CONTRIBUTION OF CATION-EXCHANGE PROPERTY OF OVERFLOW WETLAND PEAT TO REMOVAL OF NH4+ DISCHARGED FROM SOME FINNISH PEAT MINES

The importance of adsorption on peat for decreasing NH4+ was estimated in four overland flow areas (OFA) in northern Finland, where peat mining water is purified by conducting it across a natural mire of a given size. The effective cation exchange capacity (ECEC) values of peat in the OFAs ranged from 21.4 to 92.7 meg per 100g, being generally highest in the surface 0-15 cm. It was estimated that about 4.6-5.8% of the peat cation exchange sites could be occupied by NH4+, corresponding to a NH4+ retention capacity of about 0.18 to 0.77 g kg(-1) peat. Assuming that the retention was attributable to the 0-15 cm gkg surface pear layer alone, the calculated NH4+ retention potential of OFA peat should have lasted under 6 months with the loadings imposed on the OFAs and the decreases in NH4+ amounts in peat mining water considered here. The actual duration of peat capacity to retain NH4+ in the OFAs has, however, already been shown in this research to be longer, and apparently will be so also in future, probably as a result of two processes: nitrification and subsequent N loss through denitrification, and biological assimilation. Hence, cation exchange capacity of OFA was an important property that contributed to surface water protection against eutrophication by N.