2016 Volume 6 Pages 33-48
Effects of migratory waterfowls on nutrient concentration were examined in a hypereutrophic lake, Lake Miyajima-numa, which is a major stopover for greater white-fronted goose (Anser albifrons) in Japan. Hydrological budget and water-borne fluxes of total nitrogen (TN) and total phosphorus (TP) were investigated during its ice-free period (April–November) in 2007–2008. We calculated the residuals in a nutrient budget model. To estimate the nutrient loads from the migratory waterfowls, we compared the residuals between the period when waterfowls had stayed in the lake and the period when waterfowls had flown away. TN and TP loads from migratory waterfowls represented 11–18 kg d-1 and 2.0–3.6 kg d-1, respectively, during the early parts of waterfowls’ staying periods. The loads from migratory waterfowls represented 1–3 times (TN) and 4–30 times (TP) higher than those of water-borne nutrient loads during the same period, corresponding to non-irrigation period. This suggested the significant contribution of migratory waterfowls as an allochthonous TP source in lake water. Reducing not only water-borne but also bird-borne nutrient loads appeared to be important for inhibiting eutrophication in Lake Miyajima-numa.