Ion leaching from a sugar maple forest in response to acidic deposition and nitrification

Year-to-year variation in acidic deposition within a mature sugar maple-dominated forest and in leaching of ions from the associated podzolic soil were examined at the Turkey Lakes Watershed between 1981 and 1986. Below-canopy inputs to the soil of SO₄ ^2? and NO₃ ^? in throughfall averaged 640 and 295 eq. ha^?1 yr^?1; the corresponding ranges were 493–917 and 261–443 eq. ha^?1 yr^?1. The contribution of atmospheric deposition to SO₄ ^2? NO₃ ^? and Ca²⁺ leaching decreased over the six years. During the study period, the mean annual volume-weighted NO₃ ^? concentration decreased in throughfall and forest-floor percolate and increased in the mineral-soil solution collected below the effective rooting zone. A substantial shift in the balance between SO₄ ^2? and NO₃ ^?leaching from the mineral soil was observed; leaching of SO₄ ^2?decreased and NO₃ ^? leaching increased with time. Leaching of Ca²⁺ and Mg²⁺ from the soil was increased as a result of excess NO₃ ^? production in the soil. The calculated output of NO₃ ^? from the soil, which averaged 1505 eq. ha^?1 yr^?1, considerably exceeded the atmospheric deposition of NO₃ ^?, whereas SO₄ ^2? outputs were only moderately greater than inputs.     

Nature and Magnitude of Atmospheric Fluxes of Total Inorganic Nitrogen and Other Inorganic Species to the Tampa Bay Watershed, FL, USA

We estimated the total inorganic fluxes of nitrogen (N), sulfur (S), chloride (Cl^?, sodium (Na⁺, calcium (Ca²⁺, magnesium (Mg²⁺, potassium (K⁺ and hydronium (H⁺. The resistance deposition algorithm that is programmed as part of the CALMET/CALPUFF modeling system was used to generate spatially-distributed deposition velocities, which were then combined with measurements of urban and rural concentrations of gas and particle species to obtain dry deposition rates. Wet deposition rates for each species were determined from rainfall concentrations and amounts available from the National Acid Deposition Program (NADP) monitoring network databases. The estimated total inorganic nitrogen deposition to the Tampa Bay watershed (excluding Tampa Bay) was 17 kg-N ha^?1 yr^?1 or 9,700 metric tons yr^?1, and the ratio of dry to wet deposition rates was ～2.3 for inorganic nitrogen. The largest contributors to the total N flux were ammonia (NH₃ and nitrogen oxides (NO _x at 4.6 kg-N ha^?1 yr^?1 and 5.1 kg-N ha^?1 yr^?1, respectively. Averaged wet deposition rates were 2.3 and 2.7 kg-N ha^?1 yr^?1 for NH₄ ⁺ and NO₃ ^?, respectively.     

Deposition Patterns of SO4 2−, NO3 − and H+ in the Brazilian Territory

SO₄ ^2?, NO₃ ^? and H⁺ depositions are estimated in the Brazilian territory based on the existing rainfall chemical data and on annual rainfall distribution over the whole territory. Local and regional depositions are estimated. Rainfall chemical data over the Braziliian territory shows that the average pH values are usually low (between 4.0 and 5.5). These values are observed in the tropical Amazon forest as well as in urban areas. However, the rainwater acidity in the tropical forests are due to organic acids naturally produced by the vegetation while in urban areas the acidity is mainly due to acidic anion deposition (NO₃ ^? and SO₄ ^2?). In some Amazonian areas, the average input values through rainfall for NO₃ ^? is about 0.06 keq.ha.yr^?1 and for SO₄ ^2? is between 0.23 and 0.54 keq.ha^?1.yr^?1. On the other hand, in some urban centers, such as São Paulo, values of .072 keq.ha^?1.yr^?1 for NO₃ ^? and 1.16 keq.ha^?1.yr^?1 of SO₄ ^2? are found and in sites where sulfate sources (coal mining) are present, as for the area of Florianópolis, values as high as 5.59 keq.ha^?1.yr^?1 for SO₄ ^2? are found.     

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.     

Mapping of Base Cation Deposition in South Korea

Deposition of non-seasalt base cations (Ca²⁺ + Mg²⁺+ K⁺) in South Korea was mapped for 1994 to 1997 on a 11 × 14 km grid using the so-called inferential modeling technique. It is found that the annual mean wet deposition of non-seasalt base cations is about 290 eq ha^-1 yr^-1 with a maximum of 470 eq ha^-1 yr^-1 and a minimum of 120 eq ha^-1 yr^-1 while the annual mean dry deposition is about 130 eq ha^-1 yr^-1 with a maximum of 240 eq ha^-1 yr^-1 and a minimum 70 eq ha^-1 yr^-1. Theannual mean total deposition of non-seasalt Ca²⁺ + Mg²⁺ + K⁺ is found to be about 420 eq ha^-1 yr^-1 with the predominant range of 400 eq ha^-1 yr^-1 to 550 eq ha^-1 yr^-1 thatoccupies more than 45% of total deposition of non-seasalt base cations and dry deposition constitutes on average30% of the total base cation deposition. About 30% of the annualtotal deposition of sulfur is found counteracted by depositionof non-seasalt base cations over South Korea.     

Acid deposition and ion leaching from a podzolic soil under hardwood forest

The contribution of atmospheric acids to cation leaching from a podzolic soil under mature maple-birch forest in central Ontario was examined during 1983. The movement of base cations was associated largely with NO₃ ^?, SO₄ ^2? and organic acid anions in surface soil horizons, with SO₄ ^2? and NO₃ ^? below the effective rooting zone, and SO₄ ^2? and HCO₃ ^? in streamflow. Mineral soil horizons could adsorb little additional SO₄ ^2? or associated cations at current soil solution SO₄ ^2? concentrations. Therefore it is concluded that the soil in situ lacks a strong affinity for SO₄ ^2?. Current annual inputs to the forest of SO₄ ^2? and NO₃ ^? in bulk precipitation (26.4 and 18.2 kg ha^?1, equivalent to 8.8 kg S and 4.1 kg N ha^?1 , respectively) contributed significantly to cation leaching from the soil. In order to maintain exchangeable cations in soil at current levels, a rate of weathering yielding 29.6, 5.0, 4.4 and 2.2 kg ha^?1 yr^?1 of Ca²⁺, Na⁺, Mg²⁺ and K⁺, respectively, would be required.     

Ion mass budgets for small forested catchments in Finland

Ion mass and H⁺ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H⁺, Cl^? and SO ₄ ^2? by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H⁺ budgets, and the ratio between external (anthropogenic) and internal H⁺ sources. In general, output exceeded input for Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO ₃ ^? (if present) and A^? (organic anions), whereas retention was observed in the case of H⁺, NH ₄ ⁺ , NO ₃ ^? and SO ₄ ^2? . The range in the annual input of H⁺ was 22.8–26.3 meq m^?2 yr^?1, and in the annual output, 0.3–3.9 meq m^?2 yr^?1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H⁺ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO ₄ ^2? (17–49 %). The maximum net retention of SO ₄ ^2? was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H⁺ budgets. The ratio between external and internal H⁺ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.     

Acid deposition to nature areas in the Netherlands: Part I. Methods and results

In this paper estimates of dry and wet deposition of acidifying substances in the Netherlands are presented. The deposition was estimated from measured concentrations in the atmosphere and in precipitation or if these were not available, from modelled concentrations. The method was applied for the Netherlands on a 5×5 km scale. The most important components are sulphur oxides and ammonia and their reaction products. It was estimated that the annual average deposition of SO _x in the Netherlands decreased from 1570 to 670 mol ha^?1 a^?1 between 1980 and 1989. In 1989, the annual average NO _y deposition was estimated to be 1220 mol ha^?1 a^?1 in 1980 and 1160 mol ha^?1 a^?1 in 1989. The annual average NH _x deposition in the Netherlands was estimated to be 2330 and 2190 mol ha^?1 a^?1 in 1980 and 1989 respectively. HCI deposition was about 100 mol ha^?1 a^?1 in all years. Dry deposition contributes most to the total deposition for each component. The spatial distribution of the total deposition shows a gradient over the Netherlands with highest values in the South and lowest in the North of the country. Meteorological conditions are also of influence on the deposition fluxes for all components. During 1988 and 1989 meteorological conditions favoured low deposition. The estimated uncertainty in the average fluxes of SO _x , NO _y , and NH _x for the Netherlands is 15, 25, and 30% respectively. The wet deposition fluxes can be estimated more accurately than the dry deposition.     

Measurements of wet and dry deposition in a Northern Hardwood forest

Inputs of wet and dry deposition were monitored at the Huntington Forest in the Adirondack Mountains of New York for two years in the open and beneath the canopy of a northern hardwood forest. In the open, ion flux estimates were similar using wet-only weekly (NADP protocol) and event collections, but bulk collections were higher for all ions except H⁺, which was much lower. These differences were due to the contribution of dry deposition and possible biotic alterations in bulk collectors. Dry deposition was estimated using air concentrations and ion-specific depositional velocities modeled with meteorological data, and contributed substantially to the input of all ions [H⁺ (45%), Na⁺ (24%), K⁺ (22%), NH₄ ⁺ (12%), Ca²⁺ (58%), Mg²⁺(43%), NO₃ ^? (55%), Cl^? (27%) and SO₄ ^?2 (26%)]. Dry input of base cations was dominated by coarse particles, whereas gaseous inputs were more important for S and NO₃ ^?. Atmospheric concentrations of SO₂ and inputs of SO₄ ^2? and H⁺ were lower at this site than sites closer to point sources of S gas emission. The importance of estimating atmospheric inputs was examined using examples of elemental budgets. For example, different estimates of the contribution of dry deposition of SO₄ ^2? (9–21 meq m^?2 y^?1) resulted in conclusions ranging from no net retention to a net loss of this element. Such differences have important implications in assessing the current and future role of atmospheric inputs in affecting elemental cycling.     

Biogeochemistry of a forested watershed in the central Adirondack Mountains: Temporal changes and mass balances

Information on atmospheric inputs, water chemistry and hydrology were combined to evaluate elemental mass balances and assess temporal changes in elemental transport from 1983 through 1992 for the Arbutus Lake watershed. This watershed is located within a northern hardwood ecosystem at the Huntington Forest within the central Adirondack Mountains of New York (USA). Changes in water chemistry, including increasing NO₃ ^? concentrations (1.1 μmol _c , L^?1 yr-1), have been detected during this study period. Starting in 1991 hydrological flow has been measured from Arbutus Lake and these measurements were compared with predicted flow using the BROOK2 hydrological simulation model. The model adequately (r²=0.79) simulated flow from this catchment and was used to estimate drainage for earlier periods when direct hydrological measurements were not available. Modeled drainage water losses coupled with estimates of wet and dry atmospheric deposition were used to calculate solute budgets. Export of SO₄ ^2? (831 mol _c ha^?1 yr^?1) from the greater Arbutus Lake watershed exceeded estimates of atmospheric deposition in an adjacent hardwood stand suggesting an additional source of S. These large drainage losses of SO₄ ^2? also contributed to the drainage fluxes of basic cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺). Most of the atmospheric inputs of inorganic N were retained (average of 74% of wet precipitation and 85% total deposition) in the watershed. There were differences among years (56 to 228 mol ha^?1 yr^?1) in drainage water losses of N with greatest losses occurring during a warm, wet period (1989–1991).     

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.     

Recovery of acidified catchments in the extremely polluted Krusne hory Mountains,Czech Republic

Runoff and atmospheric chemistry in the Krusne hory Mts. have changed significantly from 1978 to 1994. Forest die-back related deforestation resulted in decreased dry deposition of SO₂ and changes in streamwater chemical composition. Atmospheric sulphur (S) deposition decreased from extremely high values of 66.6 kg S ha^?1 year^?1, in the early 1980s to 35.5 kg S ha^?1 year^?1 in 1994. Decreasing S input is reflected in decrease of streamwater sulphate (SO₄ ^2?) concentrations, which decreased from 1560 μeq l^?1 to 1164 μeq l^?1. Runoff export of S was 53 kg S ha^?1 year^?1 in 1993, S is not retained in the catchments. Nitrogen (N) budget indicates accumulation in the catchment, which is attributed to forest regrowth.     

Estimation of the Maximum Critical Load for Sulfur in South Korea

The maximum critical load of sulfur and its exceedance by the sulfur deposition of 1994–1997 were mapped for South Korea with a spatial resolution of 11 × 14 km using the steady-state mass balance method. The Korean soil and geological maps were used as basis for the estimations of the critical alkalinity leaching and the weathering rate of base cations. The normalized difference vegetation index data obtained from the Advanced Very High Resolution Radiometer (AVHRR) together with the observed primary productivity of plants were used for the estimation of the critical uptake of base cations. Wet deposition of the non-sea-salt base cations was derived from measured base cation concentrations in precipitation, precipitation rate and air concentration of total suspended particulate while dry deposition of base cations was estimated using the inferential technique using scavenging ratios. The predominant ranges of base cation weathering, uptake and deposition were estimated to be of 200 – 600 eq ha^?1 yr^?1, 200 – 400 eq ha^?1 yr^?1 and 400 – 600 eq ha^?1 yr^?1, respectively. Critical alkalinity leaching was mainly in the range of 1000 – 2000 eq ha^?1 yr^?1 due to relatively high value of precipitation runoff. Exceedance of sulfur critical load was found at 40 % of the ecosystems considered mainly in the southeastern part of Korea, and about 60 % of Korea ecosystems were sustainable against sulfur acidity loadings.     

Long-term development of element budgets in a Norway spruce (Picea abies (L.) Karst.) forest of the German solling area

To evaluate ecosystem response to changing atmospheric deposition, element budgets were established over the period from 1973 to 1991 for a Norway Spruce (Picea abies (L.) Karst.) site. Budgets for Na⁺, Cl^?, Ca²⁺, Mg²⁺, N, S and H⁺ were based on total deposition and seepage water fluxes. The deposition of Ca²⁺, Mg²⁺, particularly, of S and H⁺ decreased with time, while calculated N deposition remained constant at a high level. The decrease in Ca²⁺ deposition led to a reduction of Ca²⁺ fluxes with seepage water. The decrease of Mg²⁺ deposition did not have an effect on the output fluxes of Mg²⁺. The reversibility of soil and seepage water acidification by reduced S deposition was delayed by the release of previously accumulated soil SO ₄ ^2? . The highest NO ₃ ^? fluxes were observed during the period of 1986 to 1988; NO ₃ ^? fluxes in general demonstrated a considerable annual and periodic variation. Total N accumulation in the ecosystem amounted to nearly 590 kg ha^?1 yr^?1 during the observation period. The major sink of N in the spruce site is the aggrading humus layer. The results emphasize the need for measurements over several years to make conclusions regarding the function of ecosystems in response to atmospheric deposition.     

Acidification of Nova Scotia Lakes

Although water chemistry of precipitation and lakes in Nova Scotia is dominated by C1 from sea salt, correction for marine influence reveals that the dominant anion in acidified lakes is SO₄. Atmospheric deposition of non-marine SO₄ (SO₄) and NO₃- for the period 1977–1980 at 4 stations in southwest Nova Scotia averaged 47 meq SO₄ ^* m^?2 yr^?1 and 21 meq NI₃-m^?2 yr^?1 compared with 38 and 13 meq, respectively, for the average of 3 stations in the northeastern third of the province. Precipitation pH increased from 4.5 to 4.8 along the same axis. Almost 50% of the SO₄ deposition occurred when storms came from the southwest, indicating low pressure tracks which pass south of major Canadian sources of S. SO₄ ^* deposition in metropolitan Halifax (1982 bulk data) was 87 meq m^?2 yr^?1, due to local emissions of ca. 28 300 tonne S in the area, as well as LRTAP. Concurrent deposition of NO₃-N was 15 meq m^?2 yr^?1 (2.1 kg ha^?1 yr ^?1). Loadings from SO₄ deposition in the Halifax area amount to 42 kg ha^?1 yr^?1 and clearly exceed the federal guideline (M.O.I., 1983) of 20 kg ha^?1 yr^?1. Water chemistry of southwest, northeast, and Halifax area lakes show the same general SOI trends as observed for atmospheric deposition. In addition we find a positive relationship between SOI concentrations in the urban lakes and proximity to the center of the urban area.     

Concentrations of Nitrogen and Sulfur Species in Gas and Rainwater from Six Sites in Indonesia

Gas mixing ratios of SO₂, NO₂ and HNO₃ and nitrate and sulfate concentrations in rainwater have beenmeasured at six sites in Indonesia. The sites, Jakarta, Serang,Cilegon, Merak and Bogor, in Java, and Bukit Koto Tabang inSumatra, provide a range of pollution regimes in Indonesia.Jakarta and Bogor are heavily polluted sites in Java, whereasBukit Koto Tabang is a clean air station in a relativelyunpopulated area on the west coast of equatorial Sumatra. At thesesites rainwater was collected daily and gas samples weeklyduring 1996. The other three sites Serang, Cilegon and Merakrepresent smaller regional towns in west Java. At these sitesrainwater samples were collected weekly from June 1991 untilJune 1992.The results show that Jakarta has the highest volume-weightedmean sulfate concentrations in rainwater while the lowest weremeasured at Bukit Koto Tabang. Volume-weighted mean nitrateconcentration was about 24 μeq L^-1 at Jakarta and Bogor,significantly higher than the 0.8 μeq L^-1 measured atBukit Koto Tabang.Sulfur dioxide mixing ratios ranged from 4–7 ppbv in Jakarta toan average of 1.3 ppbv at Bukit Koto Tabang. Nitrogen dioxidemixing ratio was highest in Jakarta averaging 28 ppbv comparedwith the background mixing ratio of 1.2 ppbv at Bukit KotoTabang. Using dry deposition velocities estimated during aseparate study in the similar conditions of Malaysia enabled drydeposition estimates of SO₂, HNO₃ and NO₂.Results of estimated total acidic S and N deposition (wet anddry) were greater than 250 meq m^-2 yr^-1 at the Jakartaand Bogor sites compared with about 23 meq m^-2 yr^-1 atBukit Koto Tabang. At Jakarta and Bogor dry deposition accountedfor more than 50% of the total deposition estimates compared with about 20% at Bukit Koto Tabang. Such deposition rates arehigh when compared to critical loads estimated for Indonesia bythe RAINS-Asia model. In this model, critical loads in western Java and equatorial western Sumatra fall into one of twoclasses: 50–100 and 20–50 meq m^-2 yr^-1. Thus acidic deposition flux at Jakarta and Bogor wasfound to be above the predicted critical loads even for the moreacid insensitive soils.     

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.     

Average critical loads for nitrogen and sulfur and its use in acidification abatement policy in the Netherlands

Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO₃ pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol _c ha^?1 yr^?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol _c ha^?1 yr^?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha^?1 yr^?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol _c ha^?1 yr^?1 has been set in the Netherlands from which the N input should be less than 1000 mol _c ha^?1 yr^?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO₂, NO _x and NH₃ in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.     

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.     

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.