The Distribution of Urea in Lake Yunoko

Abstract

Urea in waters collected from a central water column of Lake Yunoko was determined from July of 1971 to April of 1972. The annual minimum of the urea standing stack in the central water column was 3.75 mg-at-N·m^-2 in November of 1971. The annual maximum was 61.0mg-at-N·m^-2 in ice-covered March of 1972. Three depth profiles of urea out of six appeared to be nutrient types with depression of urea in the traphogenic layer, but increase in the tropholytic layer. In these cases, photosynthetic activities might regulate the urea depth profile. The ratios of urea-N/TIN (total inorganic nitrogen) suggest that urea was a major constituent of nitrogenous nutrients in ice-covered March, but a minor component throughout the rest of the year. Allochthonous urea, which originated from waste water treatment, seems to have been an important source of urea in water of Lake Yunoko.