Fine Sediment Influence on Salmonid Spawning Habitat in a Lowland Agricultural Stream: A Preliminary Assessment

In Newmills Burn, which is a small tributary of the River Don in Aberdeenshire, UK, the effect of fine sediments on Atlantic salmon and sea trout spawning success was examined. The tributary drains an area of intensive agriculture. The physical characteristics of spawning habitat in degraded areas were compared with those of less disturbed upland sites, and effects on egg survival were determined. The results showed that, although the physical characteristics of the stream indicated that it was highly degraded, it was utilized intensively by spawning salmonids. The deposition of fine sediments into spawning gravels appeared to relate directly to sediment transport rates, which were greatest during periods of elevated stream flows. Egg survival differed among redds. Poor egg survival was attributed to reduced permeability, exacerbated by the oxidation of organic matter, which could have reduced DO levels.