Diatoms taken from the bottom mud of Lake Ashinoko and from the Paleo-Ashinoko deposit were investigated. 108 taxa of diatoms were found in the former. The total taxa of diatoms, including the previous records, found in the present Lake Ashinoko have now become to be 161. The ratios of occurrence of Cyclotella comta and Fragilaria crotonensis, with 90 percent reliance, were 12-18 percent and 5-10 percent, respectively. The Paleo-Ashinoko deposit is divided into the upper and the lower layers, each layer of which is further divided into fine, medium and coarse sands. Examination of the samples from those layers revealed that the diatom flora of the Paleo-Ashinoko deposit differed markedly from that of the bottom deposit of the present Lake Ashinoko. The results suggest that depositing conditions in the Paleo-Ashinoko may have differed from those in the present Lake Ashinoko. The abundant occurrence of diatoms in the Paleo-Ashinoko deposit reminds us of inferring that water of the past lake basin may have contained certain kinds of rich inorganic salts.

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The effect of ammonia removal by aeration during the cultivation of phytoplankton was investigated. The results obtained are as follows.
1) Ammonia removal by aeration was observed during the cultivation of Chlorella in domestic waste.
2) The decrease of total nitrogen concentration was mainly dependent on ammonia removal. Gaseous nitrogen release was not likely to occur during the cultivation.
3) The following equation was obtained for the rate of ammonia removal (R) :
R (%/hr) =3.38×10^-11·P^10.53·Q·e^0.046T where R is temperature (°C), P is pH and Q is air volume per water volume per minute.
4) The rate of aeration is not enough to remove ammonia in outdoor ponds like oxidation pond. But more effective method of aeration will be able to release ammonia from water bodies.

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Studies on the bottom fauna in a tropical fresh-water fish pond were carried out during the period of January to December, 1971. Total volume of the bottom fauna was the highest in January and the lowest in October. Numerical abundance (population density) of the benthos varied from 186 to 385 organisms per sample. The maximum number was recorded in July and the minimum in November. The percentage composition of Chironomus larvae fluctuated from 11.6 per cent to 88.3 per cent, crustaceans varied from 4.3 to 25.0 per cent, oligochaetes varied from 6.2 to 63.3 per cent and the percentage of molluscs ranged from 1.6 to 5.8 per cent of the total benthos. Chironomus larvae were abundant throughout the period of studies. Crustaceans were abundant during summer months while the oligochaetes and the molluscs were plentiful during the monsoon months. The bottom fauna recorded in the present studies included one copepod, four species of ostracods, six species of oligocheates, five species of molluscs and Chironomus larvae.

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In the period 19711973, the hydrogeological studies were done in the area of the Koga basin, Shiga Prefecture. The conclusions are summarized as follows :
1) The geology of the Koga basin consists of the Kobiwako Group, The main confined aquifers are Katuragi sand bed and Aburahi sand bed.
2) The artesian wells in this basin are about 100 to 170 meters in depth and their discharge is about 5002, 000 m³/day.
3) The depth of the basement was presumed from the result of gravity survey. The maximum value in depth situated near Ueno is approximately 220 meters under the ground.
4) On the basis of the result of gravity survey and the interpretation of chemical characteristics of groundwater samples, the groundwater basin of this area was divided into the northern part (Konan area) and the southern part (Koga area).
5) The mineral springs of sodium chloride type are flowing out at about 1 km west of Konan Station. The chemical composition of artesian groundwater of the northern end of this basin is affected by the mineral water.

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