Potential allelopathic impact of Potamogeton schweinfurthii on phytoplankton in Lake Ziway, Ethiopia

Abstract

We hypothesized that allelopathic interaction could occur between the submerged macrophyte, Potamogeton schweinfurthii, and the phytoplankton population in Lake Ziway (Ethiopia). Potential interactions were assessed using field and laboratory studies between January and July 2012. Mean phytoplankton biomass (as measured by chlorophyll a) was lower in P. schweinfurthii beds (29.04 ± 6.9 μg/L) compared to open water (56.34 ± 8.1 μg/L). Field incubation experiments showed that chlorophyll a increased slowly (2.5 μg/L per day), when incubated with P. schweinfurthii exudates, significantly different (t-test, p < 0.05) from values measured (10 μg/L per day) in controls. A similar observation was made in the laboratory experiments with phytoplankton growth inhibited when exposed to P. schweinfurthii extracts. These results suggest that extract of P. schweinfurthii may be useful for controlling phytoplankton blooms in some Ethiopian lakes.