PHOSPHORUS FIXATION WITH IRON(III)CHLORIDE - A NEW METHOD TO COMBAT INTERNAL PHOSPHORUS LOADING IN SHALLOW LAKES

Laboratory experiments using continuous flow experiments and batch exp eriments showed that additions of 100gFe(3+) m(-2) to lake sediments d ecreased the phosphorus release rates substantially. Treatment of the sediments of the shallow lake Groot-Vogelenzang, part of the Reeuwijk lakes area (the Netherlands), with this amount of iron resulted in an immediate threefold decrease in the total phosphorus concentration in the lake. This improved water quality lasted for three months. The mos t important reason for this only transient improvement was the unexpec ted short residence time of the lake of only 35 days. Phosphorus budge t calculations, phosphorus release experiments and determinations of b ioavailable phosphorus all indicated that the phosphorus binding capac ity of the sediments increased due to the treatment, although the thre e methods gave different results. Treatment of lake sediments with iro n(III)chloride is potentially an effective method to decrease internal phosphorus loading, but the durability of this method still needs to be proven.