A method for measuring effects of bioturbation and consolidation on erosion resistance of aquatic sediments

Sediment erosion by water movement affects turbidity and thus benthic communities in numerous aquatic systems. This aspect has been widely studied in coastal habitats and estuaries, but less studied in freshwater systems such as shallow lakes. Here we present a simple device to study the effects of biota on the resistance of aquatic sediments to erosion by water movement. Circular 75 l tanks are used to incubate selected sediments with microbial communities. The tank size allows addition of organisms such as small fish, invertebrates and aquatic plants. Effects are studied by gradually increasing water movement by means of a rotor and continuously monitoring the increase of suspended solids. The water speed needed for resuspension is a measure of sediment erosion resistance. With this device we found a linear increment of erosion resistance over time if sediments are left undisturbed, and a significant reduction of erosion resistance with small holes punched randomly in the top layer of sediment (to mimic the effect of benthivorous fish foraging behaviour). Fish biotic perturbation was indicated by a reduction of sediment resistance associated with benthivorous fish presence. However, three spined stickleback did not create the same effect. Measurements with this simple device are reasonably precise and suggest that the set-up can be used to study effects of numerous factors that may affect sediment erosion resistance. For example, sediment consolidation associated with light, temperature, and microbial and plant colonization, along with sediment perturbation related to big invertebrates and fish behaviour.