Lake catchments

David Hamilton of Waikato University works in a field of science called limnology – he studies inland waters such as lakes. Scientists have come to realise that the area around a lake (called a catchment) is extremely important to the health of the lake.

For example, before 1991, wastewater was discharged into Lake Rotorua. When people realised that the lake developed algal blooms, it was decided that pumping wastewater into the lake should be stopped. However, the algal bloom did not stop, and scientists realised that the groundwater that feeds into Lake Rotorua was becoming enriched with nutrient-rich water from what had infiltrated in the Rotorua catchment over many years.

Transcript

PROF DAVID HAMILTON My particular field is called limnology, and it’s the study of inland waters. And for perhaps decades, preceding scientists like me, we looked upon lakes as just being holes in the ground and effectively isolated from what takes place around them. As we've gone on, we've realised that what happens on the landscape around the lake – and we call that the catchment – is extremely important to the amount of water that enters the lake and also the water quality within the lake. In 1991, the wastewater from Rotorua city that went into the lake was taken out. Everybody thought at the time that would solve the problem of algal blooms in Lake Rotorua. 20 years on, we still had the same problem because the groundwater is slowly becoming enriched in nutrients. That groundwater is feeding into Lake Rotorua, and all the benefits of taking wastewater and nutrients out in 1991 had been lost because it had been replaced by the effects of that older age groundwater, that now reflects more intense land use in the catchment of the lake.