Effects of water level fluctuation on the growth of submerged macrophyte communities

Aquatic plant communities are frequently subjected to water level fluctuation. While many experimental studies have examined effects of water level fluctuation on the growth of individual aquatic plant species, very few have tested those on aquatic plant communities. We constructed aquatic communities consisting of four submerged macrophytes (Potamogeton perfoliatus, Myriophyllum spicatum, Chara fragilis and Ceratophyllum demersum), and subjected them to three static water depths (30, 90 and 150 cm) and three water level fluctuations with low, medium and high frequency (two, four and eight cycles of water depth change between 30 cm to 150 cm). Water depth in each of the three fluctuation treatments was on average 90 cm, which was comparable to the static water depth of 90 cm. Increasing water depth significantly decreased the growth of the communities in terms of biomass, number of shoot nodes and shoot length because it decreased the growth of most species (P. perfoliatus, M. spicatum and C. fragilis). Compared to the static water depth of 90 cm, water level fluctuation increased number of shoot nodes and shoot length of the communities, whereas fluctuation frequency had little impact. We conclude that water level fluctuation may potentially increase the vegetative spread of submerged macrophyte communities and managing water level fluctuation may be helpful for the restoration of submerged macrophyte communities in degraded wetlands.