Microscale biogeotechnical differences in intertidal sedimentary ecosystems

Abstract

Abstract Intertidal sediments are inhabited by organisms that can modify the geotechnical and sedimentological properties of the sediment. We have analysed small scale differences in these properties at four closely adjacent sites on Ardmore Bay, Clyde Estuary, Scotland. The sites were an Enteromorpha algal mat site (EAM), a Corophium volutator site (CV), the head shafts of Arenicola marina (AMHS) and the tail shafts of Arenicola marina (AMTS) burrows. Three replicate cores were taken from each site. We measured load resistance, particle size parameters of mean particle size, sorting, skewness and kurtosis, and total organic matter (TOM) and carbonate. Load resistance was measured with a newly developed microscale load resistance penetrometer which measured load resistance of the sediment at 1 mm intervals through the sediment core from the surface to 100 mm. Sediment cores were then sectioned every 10 mm and particle size, total organic matter and carbonate content measured. In situ shear strength measurements were also taken at the four sites. The data were analysed by bivariate correlation analysis and multivariate cluster analysis. There was a number of significant positive and negative correlations between the parameters at the four sites. Significant down-core changes in the sediment parameters and their correlations were noted. These differed between the four sites. The CV site had the largest number of significant correlations, the EAM site had the least. Cluster analyses of the sites showed that in general the sites clustered separately, although there were a number of overlaps. The EAM site showed distinct clusters for its three separate replicate cores, while the CV site clustered into a top part and a bottom part of the core. Cluster analyses of the depths across all the sites identified a break in the data at depths of between 40 and 70 mm. There was a linear relationship between field shear strength and laboratory penetration resistance. The results are discussed in relation to the fine-scale geotechnical and sedimentological heterogeneity of intertidal sediments, and the effects of biological activity.