Nutrient dynamics in a semi-natural treatment reedbed

Constructed wetlands are increasingly being used to treat polluted water and reedbeds in particular are widely favoured for removing nutrients from wastewater. Reedbed systems are generally considered cheaper to operate than their industrial counterparts, and have the additional benefit of providing valuable habitat which has the potential to support a wide range of wetland species. Whilst the nutrient removal rates of these systems may be monitored for a period following creation, there is a lack of long term monitoring and as a result there is a poor understanding of how removal efficiency changes with time. In addition, factors such as vegetation type, residence time and latitude of the reedbed all affect the nutrient removal rates. This work focuses on a treatment system at the Wildfowl and Wetlands Trust Reserve at Slimbridge in Gloucestershire, which receives a high nutrient load from the reserve’s bird populations. Recently collected hydrochemical data is compared to data collected shortly after the creation of the reedbed and show that comparing the inflow and outflow concentrations, the system currently reduces only ammonia concentrations; nitrate concentrations are unchanged and phosphorus concentrations increase. Potential management options that may improve removal capacity are discussed.