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Lakes where the Trophic Level Index (TLI) is monitored and reported on as part of the State of the Environment monitoring process by Environment Canterbury.
The Trophic Level Index (TLI) provides information on water quality in lakes. The TLI is determined by measuring:
- total nitrogen
- total phosphorus
- visual clarity
- algal biomass.
Lakes are classified:
Trophic Level 0-1 = Ultra-microtrophic
Trophic Level 1-2 = Microtrophic
Trophic Level 2-3 = Oligotrophic
Trophic Level 3-4 = Mesotrophic
Trophic Level 4-5 = Eutrophic
Trophic Level 5-6 = Supertrophic
Trophic Level 6-7 = Hypertrophic
The main trophic states determined by these indicators are:
- Oligotrophic lakes are clear and blue, with very low levels of nutrients and algae.
- Mesotrophic lakes have moderate levels of nutrients and algae.
- Eutrophic lakes are green and murky, with higher amounts of nutrients and algae.
- Supertrophic lakes are fertile and saturated in phosphorus and nitrogen, often associated with poor water clarity. Excessive phytoplankton growth can occur in ideal conditions - when there's a calm, hot and sunny period of a few weeks.
- Hypertrophic lakes are highly fertile and supersaturated in phosphorus and nitrogen. They have excessive phytoplankton growth which contributes to poor water clarity, poor suitability for recreational uses, and restricts the habitat for desirable fish. |