Abstract:
The northern Motuoapa hot springs and their potential link to the nearby marina hot springs and the Lake Taupo Volcano have not been studied before. Analyses of the near neutral 56.0 oC water samples from the Motuoapa hot springs collected in 1967 and 2014 imply dilution of mature deep, hot alkali chloride-rich water with cooler peripheral bicarbonate-rich fluid over a period of 50 years. This is supported by a different Cl/B ratio obtained for samples collected in 1967 (Cl/B =44) and 2014 (Cl/B =26) indicating two distinct fluid sources, and by 18O value of -5.16‰, but it can also reflect the recharge by cooler waters due to a different water level at the time of sampling. The concentrations of reactive metal components and non-metal components imply relatively significant mineralization of the hot springs; however, the F− and SO42− contents decreased, whereas the NH3 content has slightly increased over the last ca 50 years.
