Spatial Distribution of Denitrification Activity and Effects of Water Temperature and Nitrate Concentration on Denitrification in the Sediments of the Lake Kasumigaura

The denitrification activity in the sediment of rivers flowing into Lake Kasumigaura (the general term for Lake Nishiura, Lake Kitaura, and the Hitachitone River) and the entire lake region was investigated. The distribution characteristics and dependence according to water temperature and nitrate (NO3-) of denitrification activity were examined. A high denitrification activity was observed in sediment collected from the river flowing into Lake Kitaura and those collected in the upper parts of the Lake Kitaura. Denitrification activity increased with increasing water temperature or NO3-N concentration under laboratory conditions, which occurred up to 25°C in the sediment of the lake and up to 40°C in the sediment of the river flowing into Lake Kitaura. The maximum denitrification rate obtained by a Michaelis-Menten kinetic analysis was six times larger in the sediment collected from the river flowing into Lake Kitaura than in the lake sediment. Multiple regression analysis suggested that the dissolved organic carbon (DOC) concentration in interstitial water is a crucial contributory factor to denitrification activity.