A comparison of the geochemistry of aquatic sediments and the fine (<63 μm) till fraction in Finland

摘要

A comparison is provided of the composition of aquatic sediments in Finland relative to that of the fine fraction (<63 μm) in till. The study is based on till samples collected throughout the country and 158 sediment cores from 122 Finnish lakes. Element concentration data were obtained by aqua regia (till) and nitric acid (sediment) extraction. The material was divided stratigraphically into four classes: till, pre-isolation sediments, immediate post-isolation sediments, and the top of the sediment column. Mean element concentrations were usually lower in the till fines than in the sediments; only Cu, K, Mg and Ni in the top sediments from the lakes approach the mean concentrations in till. The mean P concentration in the pre-isolation sediments was lower than that in till. Spatial comparison showed the highest statistically significant Pearson and Spearman correlations between the till and lake sediment results to be for Al, Cr, Cu, K, Mg and Ni (r = 0.34-0.64), although still higher coefficients were recorded for certain ratios between elements (r = 0.73 for K/Cr). No statistically significant correlations within the till-sediment system were observed in the case of Mn, P and V concentrations, and correlation for Fe varied depending on the system. A better correlation between till and lake sediments was observed in supra-aquatic than in sub-aquatic areas. The results also indicate that the sediments of large lakes (>10 km~2) resemble the mean composition of till better than do those of small lakes (<10 km~2), and that a statistically significant relationship exists between the clay fraction (<2 μm) in sediments and the K concentration in till.