A remote sensing technique, using an echosounder, a water proof illuminometer and a submarine electric torch, was effective for the ecological survey of aquatic macrophytes in Lake Oze-numa located in the Nikko National Park, Japan. Among fifteen aquatic macrophytes, seven submerged plants, three floating-leaved plants, one free floating plant and four emergent plants were found.
Potamogeton perfoliatus L. was one of the dominant submerged species in a shallow zone up to 3.7 m in depth. The plant grew at the rate of 3 cm·day
-1 towards the maximum length of 1 m from June to July, and flowered in the middle of July. The plant prepared wintering smaller plants and died off in September. Another
Potamogeton, P. maachianus A. Benn. was dominant in deeper water to the maximum depth of 6.3 m and made a thick stand of 1.5 m in height in summer. The plant was thought to overwinter with the same height. The maximum standing crop of an alian submerged plant of
Elodea nuttallii (Planch.) St. John was estimated as 440 g·m
-2 by an optical method in August 1987. The pure and dense stand seemed to overwinter keeping 0.5 m in height. The plant had a vigorous adventive spread at the most littoral area in the depth between 1 and 6 m.
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