Gillon, NicholasWhite, PaulHamilton, David P.Silvester, Warwick B.2024-08-062024-08-062009-09https://hdl.handle.net/10289/16744Protection and restoration of water quality are a major priority of the New Zealand government. To support this objective, a monitoring and an action programme named “The Regional Water and Land Plan” was set up by the Environment Bay of Plenty Regional Council in February 2005 for the Rotorua lakes district. Lake Tarawera is part of this programme. The plan includes a Tarawera River management plan developed originally by Bay of Plenty Catchment Commission (1985). Currently water quality of Lake Tarawera is slightly worse than during the 1990s (Environment Bay of Plenty 1997). The Trophic Level Index (TLI), a measure of water quality, is 2.9 in Lake Tarawera. Environment Bay of Plenty wishes to reduce the TLI to 2.6, to improve the water quality of the lake. Actions have already been programmed to support this initiative, including sewage treatment. Most of the water inflow to the lake is from groundwater. Nitrogen loads to the lake from groundwater are largely unknown as there is limited monitoring data. Development of highly productive pasture in the last 50 years, coupled with a residence time for the groundwater estimated on average to be c. 200 years, look likely to result in increasing nutrient loads to the lake with potential for deterioration of water quality. The objective of this study was to assess current and future groundwater nutrient loads to Lake Tarawera, particularly nitrogen loads. Following a consideration of the Lake Tarawera catchment water balance, a hydrogeological model was created. Nitrogen discharge with groundwater to Lake Tarawera is assessed based on pre-development land use, current land use and scenarios of future land use, allowing conclusions to be made for priorities for the maintenance of lake water quality.enCommissioned Report for External Body