Nature of Dissolved Organic Matter in the Drainage Basin of a Boreal Humic River in Northern Finland

Abstract

AbstractThe nature of dissolved organic matter in river, brook, and peat mining water in the drainage basin of the humic Kiiminkijoki River, located in an area of minerotrophic peatlands in northern Finland in the boreal region, was studied by gel filtration. Special emphasis was paid to changes in the nature of high molecular weight organic Fe‐P colloids that result from peat mining. The river water is organically colored, with high organic matter and Fe concentrations. High apparent molecular weight (HAMW) organic colloids are important for the transport of Fe and P in the basin. The gel filtration data suggest that the DOM in the water consist mainly of fulvic acids (FA), although humic acids (HA) are also important. The proportion of dissolved organic C (DOC) and Fe in the HAMW organic colloids increases with increasing DOC and iron concentrations in the river water. The apparent molecular weight of the DOM is higher than in the lakes in the area of ombrotrophic peatlands in southern Finland. Color in this humic water increases with DOC and Fe concentrations. The effect of Fe on color values can be seen in filtered (<1.2 µm) river water and in all the gel filtration fractions. The results indicate an increase in the mobilization of HAMW organic Fe‐P colloids in the peatlands of the area following drainage and peat mining. The average ratio of Fe to DOC in the HAMW organic fraction is higher in the peat mining water than in the Keihäsoja brook in a natural peaty urea. It is possible that the Fe to DOC ratio in these colloids transported in the river increases following drainage and peat mining, especially under low flow conditions in summer. This may lead to gradual changes in the detritus food webs of the river ecosystem.