The influence of an extracellular polymeric substance (EPS) on cohesive sediment stability

Abstract

Extracellular polymeric substances (EPS) are secreted by a variety of benthic organisms including diatoms and bacteria. These substances are often considered the primary mechanism by which intertidal benthic organisms increase sediment stability. The stabilisation is caused by physico-chemical interactions between clay minerals and EPS and physical strengthening and gluing by EPS strands. The effects of an EPS (xanthan gum) on the erosion characteristics (threshold and rate) of cleaned cohesive sediments were investigated in the laboratory for the first time using two erosion devices, and compared to in situ measurements on natural sediments. The addition of EPS was found to increase the erosion threshold and to decrease the erosion rate of the cohesive sediment, even at the lowest EPS content. Low-temperature scanning electron microscopy (LTSEM) images of the sediment revealed differences in the microstructure and EPS distribution between the five laboratory treatments and natural sediments. This study supports the contention that EPS secretion is partly responsible for the increases in sediment stability caused by many intertidal benthic organisms.