Temporal variations in dissolved and suspended iron and manganese in the Kalix River, northern Sweden

Abstract

Particulate and dissolved Fe and Mn were measured once a week from May to September 1982 in the Kalix River, north Sweden. During winter baseflow the dissolved Fe concentration was 450 μg l −1. Early snow-melt discharge increased the concentration slightly but during springflood maximum the concentration decreased to a minimum value of 60 μg l −1 in mid-July. Particulate matter in the Kalix River is dominated by Fe which ranges between 14% and 38% of the ashed suspended load, ∼ 70–80% of the total Fe load being retained by 0.45-μm filters. Approximately 10% of particulate Fe can be accounted for by a detrital phase. The particulate Fe/Al ratio showed a mean value of 6.5 which is more than ten times the ratio in mean world river. Particulate Fe showed a peak during early snowmelt and decreased during maximum discharge similar to dissolved Fe. Dissolved Mn concentrations ranged from 1.1 to 53.4 μm l −1 with a mean value of 11.2 ± 12.4 μg l −1, whereas particulate Mn ranged from 3.1 ti 18.2 μg l −1, with a mean concentration of 10.6 ± 4.9 μg l −1. During May and June most Mn was transported in the dissolved phase whereas in July and August the particulate fraction dominated. There was a drastic increase in non-detrital particulate Mn with a concomitant decrease in the dissolved fraction in early July with peak values in mid-July and early August. The decrease in dissolved Mn and increase of particulate Mn is probably the consequence of two processes, namely addition of non-detrital particulate Mn to the river, possibly from lakes, and transformation of dissolved Mn to a particulate phase within the river. A combination of increased pH, temperature and particulate Mn triggered the precipitation of dissolved Mn, although the significance of each factor can not be evaluated from this study.