Mitigating sediment delivery to watercourses during the salmonid spawning season: Potential effects of delayed wheelings and cover crops in a chalk catchment, southern England

Abstract

Identification of diffuse sediment pollution ‘hotspots’ requiring improved management in catchments supporting salmonids can be achieved using computer models. Accordingly, the PSYCHIC (Phosphorus and Sediment Yield CHaracterization In Catchments) model, which has been evaluated against empirical data, was used to simulate sediment pollution and its potential mitigation during the salmonid spawning season in a priority catchment identified by the England Catchment Sensitive Farming Delivery Initiative, drained by the Rivers Test and Itchen, in southern England. PSYCHIC predicted that approximately 83% (3912 t or 24 kg ha⁻¹) of the baseline annual total sediment transfer to watercourses (4694t or 29 kg ha⁻¹) coincided with salmonid spawning. Blanket adoption of delayed wheelings on all winter cereal fields (34,000 ha) was predicted to attenuate baseline sediment delivery during the spawning season by 21%. Cover cropping for all spring crops (24,000 ha) was predicted to reduce baseline sediment transfers by 8%. Targeted deployment of these two mitigation methods to 900 ha of winter cereals and 730 ha of spring crops, representing just 3% of the study catchment characterized by a baseline sediment transfer during the spawning season of > 200 kg ha⁻¹, was predicted to reduce corresponding sediment inputs to river channels by 6% and 3%, respectively.

Keywords:

• Sediment delivery
• salmonid spawning season
• mitigation
• modeling
• wheelings
• cover crops