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 diss olved organic matter and phosphorus into runoff and thus cause eutroph ication 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 fro m dead-wood hedges were exposed to erosive rain in a laboratory study. Chemical oxygen demand and phosphorus concentration of the runoff wer e determined. Runoff from both fresh and aged materials had high conce ntrations of phosphorus (0.5-5 mg/l) and a large chemical oxygen deman d (25-380 mg/l). Both levels exceeded the quality criteria of surface waters by up to two orders of magnitude. Concentrations decreased in t he course of the rain. This was most pronounced for the aged material. Runoff from short, high-intensity rainstorms or rains on frozen or ot herwise impermeable soil can be heavily polluted. Care must be taken d uring the piling of the hedges to avoid soil compaction, thus stimulat ing runoff from newly built hedges.