RETENTION OF PHOSPHORUS IN SOIL AND VEGETATION OF A BUFFER ZONE AREA DURING SNOWMELT PEAK FLOW IN SOUTHERN FINLAND RIITTA V ¨ A ¨ AN ¨ ANEN 1,∗ , MIKA NIEMINEN 2 , MARTTI VUOLLEKOSKI 2 and HANNU ILVESNIEMI 2 1 Department of Forest Ecology, University of Helsinki, P.O. Box 27 00014, Finland; 2 Finnish Forest Research Institute, Vantaa Research Centre, Finland ( ∗ author for correspondence, e-mail: riitta.vaananen@helsinki.fi) (Received 15 April 2005; accepted 2 February 2006) Abstract. In regions with a distinct winter-period, nearly half of the annual runoff occurs during a short snow-melt period early in spring. During this time functioning buffer zones are important means of preventing the leaching of phosphorus from forest land into downstream watercourses. Sparse vegetation restricts biological P accumulation and high flows reduce the capacity of deeper soil layers to adsorb P, indicating that the effectiveness of buffer zones may be low. Our aim was to increase the understanding of phosphorus retention in a buffer zone area under such unfavourable conditions for P removal, and to estimate the amount of P sorbed by soil and taken up by vascular plants and mosses. Over a five-day period in spring we added 10 kg (60 kg ha −1 ) of PO 4 -P and 185 MBq (1100 MBq ha −1 ) 32 P to a 25–50 m wide buffer zone area (0.17 ha) in southern Finland. We measured the total P retention and recovery during ten days after the beginning of the experiment. Recovery of 32 P was 16% of added P, of which 92% was in soil, 3% in vascular plants and 5% in mosses. Thus, our results showed that the total P retention was low, most likely because the water flow did not slow down sufficiently and penetrate deeply enough to enable a close contact between P in the runoff and the soil matrix. Most of the recovered P was in the soil suggesting that adsorption by soil was the most important sink for P under early spring high flow conditions. Keywords: 32 P, buffer zone, peatland, phosphorus, retention 1. Introduction In northern temperate and boreal regions the primary production in freshwater ecosystems is related to phosphorus (P) availability (Pietil¨ ainen, 1997; Correll, 1998). Increased P loads caused by human activities generally lead to eutrophication of recipient aquatic ecosystems. Hydrological losses of P from forested catchments increase when forests are harvested, drained or fertilized (Kentt¨ amies, 1981; Ahti- ainen and Huttunen, 1999). The most harmful consequences of operational forestry occur in non-polluted, sensitive headwater areas where human activities other than forestry operations are unimportant (Saukkonen and Kortelainen, 1995). In Finland such sensitive headwater areas are common; therefore, forest management practices that aim at reducing P leaching to surface waters are being developed. Water, Air, and Soil Pollution (2006) 177: 103–118 DOI: 10.1007/s11270-006-9106-1 C  Springer 2006