Trophic level index
# Trophic level index

The trophic level index (TLI) is used in New Zealand as a measure of nutrient status of lakes. It is similar to the trophic state index but was proposed as alternative that suited New Zealand.

The system uses four criteria, phosphorus and nitrogen concentrations, as well as visual clarity and algal biomass weighted equally.

| Lake type | Trophic level | Chla (mg $m^{−3})$ | Secchi depth (m) | TP (mg P $m^{−3})$ | TN (mg N $m^{−3})$ |
| - | - | - | - | - | - |
| Ultra-microtrophic | 0-1 | 0.13-0.33 | 31-24 | 0.84-1.8 | 16-34 |
| Microtrophic | 1-2 | 0.33-0.82 | 24-15 | 1.8-4.1 | 34-73 |
| Oligotrophic | 2-3 | 0.82-2.0 | 15-7.8 | 4.1-9.0 | 73-157 |
| Mesotrophic | 3-4 | 2.0-5.0 | 7.8-3.6 | 9.0-20 | 157-337 |
| Eutrophic | 4-5 | 5.0-12 | 3.6-1.6 | 20-43 | 337-725 |
| Supertrophic | 5-6 | 12-31 | 1.6-0.7 | 43-96 | 725-1558 |
| Hypertrophic | 6-7 | >31 | <0.7 | >96 | >1558 |
