Nickel diagenesis and partitioning in lake sediments

Abstract

Nickel discharged into the Moira River has accumulated in the sediments of Moira Lake during the past 125 years. Depth profiles of total Ni in the sediments reflect variations in Ni input into the lake. In the porewaters the Ni concentration decreased below the mud-water interface and was not correlated with the concentration of Ni on the solid phase. Subsamples of each core section were leached sequentially with progressively stronger agents to identify the geochemical fractions with which the Ni was associated. The partitioning of anthropogenic Ni between fractions changed with depth. The fraction of Ni in the exchangeable (1–8%) and in the carbonate-ound (1–45%) fractions decreased with depth, and the percentage in the organic and sulphide fractions (15–60%) increased deeper in the sediments. Very little (< 5%) of the anthropogenic Ni was present in the residual fraction. In much older sediments that predate the input of anthropogenic Ni, > 80% of the total Ni is found in the residual extract. A simple diagenetic model using the changes in redox conditions and NiS solubility can explain the anthropogenic Ni distribution in the sediments.