Simetryn is one of the popular herbicides and detected often in river water in Japan. Therefore, runoff behavior of simetryn from paddy field was estimated under several conditions of precipitation and irrigation by a new fate model. It uses the rates of chemical degradation, aerobic and anaerobic biodegradation in water and soil, diffusion rate in void water of soil, Freundlich type adsorption equilibrium and the rates of two step adsorption onto soil.
It was estimated that the highest runoff concentrations from Niigata and Kumamoto paddy fields were as high as several times of the water quality guide value by the Environment Agency of Japan, and that the total runoff amounts in 60 days were ca. 10-60% of the applied amounts. Besides, the concentration in soil of Niigata paddy field was estimated to be as high as several times of that of Kumamoto paddy field. Thus it was shown that the runoff load could be decreased by scheduling the weed to avoid rainy day, controlling irrigation, and applying the optimum amounts for each area.

View full abstract

Eighty two wastewater samples which had met the Japanese conventional wastewater quality standards were collected to investigate their mutagenicity and the mutagen formation potential (MFP). Though the mutagenicity was detected from few samples, the MFP was detected from most samples. The highest MFP of 2.1 × 10⁶ net rev. · l^-1 was observed from a landfill leachate sample. Most of the MFP values observed from the wastewater samples were within the range of 1 × 10³∼3 × 10⁵ net rev. · l^-1 which were 1∼300 times the mutagenicity level of the urban tap water in Japan, i.e., 1 × 10³ net rev. · l^-1. The highest MFP load of 1.9 × 10¹³ net rev. · d^-1 was observed from the landfill leachate sample. Most of the MFP load values observed from the wastewater samples were within the range of 1 × 10⁸∼1 × 10¹² net rev. · d^-1. It was concluded that a lot of wastewater causes significant adverse effect on the mutagenicity of tap water. Chemical industry wastewater, landfill leachate and sewage were remarkable as a considerable pollution source of the MFP of water sources for drinking water. Since the correlation between MFP and TOC, COD, BOD, A₂₆₀, THMFP was weak, the MFP cannot be estimate from these conventional water quality indices.

View full abstract

In order investigate the dynamics of dissolved organic carbon (DOC) in Hiroshima Bay, water samples from 7 stations in the bay, its three inflowing rivers and two wastewater treatment plants (WWP) were taken from Aug. 1997 to Aug. 1998. The filtrated organic matter was fractionated into hydrophobic (Hob-DOC) and hydrophilic (Hil-DOC) components using XAD-8 resin. Biodegradation tests by a 100-day incubation and mixing experiments of those samples for evaluating the sedimentation of DOC were also conducted.
The concentrations of DOC and Hil-DOC in the bay showed clear seasonal changes (high in summer and low in winter), suggesting aquagenic production of Hil-DOC. Those of river waters had similar seasonal changes, but not so clear. The percentages of Hob-DOC were 31-35% for the bay waters, 34-46% for the river waters, and 31-35% for the effuent from the WWP waters, whereas those of labile DOC were 9-25%, 18-51%, and 17-30%, respectively. The DOC concentrations had positive correlation with chlorophyll a (increments of DOC to Chlorophyll a : 0.01-0.04mg · l^-1/μg · l^-1), and negative correlation with salinity. The mixing experiment suggested negligible deposition of DOC at the estuaries of inflowing rivers. In conclusion, Hob-DOC went through the estuaries and the bay with negligible change in the concentration in both summer and winter. In contrast, both labile and refractory components of Hil-DOC were produced mainly in the inner part of the bay during summer, and a large part of the former component was subjected to biodegradation during the transport to the outer part.

View full abstract

The seasonal variations in pollutant loads and water qualities in Hiroshima bay, in order to get basic data for water quality modelling in that bay, were investigated. We have estimated inflow pollutant loads of freshwater, COD and nutrient into Hiroshima bay, also the budgets of the freshwater, salt, dissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) by applying a simple box model in the northern coastal area (NH region) of Hiroshima bay were calculated.
In the NH region of Hiroshima bay, influence of pollutant loads from land area was remarkable. We understood that phosphorus became limiting factor in the process of primary production because the standing stocks of nitrogen are enriched. The yearly averaged residence time of freshwater in the region is 16 days, and that of DIP and DIN is 24 days and 21 days, respectively. On the other hand, the yearly averaged internal sink or source of DIP and DIN, Δ DIP and Δ DIN in the NH region is estimated 25.5 ton · month^-1 and 291.4 ton · month^-1, respectively, and the ratio of Δ DIP to DIP loads (summation of inflow load and release flux from bottom sediments) is about 43 %, which is smaller than that of Δ DIN to DIN loads of 67 %.

View full abstract

We found a special irrigation reservoir in which there are no algae, insects, or fish. Therefore, we have surveyed the water quality of an irrigation reservoir to find the reason for no living creatures. As the results of the survey, we found three factors such as high nitrate concentration, high aluminum concentration, and low pH value which will affect the lives of creatures in this irrigation reservoir. Among these three factors, the most important one is low pH in this irrigation reservoir. This low pH of the irrigation reservoir is derived from the overuse of nitrogen fertilizer at tea yards. About 1,000kg · ha^-1 · y^-1 of nitrogen fertilizer has been used to the tea yards for a long time. The remained nitrogen fertilizer which was not taken up by tea crop infiltrates through soils and enters into the ground water. This causes an over the Cation Exchange Capacity of soil and high aluminum concentration of this irrigation reservoir. To prevent this phenomenon from occurring, dozing lime under the root zone and reducing use of nitrogen fertilizer might be effective.

View full abstract