On 7 April University of Waikato Professor David Hamilton, presented their latest research on phosphorus loads to Lake Rotorua. This research focused on the phosphorus share due to human activity (‘anthropogenic’ P). Key findings include:
- The total annual average P load is approximately 49 tonnes. This is higher than previous estimates, mainly due to storm loads
48% (or 23.4 tonnes) of the total annual P load comes from anthropogenic activity
- P loads from the groundwater dominated streams on the western side of the lake are mainly natural P from old-age groundwater, despite the dominance of pastoral land-uses in these sub-catchments
- Alum dosing has been highly effective in reducing dissolved P loads to Lake Rotorua, but less effective with particulate P
- P mitigation efforts should focus on reducing the particulate P load through improved land and stormwater management
- To meet the lake target TLI of 4.2 without alum dosing, the annual lake P load would need to reduce by 10-15 tonne.