Hydrological and chemical budgets of Akanuma Pool in Kushiro Mire, northern Japan

In Japan, many mire pools have been disappeared because of agricultural and residential development that has taken place since the latter 20th century. Recently, the remaining pools have been recognized as important habitats for numerous organisms, and have been conserved similarly to those in foreign countries. However, the health of their hydrochemical conditions remains unknown because few studies have examined the mire pools’ hydrochemistry. Only two studies of mire pools’ hydrological and chemical budgets have been reported--both for North America. We investigated the hydrological and chemical budgets of a primitive mire pool, Akanuma Pool (area 95,280 m2; mean depth 1.8 m), located in Kushiro Mire, Hokkaido, northern Japan during its ice-free period (April-November) in 2007-2008. The hydrological budget was dominated by surface flow input and surface flow output, respectively representing 17 and 19 mm day-1. Total nitrogen, total phosphorus, and Ca2+ were supplied to the pool water mainly by groundwater seepage through the pool bottom and were run off from the pool mostly by surface flow output. The input and output fluxes of water were about 20 times greater than those of mire pools in North America because of higher values of precipitation minus evapotranspiration in Japan. Moreover, the Ca2+ input of the Akanuma Pool was 7-17 times greater than reported in North America studies. Probably, mineral ions including Ca2+ were supplied by alluvial mineral soils under the peat layer. These results reflect that hydrochemical characteristics of mire pools in Japan differ greatly from those in North America. Furthermore, the characteristics might be general because Japanese mire pools form on alluvial lowlands and have greater precipitation.