RETENTION OF ORGANIC FE-P-COLLOIDS FROM PEAT MINING WATER IN AN OVERLAND-FLOW WETLAND TREATMENT SYSTEM IN NORTHERN FINLAND

The importance of dissolved organic matter (DOM) for the organic, Fe a nd P reductions achieved in an overland flow area (OFA) was estimated and the changes in the nature of DOM studied by gel filtration at a si te in northern Finland. In the OFAs peat mining water is purified cond ucting it across a natural mire of a given size. DOM plays an importan t role in the transport and reduction of organic matter, Fe and P in O FAs. The retention of Fe in filtrates, dissolved organic P and to some extent also DOM in the OFA under low flow conditions in summer is pro bably promoted by the high Fe content of the highest apparent molecula r (HAMW) weight DOM in the peat mining water. On the other hand, the o riginally low Fe content of the DOM in the HAMW fraction may be one re ason for the generally low reductions in these water quality parameter s achieved during flood periods.