Grain size normalization: a case for post extraction normalization and inclusion of selective extraction procedures

D.J. Akhurst, M.W. Clark, A. Reichelt-Brushett, G.B. Jones

Limnol. Oceanogr. Methods 9:215-231 (2011) | DOI: 10.4319/lom.2011.9.215

ABSTRACT: The spatial mapping of trace metal and/or nutrient elemental concentrations in surface is often aided by normalization approaches that allow comparison of texturally, geochemically, and mineralogically dissimilar sites. Frequently, this is a grain-size normalization at < 62.5 μm before chemical analysis. However, material that is >62.5 μm (generally geochemically inert) may have fine-grained coatings that bind components of interest and/or may consist of aggregates of fine-grained sediment. The misplacement of these essential components within the coarse fraction of size-normalized sediments may skew data and subsequent geochemical interpretations, especially when these components make up a substantial proportion of the sediment metal and/or nutrient binding capacity. In this article, sedimentary contaminant data were normalized using size normalization (wet sieving < 62.5 μm) and a post-extraction normalization (PEN). PEN is a size-based normalization procedure devised to minimize the misplacement of fine-grained coatings/aggregates by applying a size and mineralogical normalization to inert digestion residuals, post-chemical extraction. The data show that PEN provides a more ecologically and diagenetically interpretable representation of partitioning of elements between sediments in a freshwater reservoir. In addition, PEN samples are more rapidly collected, and consequently, PEN provides a cheaper alternative to traditional size normalization. In addition, application of the PEN allows the collection of data not only relevant to ecological health, but also relevant sedimentary diagenetic mobility data using a single sediment sample.