Aquatic macrophytes in a tropical African reservoir: diversity, communities and the impact of reservoir-level fluctuations

Abstract

ABSTRACT Variation in species composition, distribution and abundance of macrophytes in the Malilangwe reservoir, a tropical African reservoir, was investigated at four sites in three seasons; March (hot-wet season), June (cool-dry season) and September (hot-dry season) over a nine-month period. Thirteen macrophyte species, representing nine families, were recorded during the study period. Submerged macrophytes had a patchy distribution and the mean transect cover per species was below 3% with the exception of Ceratophyllum demersum and Potamogeton pusillus. Canonical Correspondence Analysis (CCA) identified four distinct macrophyte groups closely associated with the three seasons; hot-wet, cool-dry and hot-dry and environmental factors; pH, dissolved oxygen, phosphorus and water level. Change of seasons and subsequent fluctuations in water levels resulted in changes in macrophyte community structure from the dominant emergent macrophytes (Cyperus involucratus, Panicum repens, Ludwigia stolonifera, Phragmites mauritianus and Schoenoplectus corymbosus) in the hot-wet season to submerged macrophytes (Najas horrida, Potamogeton crispus, Potamogeton pusillus, Potamogeton tricarinatus and Persicaria decipiens) in the hot-dry season. Although changes in water level variations seemed to influence macrophyte structure and composition changes, further research is needed to evaluate to what extent water level fluctuations interact with other seasonal factors acting independently.