Ecological impact of dead-wood hedges: Release of dissolved phosphorus and organic matter into runoff

Dead-wood hedges, created by piling branches from tree trimming, have favorable biotic effects. During rains, however, they may release dissolved organic matter and phosphorus into runoff and thus cause eutrophication of surface waters. Field measurements showed that such runoff is polluted with high concentrations of phosphorus at least during the first year after establishing the hedge. Fresh and aged materials from dead-wood hedges were exposed to erosive rain in a laboratory study. Chemical oxygen demand and phosphorus concentration of the runoff were determined. Runoff from both fresh and aged materials had high concentrations of phosphorus (0.5-5 mg/l) and a large chemical oxygen demand (25-380 mg/l). Both levels exceeded the quality criteria of surface waters by up to two orders of magnitude. Concentrations decreased in the coarse of the rain. This was most pronounced for the aged material. Runoff from short, high-intensity rainstorms or rains on frozen or otherwise impermeable soil can be heavily polluted. Care must be taken during the piling of the hedges to avoid soil compaction, thus stimulating runoff from newly built hedges.