Retention of nitrogen in beaver ponds depends on colonization history : use of Fontinalis antipyretica as an integrative sampler of nitrogen

Abstract: Beaver ponds affect the environment in many ways and beaver ponds have the potential to retain macronutrients. The retention of nitrogen in beaver ponds has mainly been suggested to be due to denitrification by bacteria. The aquatic moss Fontinalis antipyretica are frequently used as an integrative measure of water quality and the moss might potentially retain nitrate, nitrite and ammonia in beaver system. The aim of the study is to investigate nitrogen retention in beaver ponds using F. antipyretica as an integrative sampler and if N-retention is dependent on the colonization history of the beaver pond. Twelve beaver systems were investigated in the study; Luleå (N=3), Sundsvall (N=3), Skinnskatteberg (N=2), Surahammar (N=2) and Örebro (N=2). Seven of the beaver systems were recolonization of abandoned ponds and five of them were colonized for the first time since extirpation by beavers, i.e. were reused and pioneer systems, respectively. F. antipyretica was picked in water systems with good ecological status, put in mesh bags and transplanted to sites up- and downstream the beaver ponds. The bags were left in the stream for 2, 4, 6 and 12 weeks. N content in F. antipyretica was higher upstream than downstream (p<0.05) and this result was stronger in reused than in pioneer beaver systems (p<0.001). The study suggests that F. antipyretica can be used as an integrative measure for retention of nitrogen in beaver systems. Especially, the results indicate that reused beaver dams have higher nitrogen retention potential than pioneer ones.