Study on the Vertical Distributions of Dissolved Oxygen and Heterotroph in the Tsengwen Reservoir

Abstract

In this paper, author dealt with the studies on dissolved oxygen (DO) and heterotroph in the Tsengwen Reservoir. In October, DO was abundant but the heterotroph was less in the epilimnion. Below 5m where the thermocline began to appear, DO gradually decreased and was 1.0ppm at the lower strata of the thermocline from 10m to 15m in deepth, but the heterotroph had the higher level from 10m to 30m and with the highest level of 220×10^3 counts/mi at 15m. The thermocline showed to have higher conductivity than the epilimnion and hypolimnion. In April, the strata below 14m belonged to hypolimnion. DO at epilimnion and thermocline was higher than that at hypolimnion. Generally the number of heterotroph had larger than that appeared in October and was found having more abundant at 13m or 15m. Concerning the vertical distribution in number of heterotroph, there was no apparent difference between down and toward evening. Usually conductivity at epilimnion and thermocline was little higher than that at hypolimnion. A lot of organic substances such as broken plankton or organic debris precipitated and suspended on the upper layer of hypolimnion where the water had higher specific gravity and lower temperature. These organic substances were decomposed by heterotroph in this area into inorganic compound which might be dissolved and dissociated in water and at the same time a larger amount of DO was consumed. This might be the reason why heterotroph appeared in larger quanity at upper layer of thermocline and lower layer of hypolimnion and DO and conductivity varied so much in the Tsengwen Reservoir.本篇乃就曾文水庫溶氧量與微生物數量之垂直分佈做初步調查之結果。10月間於表水層(Epilimnion)溶氧量高，微生物數量少，由水深5公尺起開始之變溫層(Thermocline)溶氧量逐漸降低，至變溫層之下綠約只有1.0ppm左右，而微生物數量則以10公尺到30公尺較多，最多為15公尺水深處達220×10^3counts/ml，且導電度於變溫層為270~290μmhos/cm較大，於底水層(Hypolimnion)較小為210~230μmhos/cm。4月時，水深約14公尺以下屬於底水層，溶氧量於表水層及變溫層較高，底水層較低，一般說來微生物量較10月時為多，其垂直分佈則以13公尺或15公尺處較多，傍晚與清晨微生物數量的垂直分佈雖然稍有差異但不很明顯。導電度由表水層到變溫層較大，由於爲360μmhos/cm到310μmhos/cm，底水層較小為310μmhos/cm。由於動植物性浮游生物之屍體及有機碎片等沉澱下來，懸浮於比重較大之底水層的上綠附近，受到微生物的分解，消耗大量的氧，使得微生物數量於變溫層之下綠及底水層之上緣較多，溶氧較少。