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Acidity and chemistry of bulk precipitation, throughfall and stemflow in a Chinese fir plantation in Fujian, China
Forest Ecology and Management 122 (1999) 243±248
Acidity and chemistry of bulk precipitation, throughfall and stem¯ow in a Chinese ®r plantation in Fujian, China Fan HouBaoa,*, Hong Weia, Ma Zhuanga, Waki Kosukeb a
Department of Resources and Environment, Fujian Forestry College, Nanping 353001, China b Japan International Forestry Promotion and Corporation Center, Tokyo, Japan Received 19 May 1998; accepted 2 December 1998
Abstract Acidity and chemistry of open and intercepted precipitation in a Chinese ®r plantation in Fujian, China, were monitored at two sites located at varying distances from the SO2 sources. Acidi®cation and chemical enrichment were observed to be extremely signi®cant for stem¯ow, but only slightly for throughfall. The pH values for rainfall showed some seasonal patterns. In contrast, the electric conductivity and chemical components showed a strong seasonal trend over the three-year period, which were supposed to be negatively correlated with the amount of rainfall. Differences in pH values between two sites suggested the acidifying effects of sulfur dioxide on precipitation. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Acidity; Electric conductivity; Bulk precipitation; Throughfall; Stem¯ow
1. Introduction Large-scale industrialization came late to China, not really until the late 70s of this century. However, coal, with an average sulfur content of 1.12%, is used at present as the most important fuel resource which occupies more than 20% of the total coal consumption in the world (Zhang et al., 1991; Wang et al., 1996). Annual discharges of SO2 and NOx into the atmosphere in 1990 were estimated to be ca. 17.52 106 t and 8.42 106 t, respectively, and the annual emitted SO2 is expected to reach 27 106 t by 2000 unless more ef®cient control measures are employed (Wang
*Corresponding author. Tel.: +86-599-8501271; fax: +86-5998508194/8508702; e-mail: [email protected]
et al., 1996; Zhou et al., 1996). Acidity in precipitation has increased considerably in South China over the last decade, and it was observed that precipitation hydrogen-ion content was 80±90% due to sulfuric acid as caused by sulfur dioxide (Yang, 1989; Fan, 1993). Acceleration of foliar nutrient leaching is an important impact of acid precipitation on forest ecosystem (Likens et al., 1972; Smith, 1981). Precipitation chemistry was remarkably altered upon passage through forest canopies (Eaton et al., 1973; Potter et al., 1991). The washout of dry deposition by precipitation may add acidifying inputs to ecosystems, and contribute signi®cant amount of certain elements to the forest ¯oor (Lovett and Lindberg, 1984). Accelerated plant leaching may also alter the processes of nutrient cycling in forest ecosystems and result in physiolo-
0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 9 ) 0 0 0 1 1 - 0
244
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
gical stress (Wood and Bormann, 1975; Lovett et al., 1985). In 1993, a project, sponsored by Japan International Forestry Promotion and Cooperation Center, was established in Fujian, China, to monitor the potential damage of acid rain and air pollution to forest ecosystems. The purpose of this paper is to report the temporal and spatial changes in acidity and chemistry of bulk precipitation, throughfall and stem¯ow monitored from the past three years (1994±1996). 2. Methods In August 1993, two monitoring sites were established in a Chinese ®r plantation (Cunninghamia lanceolata Hook.) in Nanping, Fujian. One site is located in the Experimental Forest of Fujian Forestry College, ca. 13 km from Nanping, referred to as FFC site (268330 N, 1188060 E).The other site is located in Xiqin Experimental Forest Farm, 10 km from Nanping and near Xiqin Town where a small-scaled paper mill is located, and referred to as Xiqin site (268340 N, 1188050 E). Each site was composed of a 1000 m2 monitoring plot and surrounded by a continuous forest vegetation area. Each plot was equipped with three throughfall gauges and three stem¯ow traps which were set ca. 1.3 m above the ground level. A rainfall gauge was set in open place out of each monitoring site, which has an area of ca. 800 m2 and 580 m away from the edge of FFC site, and of ca. 1000 m2 and 660 m from Xiqin site. Precipitation collections were made daily at 9 : 00 throughout the monitoring period. All samples were analysed for pH and EC in the ®eld and, subsequently after ®ltration in laboratory. There were no signi®cant differences between the two sets of measurements, so the measurements made in the ®eld were used in this paper. Measurements for pH and EC were carried out by D-14 pH meter and ES-14 EC meter, respectively. The samples collected from the ®rst precipitation event in each month were ®ltered and stored in a refrigerator for chemical analysis. Cation analysis (k, Na, Ca2, Mg2) were completed by AA-670 atomic absorption spectrophotometer. Ammonium was determined by an alkaline phenolhypochlorite method, and sulfate by barium chloride turbidometric method.
3. Results and discussions The weighted monthly pH values for rainfall, throughfall, and stem¯ow from the two sites are shown in Fig. 1. Throughfall was observed to be slightly acidi®ed as compared to open rainfall at two sites. Within any sampling date, there was a positive relationship in pH values between rainfall and throughfall. The pH of stem¯ow was consistently much lower than rainfall and throughfall, with pH values ranging between 3.08 and 5.60 (excluding one irregular extreme value of 6.57) at FFC site, and between 2.80 and 5.58 at Xiqin site. The seasonal variation in rainfall pH shows similar pattern over the three-year period (Fig. 1). The pH values are usually minimal in summer months, intermediate in spring, and maximal in fall or winter. Based on three years of data (1994±1996), the median pH for rainfall is estimated to be 6.25 at FFC site, which is greater than that (5.95) at Xiqin site. Extremely lower median pH values are found for stem¯ow, with 4.00 at FFC site, and 3.20 at Xiqin site. The values of electric conductivity (EC) show a wide ¯uctuation over the monitoring period. The highest values consistently occurred in November or December, and the lowest was usually observed in summer months (Fig. 2). The coef®cients of variation for pH values are all <10%, indicating lower temporal variability for precipitation acidity, especially for throughfall (Table 1). The EC values, however, show great ¯uctuation with coef®cients of variation ranging from 59.78%, for stem¯ow at Xiqin site, to 137.44% for rainfall at FFC site. The neutralization components (k, Na, Ca2, Mg2, NH4) and sulfate show a strong seasonal pattern approximately identical to that for conductivity (Figs. 3 and 4). Actually the relationships between EC values and concentrations of the total measured ions in precipitation can be expressed by the following linear regression equations: at FFC site RF 18:992 0:077EC;
r 0:949
TF 40:627 0:057EC;
r 0:954
SF ÿ19:120 0:075EC;
r 0:910
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
245
Fig. 1. Seasonal patterns in monthly average pH values of precipitation and amount of monthly precipitation at two sites (RFRainfall; TFThroughfall; SFStemflow; APAmount of precipitation). Table 1 The annual mean values of pH and EC (m/cm) for the precipitation from two sites. The calculations are based on three years of data (1994± 1996) Factor
Parameter
FFC site RF (n 274)
a
Xiqin site TF (n 273)
SF (n 270)
RF (n 255)
TF (n 253)
SF (n 243)
pH
Mean SE b CV c (%)
6.31 0.04 9.63
6.26 0.03 6.79
4.14 0.02 8.30
6.00 0.03 8.75
5.77 0.03 7.62
3.33 0.02 7.96
EC
Mean a SE b CV c (%)
45.33 3.76 137.44
110.43 6.36 95.15
276.14 12.49 74.30
47.34 3.23 108.96
95.14 5.82 97.34
557.53 21.38 59.78
a
The arithmetic mean value. Standard error. c Coefficient of variation. b
246
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
Fig. 2. Seasonal trends (1994±1996) in weighted monthly EC values of precipitation from two sites (RFRainfall; TFThroughfall; SFStemflow).
at Xiqin site RF 11:461 0:078EC;
r 0:959
TF 8:181 0:066EC;
r 0:956
SF 128:388 0:068EC;
r 0:805
where RF, TF and SF represent the concentrations of total measured ions in rainfall, throughfall and stemflow, respectively. Close relationships (p < 0.01) between these two measurements suggest EC is significantly ion-dependent.
The differences in acidity and chemistry for precipitation between two sites may be due to location. The FFC site is less affected by human activities, while Xiqin site is near a paper mill and the roads. Actually the distribution of acid rain in southern China displays strong local in¯uences, precipitation with pH of <5.6 is primarily con®ned to urban areas with high sulfur dioxide pollution (Xu and Hao, 1990). Sulfur dioxide, through chemical transformations and atmospheric scavenging, is considered to be the major contribution to the precipitation acidity in China
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
Fig. 3. Seasonal trends (1995±1996) of neutralization components (K, Na, Ca2, Mg2, NH 4 in precipitation from two sites (RFRainfall; TFThroughfall; SFStemflow).
(Yang, 1989). Lack of correlation between pH and sulfate in this paper may, in part, be due to the limited chemical data for precipitation. There was also a possibility that lower pH values in throughfall and especially stem¯ow during the summer time may be caused by organic acids, such as carboxylic acids, which was not monitored in this project. The third
247
possible explanation may be that contamination and aging, such as nitri®cation, of rainwater samples may have occurred during the storage period, especially in summer, which will increase the acidity. Further research is needed in the future to determine the exact relationships between pH and acid-forming components. The greater ion concentrations in fall or winter are supposed to be the result of less precipitation volume and longer time intervals between two rain events during this period. Dilution by greater volume in summer, however, decreases the ion concentrations (see Fig. 1). Remarkable acidi®cation and nutrient enrichment for rainwater ¯owing down the inert bark surfaces reveal that a larger part of the chemicals added to intercepted precipitation is derived from dry deposition than from leached metabolites. The SO42ÿ data indicate that throughfall and stem¯ow is enriched with SO42ÿ from dry deposition of ¯y ash and dust. Sulfate particles increase the SO42ÿ concentration, but since ¯y ash is alkaline, pH in stem¯ow and throughfall may increase in winter, when emission is the greatest. The same conclusion was proposed in a previous study conducted in Norway (Abrahamsen et al., 1976). Actually the pH of tree bark, especially that with a rough surface texture such as Chinese ®r, was considered to be a sensitive indicator of regional pollution (Grodzinska, 1976; Fan, 1996). Acknowledgements This work was sponsored by Japan International Forestry Promotion and Cooperation Center (JIFPRO).
References
Fig. 4. Seasonal trends (1995±1996) of concentrations of sulfate in precipitation from two sites (RFRainfall; TFThroughfall; SFStemflow).
Abrahamsen, G., Horntvedt, R., Tveite, B., 1976. Impacts of acid precipitation on coniferous forest ecosystems. In: Dochinger, L.S., Seliga, T.A. (Eds.), Proc. Ist Internat. Symp. Acid Precipitation and the Forest Ecosystem. U.S.D.A. Forest Service, Gen. Tech. Rep. No. NE-23, Upper Darby, Pennsylvania, pp. 991±1009. Eaton, J.S., Likens, G.E., Bormann, F.H., 1973. Throughfall and stemflow and stemflow chemistry in a northern hardwood forest. Journal of Ecology 61, 495±508.
248
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
Fan, B.T., 1993. Environmental chemistry. Zhejiang University Press, Hongzhou, China, pp. 558 (in Chinese). Fan, H.B., 1996. Tree bark: An indicator of air pollution and precipitation acidity. Journal of Zhejiang Forestry College 13, 136±140 (Chinese with English abstract). Grodzinska, K., 1976. Acidity of tree bark as a bioindicator of forest pollution in southern Poland. In: Dochinger, L.S., Seliga, T.A. (Eds.), Proc. Ist Internat. Symp. Acid Precipitation and the Forest Ecosystem. U.S.D.A. Forest Service, Gen. Tech. Rep. No. NE-23, Upper Darby, Pennsylvania, pp. 905±911. Likens, G.E., Bormann, F.H., Johnson, N.M., 1972. Acid rain. Environment 14, 33±40. Lovett, G.M., Lindberg, S.E., 1984. Dry deposition and canopy exchange in a mixed oak forest as determined by analysis of throughfall. Journal of Applied Ecology 21, 1013±1028. Lovett, G.M., Lindberg, S.E., Richter, D.D., Johnson, D.W., 1985. The effects of acidic deposition on cation leaching from a deciduous forest canopy. Canadian Journal of Forest Research 15, 1055±1060. Potter, C.S., Ragsdale, H.L., Swank, W.T., 1991. Atmospheric deposition and foliar leaching in a regenerating southern Appalachian forest canopy. Journal of Ecology 79, 97±115.
Smith, W.H., 1981. Air pollution and forest: Interactions between air contaminants and forest ecosystems. Springer-Verlag, New York, pp. 379. Wang, W.X., Wang, W., Zhang, W.H., Hong, S.X., 1996. Geographical distribution of SO2 and NOx emission intensities and trends in China. China Environmental Science 16, pp. 162± 167 (Chinese with English abstract). Wood, T., Bormann, F.H., 1975. Increases of foliar leaching caused by acidification of an artificial mist Ambio 4, pp. 169±171. Xu, F.K., Hao, J.M., 1990. A review on the present situation of acid rain in China and establishment of countermeasures. Environmental Science 11, pp. 61±66 (in Chinese). Yang, H.X. (Ed.), 1989. Acid rain and agriculture. China Forestry Press, Beijing, pp. 191 (in Chinese). Zhang, H.Q., Zao, X.D., Wang, Q.L., 1991. Energy structure in China and atmospheric environmental pollution. Research of Environmental Sciences 4, pp. 50±54 (Chinese with English abstract). Zhou, X.L., Hao, J.M., Fu, L.X., Li, Q.L., 1996. Sulfuric deposition modelling research in the east part of China (Model application. China Environmental Science 16, pp. 345±349 (Chinese with English abstract).
Acidity and chemistry of bulk precipitation, throughfall and stem¯ow in a Chinese ®r plantation in Fujian, China Fan HouBaoa,*, Hong Weia, Ma Zhuanga, Waki Kosukeb a
Department of Resources and Environment, Fujian Forestry College, Nanping 353001, China b Japan International Forestry Promotion and Corporation Center, Tokyo, Japan Received 19 May 1998; accepted 2 December 1998
Abstract Acidity and chemistry of open and intercepted precipitation in a Chinese ®r plantation in Fujian, China, were monitored at two sites located at varying distances from the SO2 sources. Acidi®cation and chemical enrichment were observed to be extremely signi®cant for stem¯ow, but only slightly for throughfall. The pH values for rainfall showed some seasonal patterns. In contrast, the electric conductivity and chemical components showed a strong seasonal trend over the three-year period, which were supposed to be negatively correlated with the amount of rainfall. Differences in pH values between two sites suggested the acidifying effects of sulfur dioxide on precipitation. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Acidity; Electric conductivity; Bulk precipitation; Throughfall; Stem¯ow
1. Introduction Large-scale industrialization came late to China, not really until the late 70s of this century. However, coal, with an average sulfur content of 1.12%, is used at present as the most important fuel resource which occupies more than 20% of the total coal consumption in the world (Zhang et al., 1991; Wang et al., 1996). Annual discharges of SO2 and NOx into the atmosphere in 1990 were estimated to be ca. 17.52 106 t and 8.42 106 t, respectively, and the annual emitted SO2 is expected to reach 27 106 t by 2000 unless more ef®cient control measures are employed (Wang
*Corresponding author. Tel.: +86-599-8501271; fax: +86-5998508194/8508702; e-mail: [email protected]
et al., 1996; Zhou et al., 1996). Acidity in precipitation has increased considerably in South China over the last decade, and it was observed that precipitation hydrogen-ion content was 80±90% due to sulfuric acid as caused by sulfur dioxide (Yang, 1989; Fan, 1993). Acceleration of foliar nutrient leaching is an important impact of acid precipitation on forest ecosystem (Likens et al., 1972; Smith, 1981). Precipitation chemistry was remarkably altered upon passage through forest canopies (Eaton et al., 1973; Potter et al., 1991). The washout of dry deposition by precipitation may add acidifying inputs to ecosystems, and contribute signi®cant amount of certain elements to the forest ¯oor (Lovett and Lindberg, 1984). Accelerated plant leaching may also alter the processes of nutrient cycling in forest ecosystems and result in physiolo-
0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 9 ) 0 0 0 1 1 - 0
244
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
gical stress (Wood and Bormann, 1975; Lovett et al., 1985). In 1993, a project, sponsored by Japan International Forestry Promotion and Cooperation Center, was established in Fujian, China, to monitor the potential damage of acid rain and air pollution to forest ecosystems. The purpose of this paper is to report the temporal and spatial changes in acidity and chemistry of bulk precipitation, throughfall and stem¯ow monitored from the past three years (1994±1996). 2. Methods In August 1993, two monitoring sites were established in a Chinese ®r plantation (Cunninghamia lanceolata Hook.) in Nanping, Fujian. One site is located in the Experimental Forest of Fujian Forestry College, ca. 13 km from Nanping, referred to as FFC site (268330 N, 1188060 E).The other site is located in Xiqin Experimental Forest Farm, 10 km from Nanping and near Xiqin Town where a small-scaled paper mill is located, and referred to as Xiqin site (268340 N, 1188050 E). Each site was composed of a 1000 m2 monitoring plot and surrounded by a continuous forest vegetation area. Each plot was equipped with three throughfall gauges and three stem¯ow traps which were set ca. 1.3 m above the ground level. A rainfall gauge was set in open place out of each monitoring site, which has an area of ca. 800 m2 and 580 m away from the edge of FFC site, and of ca. 1000 m2 and 660 m from Xiqin site. Precipitation collections were made daily at 9 : 00 throughout the monitoring period. All samples were analysed for pH and EC in the ®eld and, subsequently after ®ltration in laboratory. There were no signi®cant differences between the two sets of measurements, so the measurements made in the ®eld were used in this paper. Measurements for pH and EC were carried out by D-14 pH meter and ES-14 EC meter, respectively. The samples collected from the ®rst precipitation event in each month were ®ltered and stored in a refrigerator for chemical analysis. Cation analysis (k, Na, Ca2, Mg2) were completed by AA-670 atomic absorption spectrophotometer. Ammonium was determined by an alkaline phenolhypochlorite method, and sulfate by barium chloride turbidometric method.
3. Results and discussions The weighted monthly pH values for rainfall, throughfall, and stem¯ow from the two sites are shown in Fig. 1. Throughfall was observed to be slightly acidi®ed as compared to open rainfall at two sites. Within any sampling date, there was a positive relationship in pH values between rainfall and throughfall. The pH of stem¯ow was consistently much lower than rainfall and throughfall, with pH values ranging between 3.08 and 5.60 (excluding one irregular extreme value of 6.57) at FFC site, and between 2.80 and 5.58 at Xiqin site. The seasonal variation in rainfall pH shows similar pattern over the three-year period (Fig. 1). The pH values are usually minimal in summer months, intermediate in spring, and maximal in fall or winter. Based on three years of data (1994±1996), the median pH for rainfall is estimated to be 6.25 at FFC site, which is greater than that (5.95) at Xiqin site. Extremely lower median pH values are found for stem¯ow, with 4.00 at FFC site, and 3.20 at Xiqin site. The values of electric conductivity (EC) show a wide ¯uctuation over the monitoring period. The highest values consistently occurred in November or December, and the lowest was usually observed in summer months (Fig. 2). The coef®cients of variation for pH values are all <10%, indicating lower temporal variability for precipitation acidity, especially for throughfall (Table 1). The EC values, however, show great ¯uctuation with coef®cients of variation ranging from 59.78%, for stem¯ow at Xiqin site, to 137.44% for rainfall at FFC site. The neutralization components (k, Na, Ca2, Mg2, NH4) and sulfate show a strong seasonal pattern approximately identical to that for conductivity (Figs. 3 and 4). Actually the relationships between EC values and concentrations of the total measured ions in precipitation can be expressed by the following linear regression equations: at FFC site RF 18:992 0:077EC;
r 0:949
TF 40:627 0:057EC;
r 0:954
SF ÿ19:120 0:075EC;
r 0:910
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
245
Fig. 1. Seasonal patterns in monthly average pH values of precipitation and amount of monthly precipitation at two sites (RFRainfall; TFThroughfall; SFStemflow; APAmount of precipitation). Table 1 The annual mean values of pH and EC (m/cm) for the precipitation from two sites. The calculations are based on three years of data (1994± 1996) Factor
Parameter
FFC site RF (n 274)
a
Xiqin site TF (n 273)
SF (n 270)
RF (n 255)
TF (n 253)
SF (n 243)
pH
Mean SE b CV c (%)
6.31 0.04 9.63
6.26 0.03 6.79
4.14 0.02 8.30
6.00 0.03 8.75
5.77 0.03 7.62
3.33 0.02 7.96
EC
Mean a SE b CV c (%)
45.33 3.76 137.44
110.43 6.36 95.15
276.14 12.49 74.30
47.34 3.23 108.96
95.14 5.82 97.34
557.53 21.38 59.78
a
The arithmetic mean value. Standard error. c Coefficient of variation. b
246
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
Fig. 2. Seasonal trends (1994±1996) in weighted monthly EC values of precipitation from two sites (RFRainfall; TFThroughfall; SFStemflow).
at Xiqin site RF 11:461 0:078EC;
r 0:959
TF 8:181 0:066EC;
r 0:956
SF 128:388 0:068EC;
r 0:805
where RF, TF and SF represent the concentrations of total measured ions in rainfall, throughfall and stemflow, respectively. Close relationships (p < 0.01) between these two measurements suggest EC is significantly ion-dependent.
The differences in acidity and chemistry for precipitation between two sites may be due to location. The FFC site is less affected by human activities, while Xiqin site is near a paper mill and the roads. Actually the distribution of acid rain in southern China displays strong local in¯uences, precipitation with pH of <5.6 is primarily con®ned to urban areas with high sulfur dioxide pollution (Xu and Hao, 1990). Sulfur dioxide, through chemical transformations and atmospheric scavenging, is considered to be the major contribution to the precipitation acidity in China
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
Fig. 3. Seasonal trends (1995±1996) of neutralization components (K, Na, Ca2, Mg2, NH 4 in precipitation from two sites (RFRainfall; TFThroughfall; SFStemflow).
(Yang, 1989). Lack of correlation between pH and sulfate in this paper may, in part, be due to the limited chemical data for precipitation. There was also a possibility that lower pH values in throughfall and especially stem¯ow during the summer time may be caused by organic acids, such as carboxylic acids, which was not monitored in this project. The third
247
possible explanation may be that contamination and aging, such as nitri®cation, of rainwater samples may have occurred during the storage period, especially in summer, which will increase the acidity. Further research is needed in the future to determine the exact relationships between pH and acid-forming components. The greater ion concentrations in fall or winter are supposed to be the result of less precipitation volume and longer time intervals between two rain events during this period. Dilution by greater volume in summer, however, decreases the ion concentrations (see Fig. 1). Remarkable acidi®cation and nutrient enrichment for rainwater ¯owing down the inert bark surfaces reveal that a larger part of the chemicals added to intercepted precipitation is derived from dry deposition than from leached metabolites. The SO42ÿ data indicate that throughfall and stem¯ow is enriched with SO42ÿ from dry deposition of ¯y ash and dust. Sulfate particles increase the SO42ÿ concentration, but since ¯y ash is alkaline, pH in stem¯ow and throughfall may increase in winter, when emission is the greatest. The same conclusion was proposed in a previous study conducted in Norway (Abrahamsen et al., 1976). Actually the pH of tree bark, especially that with a rough surface texture such as Chinese ®r, was considered to be a sensitive indicator of regional pollution (Grodzinska, 1976; Fan, 1996). Acknowledgements This work was sponsored by Japan International Forestry Promotion and Cooperation Center (JIFPRO).
References
Fig. 4. Seasonal trends (1995±1996) of concentrations of sulfate in precipitation from two sites (RFRainfall; TFThroughfall; SFStemflow).
Abrahamsen, G., Horntvedt, R., Tveite, B., 1976. Impacts of acid precipitation on coniferous forest ecosystems. In: Dochinger, L.S., Seliga, T.A. (Eds.), Proc. Ist Internat. Symp. Acid Precipitation and the Forest Ecosystem. U.S.D.A. Forest Service, Gen. Tech. Rep. No. NE-23, Upper Darby, Pennsylvania, pp. 991±1009. Eaton, J.S., Likens, G.E., Bormann, F.H., 1973. Throughfall and stemflow and stemflow chemistry in a northern hardwood forest. Journal of Ecology 61, 495±508.
248
F. HouBao et al. / Forest Ecology and Management 122 (1999) 243±248
Fan, B.T., 1993. Environmental chemistry. Zhejiang University Press, Hongzhou, China, pp. 558 (in Chinese). Fan, H.B., 1996. Tree bark: An indicator of air pollution and precipitation acidity. Journal of Zhejiang Forestry College 13, 136±140 (Chinese with English abstract). Grodzinska, K., 1976. Acidity of tree bark as a bioindicator of forest pollution in southern Poland. In: Dochinger, L.S., Seliga, T.A. (Eds.), Proc. Ist Internat. Symp. Acid Precipitation and the Forest Ecosystem. U.S.D.A. Forest Service, Gen. Tech. Rep. No. NE-23, Upper Darby, Pennsylvania, pp. 905±911. Likens, G.E., Bormann, F.H., Johnson, N.M., 1972. Acid rain. Environment 14, 33±40. Lovett, G.M., Lindberg, S.E., 1984. Dry deposition and canopy exchange in a mixed oak forest as determined by analysis of throughfall. Journal of Applied Ecology 21, 1013±1028. Lovett, G.M., Lindberg, S.E., Richter, D.D., Johnson, D.W., 1985. The effects of acidic deposition on cation leaching from a deciduous forest canopy. Canadian Journal of Forest Research 15, 1055±1060. Potter, C.S., Ragsdale, H.L., Swank, W.T., 1991. Atmospheric deposition and foliar leaching in a regenerating southern Appalachian forest canopy. Journal of Ecology 79, 97±115.
Smith, W.H., 1981. Air pollution and forest: Interactions between air contaminants and forest ecosystems. Springer-Verlag, New York, pp. 379. Wang, W.X., Wang, W., Zhang, W.H., Hong, S.X., 1996. Geographical distribution of SO2 and NOx emission intensities and trends in China. China Environmental Science 16, pp. 162± 167 (Chinese with English abstract). Wood, T., Bormann, F.H., 1975. Increases of foliar leaching caused by acidification of an artificial mist Ambio 4, pp. 169±171. Xu, F.K., Hao, J.M., 1990. A review on the present situation of acid rain in China and establishment of countermeasures. Environmental Science 11, pp. 61±66 (in Chinese). Yang, H.X. (Ed.), 1989. Acid rain and agriculture. China Forestry Press, Beijing, pp. 191 (in Chinese). Zhang, H.Q., Zao, X.D., Wang, Q.L., 1991. Energy structure in China and atmospheric environmental pollution. Research of Environmental Sciences 4, pp. 50±54 (Chinese with English abstract). Zhou, X.L., Hao, J.M., Fu, L.X., Li, Q.L., 1996. Sulfuric deposition modelling research in the east part of China (Model application. China Environmental Science 16, pp. 345±349 (Chinese with English abstract).