Calculating net annual accumulation rates of sediment components exemplified by pollen

Abstract

The net annual accumulation rate of a sediment component can easily be estimated by determining the total content of the specific component (x) in a sediment sample, which represents a known number of years (yr) and certain area of the lake bottom (a), using the formula: annual accumulation =x/(yr·a). To illustrate and test this procedure we have calculated mean net annual accumulation rates for sediment dry matter, mineral matter, organic matter and pollen grains of Scots Pine (Pinus sylvestris L.) for one short sequence of a varved lake sediment core. This paper includes descriptions of a simple method for sub-sampling fresh cores of consolidated sediments and an alternative method for making absolute pollen counts. The test results clearly show that in varved sediments quantitative sediment samples can be cut out with very high precision, Le. the variable a and in this case also yr can be very accurately determined. They also show that dry sediment, mineral and organic matter and pine pollen grain contents (i.e. x) and thus, mean net annual accumulation values could be estimated with a good precision (C < 30%). This procedure for estimating net annual accumulation rates is, of course, applicable in non-varved sediments and for many other sediment compounds provided that a reliable chronology can be determined.