The trophic level index (TLI) is used in New Zealand as a measure of nutrient status of lakes.[1] It is similar to the trophic state index but was proposed as alternative that suited New Zealand.[2]
The system uses four criteria, phosphorus and nitrogen concentrations, as well as visual clarity and algal biomass weighted equally.[3]
| 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 |