Fe and Al sedimentation and their importance as carriers for P, N and C in a large humic lake in northern Sweden

The sedimentation of organic, amorphous oxides, crystalline oxides and crystalline silicate species of Fe and Al was investigated in humic Lake Ortrasket. The covariation with C, N and P sedimentation also was studied. The results showed a strong temporal variation in the occurrence of different Fe species. During high discharge, such as in spring, Fe mostly occurred as crystalline Fe-silicate species, while the amorphous form dominated at other times of the year. Al generally sedimented as crystalline Al-silicate species (95%). Amorphous Fe species showed a strong relation with organic C and N, suggesting an association between organic material and amorphous Fe oxides. P was not as strongly related to amorphous Fe, probably as a result of apatite or clay bound-P species sedimentation.