Stream Water Monitoring Site Measurement: organic portion of nitrogen (TKN)
TKN = Total Kjeldahl Nitrogen and is named after Johan Kjeldahl.  TKN is the sum of organic nitrogen; ammonia (NH₃) and ammonium (NH₄⁺) in the chemical analysis of soil, water, or wastewater (e.g. sewage treatment plant effluent). To calculate Total Nitrogen (TN), the concentrations of nitrate-N and nitrite-N are determined and added to TKN.  TKN is determined in the same manner as organic nitrogen, except that the ammonia is not driven off before the digestion step.

The TKN measurement was first done for Snapshot Day in 2005 and allows for the calculation of total nitrogen.  The California State standard (established by LRWQCB) for Total Nitrogen ranges from 150-230 µg/L for tributaries to Lake Tahoe and 120-410 µg/L for the Truckee River Hydrologic unit.  The exception is Martis Creek at the mouth (Middle Truckee = MTRMART00) with an objective of 1,450 µg/L - the sewage treatment plant discharges to Martis Creek near the mouth (the objective for the Truckee River below the mouth of Martis Creek is 400 µg/L).  Nevada State Standards for Nitrogen are Total N for Lake Tahoe between 250 to 320 µg/L.