Content versus concentration: Effects of units on measuring the biogeochemical properties of soft sediments

A variety of scientific disciplines require measurements of the biological, physical and chemical (biogeochemical) properties of soft sediments. These properties vary temporally and spatially in a highly complex fashion, due to interaction and feedback between the processes that control them. This paper presents theoretical and real examples showing how interaction between the properties of sediments and the use of different units of expression (i.e. content and concentration) can change patterns in the data and thereby alter the interpretation of results. Common mistakes leading to incorrect measurements being taken and incorrect inference of data are presented and a new conceptual way of thinking about natural sediments is discussed. We conclude that the presentation and interpretation of data expressed as concentration is preferable to content for biogeochemical measurements in sediments, because content data is confounded by various factors (including core density/mass), leading to mistaken inference.