Modification of sediment permeability and shear strength by two burrowing invertebrates

Laboratory experiments have been conducted on the effects of bioturbation by the amphipod Corophium volutator (Pallas) and the polychaete Nereis diversicolor (O.F. Müller) on the physical properties of estuarine muddy sand. Invertebrates and muddy sediment were collected from Langbank, Firth of Clyde, Scotland. Sediment columns were seeded with low, medium and high densities of invertebrates in single-and mixed-species experiments. Permeability decreased with increasing density of C. volutator, but increased with increasing density of N. diversicolor. Water content decreased with increasing density of both species. Shear strength increased with increasing density of both species, but more so with C. volutator than with N. diversicolor. Mixed-species effects on shear strength were additive, but some of the permeabilities were lower than predicted. Bivariate and multivariate correlation, and partial correlation analyses were applied to the data. Shear strength was negatively correlated with water content. The correlations between shear strength and permeability and between permeability and water content were affected differently by the two species. There were few partial correlations between the variables.