Indian Creek reservoir

There are other such examples. Many unsaturated soils are known to convert to N2(g> via NO3 (i.e., nitrification then denitrification). They achieve this because there are local oxic and anoxic environments in the soil waters that, respectively, allow nitrification and denitrification to proceed. In stratified lakes, nitrification may occur in the oxygenated epilimnion (upper layer) and denitrification in the hypolimnion (bottom water) and in the sediment pore water where dissolved oxygen concentrations fall to zero. The nitrification and denitrification process is important in preserving the fishery in Indian Creek Reservoir in the Sierra Nevada mountains. This reservoir is fed by the tertiary effluent from the City of South Lake Tahoe sewage treatment plant. The effluent has at times contained 15 to 20 mg NH4 N/liter. Levels of ammonia of this magnitude are toxic to fish, yet in the reservoir there is a thriving fishery. This is achieved because the top waters of the lake nitrify the ammonia to nitrate and this is reduced to N2(g) by the anoxic bottom waters. The summer concentrations of nitrogen species of the reservoir are approximately 4 mg NOa -N/Iiter and 4 mg NH4-N/liter. 

Eutrophication of Surface Water—Lake Tahoe s Indian Creek Reservoir, EPA... 

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