A Study of Carbon and Nitrogen Stable Isotope and Elemental Ratios as Potential Indicators of Source and Fate of Organic Matter in Sediments of the Forth Estuary, Scotland

Swimming behaviour in post-settlement Corophium volutator is more frequent at times of flow and is an important process controlling its distribution. It is not known, however, if swimming behaviour differs in still and flowing water, a question whose answer has important consequences for scales of movement of C. volutator. This study investigates the effect of flowing water on the initial 20 min of swimming and settling behaviour of C. volutator. In addition, this study tests the applicability of Gustʹs Microcosm, a new recirculating flume designed for stability testing of sediments, for use in behavioural observations of organisms in flow. Settling behaviour does not differ between still and flowing water. The same behaviour in flowing water can however result in a 60-fold increase in dispersal distance for the studied site, (from 0·7 to 43 cm) without any increase in time in the water column. Settling has been observed as an active process up to a friction velocity (U*) of 0·75 cm s-1, with C. volutator controlling both their time of entry to and length of time within the water column. Below a U*of 0·75 cm s-1settling is affected by the size of the amphipod. Increased current alone was also observed not to initiate swimming behaviour from non-desirable sediments up to a friction velocity (U*) of 1·02 cm s-1. These findings are discussed in light of their significance in the field. Gustʹs Microcosm is concluded to create realistic flow conditions for the field and will be useful when suspended sediment loads are low and complete viewing of the behavioural chamber from above is unnecessary.