A Tale of Two Extremes- floods, droughts and salmon spawning habitat
Ian Pattison, Loughborough University
Room 311, 4pm
Room 311, 4pm
Land use changes are also thought to have increased fine sediment delivery to our river systems, which degrade salmon spawning gravels and decrease egg survival rates. The main hypotheses used to explain this being (a) fine sediment reduces gravel permeability and intra-gravel flow velocities; and (b) intra-gravel O2 concentrations decrease due to reduced supply and increased consumption by organic sediments. The SIDO (Sediment Intrusion and Dissolved Oxygen)-UK model is a physically based numerical model which stimulates the effect of fine sediment intrusion on the abiotic characteristics of the salmonid redd, along with the consequences for egg development and survival. This model has been used to assess the impact of varying sediment inputs upon the sediment intrusion rates, abiotic redd characteristics and fish egg survival rates. This will be used to comment on the relative importance of each of the hypotheses put forward to explain the impact of sediment on egg survival. Results indicate that the physical process of blockage, especially by larger sand particles, is more significant than the Sediment Oxygen Consumption mainly associated with silts and clays. These findings have implications for how we manage the sediment delivery problem.