Investigation on the method for measureing the amount of freshly precipitating matter in lakes.

Abstract

As an approach to studies on the decomposition process of suspended matter in lake water, the use of a funnel connected with an Ehlenmyer flask as a collection apparatus (Fig. 1-A and-B) for a short period was examined for measuring the amount of freshly precipitating matter. The results obtained are summarized as follows :
1) The amount of precipitating matter is proportional to the area of funnel, not to the whole volume of apparatus. This may suggest that the trapping effect on suspended matter is not so significant (Fig. 2).
2) The amount of precipitating matter also increases linearly with time spent for collection, unless there is any unusual effect of the temporary movement of lake water or of artificial events (Fig. 3 and 4).
3) The unusual effect of the temporary movement of lake water can be detected by measuring the amount of precipitating matter successively for a few days and plotting its values against the time spent for collection. Insuch a way, the following events were expected : the inflow of water mass heterogeneous in algal concentration (Fig. 4-2), the contamination of bottom mud caused by wind (Fig. 5) or by the effect of artificial events such as anchoring or dredging (Fig. 3), and the stagnation of lake water immediately after being closed by ice (Fig. 6).
4) It is concluded that dynamic status of freshly precipitating matter can be pursued by this method.