Variation in nutrient removal in three wetland blocks in relation to vegetation composition, inflow nutrient concentration and hydraulic loading

Wetlands provide vital ecosystem services such as water quality improvements, and are important sites of biodiversity conservation. Their optimal use and management depends, in part, on vegetation management and the quality and quantity of the water flowing through them. The South-finger wetland, situated on a Wildfowl & Wetlands Trust wetland visitor centre at Slimbridge, UK, receives waters of high nutrient concentrations from the wildfowl collection. The nutrient removal functioning of three constructed beds was compared and related to variations in input nutrient concentrations and hydraulic loading over 1 year (October 2005–October 2006). None of the beds removed nitrate, orthophosphate or total phosphorus over the year as a whole. The beds planted with Iris and mixed vegetation were found to remove the greatest proportion of ammonium, and increased nitrate concentrations in the water to a lesser extent than the Phragmites bed. Nutrient functioning in all three beds varied in a non-linear manner in relation to input nutrient concentrations and water residency time. Possible reasons for the differences in functioning between nitrogen and phosphorus, vegetation types and between seasons are discussed.