Distribution of aquatic macrophytes in Lake Alexandrina, New Zealand

Abstract

Abstract The macrophyte distribution of Lake Alexandrina (737 m a.s.l.), a small, homothermous, South Canterbury high‐country lake, is closely related to depth. Shallow water communities, mostly dominated by Isoetes alpinus Kirk, extend to a depth of about 4 m, but do not grow above 0.7 m because of strong wave action. Mid‐depth communities consist of a tall Elodea canadensis Michx./ Myriophyllum triphyllum Orchard community between 2 and 4 m at the shallow northern end of the lake, large areas of Chara fibrosa var. acanthopitys (A.Br). Zanev. at the southern end, and a Myriophyllum triphyllum/Nitella hookeri A.Br. community at 2–6 m on the steeply descending eastern and western sides of the lake. Pure stands of Elodea canadensis may replace the last community, particularly on the eastern side. A deep water characean community of Chara globularis Thuill. and Chara corallina Kl. ex Willd. extends from 4 m to 10–11 m with 100% cover; C. corallina continuing sparsely to 16 m. Maximum above‐ground biomass recorded for the summer 1982–83 was 1350 g m ‐2 (dry weight) for C. globularis and 1100 g m ‐2 for E. canadensis.