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1.
The reversibility of acidification is being investigated in a full scale catchment manipulation experiment at Lake Gårdsjön on the Swedish west coast using isotopes as environmental tracers. A 6300 m2 roof over the catchment enables researchers to control depositional variables. Stable S isotope values were determined in bulk deposition, throughfall, runoff, groundwater and soil-extracted water during one year prior to and two years of experimental control. Data collected prior to experimental control suggest that the inorganic SO 4 2? pool within the catchment has a homogeneousδ 34S value of about+5.5‰. Sprinkling of water spiked with small amounts of sea-water derived SO 4 2? started in April 1991. Theδ 34S value of this SO 4 2? is around+19.5‰. Since April 1991, the SO 4 2? concentration in runoff has decreased by some 30%, however, theδ 34S value have increased by only 0.5‰. This suggests mixing of sprinkling water S with a large reservoir of S in the catchment. Oxygen isotopes in SO 4 2? suggest that less than one third of the SO 4 2? in runoff is secondary SO 4 2? formed within the soil profile. This is, however, no evidence for net mineralization of S. The SO 4 2? in runoff in the roofed catchment is a mixture of SO 4 2? previously adsorbed in the soil, mineralized organic S and SO 4 2? from the sprinkler water. Calculations based on isotope data indicate that the turnover time of S within the catchment is on the order of decades. Since SO 4 2? facilitates base cation flow, the acidification reversal will take a much longer time than concentration decreases of SO 4 2? would suggest.  相似文献   

2.
The objectives of this study are to assessδ 34S as a tracer of anthropogenic SO 4 2? in groundwater and to document geochemical interactions that take place as a result of industrial SO 4 2? loading. During four separate sampling excursions, groundwater samples were obtained from 13 piezometers which surround the elemental S storage blocks at a processing facility for sour (H2S) natural gas in Alberta, Canada. Each sample was analyzed forδ 34Ssulfate,δ 18Osulfate,δ 18Owater,δDwater, major aqueous species, alkalinity, pH, temperature and dissolved O2. Hydraulic head measurements were taken to define the groundwater flow field. In the study area, anthropogenic SO 4 2? has aδ 34S of approximately +18‰ (CDT), while natural groundwater SO 4 2? is depleted to about ?12%. Low activity of sulfate reducing bacteria in the groundwater at this site assures thatδ 34S is a conservative tracer. Groundwater SO 4 2? concentrations increase asδ 34S approaches +18‰, suggesting that elevated SO 4 2? concentrations are due to S released by sour gas processing. Acidic waters generated by the oxidation of industrial S from the gas plant are neutralized by rock-water reactions.  相似文献   

3.
The effects of elevated atmospheric SO 4 2? deposition on S cycling in forest soils were assessed in an irrigation experiment using stable S isotopes. Over a period of 20 months, core lysimeters of five acidic forest soils from Southern Germany with different parent material and pedogenesis were irrigated with solutions chemically similar to canopy throughfall. Sulfate deposition in three experimental variants corresponded to 23, 42 and 87 kg S ha?1 yr?1. The SO 4 2? used for irrigation had aδ 34S ratio of +28.0‰ CDT (Canon Diablo Troilite standard), differing by more than +25‰ from natural and anthropogenic S in Southern Germany. A combination of chemical and isotopic analyses of soil and seepage water samples was used to elucidate the fluxes and transformations of simulated wet SO 4 2? deposition in each soil core. Retention of experimentally deposited S ranged from 57±5% in coarse-grained soils low in sesquioxides and clay, to 80±8% in loamy soils with high sesquioxide content. The sesquioxide content proved to be the major factor governing S retention. The ratio of S retained as inorganic SO 4 2? (mainly by adsorption) to that incorporated into organic compounds (presumably by microbial synthesis) ranged from 2 to 4. For the organic S pool, the amount of S retained as C-bonded S exceeded by far that immobilized as ester sulfate in four of the five soils. Application of34S-enriched SO 4 2? appears to be a suitable experimental tool to assess fluxes and transformations of deposited S in forest soils, if aerobic conditions are maintained. In contrast to radioactive S tracers, the concept should be applicable not only in laboratory and lysimeter experiments, but also in long term studies of whole forest ecosystems (e.g., experimental watersheds).  相似文献   

4.
Sulfate concentrations in rainwater and in air measured on four summer days at St. Louis were highly variable, both spatially or temporally. Maximum/minimum ratios of aerosol SO inf4 sup? varied by up to a factor of 9, and those in rainwater by a factor of 3 on the average. Generally, SO inf4 sup? concentration patterns in air and rainwater were similar, and consistent with wind direction and the location of sources. Direct relationships between SO inf4 sup? in air and in water were evident on two of the individual days, but not for all days together. The non-uniformity of the SO inf4 sup? pattern plus consideration of possible sources of SO inf4 sup? suggests that nucleation of SO inf4 sup? particles must be a major cause of S scavenging, with some possible influence from sub-cloud impaction.  相似文献   

5.
At Lange Bramke (Harz) soil solution and runoff concentrations of major elements were observed over 16 yr. During this period acid deposition was high but showed a marked decrease of H+ and SO 4 2? both in concentrations and fluxes over the last five years. Among others, this record reveals the following patterns: seasonality in the signals for SO 4 2? and NO 3 ? in runoff which are synchronous; an accumulation of SO 4 2? in the soil, initially up to 50% of the deposition fluxes; apparently no correlation between runoff and SO 4 2? concentration, and no long-term trend in runoff concentration of SO 4 2? . In this paper we use these patterns in the data set from Lange Bramke to test two established acidification models. The test criterion is that the algorithms employed by the SO 4 2? modules of these models must be able to reproduce these features. To that end, both models need not to be run as it can be shown that even with completely unrestricted parameter values the two algorithms are unable to match the observed SO 4 2? dynamics. The MAGIC model (Cosbyet al., 1985) is unable to reproduce, given the existence of net SO 4 2? accumulation, the constant SO 4 2? concentration in runoff during the last 16 years. The second model, BEM (Prenzel, 1986), is succesful in reconstructing the constant SC>4~ levels in runoff. However, on a monthly time scale BEM predicts a shift between the periodic maximum concentrations of SO 4 2? and NO 3 ? which is not observed in the data.  相似文献   

6.
In many forested wetlands of Louisiana, surface water quality is being deteriorated by nutrient input from adjacent agricultural production areas. This field study assesses the input of fertilizer N, applied to sugarcane fields, to forested wetlands. The potential use of natural abundance variations in 15N14N ratios for identification and tracing surface water N sources (NH 4 + - and NO3 --N) was evaluated. Runoff and surface water samples were collected from sugarcane fields and bordering forested wetlands (6 stations) over a 16 month period and analyzed for NH 4 + -N, NO 3 - -N, and associated NH 4 + -δ15N and NO 3 - -δ15N ratios. Fertilizer N draining into adjacent forested wetland was estimated to be only a small fraction of the amount applied. Concentrations of NH 4 + - and NO 3 - -N in the collected water samples were low and ranged from 0.02 to 1.79 mg L-1. Isotopic analysis revealed NH 4 + -δ15N and NO 3 - -δ15N means were distinctive and may have the potential to be used as tracers of N contamination. The mean NH 4 + -δ15N value was +18.6 ± 7.1‰ and the NO 3 - -δ15N mean was +8.3 ± 3.1‰. Anomalously high NO 3 - -δ15N values (>30‰) were attributed to denitrification.  相似文献   

7.
Depth profiles of total S, organic S, soluble SO 4 2? -S, FeS, and FeS2 were characterized for Sphagnum-derived peat cores collected from 9 sites. Marcell S-2 Bog (MN), Tamarack Swamp (PA), Cranesville Swamp (MD/WV), and Big Run Bog (WV) receive water from precipitation and upland runoff; atmospheric S deposition is 13, 47, 54, and 114 mmol m?2, yr?1, respectively. McDonald's Branch Swamp (NJ) is predominantly groundwater fed. Tub Run Bog (WV) and Allegheny Mining Bog (MD) receive augmented SO 4 2? inputs through acid coal mine drainage. Jezerní slat' and Bo?í Dar Bog in Czechoslovakia receive atmospheric S inputs of 33 and 243 mmol m?2 yr?1, respectively. In the peat from all sites except Allegheny Mining Bog, where the substantially augmented SO 4 2? input was reflected in an unusually high dissolved SO 4 2? pool in the surface peat, organic S (probably mostly carbon bonded S) was the dominant S fraction; FeS2 was generally the dominant inorganic S fraction. Subsurface peaks in total S, organic S and FeS2-S in peat from the runoff water fed sites were interpreted as indicative of depth-dependent patterns in S reduction/oxidation and in S immobilization/mineralization. Unless SO 4 2? inputs to a site are tremendously augmented (e.g., Allegheny Mining Bog), the rapid turnover of the dissolved SO 4 2? pool combined with the relative stability of the other inorganic and organic S pools, apparently functions as an effective buffer against site differences in S inputs, leading to a general similarity in vertical S profiles in the peat deposits.  相似文献   

8.

Purpose

Nitrate (NO 3 ? ) is often considered to be removed mainly through microbial respiratory denitrification coupled with carbon oxidation. Alternatively, NO 3 ? may be reduced by chemolithoautotrophic bacteria using sulfide as an electron donor. The aim of this study was to quantify the NO 3 ? reduction process with sulfide oxidation under different NO 3 ? input concentrations in river sediment.

Materials and methods

Under NO 3 ? input concentrations of 0.2 to 30?mM, flow-through reactors filled with river sediment from the Pearl River, China, were used to measure the processes of potential NO 3 ? reduction and sulfate (SO 4 2? ) production. Molecular biology analyses were conducted to study the microbial mechanisms involved.

Results and discussion

Simultaneous NO3 ? removal and SO4 2? production were observed with the different NO 3 ? concentrations in the sediment samples collected at different depths. Potentially, NO 3 ? removal reached 72 to 91?% and SO 4 2? production rates ranged from 0.196 to 0.903?mM?h?1. The potential NO 3 ? removal rates were linearly correlated to the NO 3 ? input concentrations. While the SO 4 2? production process became stable, the NO 3 ? reduction process was still a first-order reaction within the range of NO 3 ? input concentrations. With low NO 3 ? input concentrations, the NO 3 ? removal was mainly through the pathway of dissimilatory NO 3 ? reduction to NH 4 + , while with higher NO 3 ? concentrations the NO 3 ? removal was through the denitrification pathway.

Conclusions

While most of NO 3 ? in the sediment was reduced by denitrifying heterotrophs, sulfide-driven NO 3 ? reduction accounted for up to 26?% of the total NO 3 ? removal under lower NO 3 ? concentrations. The vertical distributions of NO 3 ? reduction and SO 4 2? production processes were different because of the variable bacterial communities with depth.  相似文献   

9.
Atmospheric deposition and surface water chemistry have been monitored intensively at 5 geologically “sensitive” sites in southeastern Canada. The sites receive differing acid inputs that span the entire range found in Canada. Surface water data collected at 9 stations from 1981 to 1993 for SO 4 2? , NO 3 ? , Alkalinity, DOC, pH, Ca2+ and Mg2+ have been analyzed to detect monotonic trends. Similarities between the temporal patterns and trends for SO 4 2? in deposition and surface water suggest that they are strongly linked at our sites. Our 13-year datasets showed significant negative SO 4 2? trends at the 3 Ontario sites and a positive trend in Nova Scotia. A climatically-induced SO 4 2? increase in northwestern Ontario has been reversed. Mobilization and export of adsorbed SO 4 2? and/or reoxidized S from the basins of central Ontario sites is delaying their recovery. Two of our 9 stations (in Quebec and central Ontario) are continuing to acidify. The 2 Nova Scotia stations have the highest DOC levels and both exhibit a decreasing trend. Ionic compensation for declining SO 4 2? varies from station to station, sometimes involving an Alk increase, sometimes a base cation decrease, and sometimes more complex combinations. Additional factors (e.g. climatic variation) also influence variable trends, and data records longer than those presently available will be needed to unequivocally verify acidification recovery.  相似文献   

10.
Brine shrimp excystment, although highly resistant, is severely inhibited by mmolar mercuric chloride. The presence of 100 mmolar NaCl largely prevents the toxic response. The chloride effect can be explained if the toxic Hg species, neutral HgCl2, is converted into HgCl inf3 sup2? and HgCl inf4 sup2? since charged species not likely to penetrate cyst walls. Other Hg antagonists include SO in3 su2? , SeO inf3 sup2? , TeO inf3 sup2? and TeO inf4 sup2? , but not SO inf4 sup2? and SeO inf4 sup2? . The activity of both Te species can be explained by ready reduction of Te(VI) to Te(IV). Significant anti-mercurial effects were seen in mmolar thiols, ethionine and organoselenium compounds. Thiamine and methionine were both active Hg antagonists at 10 to 30 mmolar levels. The activities of S, Se and Cl? compounds show that both geochemical and physiological modes of defense against and adaptation to high Hg levels exist.  相似文献   

11.
In the Vosges Mountains (NE of France), integrated plot-catchment studies have been carried out since 1985 in the Strengbach basin to study the influence of acid atmospheric inputs on surface water quality and element budgets. In this paper, available mid-term time series (1985–1991) have been considered to detect obvious trends, if any, in surface water chemistry and element budgets. Air quality data showed a slight decline for SO2, whereas NO2 slightly increased over the period, but these trends are not very significant. This is in agreement with increased N concentration (mainly as NH 4 + ) and with the stability of SO 4 2? in open field precipitation. Because of a significant decrease in rainfall amount over the period, only inputs of NH 4 + increased significantly whereas H+ and SO 4 2+ inputs declined. In spring and streamwaters, pH and dissolved Si concentration increased mainly as a result of a reduced flow. Na+, K+, Cl? and HCO-3~? concentrations remained stable whereas Ca2+, Mg2+ and SO 4 2+ concentrations declined significantly. Only NO 3 ? concentration increased significantly in springwaters. The catchment budgets revealed significant losses of base cations, Si and SO 4 2? . These losses decreased over the period. Nitrogen was retained in the ecosystem. However, a longer record is needed to determine whether or not changes in surface water chemistry have resulted from short-term flow reductions or long-term changes in input-output ion budgets. This is specially true with N because the decline in SO 4 2? output was accompanied by N accumulation.  相似文献   

12.
The chemical composition of snowmelt, groundwater, and streamwater was monitored during the spring of 1991 and 1992 in a 200-ha subalpine catchment on the western flank of the Rocky Mountains near Steamboat Springs, Colorado. Most of the snowmelt occurred during a one-month period annually that began in mid-May 1991 and mid-April 1992. The average water quality characteristics of individual sampling sites (meltwater, streamwater, and groundwater) were similar in 1991 and 1992. The major ions in meltwater were differentially eluted from the snowpack, and meltwater was dominated by Ca2+, SO 4 2? , and NO 3 ? . Groundwater and streamwater were dominated by weathering products, including Ca2+, HCO 3 ? (measured as alkalinity), and SiO2, and their concentrations decreased as snowmelt progressed. One well had extremely high NO 3 ? . concentrations, which were balanced by Ca2+ concentrations. For this well, hydrogen ion was hypothesized to be generated from nitrification in overlying soils, and subsequently exchanged with other cations, particularly Ca2+. Solute concentrations in streamwater also decreased as snowmelt progressed. Variations in groundwater levels and solute concentrations indicate that most of the meltwater traveled through the surficial materials. A mass balance for 1992 indicated that the watershed retained H+, NH 4 + , NO 3 ? , SO 4 2? and Cl? and was the primary source of base cations and other weathering products. Proportionally more SO 4 2? was deposited with the unusually high summer rainfall in 1992 compared to that released from snowmelt, whereas NO 3 ? was higher in snowmelt and Cl? was the same. The sum of snowmelt and rainfall could account for greater than 90% of the H+ and NH 4 + retained by the watershed and greater than 50% of the NO 3 ? .  相似文献   

13.
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   

14.
The present work discusses the startup and operation of different biotrickling filters during the simultaneous removal of NH3, H2S, and ethyl mercaptan (EM) for odor control, focusing on (a) the impact of pH control in the stability of the nitrification processes during reactor startup and (b) the crossed effects among selected pollutants and their by-products. Two biotrickling filters were packed with poplar wood chips (R1 and R2A), while a third reactor was packed with polyurethane foam (R2B). R2A and R2B presented a pH control system, whereas R1 did not. Loads of 2?C10?g N?CNH3 m?3?h?1, 5?C16?g S?CH2S m?3?h?1, and 1?C6?g EM m?3?h?1 were supplied to the bioreactors. The presence of a pH control loop in R2A and R2B proved to be crucial to avoid long startup periods and bioreactors malfunctioning due to biological activity inhibition. In addition, the impact of the presence of different concentrations of a series of N species (NH 4 + , NO 2 ? , and NO 3 ? ) and S species (SO 4 2? and S2?) on the performance of the two biotrickling filters was studied by increasing their load to the reactors. Sulfide oxidation proved to be the most resilient process, since it was not affected in any of the experiments, while nitrification and EM removal were severely affected. In particular, the latter was affected by SO 4 2? and NO 2 ? , while nitrification was significantly affected by NH 4 + . The biotrickling filter packed with polyurethane foam was more sensitive to crossed effects than the biotrickling filter packed with poplar wood chips.  相似文献   

15.
A long-term hydrological and water chemistry research was conducted in three experimental microbasins differing in land cover: (1) a purely agricultural fertilized microbasin, (2) a forested microbasin dominated by Carpinus betulus (European hornbeam), and (3) a forested microbasin dominated by Picea abies (L.) (Norway spruce). The dissolved inorganic nitrogen (DIN: NH 4 + , NO 2 ? , NO 3 ? ) budget was examined for a period of 3 years (1991–1993). Mean annual loads of DIN along with sulfate SO 4 2? and base cations Ca2+, Mg2+, Na+, K+, and HCO 3 ? were calculated from ion concentrations measured in stream water, open-area rainfall, throughfall (under tree canopy), and streamwater at the outlets from the microbasins. Comparison of the net imported/exported loads showed that the amount of NO 3 ? leached from the agricultural microbasin is ～3.7 times higher (43.57 kg ha?1?a?1) than that from the spruce dominated microbasin (11.86 kg ha?1?a?1), which is a markedly higher export of NO 3 ? compared to the hornbeam dominated site. Our analyses showed that land cover (tree species) and land use practices (fertilization in agriculture) may actively affect the retention and export of nutrients from the microbasins, and have a pronounce impact on the quality of streamwater. Sulfate export exceeded atmospheric rainfall inputs (measured as wet deposition) in all three microbasins, suggesting an additional dry depositions of SO 4 2? and geologic weathering.  相似文献   

16.
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   

17.
The fluxes of N–NO 3 ? , N–NH 4 + , S–SO 4 2? , Na+, K+, Ca2+ and Mg2+ from bulk precipitation to throughfall, stemflow and soil water surface flows were studied during 1999–2003 in planted Norway spruce forest stands of different ages (11, 24, 91 and 116 years in 1999). Also, runoff from the corresponding Potok Dupniański Catchment in the Silesian Beskid Mts was studied. N deposition was above the critical load for coniferous trees. The interception increased with stand age as well as leaf area index and so did the leaching from the canopy of almost all the analysed elements, but especially S–SO 4 2? , H+ and K+. The nutrient fluxes varied with age of the spruce stands. Throughfall showed a high amount of S and of the strong acids (S–SO 4 2? and N–NO 3 ? ) deposited to the soil, especially in older spruce age classes. Decomposition of organic matter caused a rise in water acidity and an increase in the concentrations of all the analysed ions; the leaching of minerals, however, was low (under 1%). The horizontal soil water flow showed an increase in the amount of water and amount of ions and contributed to a further decrease of pH at the soil depth of 20 cm. Element concentrations and their amounts increased with water penetrating vertically and horizontally on the slopes. Considerable amounts of ions, especially S and alkaline cations, were carried beyond the reach of the root system and then left the catchment. In the long term, these mineral losses will adversely affect health and growth of the spruce stands, and the increased acidity with stand age will presumably have negative effects on the runoff water ecosystem.  相似文献   

18.
The Nandong Underground River System (NURS) is located in Southeast Yunnan Province, China. Groundwater in NURS plays a critical role in socio-economical development of the region. However, with the rapid increase of population in recent years, groundwater quality has degraded greatly. In this study, the analysis of 36 groundwater samples collected from springs in both rain and dry seasons shows significant spatial disparities and slight seasonal variations of major element concentrations in the groundwater. In addition, results from factor analysis indicate that NO 3 ? , Cl?, SO 4 2? , Na+, K+, and EC in the groundwater are mainly from the sources related to human activities while Ca2+, Mg2+, HCO 3 ? , and pH are primarily controlled by water–rock interactions in karst system with Ca2+ and HCO 3 ? somewhat from anthropogenic inputs. With the increased anthropogenic contaminations, the groundwater chemistry changes widely from Ca-HCO3 or Ca (Mg)-HCO3 type to Ca-Cl (+NO3) or Ca (Mg)-Cl (+NO3), and Ca-Cl (+NO3+SO4) or Ca (Mg)-Cl (+NO3+SO4) type. Concentrations of NO 3 ? , Cl?, SO 4 2? , Na+, and K+ generally show an indistinct grouping with respect to land use types, with very high concentrations observed in the groundwater from residential and agricultural areas. This suggests that those ions are mainly derived from sewage effluents and fertilizers. No specific land use control on the Mg2+ ion distribution is observed, suggesting Mg2+ is originated from natural dissolution of carbonate rocks. The distribution of Ca2+ and HCO 3 ? does not show any distinct land use control either, except for the samples from residential zones, suggesting the Ca2+ and HCO 3 - mainly come from both natural dissolution of carbonate rocks and sewage effluents.  相似文献   

19.
The effect of different anions on the balance of heavy metal cations in the soil-solution system has been assessed under model laboratory conditions. It has been found that the uptake of the Cu, Zn, and Pb cations by an ordinary chernozem from solutions of different salts is accompanied by the displacement of the exchangeable cations to the solution in the following order: Ca2+ > Mg2+ > Na+ > K+. The sum of the displaced exchangeable cations in most cases exceeds the amount of the adsorbed heavy metal cations. According to the effect of the anions on the displacing capacity of the metal cations, the following series are formed: for copper, SO 4 2? ? Cl? > OAc? > NO 3 ? ; for lead, Cl? ? NO 3 ? > OAc?; and, for zinc, SO 4 2? ? Cl? ? OAc? > NO 3 ? .  相似文献   

20.
The atmospheric deposition of air pollutants at a forest edge was studied by means of monitoring canopy throughfall at the edge and at five different parallel lines in the forest behind the edge. The investigation was carried out at a pine forest on the Swedish west coast. Throughfall and bulk deposition samples were analyzed for volume, SO 4 2? , NO 3 ? , Cl?, NH 4 + , Na+, K+, Mg2+, Ca2+, and for pH. The results show that the throughfall flow at the edge was increased substantially for most ions. The ratios in throughfall flows between the edge and the line 50 m into the forest were for SO 4 2? , 1.5, NO 3 ? 2.9, NH 4 + 2.7, and Na+ 3.1. Since this effect is not only valid for forest edges but also for hillsides, hilltops, and edges between stands of different age, etc., there might be substantial areas which get much larger total deposition than the normally considered closed forest.  相似文献   

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