Sediment quality characteristics of salmonid spawning grounds

2013-03-08T13:45:38Z (GMT) by David J. Milan
This thesis focuses upon the sediment characteristics of salmonid spawning grounds in a number of lowland and upland catchments in England and discusses the implications of spatial and temporal variability of channel-bed sediment composition upon different stages of the salmonid life-cycle. Substrate samples were obtained by using freeze-coring techniques, thus avoiding the problems of elutriation of fine-sediments which have hindered many studies in the past. Spatial variability is assessed within-site, between-sites and between catchments. Temporal development of channel-bed sediments is assessed both between and within spawning seasons in two upland streams, one of which is regulated. Overall change in sediment quality is demonstrated by changes in armour layer particle-size and variability in the fine-grained sediment population. Vertical infiltration of fine-grained sediments was successfully quantified by analysing core-section loadings over time. Results are explained in terms of mechanisms and processes occurring at each scale. A typology of streams has been developed based upon a continuum of granulometric characteristics which ranged from coarse-grained upland sites to fine-grained (sandy) lowland sites. Sediment quality of a number of lowland streams, based upon indices derived from the literature, were classed as unsuitable by this methodology, largely because of the high loadings of fine-grained sediments (in excess of 14% sub 1.0 mm material). As these streams are known to support good salmonid populations, the usability of such indices is criticised. A model is presented to predict percent weight fine-sediment (sub 1.0 mm) from maximum unit stream power. Error margins limited this application however. The use of freeze-coring techniques for sediment quality assessment are discussed in the light of the results.