The Contribution of Typha Components to Floating Mat Buoyancy

The seasonal contribution of living Typha components to the buoyancy of floating mats was investigated in a diked, freshwater impoundment near the head of the Bay of Fundy in New Brunswick, Canada. The objectives were (1) to examine the potential influence of a dominant, mat—building species on hydrologic conditions at the mat surface, and (2) to predict whether a complete killing of the dominant species could cause mats to sink. The Typha component contributing most to mat buoyancy was the rhizomes, which added a net buoyancy pressure of °20 Pa throughout the growing season. The seasonal maximum buoyancy contribution of 28 Pa for all living Typha components combined was reached in spring, followed by a decline to 11 Pa in late summer as the aboveground shoots developed. This positive and seasonally variable contribution of Typha to mat buoyancy is expected to be most important during the early stages of mat development, when mats are thin and composed largely of living, belowground organs. However, on older and thicker mats the living Typha is less important because of the large volumes of gas bubbles from anaerobic decomposition that are trapped in the dead organic material. For the 50 cm thick floating mats under study, it is concluded that trapped gas is the main cause of buoyancy and would lead to the continued flotation of mats even if the living Typha were removed. Implications of the results are discussed in relation to the resiliency of floating mat systems.