Lake Rotorua water quality

In this video, David Hamilton explains what time and space means for the water cycle by taking a closer look at Lake Rotorua.

Lake Rotorua’s water quality is the result of what happened to the water that infiltrated the land around the lake – the catchment area – a long time ago.

Point of interest Think about the factors we need to consider in lake restoration projects.

Nature of Science

Scientists sometimes work with hypothetical examples, to ask ‘what if’ questions. Using models allows them to experiment without having an impact on the natural environment.

Transcript

PROF DAVID HAMILTON A good example to consider time and space in lakes is to think about water in Lake Rotorua. Lake Rotorua has an area of about 80 square kilometres. About 80% of that water or more comes from groundwater that supplies streams that pop up out of the ground just before they enter the lake, and that water has been often underground for a long period of time, and the largest of the Rotorua Lake inflows is the Hamurana stream. That stream flows at 3 cubic metres per second – that is a huge amount of water – 3,000 litres per second coming into Lake Rotorua from one source. And it’s been under the ground for 140 years. In 1991, the wastewater from Rotorua City that went into the lake was taken out. Everybody thought at the time that that would solve the problem of algal blooms in Lake Rotorua. 20 years on, we still had the same problem. Why did we have that problem? It was actually because the groundwater is slowly becoming enriched in nutrients, that groundwater is feeding into Lake Rotorua, and all of the benefits of taking the wastewater and the nutrients out in 1991 had been lost because they had been replaced by the effects of that older aged groundwater that now reflects more intense land use in the catchment of the lake.