A reconnaissance survey of the source of interstitial fine sediment recovered from salmonid spawning gravels in England and Wales

The declining salmonid populations reported for many rivers in England and Wales have frequently been attributed to spawning gravel siltation and the need to address this problem through sediment control strategies has been widely recognised. The planning of such sediment control strategies is, however, severely hampered by the lack of reliable information on the source of the fine sediment deposited within spawning gravels. Given the need for information on the source of the fine sediment accumulating in salmonid spawning gravels, a reconnaissance survey, based on the source fingerprinting approach, has been undertaken to establish the source of fine interstitial sediment recovered from spawning gravels in 18 important salmonid rivers in England and Wales. The findings confirm the potential of the fingerprinting approach for establishing the provenance of interstitial fines. More specifically, the results provide useful information on the relative importance of surface and channel/subsurface sources as the source of the interstitial fines collected from the individual study rivers. Significant regional contrasts in the source of this sediment are reported. The findings have important implications for the design and implementation of effective sediment management strategies aimed at protecting salmonid spawning gravels, in terms of both the sources to be targeted and the associated need to adopt different approaches in different rivers.