DO ROOTED MACROPHYTES INCREASE SEDIMENT PHOSPHORUS RELEASE

Sediment cores were collected from two of the Norfolk Broads and two o f the West Midland Meres, to test the hypothesis that rooted macrophyt es increase the sediment release rate of phosphorus during the growing season. These were taken from inside and outside plant beds (mixed My riophyllum spicatum and Chara sp. in Hickling Broad and Nuphar lutea i n Burntfen Broad, Mere Mere and Little Mere). The overlying water was replaced with a standard water designed to mimic lowland freshwater. A fter an overnight 'batch' incubation the water was analysed for TP and SRP. From this their release rates were calculated. Interstitial meas urements of SRP were also made for some of the Broads cores at the end of the incubation period. The data were analysed using General Linear Models. TP and SRP were the responses for both data sets. Factors for the Broads were inside/outside plant beds, date, and site, whilst for the Meres the factors of date and site could not be delineated. Relea se rates in this study were affected by a number of factors (plants, s ite and date). The picture emerging so far is that when rooted macroph ytes have a significant effect on phosphorus release they increase it. However the large variability between replicates highlights the logis tical difficulties in running such experiments.