Harvesting effects on biomass and nutrient retention in Phragmites australis in a free-water surface constructed wetland in western Ireland

Abstract

The aim of this study was to examine the seasonal variation in biomass, total nitrogen (Tot-N) and total phosphorus (Tot-P) content of Phragmites australis in a 3-cell free-water surface (FWS) constructed wetland in western Ireland and to investigate the effects of harvesting on their biomass and nutrient content. One cell of the wetland was divided into two plots: one plot, measuring 80 m2, was completely harvested on the 16th June, 2005, while the other plot, the control plot, remained uncut throughout the study duration. At approximately monthly intervals over an 8-month study duration, completely randomised 0.64m2 areas within each plot were harvested to water level and the shoot biomass and nutrient content were measured. In the control plot, the plant biomass, Tot-N and Tot-P content peaked in August. In the June-cut plot, the shoot biomass, total nitrogen (Tot-N) and total phosphorus (Tot-P) content peaked in September. The mean rate of dry matter production (RPD), defined as the mean daily rate of dry matter production per unit area per day between harvests, attained maximum rates of 12.8g m-2d-1 and 4.2g m-2d-1 for the control and June-cut plots, respectively, indicating that annual harvesting of emergent vegetation may not have any beneficial effect on biomass production or nutrient content under Irish climatic conditions.