Correlation of carbon with acid-soluble elements in Finnish lake sediments: two opposite composition trends

摘要

Rank order correlation coefficients (r_(C,X)) were determined between C and the nitric acid-soluble elements Al, Ba, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, P, S, Sr, Ti, V, Zn and N in lake sediments. Nitrogen and S concentrations increased together with C from the point of isolation towards the top of the sediment, whereas Ca, Cr, Cu, K, Mg, Na, Ni and Ti concentrations decreased. In the case of Al, Ba, Co, Fe, Mn, V and Zn, two divergent patterns were seen, their concentrations either decreasing or increasing towards the top of the sediment. Of the r_(C,P) values, 91% were positive and 9% negative. The sediment cores were classified into three groups on the basis of the correlations between C and Co, Fe, Mn and Zn: (1) rC,Co, rC,Fe, r_(C,Mn) and r_(C,Zn) statistically significant and negative; (2) r_(C,Co), r_(C,Fe), r_(C,Mn) and r_(C,Zn) not statistically significant; and (3) r_(C,Co), r_(C,Fe), r_(C,Mn) and r_(C,Zn) statistically significant and positive. In the light of the geochemical properties of the sediments, it was concluded that those in group 1 had been deposited under reducing and/or acidic conditions in small, shallow lakes containing high concentrations of C and those in group 3 under oxidative and/or alkaline conditions in large, deep lakes, while those in group 2 represent intermediate forms. It was approximated that C ≤ 9% in sediment provides precipitation of Fe-Mn oxides, but it is impeded by greater C concentrations. Also, sedimentation of terrigenous till material was found to be more effective in small than in large lakes.