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Method for Estimating Bulk Density of Soft-Bottom Sediment Cores

TNO Environmental Sciences, Energy Res. and Process Innovation, Dep. for Ecological Risk Studies, Den Helder (formerly Wageningen Agric. Univ.), the Netherlands;
Wageningen Agric. Univ., Dep. of Water Quality and Aquatic Ecology, Wageningen, the Netherlands;
Univ. of Florida, Everglades Res. and Education Center, Belle Glade, FL 33430;
Grontmij, Zeist (formerly Wageningen Agric. Univ.), the Netherlands.

^* Corresponding author (dlan{at}gnv.ifas.ufl.edu).

ABSTRACT

Soft-bottom highly porous sediment samples can be frozen to facilitate handling, preservation, and especially separation of sediment layers before laboratory analysis. Due to core expansion upon freezing, bulk density measurements are biased (underestimation of up to 8.9% for pure water), but bulk density in separate sediment layers can only be measured after freezing. Therefore, the objective of this study was to develop a methodology that allows the actual field bulk density to be estimated from measurements on frozen cores in the laboratory. Homogeneous soft-bottom undisturbed sediment cores (single layer) were sampled with a transparent cylindrical device in the Everglades Agricultural Area. The bulk density of the undisturbed, unfrozen sediment cores (field bulk density) was calculated by measurement of the volume and weight of sediment cores. After freezing, the solids fraction and frozen bulk density on a wet-basis were determined. From the collected data, the field (i.e., before freezing) bulk density could adequately be predicted from the frozen bulk density and the solids fraction. The method described in this paper allows field bulk density of separate sediment layers to be estimated from parameters easily measured on frozen sediment cores, and is therefore useful when different sediment layers require delineation.

Contribution from the Univ. of Florida, Inst. of Food and Agric. Sciences. Florida Exp. Stn., J. Series no. R-04337.

Received for publication January 31, 1997.