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Visibility; Secchi disks; Lakes--Minnesota


A threefold study was undertaken to:

1) determine the nature of the mathematical relationship between vertical and horizontal visibility underwater

2) examine the feasibility of using the Secchi disc method to measure horizontal visibility in the photic zone;

3) obtain descriptive data on vertical and horizontal visibility in selected lakes of southern Minnesota.

The Secchi disc technique for measuring· visibility was modified to accommodate horizontal readings, and data were col1lected from 12 lakes at 5, 15 and 25 feet depths under controlled conditions. Reliability correlations were significant (p ( .01) and ranged from .764 to .994. Correlations and regression equations were computed among visibility measures. A strong positive relationship was noted between vertical visibility and horizontal visibility at the 5-foot depth; weak positive correlations occurred between vertical visibility and the other measures of horizontal visibility; the Secchi disc method of measuring water transparency proved reliable for taking horizontal visibility readings; and data obtained from the 12 sample lakes were compatible with parameters established by studies on similar lakes. A system for providing comparative visibility data is proposed.

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