Soil Degradation Due to Acidification

Transcription

1 1 Soil Degradation Due to Acidification Masanori OKAZAKI Tokyo University of Agriculture and Technology Graduate School of Bio-Applications and Systems Engineering Abstract Soil degradation due to acidification is progressing in the world. In coastal lowland areas the reclamation of tropical peat soils and potential acid sulfate soils by drainage and oxidation resulted in the strong acidification. More than 4 million ha in Asia has been acidified with light (0.4 million ha), moderate (2.5 million) and strong (1.2 million ha) severity (1). The level of atmospheric acid deposition in Southwest China and Japan is similar to those in Europe and North America. Although acid deposition has caused the nutrient loss from soils, the excess of element input (pollution), and soil and soil solution acidification, there are few reports on the soil and area affected by acid deposition in East Asia. To simulate the soil acidification due to acid deposition, the input and output budget study of water and elements should be done in a small catchment. 1. Introduction The intensive demand for agriculture and industrial development has resulted in soil degradation. Tropical peat soils and acid sulfate soils are prevalent in coastal lowland areas in Southeast Asia, which are 368 million ha (2) and 4 million ha (3), respectively. Table 1 Human-induced soil degradation in Asia (1) Type Light Moderate Strong Extreme Total Wt Loss of topsoil Wd Terrain deformation W WATER (59%) Et Loss of topsoil Ed Terrain deformation Eo Overblowing E WIND (30%) Cn Loss of nutrients Cs Salinization Cp Pollution Ca Acidification C CHEMICAL (10%) Pc Compaction Pw Waterlogging Ps Subsided organic soils P PHYSICAL (2%) Total (39%) (46%) (14%) (1%) (100%) Asia includes the Asian part of Russia. Drainage causes the stimulation of decay of woody materials in tropical peat soils. This leads to the disappearance of

2 2 tropical peat horizons and the leaching of nutrients (Table 1) (4). Meanwhile, marine alluvium contain a high content of sulfide-sulfur formed from reduction of sulfate-sulfur in sea water by microorganisms having the ability to reduce the oxidation of sulfide, thus forming the actual acid sulfate soils (5). With drainage the potential acid sulfate soils will exhibit a strong acidity by oxidation. The atmospheric acid deposition derived from the emission of air pollutants gave rise to the decrease of soil ph (6, 7, 8, 9), comparing the soil ph values between before and after years experiencing serious emission of air pollutants. The changes in soil ph values have not obviously clear, because of large buffering capacity of soils. However, it is evident that soils around tree trunk bases are exposed to larger amount of acid substances by the stemflow which contains dry deposition attached on tree crown (10, 11, 12, 13, 14, 15, 16). In Europe soil degradation due to acid deposition has been mapped, marked with Cn (loss of nutrients/organic matter) and Cp (pollution), based on the data of high deposition level and accumulation of acid substances elucidated by long-term monitoring studies (Table 1)(1). However, few long-term monitoring studies and results on acid deposition and its effect have been available in East and Southeast Asia. The objective of this study is to elucidate the soil degradation due to nutrient loss and acidification in East and Southeast Asia through long-term monitoring studies. 2. Monitoring Long-term monitoring sites were settled in the study areas of East and Southeast Asia. Water samples; precipitation, throughfall and/or stemflow, and litterfall, plant and soil samples were taken for element determination. The uptake of elements by plants was estimated by harvested portion of trees and literature. The output of elements through streamflow was calculated by multiplying each element concentration by the estimated amount of streamflow. The discharge rate of water was calculated based on the relationship between water levels and water flux. 3. Nutrient loss and acidification in tropical peat soils Tropical peat soils under swamp forest in Sarawak show low values in ph and nutrients (17). The reclamation Table 2 Annual input and output budget for swamp forest ecosystem and change after deforestation (18) Input Output Net(1) Net(2) Throughfall Litter Streamflow Vegetation Precipitation Dead leaf removal kgha -1 yr (a) (b) (c) (d) Swamp forest C N P Na K Mg Ca Palm plantation C N P Na K Mg Ca Input of swamp forest is due throughfall and litterfall. Input of palm plantation is due to precipitation and dead leaf. Net(1): a + b - c, +: gain, -: loss Net(2): a + b - c - d

3 3 with drainage for palm plantation caused the further nutrient loss from tropical woody peat soils. The palm plantation remarkably gave losses in P, Na and Mg from tropical peat soils prior to the harvest (Table 2) (18). Calcium application for ph control in the palm plantation suppressed the ph lowering of tropical peat soils. 4. Soil degradation due to acid deposition Continuous monitoring studies were conducted in Chongqing (China), Chunchon (Korea), and Hachioji (Japan) from 1990 to The acid depositions through precipitation, throughfall and stemflow were determined and estimated as the determining factors of soil acidification. The preliminary input and output budget of elements were provided by the difference between the input through open bulk, and throughfall and stemflow and the output through streamflow. Chongqing is one of the most serious air polluted city in the world. The deposition of sulfate-sulfur in open bulk and under dominant masson pine forest in Mt. Zhenwu of Chongquing from 1993 to 1994 was more than 7 times as high as in Chunchon in 1997 and Hachioji from 1990 to 1998 (Table 3). However, proton in open bulk, 0.53 kmol c ha -1 yr -1, was compensated for by other cations such as calcium and magnesium to the amount of anions, which indicated the similar level of proton in the deposition from 1988 to 1989 (20), although the proper small catchment for the budget study was not found in Chongqing area. The contribution of acid deposition to soil acidification indicated the predominance of aluminum at the exchangeable sites of soils. Table 3 Input of elements through open bulk precipitation, throughfall and stemflow and output from streamflow in masson pine forest of Zhenwu, Chongqing (19) Ca Mg NH 4 H SO 4 NO 3 Cl kmol c ha -1 yr Open bulk Throughfall Stemflow The density of masson pine trees in Mt. Zhenwu was 700 trees ha -1. In Chunchon the input and output of elements in red pine forest of a small catchment were estimated (Table 4). The losses of almost all elements studied occurred in this catchment except for ammonium nitrogen and proton. Ammonium nitrogen inputted will be nitrified to nitrate nitrogen in soil ecosystems with producing proton, which causes the soil and soil solution acidification. Table 4 Input of elements through open bulk precipitation, throughfall and stemflow and output from streamflow in red pine forest of Chunchon (21) Ca Mg K Na NH 4 H SO 4 NO 3 Cl kmol c ha -1 6month Input Open bulk Site 1 Throughfall Stemflow Site 2 Throughfall Stemflow Output Streamflow The density of red pine trees in Chunchon was 2200 trees ha -1.

4 4 The input of elements through open bulk and throughfall and stemflow of Hinoki cypress in Hachioji indicates the same level as those of elements in Europe and North America (Table 5) (22). The output of proton from the Hinoki cypress forest was quite small and proton accumulated in soil under Hiroki cypress. The losses of Mg, Na and nitrate nitrogen and the gains of Ca, H, ammonium nitrogen, sulfate-sulfur and Cl were found in the study site of Hachioji. Spatial variability of soil solution chemistry around the Hinoki cypress trunks showed the acidification of soil solution and high concentrations of aluminum as a dominant cation (16). Table 5 Input of elements through open bulk precipitation, throughfall and stemflow of Hinoki cypress and output of elements through streamflow in Hachioji (22) Ca Mg K Na H NH 4 SO 4 NO 3 Cl kmol c ha -1 yr Input Open bulk Throughfall (Hinoki cypress) Output Streamflow The density of Hinoki cypress trees in Hachioji was 2500 trees ha Simulation and countermeasure of soil acidification due to acid deposition The simulation model of soil acidification in Japan due to acid deposition is developing. Although basic weathering data on primary minerals including volcanic glass are still not enough, some simulation models are proposed in Japan; a main equation in soil acidification is ion balance, associated by mass balance equation of major elements and calculated by the equilibrium equation of minor elements (23). The regulation of air pollutant emission should be required on the base of simulation of soil acidification. Acknowledgements This study was supported in part by a Grant-in-Aid for A New Program for Promotion of Basic Sciences, Studies of Global Environmental Change with Special Reference to Asia and Pacific Regions, from the Ministry of Education, Science, Sports and Culture, Japan and by a Grant for the Budget Study on Acidic Substances to Environment and its Effect on Forest Ecosystem from the Forestry Agent, the Government of Japan. References 1) UNEP and ISRIC (1990): World Map of the Present Status of Human-induced Soil Degradation (1:10 M). 2) P. M. Driessen (1978):Peat soils, Soils and Rice, Ed. IRRI, pp , IRRI, Los Banos. 3) N. van Breemen and L. J. Pons (1978):Acid sulfate soils and rice. Soils and Rice, Ed. IRRI, pp , IRRI, Los Banos.

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