Yearly changes and spatial variation of ammonia emission from agricultural activities were evaluated for 13 countries of eastern Asia from 1981 to 2002 based on the data of each country and each province in China derived from FAO statistics, China statistical year book etc.. Ammonia emission from livestock excreta estimated from the production of stock farm products (several kinds of meat, egg and milk) and their feed efficiencies showed a tremendous increase during the study period especially in China. The total amount of emitted ammonia in 2002 was estimated as 4.0 × 106 t N y-1, which tended to be lower than the estimate based on the nitrogen excretion rate per animal. Ammonia emission from applied chemical fertilizer, which was estimated based on the consumption amount of several types of fertilizer and their ammonia emission rates, also increased rapidly in China and in some of the Southeast Asian countries. The total amount of ammonia emission from fertilizer is 4.8 × 106 t N y-1. There was a wide variation in ammonia emission rates per unit land area by country and by province: the eastern part of China generally had high emission rates from the both sources, the maximum rate was located in Singapore and Shanghai for livestock excreta and Jiangsu Province for fertilizer. Amount of ammoniacal nitrogen emitted to the atmosphere due to agriculture was estimated to be twice of the nitrogen emission as nitrogen oxides due to fossil fuel and biofuel combustion in the study area.
In the Maekawa River catchment at the east slope of Mt. Norikura, the water balance and mass balance were examined for three years. The precipitation frequency is high from the rainy season to the autumn in the catchment. Then, the stream discharge increases temporarily in these seasons. The base flow discharge becomes biggest for the spring snowmelt season. The pH and electric conductivity of stream water increase gradually during the winter. The pH and electric conductivity of stream water decline rapidly with the beginning of the snowmelt runoff. When the discharge increases temporarily in the rainy season or at a typhoon event, the pH and electric conductivity of stream water decline temporarily. The Cl- concentration of stream water increases in the early stage of snowmelt season. In addition, the NO3- concentration of stream water increases when the rainfall increases discharge. The major ion concentration of stream water except Cl- and NO3- almost synchronizes with the change of electric conductivity. In the mass balance of the cation, the runoff rate from the catchment exceeds absolutely compared with the atmospheric deposition rate to the catchment. The reason is because there is extremely much elution of ions from rock and soil which are composed by the new volcanic structure. As for the Cl- ion, the runoff rate from the catchment balances with atmospheric deposition rate to the catchment. Also, the atmospheric deposition rate of NO3- ion is bigger with the biological consumption in the catchment than the runoff rate from the catchment.
Nitrate was the dominant form of dissolved nitrogen in stream waters in Nagano Prefecture. Nitrate concentration showed a large geographical variation, ranging from 0.02 to 1.20 mg N L-1. Although there are significant negative relationships between nitrate concentration and altitude or annual precipitation, artificial influence accompanying with rainfall has not yet been confirmed on nitrate concentration in stream waters in Nagano Prefecture. In the Chikuma and Tenryu Rivers, dissolved organic nitrogen was observed in addition to the dominant nitrate. Dissolved total nitrogen concentration was around 1.5 mg N L-1 in the middle part of the both rivers. Nitrogen stable isotope ratio of periphyton increased downstream in the Chikuma River, whereas it was high in the upper reach and then decreased downstream in the Tenryu River. Nitrogen sources might shift from agricultural and mountain origins to sewage and livestock waste in the Chikuma River. Nitrogen derived from a sewage treatment system mainly contributed to the river nitrogen in the upper reach of the Tenryu River.
Nitrogen budget relating with food production and consumption in 1885 was calculated from the agricultural statistics. The amount of protein supply per capita was estimated to be about 70% of that in today. In 1885, one hectare of arable land fed 5 people. This number is grater than that of the current world average. This intensive agriculture required much nitrogen, and nitrogen supply was the limiting factor of food production. They had used green manure and human excrement. This let the society circulatory and prevents water pollution in rivers and lakes.
Studies of the agricultural production, the vegetative productivity and the environmental change on a continental/global scale have been possible using remote sensing data and geographical information. This paper describes roles of remote sensing and geographical information system (GIS) in running a material cycle model, and introduces an example of analysis of nitrogen cycle in East and Southeast Asia, combining the nitrogen cycle model with remote sensing and GIS. The nitrogen cycle model was constructed using findings on geochemistry and socioeconomics, and some of its parameters were tuned to chemical analysis values of water sample. The results from the model simulation study clarified the regional differences of nitrogen load and concentration. GIS can help a model- based analysis to change the spatial resolution of data used and sum up the nitrogen load for each category.
To overview the stream water chemistry in Japan, we conducted systematic stream water sampling and chemical analyses as the Japan-Wide Stream Monitoring (JWSM) 2003. The total numbers of 1278 samples from head water streams from all over Japan were analyzed in this study. The Japanese average values and concentrations of E.C., pH, Cl-, NO3-, SO42-, Anion deficit (HCO3-),
Na+, NH4+, K+, Mg2+ and Ca2+ were 7.01mS/m, 6.84, 120μmol/l, 25.7μmol/l, 60.1μmol/l, 341μeq/l, 216μmol/l, 6.1μmol/l, 16.2μmol/l, 53.7μmol/l, 133μmol/l, respectively. Stream water chemistry calculated at every prefecture showed regional distributions, background level of natural stream chemistry was quite different depended on the area in Japan. NO3- concentrations showed most distinctive difference, Saitama prefecture (113μmol/l) was more than 13 times higher than Hokkaido prefecture (8.2μmol/l).
Changes in the components of the hydroclimatological water balance over the last 100 years were comparatively investigated in the Kiso and Kumozu River basins, central Japan. Annual precipitation has been inclined to decrease since the first half of the 1970s. Smoothed secular changes in the difference between the annual values of precipitation and potential evapotranspiration are analogous to those in the annual precipitation. The average annual runoff ratio for each ten years showed a tendency to decrease during the last few decades. The notable characteristics on current frequency-magnitude distributions in annual precipitation are both the reduction of interval of drought events and the increase of range in each year. Under the conditions of extreme meteorological events in the summer of 1994, river water quality showed the remarkable change as compared with its average value in normal year. The most striking feature on water quality due to high temperature was very low value of the concentration of dissolved oxygen through July into August. The facts identified in the present paper would provide a meaningful perspective on the variability of hydrological element, and be useful as basic data to evaluate the effect of climate change on aquatic environment.