Siltation
Silt is very bad news for rivers and many of their inhabitants. With faster run offs from forestry, increased grazing pressures and typically potato, strawberry or maize crops, fine sediment loads on some streams smother the bed, killing off invertebrates and fish eggs, resulting in fish not using them or reduced spawning success. The fine sediment loading of our rivers has trebled since 1980 and in the most severely affected streams, egg survival has been reduced to 0%. Much of this damage is avoidable and knowledge is increasing about the whereabouts of vulnerable sites and which farming practiuces put the rivers at the greatest risk.
Following on from more than a decade of leaflet drops and advisory booklets, the "Catchment Sensitive Farming Initiative" aims to mitigate damage in the most vulnerable catchments such as Lugg, Ithon and Garren but it too has the disadvantage of being only voluntary and funding for remedial work is limited. Cross compliance is built into the current grant scheme, whereby grants may be reduced or removed in the event of bad agricultural practices but it lacks enforcement teams on the ground.
The Foundation continues to be alert to the damage caused by siltation and fencing out stock remains an absolute priority where siltation is a problem, as is preventing and repairing erosion.
To summarise: silt affects aquatic life is in several ways:
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Reduced rate of egg survival
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Spawning gravels become compacted
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Invertebrate types and numbers are reduced
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Acts as a vehicle for certain pesticides and phosphates
