The relationship between zinc and organic content in centre-lake bottom sediments

Abstract

Abstract The relationship between Zn and organic content, the latter measured by percentage weight loss on ignition (LOI) is investigated in a suite of 3844 centre-lake bottom sediments from east-central Saskatchewan. The data indicate that Zn values have a strong sympathetic increase with LOI below 12% LOI. Zn values tend to stabilize above 12% LOI, in actuality they decrease slowly from 12 to 50% LOI before decreasing at an accelerated rate over 50% LOI. It is proposed that the change from a sympathetic Zn vs. LOI relationship to an antipathetic relationship occurs because there is insufficient Zn available, from weathering, etc., in the lake water of sampled lakes to maintain the sympathetic relationship. Therefore, the lack of Zn, together with the increasing availability of organic material, creates an excess adsorption capacity of the lake sediments. Below 12% LOI, in lake sediments that do not have an excess adsorption capacity, Zn distribution patterns will be partly controlled by the amount of organic material present. Thus, Zn in these lake sediments may not truly reflect the chemistry of a drainage basin. Whereas, above 12% LOI, where there is an excess adsorption capacity in the sediments, the Zn distribution patterns will more closely reflect the chemistry of a drainage basin. The observed decrease in Zn values obvious over 50% LOI may be reflecting a dilution factor introduced by the ever increasing load of organic material to a system which is not receiving more Zn. It is concluded that centre-lake bottom sediments whose organic content is dominantly in the range of 12–50% LOI form the most effective sample media for regional lake sediment surveys.