The Comparison on the Limnological Study of Coral Lake and Tsengwen Reservoir

Abstract

The cage culture in some lakes and reservoirs was developed under the supports of the Joint Commission on Rural Reconstruction (J. C. R. R.) and the Fisheries Bureau. In this paper, authors dealt with the results of investigation on the Coral Lake and the Tsengwen Reservoir at the area of cage culture in aquatic environment and compared these two waters in vertical variations of water temperature, dissolved oxygen content (DO) and pH value. The water depth of the Coral Lake was quite shallower than that of the Tsengwen Reservoir. The lowest water temperature of both waters was above 20℃. Water temperature was mild in all layers of water in the Coral Lake and the epilimnion of the Tsengwen Reservoir which had a thermal stratification from April to October. Thermocline occuredat 4 m-10 m in April, 5 m-10 m in June, 5m-14m in August and 8m-20m in October. The vertical variations of water temperature, DO and pH in this region were great. The pH values of both waters were slightly alkaline, but it also varied at the thermocline from April to October and even in November when thermocline disappeared in the Tsengwen Reservoir. DO was abundant in all layers of the Coral Lake and in the epilimnion of the Tsengwen Reservoir. From April to November, DO in the metalimnion of the Tsengwen Reservoir decreased slightly according to the increasing of depth. At the lowest region of metalimnion, DO was reduced to only about 1ppm. After that, DO increased again gradually. The amount of organism which will decompose organic debris in the metalimnion was mainly considered to have the relation to DO variation. From the above results, we realize that both waters are suitable for cage culture. Increasing the depth of cage and density of cage culture are appropriate to all layers of waters in the Coral Lake, but in the Tsengwen Reservoir, it is no more than 5m. Furthermore, using the nature of high capacity of heat in these large waters for fingerlings during the winter season is also considered.本篇乃就已有箱網養魚的珊瑚潭與曾文水庫做初步水族環境之調查，比較此二處的水溫、溶氧量及pH值之垂直變化情形。 珊瑚潭水深較曾文水庫為淺，兩水庫最低水溫均在20℃以上。珊瑚潭水域與曾文水庫的表水層(epilimnion)之溶氧量均在6 ppm以上，而曾文水庫於5m以下至10 m、14 m或20 m之間有變溫層(thermocline)和耗氧層(deoxygenal layer)，使得水溫和溶氧量之垂直變化較大。兩水域之pH值皆呈微鹼性。兩水域均可考慮加深養殖之箱網及增加放養密度，而曾文水庫之箱網養殖也可考慮加深至5 m，充分利用養殖空間並且可利用此大型水庫，做為魚苗越冬之場所。