasattributed to its higher exposure to pollutants, and forleaching-derived elements, to its higher site fertility.     

An analysis of spatial variability of the dominant ions in precipitation in the eastern United States

Data of the Multistate Atmospheric Power Production Pollution Study (MAP3S) and the National Atmospheric Deposition Program (NADP) were utilized to develop wet deposition spatial distribution patterns for the eastern United States for 1979. The ions of SO₄ ^?, NO₃ ^?, H⁺, and NH₄ ⁺ were selected for study since they are the most prominent ones found in precipitation. Total wet deposition for 1979 was normalized to one centimeter of precipitation and objectively analyzed using the Synagraphic Mapping System (SYMAP) technique. Gradients of SO₄ ^? and NO₃ ^? were found to be essentially uniform, both to the east and west of the major pollution regions. An increased gradient in normalized deposition for SO₄ ^?, NO₃ ^?, and H⁺ was found in the Appalachian Mountain region. Estimates of total wet deposition were obtained by using the normalized deposition values in conjunction with precipitation as reported by the National Climatic Center. SYMAP analyses of the estimated total wet deposition were localized in nature due to precipitation variations between sites.     

Study on Dry Deposition of SO2-NOX onto Loess

In order to obtain information on dry deposition of SO₂ onto loess in China, the effects of water vapor and NO₂ on SO₂ deposition-oxidation processes were investigated in laboratory measurements. The deposition velocities of SO₂ onto loess particles were 2.34–7.33 cm s^?1, were high in comparison with the other studies. Deposition of SO₂ onto the particles was decreased with exposed time and amounts of SO₂, but was influenced by adsorption of water vapor onto the particles. On the other hand, oxidation of SO₂ physically8 adsorbed was promoted by the coexistence of water vapor and NO₂. So, it was indicated that it was possible for water vapor and NO₂ in the atmosphere to play an important role in dry deposition for the deposition-oxidation interaction between SO₂ and loess particles.     

Sources of acidity in forest-floor percolate from a maple-birch ecosystem

Ion concentrations in water collected within a forest of sugar maple and yellow birch at the Turkey Lakes Watershed near Sault Ste. Marie, Ontario were examined from 1982 to 1984 to determine sources of acidity and the extent of cation leaching from forest floor horizons. Volume-weighted concentrations and ion fluxes in throughfall and forest-floor percolate during the growing and dormant seasons were calculated. Hydrogen ion content of the forest-floor percolate decreased in relation to that of throughfall in the dormant season and increased in the growing season. Hydrogen ion deposition in throughfall could account for 100% of the flux of H⁺ through the forest floor in the dormant period, and 40% of the flux during the growing season. In forest-floor percolate, Ca²⁺ concentrations were positively correlated with those of SO₄ ^2-, NO₃ ^- and organic anions during both dormant and growing seasons. Sources of NO₃ ^- and organic anions within the ecosystem and major external inputs of NO₃ ^- and SO₄ ^2- were critical factors that influenced cation mobility in the forest floor.     

Trends in the Chemistry of Acidified Bohemian Lakes from 1984 to 1995: I. Major Solutes

Temporal changes in major solute concentrations in six Czech Republic lakes were monitored during the period 1984–1995. Four chronically-acidic lakes had decreasing concentrations of strong-acid anions (C_SA = SO₄ ^2- + NO^{3 -} + Cl^-), at rates of 3.0 to 9.0 μeq L^-1 yr^-1. Decreases in SO₄ ^2-, NO₃ ^-, and Cl^- (at rates up to 5.1 μeq L^-1 yr^-1, 3.2 μeq L^-1 yr^-1, and 0.6 μeq L^-1 yr^-1, respectively) occurred. The response to the decrease in deposition of S was rapid and annual decline of SO₄ ^2- in lake water was directly proportional to SO₄ ^2- concentrations in the acidified lakes. Changes in NO₃ ^- concentrations were modified by biological consumption within the lakes. The decline in C^SA was accompanied in the four most acidic lakes by decreases in Al_T, increases in pH at rates of 0.011 to 0.016 pH yr^{- 1}, and decreases of Ca²⁺ and Mg²⁺ (but not Na⁺) in three lakes. The acid neutralizing capacity (ANC) increased significantly in all six lakes. Increases in base cation concentrations (CB = Ca²⁺ + Na⁺ + Mg²⁺ + K⁺) were the principal contributing factor to ANC increases in the two lakes with positive ANC, whereas decrease in C_SA was the major factor in ANC increases in the four chronically-acidic lakes. The continued chemical recovery of these lakes depends on the uncertain trends in N deposition, the cycling of N in the lakes and their catchments, and the magnitude of the future decrease in S deposition.     

Fluxes and Trends of Nitrogen and Sulphur Compounds at Integrated Monitoring Sites in Europe

The International Cooperative Programme on Integrated Monitoring (ICP IM) is part of the effects monitoring strategy of the UN/ECE Convention on Long-Range Transboundary Air Pollution. We calculated input-output budgets and trends of N and S compounds, base cations and hydrogen ions for 22 forested ICP IM catchments/plots across Europe. The site-specific trends were calculated for deposition and runoff water fluxes and concentrations using monthly data and non-parametric methods. The reduction in deposition of S and N compounds, caused by the new Gothenburg Protocol of the Convention, was estimated for the year 2010 using atmospheric transfer matrices and official emissions. Statistically significant downward trends of SO₄, NO₃ and NH₄ bulk deposition (fluxes or concentrations) were observed at 50% of the ICP IM sites. Implementation of the new UN/ECE emission reduction protocol will further decrease the deposition of S and N at the ICP IM sites in western and northwestern parts of Europe. Sites with higher N deposition and lower C/N-ratios clearly showed an increased risk of elevated N leaching. Decreasing SO₄ and base cation trends in output fluxes and/or concentrations of surface/soil water were commonly observed at the ICP IM sites. At several sites in Nordic countries decreasing NO₃ and H⁺ trends (increasing pH) were also observed. These results partly confirm the effective implementation of emission reduction policy in Europe. However, clear responses were not observed at all sites, showing that recovery at many sensitive sites can be slow and that the response at individual sites may vary greatly.     

Dry Deposition of Atmospheric Sulphur and Nitrogen in Russia and the Former USSR

Generally, dry deposition processes are very important for atmospheric chemistry of pollutants providing up to 30–80 % of the removal for certain compounds from the atmosphere. The model for calculating of dry deposition fluxes for a large territory seems unsophisticated in spite of the dependence on surface characteristics, pollutant properties and atmospheric conditions. The approach of combining monthly average concentrations measured at the Integrated Background Monitoring Network (IBMoN) and EMEP stations and linear dry deposition velocity was used to calculate total sulphur and nitrogen fluxes for the whole of the former Soviet Union (FSU) taking into account large-scale geographical variability in climate and lands. Most values of all SO₂ and SO₄ ^2? concentrations were below 2.9 and 3.1 mgS/m³, and NO₂ concentration were 1.5 mgN/m³ over European part and 0.6 mgN/m³ in Western Siberia. The long-term trends of oxidised sulphur and nitrogen compounds in the atmosphere were examined for 1982–1998 in certain FSU regions. Annual dry deposition of sulphur was estimated as 3.64 Mt S (in sulphate form) and 2.76 Mt S (in SO₂ form) for the whole area of FSU. Annual removal of NO₂ by dry deposition was calculated at 1.27 Mt N. These values constituted between 44 and 50% of total oxidised sulphur and nitrogen deposition.     

recent lake acidification and recovery trends in southern quebec,canada

A total of 51 lakes in southern Quebec, Canada, were sampled between 1985 and 1993 to study changes in water chemistry following reductions in SO₂ emissions (main precursor of acid precipitation). Time series analysis of precipitation chemistry revealed significant reductions in concentrations and deposition of SO₄ ^2- from 1981 to 1992 in southern Quebec as well as reductions in concentrations and deposition of base cations (Ca²⁺, Mg²⁺), NO₃ ^- and H⁺ in the western section of the study area. Reductions in atmospheric inputs of SO₄ ^2- have resulted in decreased lakewater SO₄ ^2- concentrations in the majority of the lakes in our study, although only a small fraction (9 of 37 lakes used in the temporal analysis) have improved significantly in terms of acidity status (pH, acid neutralizing capacity – ANC). The main response of the lakes to decreased SO₄ ^2- is a decrease in base cations (Ca²⁺+Mg²⁺), which was observed in 17 of 37 lakes. Seventeen lakes also showed significant increases in dissolved organic carbon (DOC) over the period of study. The resulting increases in organic acidity as well as the decrease in base cations could both play a role in delaying the recovery of our lakes.     

Changes in the Chemistry of Precipitation in the United States, 1981–1998

Regulatory measures in the United States, such as Title IV of the Clean Air Act Amendments of 1990, have primarily restricted sulfur dioxide emissions as a way to control acidic deposition. These restrictions, coupled with increasing concentrations of NH₄ ⁺ in wet deposition in some regions of the U.S. and continued high emissions of nitrogen oxides have generated a significant shift in the chemistry of precipitation as measured at National Atmospheric Deposition Program/National Trends Network sites. Trends in precipitation chemistry at NADP/NTN sites were evaluated for statistical significance for the period 1981–1998 using a Seasonal Mann-Kendall Test, a robust non-parametric test for detection of monotonic trends. SO₄ ^2? declines were detected at 100 of the 147 sites examined while no sites exhibited increasing SO₄ ^2? trends. On average, SO₄ ^2? declined 35% over the period 1981–1998 with downward SO₄ ^2? trends being most pronounced in the north-eastern United States. In contrast, no consistent trends in NO₃ ^? concentrations were observed in precipitation in any major region of the United States. Although the majority of sites did not exhibit significant trends in NH₄ ⁺ concentration, 30 sites exhibited upward trends. For Ca²⁺ concentration in precipitation, 64 sites exhibited a significant decreasing trend and no sites exhibited an upward trend.     

Elevational trends in the fluxes of sulphur and nitrogen in throughfall in the Southern Appalachian Mountains: Some surprising results

From 1986–1989, a team of scientists measured atmospheric concentrations and fluxes in precipitation and throughfall, and modeled dry and cloudwater deposition in a spruce-fir forest of the Great Smoky Mountains National Park which is located in the Southern Appalachian Region of the United States. The work was part of the Integrated Forest Study (IFS) conducted at 12 forests in N. America and Europe. The spruce-fir forest at 1740 m consistently received the highest total deposition rates (～2200, 1200, and 700 eq ha^?1 yr^?1 for SO₄ ^2?, NO₃ ^?, and NH₄ ⁺). During the summers of 1989 and 1990 we used multiple samplers to measure hydrologie, SO₄ ^2?, and NO₃ ^? fluxes in rain and throughfall events beneath spruce forests above (1940 m) and below (1720 m) cloud base. Throughfall was used to estimate total deposition using relationships determined during the IFS. Although the SO₄ ^2? fluxes increased with elevation by a factor of ～2 due to higher cloudwater interception at 1940 m, the NO₃ ^? fluxes decreased with elevation by ～30%. To investigate further, we began year round measurements of fluxes of all major ions in throughfall below spruce-fir forests at 1740 m and at 1920 m in 1993–1994. The fluxes of most ions showed a 10–50% increase with elevation due to the ～70 cm yr^?1 cloudwater input at 1920 m. However, total inorganic nitrogen exhibited a 40% lower flux in throughfall at 1920 m than at 1740 m suggesting either higher dry deposition to trees at 1740 m or much higher canopy uptake of nitrogen by trees at 1920 m. Differential canopy absorption of N by trees at different elevations would have significant consequences for the use of throughfall N fluxes to estimate deposition. We used artificial trees to understand the foliar interactions of N.     

Estimation of Dry Deposition by Using a Filter Pack Method at Chunchon, Korea

Atmospheric gases and particulates were collected using four-stage filter-pack in Chunchon from January through December in 1999. Particulate SO₄ ^2? and NO₃ ^?, and gaseous HNO₃, SO₂ and NH₃ were analyzed. Annual average concentration of SO₄ ^2?(S), NO₃ ^?(S), HNO₃ (g), SO₂(g) and NH₃(g) were 5.75µg/m³, 4.98µg/m³, 0.33ppb, 1.52ppb and 7.25ppb, respectively. Annual dry deposition fluxes were estimated using the measured concentration and dry deposition velocity published by other research group. Annual dry deposition of S was 287kg · (km)^?2·y^?1, which accounted for about 30% of total S deposition. For N deposition, dry deposition is predominant; about 70% of total N deposition was through dry process mostly as forms of NH₃ and HNO₃.     

An Empirical Approach for Assessing the Relationship Between Nitrogen Deposition and Nitrate Leaching from Upland Catchments in the United Kingdom Using Runoff Chemistry

Samples were collected from 13 upland sites (main inflow and loch outflow) in the UK along an N deposition gradient of 12-50 kg ha^-1 yr^-1 to determine the relationship between N deposition and NO₃ ^- concentrations in surface waters. There was no direct correlation between NO₃ ^- leaching and soluble inorganic N deposition at these sites, but a significant relationship with NO₃ ^- was found using a deposition function incorporating dissolved organic carbon (DOC) flux from each catchment. A similar but less significant relationship was found between NO₃ ^- concentration and DOC:DON ratio in runoff water. Catchments showed evidence of N saturation, i.e., when mean NO₃ ^- concentration exceeded 5 µeq L^-1, when the mean DOC:DON ratio fell below an approximate value of 25. Five other large loch sites (LLS) with multiple subcatchments were used to test these relationships and for four of these mostly heathland sites the predicted NO₃ ^- concentrations closely matched measured values. At the fifth site, where most subcatchments were forested, the deposition function and DOC:DON ratios gave conflicting predictions and both methods generally underestimated measured NO₃ ^- concentrations. If the capacity of these catchments to retain deposited N is determined by C supply then many upland catchments in the UK may experience increasing NO₃ ^- concentrations in runoff in the future at current or increased levels of N deposition.     

Simultaneous Determination of Gas and Particle Dry Deposition onto Conditioned Surrogate Surfaces

Aerodynamically designed surrogate surfaces were used to determine the relative importance of gaseous (SO₂, HNO₃, NH₃) and particulate species (SO₄ ^2?, NO₃ ^?, NH₄ ⁺, Ca²⁺) in the dry deposition flux. For 11 sampling periods, we measured the deposition fluxes, ambient gaseous concentrations, size distributions of atmospheric aerosols and some meteorological parameters in Uji. The dry deposition of the gas to a nearly perfect sink was calculated by subtracting the greased surface flux from the total deposition flux to both the greased and reagent impregnated (or water) surface. It was found that the gas phase deposition contributed significantly more (60–93%) than the particulate phase to overall deposition of sulfur and nitrogen compounds. The dry deposition velocities of the species were also calculated using the deposition fluxes and the measured ambient concentrations. Comparisons were made between the measured and modeled particulate deposition flux.     

Trace Gas Emissions from a North Wales Fen - Role of Hydrochemistry and Soil Enzyme Activity

Fluxes of methane and nitrous oxide from a wetland were compared to hydrochemistry (NO₃ ^- and SO₄ ^2-) and soil enzyme activities (β-glucosidase) in an attempt to predict gas fluxes using chemical and enzymatic activities in north Wales, UK. In a one-year survey, the enzyme activities ranged from 0.028 to 0.065 µmol g^-1 min^-1, while NO₃ ^- and SO₄ ^2- concentrations ranged between 0-0.78 and 5-200 mg L^-1, respectively. Methane and nitrous oxide emissions varied between 0.32-240 and 0.28-5.48 mg m^-1 da^-1, respectively. The field survey was followed by laboratory-based manipulation experiments, from which pilot mathematical models were constructed, and related to the field data. The variation of methane emission was attributed to changes in SO₄ ^2- concentration and temperature at the site. In contrast, NO₃ ^- concentration, water table height, and β-glucosidase activity were major controlling factors for nitrous oxide emission. The models explained more than 80 % of the variation observed in the field study.