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1.
High-elevation red spruce-Fraser fir forests in the Southern Appalachian mountains: 1) receive among the highest rates of atmospheric deposition measured in North America, 2) contain old-growth forests, 3) have shown declines in forest health, 4) have sustained high insect-caused fir mortality, and 5) contain poorly buffered soils and stream systems. High rates of nitrogen and sulphur deposition (1900 and 2200 Eq·ha–1·yr–1, respectively) are dominated by dry and cloud deposition processes. Large leaching fluxes of nitrate-nitrogen (100–1400 Eq·ha–1·yr–1) occur within the soil profile. We have expanded the study to the watershed scale with monitoring of: precipitation, throughfall, stream hydrology, and stream chemistry. Two streamlets drain the 17.4 ha Noland Divide Watershed (1676–1920m) located in the Great Smoky Mountains National Park. A network of 50 20x20 m plots is being used to assess stand structure, biomass, and soil nutrient pools. Nitrate is the predominant anion in the streamlets (weighted concentrations: 47 and 54 eq·L–1 NO3 –; 31 and 43 eq·L–1 SO4 2–). Watershed nitrate export is extremely high (1000 Eq·ha–1 yr–1), facilitating significant base cation exports. Stream acid neutralizing capacity values are extremely low (–10 to 20 eq·L–1) and episodic acidifications (pH declines of a full unit in days or weeks time) occur. Annual streamwater sulfate export is on the order of 770 Eq·ha–1yr–1 or about one-third of total annual inputs, indicating there is net watershed sulfate retention. The system is highly nitrogen saturated (Stage 2, Stoddard, 1994) and this condition promotes both chronic and episodic stream acidification.  相似文献   

2.
A spatial and temporal investigation of dissolved inorganic nitrogen (DIN; NO3, NO2 and NH4) was conducted under various water discharge conditions in Lanyang-Hsi, a subtropical mountainous stream, which drains through distinct degrees of agriculture-influenced sub-watersheds. In both the cultivated and non-cultivated sub-watersheds, NO3 was the most abundant species accounting for >80% of total DIN, while NH4 and NO2 accounted for <15% and=" 5%=" of=" din,=" respectively.=" agricultural=" activities=" along=" the=" riverbank=" led=" to=" significantly=" higher=">3 concentrations (13–246 M) and DIN yields (1300–3800 kg N km–2 yr–1) in main channel when compared to those of non-cultivated tributaries (9–38 M for NO3 and 550–740 kg N km–2 yr–1 for yield). The much lower and less variable DIN yields observed in tributary stations (mean = 660 ± 120 kg N km–2 yr–1) are considered as the present day background of DIN yield, which is significantly higher than those of most natural watersheds in other regions. Elevated atmospheric DIN deposition is likely the cause for the high background DIN yield. Human activity within the watershed results in additional DIN yield, which accounted for 49% of total N export. However, the reported atmospheric DIN input in northern Taiwan (1800 kg N km–2 yr–1) is much higher than the background DIN yield implying that a major fraction (70%) of atmospheric inputs are retained or processed within the watershed. A dilution pattern occurred in the main channel where high NO3 concentrations from the upstream sources decreased significantly in downstream direction due to inputs of NO3-diluted water from non-cultivated areas. We adopted a two-source mixing model to predict the NO3 dilution pattern. This model revealed a third yet not recognized N source in the lower part of watershed. Model results also indicated the importance of water discharge rate in regulating the relative contribution to total DIN export among these sources.  相似文献   

3.
One of the major threats to the structure and the functioning of natural and semi-natural ecosystems is the recent increase in air-borne nitrogen pollution (NHy and NOx). Ecological effects of increased N supply are reviewed with respect to changes in vegetation and fauna in terrestrial and aquatic natural and semi-natural ecosystems. Observed and validated changes using data of field surveys, experimental studies or, of dynamic ecosystem models (the empirical approach), are used as an indication for the impacts of N deposition. Based upon these data N critical loads are set with an indication of the reliability. Critical loads are given within a range per ecosystem, because of spatial differences in ecosystems. The following groups of ecosystems have been treated: softwater lakes, wetlands & bogs, species-rich grasslands, heathlands and forests. In this paper the effects of N deposition on softwater lakes have been discussed in detail and a summary of the N critical loads for all groups of ecosystems is presented. The nitrogen critical load for the most sensitive ecosystems (softwater lakes, ombrotrophic bogs) is between 5–10 kg N ha–1 yr–1, whereas a more average value for the range of studied ecosystems is 15–20 kg N ha–1 yr–1. Finally, major gaps in knowledge with respect to N critical loads are identified.  相似文献   

4.
The SO2 emissions from the Kola Peninsula in Arctic Russia (totalling around 600 Gg(SO2) yr–1 at the beginning of the 1990s) produce an atmospheric SO2 concentration gradient to the northernmost Europe. This gradient covers the range from >50 g m–3 in the vicinity of the sources to 1 g m–3 in Finnish Lapland. In the present study, the measured sulphur concentrations in Scots pine needles were compared with the estimated distribution of atmospheric SO2. The total sulphur concentrations in the needles ranged from 741 to 2017 mg kg–1. Strongly elevated concentrations (> 1200 mg kg–1) were found within 40 km from the smelters corresponding to an area where the annual mean atmospheric SO2 concentration exceeded 10 g m–3. The foliar sulphur concentrations (total, organic and inorganic) show a high correlation with the estimated mean SO2 concentration distribution in the air. Consequently the foliar sulphur concentrations reflected the atmospheric sulphur load well. The data presented here show that uptake via stomata is an important deposition pathway also in the arctic conditions with a short growing season.  相似文献   

5.
The critical load concept is now accepted throughout Europe as a means of estimating the sensitivity of key components of aquatic and terrestrial ecosystems to atmospheric inputs of sulphur (S) and nitrogen (N). Current UK freshwater maps, based on steady-state water chemistry, are derived using a critical acid neutralising capacity (ANCLIM) value of zero eql–1, which is based on the probability of occurrence of salmonid fish in lakes. In practice most acidification damage to salmonid fish occurs in nursery streams at the emergence and first feeding stages. In general a clear relationship exists between salmon (Salmo salar L.) and trout (S. trutta L.) densities in Scottish streams and ANC values. However, differences between sites depend on which ANC value is used (eg maximum, minimum or mean). By contrast, when the exceedance of critical loads is compared with salmonid densities the relationship is less clear because many exceeded sites have good salmonid densities. Many of these latter sites are found in north-west Scotland where sea-salt inputs are high and ANC is usually greater than zero eql–1, although diatom-based studies indicated slight acidification of these waters, with a point of change in diatom flora close to ANC=20 eql–1. These false exceedances are probably due to preferential adsorption of acidic SO4 deposition which results in an overestimate of exceedance values. All sites with a mean ANC 0 are fishless but some sites with negative minimum ANC values had normal salmonid densities. Consequently a mean ANCLIM value of zero in the critical load equations for UK freshwaters appears to be too low to protect salmonid stocks. Values between 20–50 eql–1 represent a more realistic range if prevention of long term damage to salmonid stocks is to be achieved.  相似文献   

6.
The influence of light intensity on the effects of 10–6 mol L–1 99Tc on growth, chlorophyll and carotenoid contents of bush bean plants was investigated. After germination and cotyledon excision, the plants were grown in a growth chamber either under low light (photosynthetic active radiation, PAR 144 E m–2 s–1) or higher light (PAR 307 E M–2 s–1) conditions. In plants grown under the higher light conditions, 99Tc hardly affected CO2-assimilation, dark respiration, pigment contents and growth. No toxicity symptoms were observed in these plants. Under low light conditions, 99T c significantly decreased growth and the concentration of chlorophylls. Toxicity symptoms in the form of chlorosis and necrosis developed. Transmission electron microscopy (TEM) observations revealed alterations of chloroplast ultrastructure comparable to those described for plants slightly affected by paraquat toxicity or by Mo-deficiency. Our results indicate that in the low light plants 99Tc induces damage in chloroplasts by peroxidation of membrane lipids.  相似文献   

7.
The surface ozone (O3) data show an increase by 2.6 % per year during the period 1982–1994 at the rural site of Lithuania. WHO (World Health Organization), UN-ECE (United Nations Economic Commission for Europe), CES (Commission of the European Communities) guideline values for the protection of vegetation from adverse effects are exceeded during the growing season at the Preila coastal station. Ozone exposures for different concentration threshold are estimated during daylight hours in April-September. These values above 60 g/m3 varied between 10 000 and 43 000 (g/m3) ·h, above 80 g/m3 — between 1700 and 15 000 (g/m3) ·h, above 100 g/m3 — between 130 and 3700 (g/m3) ·h during separate years. Maximum hourly ozone values were observed from 116 to 228 g/m3 during this period.  相似文献   

8.
Precipitation chemistry at sinhagad-a hill station in India   总被引：1，自引：0，他引：1  
The chemistry of precipitation in remote sites such as mountain tops is of interest in the study of atmospheric pollution and acid rain. The chemical composition measured at mountain site which is away from industrial and urban areas is useful as a reference level and it allows to determine the extent of anthropogenic contamination. Hence, rain water samples were collected at Sinhagad (18°21N, 73°45E, 1450 m asl during the monsoon season (June-September) of 1992 and were analysed for major ions. The precipitation samples collected at Sinhagad were alkaline in nature and pH values ranged between 5.9 to 6.76. The ionic composition was dominated by soil dust The concentration of Ca2+ was highest among all the ions. The concentrations of excess SO3 2– and NO4 – were small (23.8 and 15.2 eq l–1 respectively) compared to the values of polluted regions in India. The correlation coefficient between the ions and pH values was calculated and it was found to be maximum in case of Ca2+. Precipitation samples collected at Sinhagad were alkaline owing to higher concentration of Ca2+ and lower levels of acidic pollutants (SO4 2– and NO3 –).  相似文献   

9.
In laboratory adsorption experiments, the comparison of podzol Bs horizons from coastal and inland moderately-impacted catchments with those from a severely-acidified inland region has demonstrated the effect of marine inputs on SO4 2– -retention. Moderate sea-salt inputs and low acid deposition leads to the retention of most of the SO4 2– and the release of soluble Mg2+; increasing the marine salt loading causes the development of a selectivity towards retention of acidic SO4 2– and the retention of Mg2+. In the highly-impacted soil, the marine input caused a decrease in SO4 2– retention in open moorland soils. The opposite occurred under forest, due to the ion-exchange of marine Mg2+ for soil Al3+, increasing soil acidity towards the pH0 (Gillman and Uehara, 1980), which is depressed below that of its moorland equivalent.  相似文献   

10.
Field studies using open-top chambers were conducted at USDA-BARC involving the growth of soybeans ('89 & '90), wheat ('91 & '92), and corn ('91), under increased concentrations of atmospheric CO2 and O3. Treatment responses were compared in all cases to plants grown in charcoal-filtered (CF) air (seasonal 7-h mean = 25±3 n mol O3 mol–1) having 350 or 500 mol CO2 mol–1. Elevated seasonal O3 levels for the soybean, wheat, and corn studies averaged 72.2±4, 62.7±2, and 70.2 n mol O3 mol–1, respectively. Results presented were obtained for plants grown in silt loam soil under well-watered conditions. Grain yield increases in response to elevated CO2 in the absence of O3 stress averaged 9.0, 12.0, and 1.0% for soybean, wheat, and corn; respectively. Reductions in grain yields in response to the elevated O3 treatments at 350 mol CO, mol–1 averaged 20.0, 29.0 and 13.0% for soybean, wheat, and corn, respectively. Reductions in grain yields in response to elevated O3 at 500 mol CO2 mol–1 averaged 20.0, 8.0, and 7.0% for soybean, wheat, and corn, respectively. Dry biomass and harvest index in wheat were significantly reduced by O3 stress at 350 mol mol 1 CO2 but not at 500 u mol mol–1 CO2. Seed weight 1000–1 for scybeans and wheat was significantly increased by CO2 enrichment and decreased by O3 stress. Seed weight 1000–1 in corn was increased by O3 stress suggesting that O3 affected pollination resulting in fewer kernels per ear.Scientific Article No. A7784, Contribution No. 9105, Maryland Agric. Exp. Sta., Univ. of MD, College Park, MD 20472  相似文献   

11.
Concentrations of CH4, a potent greenhouse gas, have been increasing in the atmosphere at the rate of 1% per year. The objective of these laboratory studies was to measure the effect of different forms of inorganic N and various N-transformation inhibitors on CH4 oxidation in soil. NH 4 + oxidation was also measured in the presence of the inhibitors to determine whether they had differential activity with respect to CH4 and NH 4 + oxidation. The addition of NH4Cl at 25 g N g-1 soil strongly inhibited (78–89%) CH4 oxidation in the surface layer (0–15 cm) of a fine sandy loam and a sandy clay loam (native shortgrass prairie soils). The nitrification inhibitor nitrapyrin (5 g g-1 soil) inhibited CH4 oxidation as effectively as did NH4Cl in the fine sandy loam (82–89%), but less effectively in the sandy clay loam (52–66%). Acetylene (5 mol mol-1 in soil headspace) had a strong (76–100%) inhibitory effect on CH4 consumption in both soils. The phosphoroamide (urease inhibitor) N-(n-butyl) thiophosphoric triamide (NBPT) showed strong inhibition of CH4 consumption at 25 g g-1 soil in the fine sandy loam (83%) in the sandy clay loam (60%), but NH 4 + oxidation inhibition was weak in both soils (13–17%). The discovery that the urease inhibitor NBPT inhibits CH4 oxidation was unexpected, and the mechanism involved is unknown.  相似文献   

12.
Summary Field studies of the effects of different N fertilizers on emission of nitrous oxide (N20) from three Iowa soils showed that the N2O emissions induced by application of 180 kg ha–1 fertilizer N as anhydrous ammonia greatly exceeded those induced by application of the same amount of fertilizer N as aqueous ammonia or urea. On average, the emission of N2O-N induced by anhydrous ammonia was more than 13 times that induced by aqueous ammonia or urea and represented 1.2% of the anhydrous ammonia N applied. Experiments with one soil showed that the N2O emission induced by anhydrous ammonia was more than 17 times that induced by the same amount of N as calcium nitrate. These findings confirm indications from previous work that anhydrous ammonia has a much greater effect on emission of N2O from soils than do other commonly used N fertilizers and merits special attention in research relating to the potential adverse climatic effect of N fertilization of soils.Laboratory studies of the effect of different amounts of NH4OH on emission of N2O from Webster soil showed that the emission of N2O-N induced by addition of 100 g NH4OH-N g–1 soil represented only 0.18% of the N applied, whereas the emissions induced by additions of 500 and 1 000 g NH4OH-N g–1 soil represented 1.15% and 1.19%, respectively, of the N applied. This suggests that the exceptionally large emissions of N2O induced by anhydrous ammonia fertilization are due, at least in part, to the fact that the customary method of applying this fertilizer by injection into soil produces highly alkaline soil zones of high ammonium-N concentration that do not occur when urea or aqueous ammonia fertilizers are broadcast and incorporated into soil.  相似文献   

13.
Carbon and nitrogen budgets of nematodes in arable soil   总被引：2，自引：0，他引：2  
Summary The amounts of C and N that pass through the nematode biomass in four cropping systems, barley without and with N fertilization, grass ley and lucerne, has been estimated. The nematodes were sampled at the field site of a Swedish integrated research project Ecology of Arable Land: The Role of Organisms in Nitrogen Cycling. The nematode biomass was lower (200 mg dry weight m–2) in the annual (barley) than in the perennial (grass and lucerne, 350 mg dry weight m–2) crops. For respiration, the nematodes used 4–71 O2m–2 year–1 corresponding to C liberation of 1.3%–2.0% of the carbon input to the soil. A higher relative contribution by bacterial-feeding nematodes to the C and N fluxes and a higher turnover rate of the nematode biomass is an indication of more rapid nutrient circulation in the annual than in the perennial cropping systems.  相似文献   

14.
We investigated the effects of Topogard 50 WP (3 kg ha–1) on soil respiration, mineral N content, and number of denitrifying and total bacteria in four coarse-textured volcanic soils for 91 days. Topogard application decreased CO2 evolution in acid soils (Tepedibi and Karaçakl) whereas soil respiration was initially increased in neutral and alkaline soils (Kaba and Balar). The herbicide application significantly stimulated ammonification in Kaba and Balar soils, while Tepedibi and Karaçakl soils showed significantly lower NH4+-N contents than the control. The treatment inhibited the activity of nitrifying microorganisms and, thus it decreased the NO3–-N content in Tepedibi, Karaçakl, and Kaba soils, whereas the NO3–-N content was increased in Balar soil. The NO2–-N content of soils was not affected by the treatment. The activity of denitrifying bacteria was stimulated by the addition of herbicide in all soils, whereas the total number of bacteria was not influenced. It may be concluded that the effects of Topogard on the microbiological characteristics of coarse-textured soils are likely to be dependent on soil pH.  相似文献   

15.
Summary A 2-year study (1983–1984 to 1984–1985) was conducted to estimate temporal and seasonal changes and the effects of fertiliser on some soil chemical, biochemical and microbiological characteristics. The soil used was a Typic Vitrandept under grazed pasture. Soil samples were taken regularly to a depth of 75 mm from paired unfertilised and fertilised (500 kg ha– 30% potassic superphosphate) plots. Except for organic C, fertiliser had little or no effect on the characteristics measured. Organic C averaged about 9.2% in unfertilised soil and was about 0.3% higher in the fertilised soil. The size of the microbial biomass fluctuated widely in the 1st year (3000 g C g–1 in February to 1300 g C g–1 in September) but there was less variation in the 2nd year (range 1900 g C g–1 to 2500 g C g–1 soil). CO2 production values (10- to 20-day estimates averaged 600 g of CO2-C g–1 soil) were generally higher in spring compared to the rest of the year. Water extractable C increased over winter and declined through spring in both years (range 50 g C g–1 soil to 150 g C g–1 soil). Mineral-N flush values were higher in summer (300 g N g–1 soil) and lower in winter months (200 g N g–1 soil). The pattern of variation of microbial N values was one of gradual accumulation followed by rapid decline. This rapid decline in values occurred in spring and autumn (range 130–220 g N g–1 soil). N mineralisation and bicarbonate-extractable N showed no clear trend; these values ranged from 100–200 and 122–190 g N g–1 soil, respectively. There was a significant correlation (0.1%) between N mineralisation and bicarbonate-extractable N in the late summer-autumn-early winter period (February–August) in both years but not in spring. These results and their relationships to climatic factors and rates of pasture production are discussed.  相似文献   

16.
Precipitation chemistry in Japan was discussed on a wet-only sample database obtained in a nationwide survey from April 1989 to March 1993. Wet-only samples were collected at 29 stations over Japan on a biweekly basis. Commonly determined chemical parameters were measured in laboratories. The volume-weighted annual mean pH at each site ranged from 4.50 to 5.83 with a mean of 4.76. Concentration ranges and means (parenthesized) on an equivalent basis for major ions were as follows: nss-SO4 2–; 5.2–58.9 (38.6), NO3 –; 1.8–25.0 (14.1), NH4 +; 0.55–29.8 (18.3), nss-Ca2+; 2.0–34.5(14.2), Na+; 6.4–275.3 (49.1), Cl–; 13.7–322.4 (63.5) eq L–1. Acid-base relationships for Phase-II records were quantitatively discussed in terms of three measures: pH, fractional acidity, and our proposed pAi.  相似文献   

17.
The Lysina catchment in the Czech Republic was studied to investigate the biogeochemical response of Al to high loadings of acidic deposition. The catchment supports Norway spruce plantations and is underlain by granite and podzolic soil. Atmospheric deposition to the site was characterized by high H+ and SO4 2– fluxes in throughfall. The volume-weighted average concentration of total Al (Alt) was 28 mol L–1 in the O horizon soil solution. About 50% of Alt in the O horizon was in the form of potentially-toxic inorganic monomeric Al (Ali). In the E horizon, Alt increased to 71 mol L–1, and Ali comprised 80% of Alt. The concentration of Alt (120 mol L–1) and the fraction of Ali (85%) increased in the lower mineral soil due to increases in Ali and decreases in organic monomeric Al (Alo). Shallow ground water was less acidic and had lower Alt concentration (29 mol L–1). The volume-weighted average concentration of Alt was extremely high in stream water (60 mol L–1) with Ali accounting for about 60% of Alt. The major species of Ali in stream water were fluorocomplexes (Al-F) and aquo Al3+. Soil solutions in the root zone were undersaturated with respect to all Al-bearing mineral phases. However, stream water exhibited Ali concentrations close to solubility with jurbanite. Acidic waters and elevated Al concentrations reflected the limited supply of basic cations on the soil exchange complex and slow weathering, which was unable to neutralize atmospheric inputs of strong acids.  相似文献   

18.
Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl–, NO3 – and SO4 2– were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a first-flush effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.  相似文献   

19.
Summary The influence of soil moisture on denitrification and aerobic respiration was studied in a mull rendzina soil. N2O formation did not occur below –30 kPa matric water potential (m), above 0.28 air-filled porosity (a) and below 0.55 fractional water saturation (v/PV volumetric water content/total pore volume). Half maximum rates of N2O production and O2 consumption were obtained between m = –1.2 and –12 kPa,a = 0.05 and 0.23, and v/PV = 0.63 and 0.92. No oxygen consumption was measured at v/PC 1.17. O2 uptake and denitrification occurred simultaneously arounda = 0.10 (at m = –10 kPa and v/PV = 0.81) at mean rates of 3.5 µl O2 and 0.3 µl N2 h–1g–1 soil. Undisturbed, field-moist soil saturated with nitrate solution showed constant consumption and production rates, respectively, of 0.6 µl O and 0.22 µl N2O h–1g–1 soil, whereas the rates of air-dried remoistened soil were at least 10 times these values. The highest rates obtained in remoistened soil amended with glucose and nitrate were 130 µl O2 and 27 µl N2O h–1g–1 soil.  相似文献   

20.
The ionic composition of 55 aerosol samples and 31 precipitation events collected in a coastal site in southern Sardinia (Capo Carbonara, 39°06 N; 09°31 E) were compared. The samples were collected during one year period (Oct'90/Oct'91) and showed high variability in composition according to meteorological conditions. Rain and soluble part of aerosol showed a strikingly similar ionic composition: most significant anions were chlorine and sulphate, and sodium is the principal cations, followed by magnesium and calcium. The acid events are associated with N-NW trajectories (anthropogenic influxes from N. Europe) with avg. pH=4.65, non sea salt (nss) Ca=60 eq/l and NO3/nssSO4=0.6. Southern precipitations are influenced by Saharan dust alkaline effects, with avg. pH=6.75,nssCa=271 eq/l and NO3/nssSO4=0.4. Na/Cl ratio in rain is similar to sea water (0.87), whilst in aerosols there is a Cl loss (Na/Cl=1.10), probably due to reaction with nitric acid. Total fluxes of Ca, Mg, NO3 and SO4 were 104, 9, 64 and 113 g/cm2, and wet deposition exceeded (65–90%) dry deposition. Scavenging ratios (SR) as defined by the equation:SR=[(Ci)rain/(Ci)air] *d, (d=1200g/m3) were calculated, using geometric means (Ci) of precipitation and aerosols collected concurrently during the period (a total of 23 samples). The SR values are Ca=3400, Cl=2400, Na, K, SO4=1700, Mg=1000 and NO3=750. These numbers could be useful to infer total fluxes by using simply rainwater ionic composition in Mediterranean semi-arid sites like Sardinia.  相似文献   

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