Horizontal and Vertical Distributions of Denitrification Rate in the Sediment and Nitrogen Removal Rate Estimated in Lake Kasumigaura

Abstract

The vertical distribution of denitrification rates in sediment and the seasonal variation of denitrification rates were investigated by measuring denitrification rates using sediment core samples of Lake Kasumigaura maintained under natural conditions. The nitrogen removal rate caused by denitrification was calculated by using those data. Denitrification mainly occurred in the surface layer (top 1 cm) of the sediment. The denitrification rates decreased from the upper to the lower part in Lake Kasumigaura, and showed spring and autumn maxima. The amounts of denitrification in the sediment were estimated as 638 kgN d^-1 in the western part (Lake Nishiura) and 325 kgN d^-1 in the eastern part (Lake Kitaura) of the lake. Nitrogen removal rates caused by denitrification in the sediments corresponded to 5% in L. Nishiura and 6% in L. Kitaura of the annual nitrogen load to each lake, averaged from 2006 to 2010.