Are horse paddocks threatening water quality through excess loading of nutrients?

The research outlines the possible negative environmental impact of horse paddocks in Sweden, specifically contributing to nutrient pollution in the Baltic Sea, through phosphorus (P) and nitrogen (N) leaching. The study highlights particularly high nutrient leaching in feeding and excretion areas, especially in paddocks with sandy topsoils.

Research Context and Objective

• This study was conducted against the backdrop of increasing eutrophication in the Baltic Sea, largely carried by waterborne flows of phosphorus (P) and nitrogen (N) originating from agricultural sources. Notably, Sweden has been identified as a major contributor to this nutrient load.
• The researchers aimed to investigate the role of horse paddocks, which now occupy nearly 10% of Swedish agricultural land, in this environmental issue. Prior to this study, the environmental impact of horse paddocks remained largely unexplored.

Methodology

• The team examined potential P, N, and carbon (C) leaching losses from two topsoils (clay and loamy sand) taken from representative horse paddocks. These top soils were subjected to simulated rainfall events in a laboratory setting.
• Emphasis was given to feeding and excretion areas within paddocks, as these were expected to present higher levels of nutrient concentration.

Results

• Findings revealed that leachate concentrations, and the overall release of phosphorous, nitrogen, and dissolved organic carbon, were highest from feeding and excretion areas.
• Furthermore, leaching rates were notably higher from the loamy sand paddock topsoil than the clay topsoil.
• The study found a significant correlation between the leaching losses of dissolved reactive phosphorous and the concentrations of water-soluble P and ammonium acetate lactate-extractable P in the soil. Similarly, a significant correlation was identified between the leaching losses of dissolved organic P and total organic N with the concentration of dissolved organic carbon in leachate.
• Generally, the leaching loads of P and N from paddock topsoils were significantly higher than average figures for Swedish agricultural topsoils.

Conclusion

• The research concluded that horse paddocks pose a potential threat to water quality via the leaching of excess phosphorus and nitrogen.
• The study flagged feeding and excretion areas within paddocks as potential hotspots for enhanced leaching losses.
• It was especially noted that paddocks with loamy sandy topsoils were particularly susceptible to high nitrogen leaching losses.