We reviewed in a series of the chemical monitoring of water, starting up from rainwater and now going down to groundwater, carried out to collect fundamental data on the Tsukuba mountainside ecosystem in central Japan. Other main projects FY 1996 were as follows: (1) crust formation and its effect on rain water infiltration and soil erosion on bare slopes, (2) phosphorous removal from hoggery sewage using natural calcium carbonate, (3) extraction factors and distribution coefficients of trace elements as estimated by batch experiments using high resolution ICP-MS. In addition, we discussed dynamics, functions and effects on environments of organic matter in soil and water of agricultural fields in "The 14th Workshop on Soil and Water".

Topic1

Current Status of Acid Precipitation in Tsukuba

Since many people suffered from eye and skin irritation arising from acidic drizzle in June and July of 1973,the significance of acid precipitation was recognized in Japan. The phase 1 survey on acid precipitation was carried out by the Japan Environment Agency at 29 monitoring stations from 1986 to 1988. We also had carried out the chemical monitoring of precipitation from 1985 to 1991 in the Tsukuba area. By analysing these data, we clarified the fact that the annual pH value had not changed significantly in Japan for the past two decades. The acidity of rainwater, which is caused by H₂SO₄ and HNO₃ mainly, is neutralized by alkaline components such as NH₃ and Ca²⁺. Therefore pH value is determined by the balance of those 4 species.

However, acid rain has grown more serious in China recently. Fig.1 shows the relationship between acidifying and neutralizing potentials (μmol L^-1) of precipitation at a typical monitoring station of east Asia. The former is the sum of the equivalent concentrations (weighted mean by rainfall) of non-sea-salt-SO₄^2- and NO₃^-. The latter is the sum of non-sea-salt-Ca²⁺ and NH₄⁺. As noted above, there was little difference in annual averages of acidifying potentials, with a value of about 50(μmol L^-1) observed from 1985 to 1991 in the Tsukuba area. This value was 10 times higher than that of Samoa located in the South Pacific Ocean.

Topic2

Relationship between Chemical Properties in Throughfalls and Kinds of Trees

In order to select suitable trees for estimating the acidification of precipitation with collecting fundamental data, we had carried out investigation of chemical properties, i.e. pH, NH₄⁺, NO₃^-, Cl^-, SO₄^2-, Ca²⁺, Mg²⁺, Na⁺ and K⁺ concentration (weighted mean by rainfall) in throughfalls of 12 kinds of trees (Himalayan Cedar, Honey-locust, Bamboo-leafed Oak, Sawara Cypress, Acacia, Enkinanthus, Spiraea, Golden-bell, Abelia, Japanese red-cedar, Hinoki-Cypress and Japanese red pine) in Tsukuba from April 29 to September 14, 1991.
Fig.2 shows the main result. All concentrations of chemical components in throughfall, except NH₄⁺ concentration in Abelia, were higher than those of rainwater that directly arrived at the surface of land as control.Especially, K⁺ concentration in Honey-locust, Acacia, Enkianthus, Spiraea, Goldenbell and Abelia were about 11-34 times higher than that of control.

The pH in throughfall of all kinds of trees (range 4.97-5.88) were higher than that of control (range 4.65-4.79). Himalayan Cedar, Sawara Cypress, Hinoki-Cypress, Japanese red cedar and Japanese red pine (range 4.97-5.37) belonged to the lower concentration group in investigated pH throughfall.

Though we could not estimate acidification of precipitation through the analysis of chemical properties, Division of Agrometeorology had estimated dry and wet deposition using our fundamental data.

Topic3

Use of Ca²⁺ and Cl^- as Tracers in a Three-end-member Mixing Model for Riverwater Generation on Rural Catchment.

The question of how water moves through rural catchments and becomes riverwater continues to be an important topic in hydrology. We tested a short term study in late autumn on riverwater quality of agro-ecosystems at 4 monitoring sites across a catchment.

The study area, which covers 270ha,was located in the Tsukuba mountainside in central Japan. The 4 monitoring sites are representative of three end members and riverwater at the lower reaches. Three end members were mountain stream, groundwater vein stream, and wastewater from population centers.In order to search for groundwater vein stream, we carried out underground temperature surveys.

Fig3 shows that groundwater was distinguished from other end members on the basis of its high Ca²⁺ concentration, and wastewater was distinguished from others on the basis of its high Cl^- concentration. From the application of a mixing model, we estimated the water-ratio of mountain stream, groundwater vein stream,and wastewater from population centers to be 51%, 35% and 14%, respectively, and this ratio was reflected the status of land use and human activities.

In short, measurements of Ca²⁺ and Cl^- in rural catchment suggest that a simple three-end-member mixing model provides a useful framework for river water generation.

Fig.1 Current status of acid precipitation in Tsukuba

Fig.2 Chemical properties in throughfalls (concentration in throuhfall / concentration in control)

1. Hony-locust
2. Bamboo-leafed Oak
3. Sawara Cypress
4. Acasia
5. Enkianthus
6. Golden-bell
7. Abelia
8. Japanese red ceder
9. Hinoki-Cypress
10. Japanese redpine
11. Spiraea
12. Himalayan Ceder

Fig.3 Distribution of Ca and Cl concentration and three-end-member mixing model