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1.
This study investigates the episodic acidification of Reedy Creek, a wetland-influenced coastal plain stream near Richmond, Virginia. Primary objectives of the study were to quantify the episodic variability of acid-base chemistry in Reedy Creek, to examine the seasonal variability in episodic response and to explain the hydrological and geochemical factors that contribute to episodic acidification. Chemical response was similar in each of the seven storms examined, however, the ranges in concentrations observed were commonly greater in summer/fall storms than in winter/spring storms. An increase in SO inf4 sup2? concentration with discharge was observed during all storms and peak concentration occurred at or near peak flow. Small increases in Mg2+, Ca2+, K+ concentrations and dissolved organic carbon (DOC) were observed during most storms. At the same time, ANC, Na+ and Cl? concentrations usually decreased with increasing discharge. In summer/fall storms, the absolute increase in SO inf4 sup2? concentration was one-third to 15 times the increase observed in winter/spring storms; the decrease in ANC during summer/fall storms was usually within the range of the decrease observed in winter/spring storms. In contrast, the decrease in Na+ and Cl? concentrations during winter/spring storms was much greater than that observed during summer/fall storms. Data show that while base flow anion deficit was higher in summer/fall than in winter/spring, anion deficit decreased during most summer/fall storms. In contrast, base flow anion deficit was lower in spring and winter, but increased during winter/spring storms. Increased SO inf4 sup2? concentration was the main cause of episodic acidification during storms at Reedy Creek, but increased anion deficit indicates organic acids may contribute to episodic acidification during winter/spring storms. Changes in SO inf4 sup2? concentration coincident with the hydrograph rise indicate quick routing of water through the watershed. Saturation overland flow appears to be the likely mechanism by which solutes are transported to the stream during storm flow.  相似文献   

2.
Solute fluxes to the ground in open plots and under the forest canopy of different species were investigated in a number of long-term ecosystem studies in West Germany. From the canopy flux balance, rates of interception deposition and canopy/deposition interactions were assessed. Chemically, both open precipitation and throughfall are dilute solutions of H2SO4 and HNO3 and their salts. For the sites investigated, mean pH in bulk precipitation ranged from 4.1 to 4.6, and in throughfall from 3.4 to 4.7. The increase in acidity after canopy passage at most sites indicates considerable interception deposition of strong acids to the forest stands, exceeding the rate of H+ buffering in the canopy. Evidence for buffering processes can be directly deduced from the fact that on sites with high soil alkalinity and high foliage base status, throughfall pH is usually higher than precipitation pH. Furthermore, the same idea can be concluded from changes in solution composition after canopy passage: the H+/SO inf4 sup2? ratio is decreasing at most sites, while alkali earth cations from exchange processes occur in throughfall (Ca2+/SO inf4 sup2? ratio increases). Solution composition and element flux data are presented for each of the sites, and the regional, orographical and site specific (species composition, ecosystem state) differentiations are discussed. A method for the assessment of total deposition and of canopy interactions such as H+-buffering and cation leaching is described, and results of calculations are shown. From these calculations it is concluded that forest ecosystems in Germany receive mean H+ loads of ca. 1 to 4 keq H+ · ha?1 · a?1 from atmospheric deposition. Acidity deposition rates seem to be related to a few key factors such as regional characteristics and ecosystem characteristics.  相似文献   

3.
A simple method is presented and used to estimate the portions of SO inf4 sup2? and NO inf? sup3 that contribute to the strong acidity in weekly precipitation samples collected at three NADP sites in the eastern United States. The method assumes that, in general, the difference between SO inf4 sup2? and NH inf+ sup4 represents acidic sulfate and the difference between NO inf? sup3 and soil-derived materials (the sum of Ca2+, Mg2+, and K+) represents acidic nitrate. Acidic sulfate and nitrate are considered to be the predominant source of H+ (determined from laboratory pH) in the weekly precipitation samples. Most of the acidity for all three sites was attributed to acidic sulfate. The highest fraction of acidic SO inf4 sup2? to H+ wet deposition values was for the east-central Tennessee site (0.95) and the northeastern Illinois site (0.90), and the lowest fraction occurred at the central Pennsylvania site (0.75). The Tennessee site had the greatest acidic fraction of sulfate (0.84) and the Pennsylvania site had the greatest acidic fraction of nitrate (0.59).  相似文献   

4.
Data from two national precipitation chemistry monitoring networks, and several regional air and precipitation chemistry networks are used to describe some broad-scale features of acidic deposition in eastern North America. In northeastern North America, the coefficient of variation is shown to increase from 10–16% for annual averages to nearly 100% for daily values. There is a strong annual cycle in H+, SO inf4 sup= and NH inf4 sup+ deposition and some of the other ions although these cycles are not all in phase. The wet NO inf3 sup? deposition contributes relatively more than SO inf4 sup= to the acidity of snow as compared to rain. Wet deposition is highly “episodic” with about 50% to 70% of the total annual deposition of SO inf4 sup= and NO inf3 sup? accumulating in the highest 20% of the days. Estimates made in various ways indicate that, over eastern North America as a whole, dry deposition is approximately equal to wet for both SO inf4 sup= and NO inf3 sup? . Dry may exceed wet in the high emissions zone but drops to about 20% of the total deposition in more remote areas. Deposition via fog or low cloud impaction is an important input to high elevation forests, but more data are required to quantify the magnitude and regional extent of this.  相似文献   

5.
The effect of acidic deposition on the soil under red pine forest in Chunchon, Korea was investigated. Precipitation, stream water, and soil solution chemistry were monitored at the watershed from 1997 to 1998. Acidity of the open-bulk precipitation was often neutralized by large amounts of ammonia (NH3) that might have originated from livestock farming and fertilization. Estimated elemental budget at the watershed showed a positive correlation between loss of base cations and proton (H+) production due to nitrogen transformation in soil (ΔH+ NT: ([NH4 +]in-[NH4 +]out)- ([NO3 ?]in-[NO3 ?]out)). When ΔH+ NT increased, concentrations of nitrate in soil solutions also increased. Consequently, pH values of soil solutions decreased, although ion exchange with base cations contributed to buffer reaction. Since acid buffering capacity of the red pine forest soil was small, it was concluded that the input of ammonium nitrogen enhanced nitrification in soil thus causing soil acidification represented by loss of base cations from the watershed.  相似文献   

6.
Over 3 yr of particulate measurements were made at two high elevation sites in the southern Appalachian Mountains of Tennessee and Virginia. Both dichotomous samplers and filter packs were used to obtain day and night, week-long samples for subsequent elemental and ionic analysis. Total No inf3 sup? (HNO3 + No in3 sup? ) and SO inf4 sup2? averaged, respectively, 1.1 and 5.0 µg m?3 at Look Rock, Tennessee and 2.0 and 6.4 µg m?3 at Whitetop Mountain, Virginia. At Whitetop Mountain, the spring and summer seasons had the highest average SO inf4 sup2? concentrations. Seasonally, total N03 varied little. The diurnal variation of elements and SO inf4 sup2? was small. Only total NO inf3 sup? varied substantially with highest values during the day. The fine fraction (particle diameter < 2.5 µm) accounted for about 67% of the total mass. Fine mass and elemental concentrations were generally higher at Look Rock. The elements comprising the principal mass fraction of the coarse samples (2.5 gm < particle diameter < 10 to 15 µm) were of crustal origin (e.g., Al, Si, Ca, Fe) while the element comprising the principal mass fraction of the fine samples (i.e., S) was of manmade origin. Cluster analysis identified two groups of elements at Whitetop Mountain. These groups, in both the coarse and fine fraction, were associate with a soil and an automobile emission component. At Look Rock, only a soil component was obvious.  相似文献   

7.
As acid deposition declines, recovery from acidification is delayed by the fact that the soil processes that earlier buffered against acidification are now being reversed. Monitoring of within catchment processes is thus desirable. However, soil sampling is destructive and not suitable for long-term monitoring at a single site, whereas sampling of soil water with suction lysimeters may be more suitable. In this paper we evaluate 8–11 years of soil water chemistry from E- and B-horizons in three acid forest soil plots within monitored catchments. Five years of sampling also included the C-horizon. To our knowledge, this is the first long-term lysimeter study including the E-horizon showing recovery from acidification, and one of few studies including the B-horizon. Soil water concentrations of SO4 decreased significantly between –9.5 and –1.4 μeq L-1 yr-1, with much higher rates of change at two southern sites compared to a northern site, where levels and changes of deposition were lower. The average annual bulk deposition of S ranged between 3 kg S ha-1 at the northernmost site to 11 kg S ha-1 at the southernmost site. The SO4 decline in E-horizons was smaller than the decline in deposition, which indicated leaching of SO4 from the O-horizon. At the two southern sites, a weaker decline in SO4 in the B-horizon compared to the E-horizon indicated desorption of SO4. The negative trends in SO4 were to a large extent balanced by decreases in base cations but there were also tendencies of recovery from acidification in soil solution at the southern sites by increasing pH and ANC. However, these were contradicted by increasing Al concentrations. A high influence of marine salts in the early 1990s may have delayed the recovery. Decreasing trends of the Ca/(H+)2 ratio in the soil solution, most pronounced at one of the southern sites, suggested that the soils were becoming more acidic, although the soil solution tended to recover.  相似文献   

8.
A survey of leaf and needle losses of European forests in 1993 revealed that 23% of the total forested area had defoliation of more than 25%. The focus of this defoliation is in Central Europe, namely in Poland, Slowakia, Czech Republic, and Germany. The annual surveys of leaf losses and discoloration indicated only small changes during the last years for the coniferous forests in Germany. However, the increasing leaf losses of oak and beech during the last years were alarming. Evaluating the potential relation between air pollutant deposition, soil changes and forest damage, we focus here on the recent changes in deposition and soil conditions, and their implication on tree root development and drought susceptability of trees. While deposition of SO4 2?, H+ and Ca2+ in many Central European forests decreased in the last decade, input of NH4 + and NO3 ? remained high or even increased. The H+ load of many forest soils today is thus still high compared to weathering rates, but the proportion of the H+ load resulting from turnover of deposited N has increased. Recent effects of changing depositions on acid forest soils were: depletion of soil Al-pools, release of formerly stored soil SO4 2?, accumulation of N in soil organic matter, increasing N availability to trees and decreasing concentration of Ca2+ in the soil solution. We hypothesise that soil acidification and increased N availability will decrease the fine root biomass of trees and shift the rooting zone to upper soil layers. Increased above ground growth, observed in many areas of Europe, will furthermore decrease the root/shoot ratio. This development will finally cause increased drought susceptability of trees and is thus of destabilizing nature. The proposed chain of events might be overlapped by other effects of air pollutants on forest ecosystems, namely direct effects of gases on leaves, nutritional inbalances, and interactions with pests.  相似文献   

9.
A four-year study in a forest catchment exposed to a moderate level of anthropogenic pollution indicated heavy accumulation of hydrogen (H+), manganese (Mn), zinc (Zn), copper (Cu) and lead (Pb) in the ecosystem and phosphorous (P), potassium (K) and cadmium (Cd) to a lesser extent. Nitrogen, which is also accumulated, is leached mainly as NO3 –, even though the input is dominated by NH4 +. Magnesium (Mg), calcium (Ca) and sodium (Na) are leached from the catchment, presumably due to intensive weathering processes in deeper layers of mineral soil. Chloride ion (Cl–) is also lost from the ecosystem. The output of sulphate (SO4 2–) with stream water exceeds its input only slightly. Although it appears that the catchment as a whole has a large buffering capacity (average stream water pH=7.43, rainfall pH=4.33), the upper biologically active soil layers are probably more susceptible to acidification and pollution. With constant accumulation of H+ and heavy metal ions this may lead to degradation of forest health.  相似文献   

10.
Increased concentrations of solutes in drainage waters following forest clearcutting may affect downstream water quality. The objective of this study was to evaluate some of the processes regulating concentrations of trace metals and Fe in soil solutions and streamwater in a clearcut watershed by determining changes in metal release by soil horizon, stand vegetation and elevation. Commercial whole-tree harvesting of a watershed at the Hubbard Brook Experimental Forest, NH, U.S.A. resulted in increased loss of NO inf3 sup? from the study watershed. This N0 inf3 sup? loss resulted in acidification of soil solutions, which was associated with release of Mn and Zn from mineral soil to soil solutions and streamwater. Significant correlations of Pb and Fe with dissolved organic C (DOC) suggested that mobilization of these metals was linked to DOC transfer. However, there was little evidence of increased release of DOC, Fe, or Pb following the whole-tree harvest, except in a high elevation spruce-fir zone with shallow soils.  相似文献   

11.
One-year field measurements were conducted in a Japanese cedar (Cryptomeria japonica) forest, located in Gunma Prefecture, Japan. On the basis of the meteorological and atmospheric concentration data, the dry deposition of SO2, HNO3, NO2 and HCl was estimated using the inferential method. The annual dry deposition of H+ was estimated at 721 eq ha?1yr?1, which was 40% larger than the measured annual wet deposition of H+ (514 eq ha?1yr?1). Therefore, dry deposition is an important pathway for the atmospheric input of H+ to the forest in the study site. The contribution of each gas to the dry deposition of H+ was as follows: SO2, 25%; HNO3, 32%; NO2, 10%; and HCl, 33%. The extremely high contribution of HCl appeared to be caused by the high emission intensity of HCl due to waste incineration in the site region. The differences between estimated deposition and throughfall and stemflow measurements indicated that about 80% of the total deposition of H+ was taken up by the canopy.  相似文献   

12.
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.  相似文献   

13.
Chongqing is among the heaviest polluted cities in China. Combustion of coal with relatively high sulfur content causes high sulfur emission and deposition in the area. Effects on soils and waters of the acid deposition in the Chongqing area have been studied in the field at a forested site outside the city. Deposition chemistry and fluxes, soil and soil water chemistry as well as surface water chemistry are presented for the period 1996–1998. There are some stress symptoms at the forest in the area and severe forest damage has been reported at Nanshan, closer to Chongqing center. Monitoring of the acidification situation in the area must be followed closely as impacts may be expected if the deposition is not reduced in the future. The deposition of sulfur, H+ as well as calcium at the site is high. Wet deposition of sulfur is estimated to 4.7 – 5.7 g S m?2 yr?1 during the three years sampled; dry deposition is probably of similar size. Annual volume-weighted pH in bulk deposition was 4.0 – 4.2 and the calcium wet deposition flux was 2.6 – 3.6 g Ca2+ m?2. There are considerable seasonal variations in the concentrations, related to the seasonal variations in precipitation amount (dry winter, wet summer). The soils at the site are acid with median base saturation of 12% and 8% in the topsoil and subsoil, respectively. In soil water, aluminum concentrations are typically in the range 3–8 mg L?1. However, due to the high base cation deposition, the Al/(Ca2++Mg2+) molar ratio is below unity in most samples, indicating little damage of forest due to aluminum in soil water.  相似文献   

14.
《Soil biology & biochemistry》2001,33(12-13):1695-1702
Sieved soil and soil core experiments were performed to determine the potential sensitivity of forest soil CH4 oxidation to oxidised N, reduced N and oxidised S atmospheric deposition. Ammonium sulphate was used to simulate reduced N deposition, HNO3 oxidised N deposition and H2SO4 oxidised S deposition. The effects of NH4+, NO3−, SO42− and H+ on soil CH4 flux were shown to be governed by the associated counter-anion or cation of the investigated ions. Ammonium sulphate, at concentrations greater than those that would be experienced in polluted throughfall, showed a low potential to cause inhibition of CH4 oxidation. In contrast, HNO3 strongly inhibited net CH4 oxidation in sieved soils and also in soil cores. In addition, soil CO2 production was inhibited and the organic and mineral soil horizons acidified in HNO3 treated soil cores. This suggested that the HNO3 effect on CH4 flux might be indirectly mediated through aluminium toxicity. Sulphuric acid only inhibited CH4 oxidation when added at pH 1. At concentrations more representative of heavily polluted throughfall, H2SO4 had no effect on soil CH4 flux or CO2 production from soil cores, even after 210 days of repeated addition. In contrast to HNO3 additions, acidification of the soil was not marked and was only significant for the mineral soil. The findings suggest that the response of forest soil CH4 oxidation to atmospheric acid deposition is strongly dependent on the form of acid deposition.  相似文献   

15.
We observed that soil cores collected in the field containing relatively high NH inf4 sup+ and C substrate levels produced relatively large quantities of N2O. A series of laboratory experiments confirmed that the addition of NH inf4 sup+ and glucose to soil increase N2O production under aerobic conditions. Denitrifying enzyme activity was also increased by the addition of NH inf4 sup+ and glucose. Furthermore, NH inf4 sup+ and glocose additions increased the production of N2O in the presence of C2H2. Therefore, we concluded that denitrification was the most likely source of N2O production. Denitrification was not, however, directly affected by NH inf4 sup+ in anaerobic soil slurries, although the use of C substrate increased. In the presence of a high substrate C concentration, N2O production by denitrifiers may be affected by NO inf3 sup- supplied from NH inf4 sup+ through nitrification. Alternatively, N2O may be produced during mixotrophic and heterotrophic growth of nitrifiers. The results indicated that the NH inf4 sup+ concentration, in addition to NO inf3 sup- , C substrate, and O2 concentrations, is important for predicting N2O production and denitrification under field conditions.  相似文献   

16.
Rain water at two forested sites in Guangzhou (south China) show high concentrations of SO4 2?, NO3 ? and Ca2+ and display a remarkable seasonal variation, with acid rain being more important during the spring and summer than during the autumn and winter. The amount of acid rain represents about 95% of total precipitation. The sources of pollutants from which acid rain developed includes both locally derived and long-middle distance transferred atmosphere pollutants. The seasonal variation in precipitation chemistry was largely related to the increasing neutralizing capacity of base cations in rainwater in winter. Soil acidification is highlighted by high H+ and Al3+ concentrations in soil solutions. The variation in elemental concentration in soil solution was related to nitrification (H+, NH4 + and NO3 ?) and cation exchange reaction (H+, Al3+) in soil. The negative effect of soil acidification is partly dampened by substantial deposition of base cations (Ca2+, Mg2+ and K+) in this area.  相似文献   

17.
A preliminary analysis of O3, SO2, SO inf4 sup2? , and total NO inf3 sup? deposition to the red spruce forest on the summit of Whitetop Mountain, Virginia, illustrates uncertainties in analysis methodologies, establishes the relative importance of three deposition pathways, and suggests areas for further research. Results are presented here for an analysis of the dry, wet (precipitation), and cloud water deposition pathways for the four chemical species during a 26-day period in April and May 1986. Dry and cloud water depositions are estimated using available models along with air and cloud water chemistry measurements made at the summit. For water soluble species, depositions by precipitation and cloud interception are found to be comparable in magnitude, while dry deposition appears to be about an order of magnitude less. High levels of atmospheric O3 lead to a large estimate of 03 deposition (on a mass flux basis) when compared to the estimated deposition of gaseous SO2. This is in spite of the fact that computed SO2 dry deposition velocities exceed those for O3. Model uncertainties are large for both dry deposition velocity and cloud water flux computations, and some bias in computations probably exists because of the application of the models to a complex terrain situation. Field evaluation of the cloud water deposition model is of greatest priority because of the apparent relative importance of that deposition pathway.  相似文献   

18.
Atmospheric dry deposition in two forest edges was studied by means of monitoring canopy throughfall in Douglas Fir stands. Throughfall fluxes in the first 50 to 100 m of forest edges were found to be substantially higher than fluxes in the interior of forest stands. Sodium and chloride showed the steepest throughfall flux gradients. Ions important for soil acidification and eutrophication showed relatively less steep but still significant gradients. The mean increase of the throughfall flux at 10 m, with respect to the flux at 200 m from the forest edge amounted to 150% for Na+, 119% for Cl?, 54% for S04 2?, 38% for NO3 ? , and 39% for NH4 + The enhancement of dry deposition in forest edges strongly depends on wind velocity and wind direction during dry deposition. Particularly trees in forest edges exposed to prevailing wind directions receive relatively large amounts of dry deposition.  相似文献   

19.
Summary The turnover of interlayer NH inf4 sup+ in a loess-derived agricultural soil from the Shaanxi Province in China was studied. The concentration of 15N-labeled interlayer NH inf4 sup+ and total interlayer NH inf4 sup+ (labeled + unlabeled) in a soil grown with winter wheat was significantly higher at the beginning of the season (March) than when the crop was mature (June). In a further experiment with winter wheat it was shown that under field conditions the concentration of interlayer NH inf4 sup+ decreased significantly in the two upper soil layers (0–20 and 20–55 cm) during March and in the deeper soil layer (55–75 cm) during April. When the heading stage of wheat was reached, about 200 kg N ha-1 of interlayer NH inf4 sup+ had been released. During the following growth period (heading until flowering of wheat) the concentration of interlayer NH inf4 sup+ increased significantly in the upper soil layers. Fertilizer application in the form of 70 kg N ha-1 as urea led to a considerable increase in the nitrate concentration in the upper soil layer but had no influence on the level of interlayer NH inf4 sup+ concentration. It is concluded that interlayer NH inf4 sup+ takes part in the N cycle of the soil and that it contributes to the N nutrition of the crop. NH inf4 sup+ originating from the mineralization of soil organic N may be rapidly incorporated into the interlayer of clay minerals and later released, when the N demand of the crop is high.  相似文献   

20.
Roots can induce significant changes in the rhizosphere soil. The aim of the present study was to investigate the influence of beech (Fagus silvatica L.) roots on the chemistry of the rhizosphere soil solution. Special emphasis was given to the effect of the NH4+ supply since many forest soils presently receive high NH4+ inputs from atmospheric deposition. In a mature beech stand, a non‐mycorrhized long root was forced to grow into a rhizotrone filled with homogenized acidic forest soil from the Bw horizon of a Dystric Cambisol. Beside the control, a NH4+ enriched treatment was installed. Thirty micro suction cups of 1 mm diameter and 0.5 cm length were placed in a systematic grid of 5 × 10 mm in each rhizotrone to enable root growth through the grid. The water potential of the soil was kept constant by supplying a synthetic soil solution. Small amounts of soil solution were sampled periodically from May to October 1999 and analyzed by capillary electrophoresis for major cations and anions. Furthermore, pH and conductivity were measured by micro electrodes. In the laboratory experiments, beech seedlings were grown in rhizotrones in a control and in a NH4+ fertilized soil. The equipment for sampling soil solutions and the soil conditions in the laboratory was similar to the field experiment. In each rhizotrone a single long root grew through the lysimeter grid. The laboratory conditions induced higher rates of nitrification as compared to the field. Thus, the overall concentration range of the soil solution was not comparable between field and laboratory studies. In all treatments average soil solution concentrations of H+ and Al3+ were significantly higher in the rhizosphere than in the bulk soil. The NH4+ treatment resulted, in the field and laboratory, in a strong increase of the H+ and Al3+ concentrations in the rhizosphere, accompanied by an accumulation of Ca2+, Mg2+, and NO3—. The observed rhizosphere gradients in soil solution chemistry were highly dynamic in time. The results demonstrate that the activity of growing beech roots results in an acidification of the soil solution in the rhizosphere. The acidification was enhanced after the addition of NH4+.  相似文献   

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