Phosphorus load from equine critical source areas and its reduction using ferric sulphate

The increasing number of horses, especially in urban areas has made the phosphorus (P) load of exercise areas (paddocks) more and more obvious but there has been a lack of information regarding how to assess this load and what can be done to lower it. In the surface soil (1-2 cm) of areas that are affected by horse manure, like paddocks, we measured very high extractable P contents. When testing soils from these areas using a rainfall simulator we found a close correlation between the extractable soil P in the surface soil and the dissolved reactive P in runoff water. In a runoff treatment test trial we used ferric sulphate to treat paddock runoff water. The chemical dosage was carried out using a tube doser placed in a well. After ferric sulphate treatment the runoff was discharged into a sedimentation pond and then filtered in a sandbed. The chemical treatment was performed during one year and the reduction of the dissolved P and total P in the runoff was 95 % and 81 %, respectively. Our Agri-Environmental Programme has not been successful in reducing the total P status in our agriculturally loaded lakes. We suggest that the cost-effective chemical treatment of waters from the high P equine areas should be included in the programme. Also in other countries in the Baltic Sea catchment area reductions of P contents in waters from equine areas should be carried out.