Nutrient Aggregation


The Loading Tool provides the user with the option of calculating aggregated loads for nitrogen-containing parameters and phosphorus-containing parameters. This page describes the nutrient aggregation methodology and is an updated version of section 3.2.3 of the Technical Users Background Document.

Nutrient aggregation approximates a Total Nitrogen and Total Phosphorus load by combining loads for various nitrogen and phosphorus species. Total nitrogen consists of organic nitrogen, ammonia, nitrate, and nitrite; or total Kjeldahl nitrogen (TKN), nitrate, and nitrite. Typically, organic nitrogen and TKN account for the majority of the total nitrogen load. As a result, if a facility is not required to report total nitrogen, TKN, or organic nitrogen; the loadings tool calculation will underestimate the aggregated nitrogen load. Phosphorus compounds may be reported as phosphorus or phosphate in ICIS-NPDES.

For nitrogen and phosphorus parameters, the Loading Tool calculates an aggregate nitrogen load and aggregate phosphorus load for each outfall and monitoring location at each facility using the following logic:

  • For Total Nitrogen (as N):
    • If Total Nitrogen is reported, use that load for total nitrogen;
    • If Total Nitrogen is not reported and TKN is > 0, then Total Nitrogen = TKN + Nitrate + Nitrite;
    • If TKN is not reported and Organic Nitrogen is > 0, then Total Nitrogen = Organic Nitrogen + Ammonia + Nitrate + Nitrite; and
    • If Organic Nitrogen is not reported, then Total Nitrogen = Ammonia + Nitrate + Nitrite
  • For Total Phosphorus (as P):
    • If Total Phosphorus is reported, then use that load for total phosphorus; and
    • If Total Phosphorus is not reported, then use the Phosphate load and convert to phosphorus

Table 3-10 presents the priorities that the Loading Tool uses to select nutrient parameters for inclusion in the total nitrogen calculation. Using these priorities, the Loading Tools selects one parameter to represent Total Nitrogen, TKN, Nitrate, Nitrite, Organic Nitrogen, and Ammonia.

Table 3-11 presents the priorities that the Loading Tool uses to select nutrient parameters for inclusion in the total phosphorus calculation.

 Table 3-10. Priorities for Nitrogen Aggregation
Parameter CodeParameter DescriptionConversion FactorCalculation ParameterParameter Selection Priority 
Equation 1: Total Nitrogen = TOTAL N
00600Nitrogen, total (as N)1TOTAL N1 
51445Nitrogen, Total1TOTAL N2 
51084Nitrogen, total available (water)1TOTAL N3 
Equation 2: Total Nitrogen = TKN + NITRATE + NITRITE
00625Nitrogen, Kjeldahl, total (as N)1TKN1 
51449Nitrogen, Kjeldahl Total1TKN2 
51087Nitrogen, Kjeldahl, total (TKN) (water)1TKN3 
82539Nitrogen, Kjeldahl1TKN4 
49579Nitrogen, total Kjeldahl1TKN5 
81639Nitrogen Kjeldahl, total (TKN)1TKN6 
00623Nitrogen, Kjeldahl, dissolved (as N)1TKN7 
00620NITROGEN, NITRATE TOTAL (AS N)1NITRATE1 
71850Nitrogen, nitrate total (as NO3)0.225806452NITRATE2 
51100Nitrogen, total, as NO3, (water)0.225806452NITRATE3 
51086Nitrogen, nitrate (NO3), (water)0.225806452NITRATE4 
00615Nitrogen, nitrite total (as N)1NITRITE1 
51447Nitrogen, Nitrite Total1NITRITE2 
00613Nitrite, nitrogen, dissolved (as N)1NITRITE3 
71855NITROGEN, NITRITE TOTAL (AS NO2)0.304347826NITRITE4 
Equation 3: Total Nitrogen = ORG N + AMMON + NITRATE + NITRITE
00605Nitrogen, organic total (as N)1ORG N1 
00607Nitrogen, organic, dissolved (as N)1ORG N2 
00610Nitrogen, ammonia total(as N)1AMMON1 
51446Nitrogen, Ammonia Total1AMMON2 
00609Ammonia, nitrogen, total, (as N) 30 day1AMMON3 
00612Nitrogen, ammonia, tot unionized (as N)1AMMON4 
34726Nitrogen, ammonia, total (as NH3)0.823529412AMMON5 
51085Nitrogen, ammonia, (NH3-N)(water)0.823529412AMMON6 
61574Ammonia (as N) + unionized ammonia0.823529412AMMON7 
00619Ammonia, unionized0.823529412AMMON8 
00608Nitrogen, ammonia dissolved0.823529412AMMON9 
82230Total Ammonia & Ammonium0.823529415AMMON10 
71845Nitrogen, Ammonia Total (as NH4)0.823529415AMMON11 
00620NITROGEN, NITRATE TOTAL (AS N)1NITRATE1 
71850Nitrogen, nitrate total (as NO3)0.225806452NITRATE2 
51100Nitrogen, total, as NO3, (water)0.225806452NITRATE3 
51086Nitrogen, nitrate (NO3), (water)0.225806452NITRATE4 
00615Nitrogen, nitrite total (as N)1NITRITE1 
51447Nitrogen, Nitrite Total1NITRITE2 
00613Nitrite nitrogen, dissolved (as N)1NITRITE3 
71855NITROGEN, NITRITE TOTAL (AS NO2)0.304347826NITRITE4 
Equation 4: Total Nitrogen = AMMON + NITRATE + NITRITE
00610Nitrogen, ammonia total (as N)1AMMON1 
51446Nitrogen, Ammonia Total1AMMON2 
00609Ammonia nitrogen, total, (as N) 30 day1AMMON3 
00612Nitrogen, ammonia tot unionized (as N)1AMMON4 
34726Nitrogen, ammonia total (as NH3)0.823529412AMMON5 
51085Nitrogen, ammonia (NH3-N), (water)0.823529412AMMON6 
61574Ammonia (as N) + unionized ammonia0.823529412AMMON7 
00619Ammonia, unionized0.823529412AMMON8 
00608Nitrogen, ammonia dissolved0.823529412AMMON9 
82230Total Ammonia & Ammonium0.776409915AMMON10 
71845Nitrogen, Ammonia Total (as NH4)0.776409915AMMON11 
00620NITROGEN, NITRATE TOTAL (AS N)1NITRATE1 
71850Nitrogen, nitrate total (as NO3)0.225806452NITRATE2 
51100Nitrogen, total, as NO3, (water)0.225806452NITRATE3 
51086Nitrogen, nitrate (NO3), (water)0.225806452NITRATE4 
00615Nitrogen, nitrite total (as N)1NITRITE1 
51447Nitrogen, Nitrite Total1NITRITE2 
00613Nitrite nitrogen, dissolved (as N)1NITRITE3 
71855NITROGEN, NITRITE TOTAL (AS NO2)0.304347826NITRITE4 

 

 Table 3-11. Priorities for Phosphorus Aggregation
Parameter CodeParameter DescriptionConversion FactorCalculation ParameterParameter Selection Priority 
Equation 1: Total Phosphorus = Phosphorus (PHOSP)
00665Phosphorus, total (as P)1PHOSP1 
51451Phosphorus, Total1PHOSP2 
70507Phosphorus, in total orthophosphate1PHOSP3 
00670Phosphorus, total organic (as P)1PHOSP4 
00662Phosphorus, total recoverable1PHOSP5 
00666Phosphorus, dissolved1PHOSP6 
Equation 2: Total Phosphorus = Phosphate (PO4)
00650Phosphate, total (as PO4)0.326315789PO41 
00660Phosphate, ortho (as PO4)0.326315789PO42 
00655Phosphate, poly(as PO4)0.326315789PO43 
71888Phosphate, total soluble (as PO4)0.326315789PO44 
70505Phosphate, total, color method (as P)0.326315789PO45