湖沼の富栄養化に及ぼす底質内栄養塩類の影響 : 諏訪湖底質中の栄養塩類の分布特性とその挙動
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During the period from May 1978 to March 1983, research was conducted on the features of horizontal and vertical distribution of nutrients contained in the sediment of Lake Suwa. Laboratory experiments were also conducted to reveal the behavior of the nutrients in the lake sediment. The following are the findings:Total phosphorus and nitrogen contents were found to be horizontally distributed in the surface sediment almost uniformly throughout the lake except for the estuary and carp-cultivating areas. Their constituent values are represented by the measurements taken in the surface sediment at the center of the lake. The values of total phosphorus and nitrogen contained in the surface sediment at the center of the lake were 3.7-4.0mgP/g dry wt. and 5.0-5.5mgN/g dry wt., respectively.Total phosphorus contents had rapidly increased during the period from 1972 to 1978. This is considered to have been caused by an increase in the phosphorus load flowing into the lake and its property to accumulate itself. Therefore, the amount of phosphorus contained in the lake sediment is expected to keep increasing in the future in proportion to the load of phosphorus flowing into the lake. However, such property has not been found with the nitrogen contents. It is therefore considered that nitrogen will maintain the current concentration level in the future.A high correlation was observed between the total phosphorus and the inorganic phosphorus in the surface sediment; 60%-80% of the total phosphorus was found to be inorganic phosphorus. Fe-P contained in the inorganic phosphorus was found to be highly concentrated in the upper layer (0-8cm) of the sediment. Fe-P showed a tendency to decrease in the 0-2cm layer after ten weeks of laboratory experiments as some of it had apparently dissolved out into the upper water layer. However, the amount of Fe-P increased in the 2-6cm layer. From these observations, it became clear that Fe-P had moved up from the lower layer of the sediment to the upper.A close correlation was found between the density of ammonium in the sediment and the temperature of the sediment. The relationship between the speed at which ammonium is generated and the temperature of the sediment is shown by the following formula:GNH4-N=0.018exp0.153T+0.427
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