title: A coupled hydrodynamic-ecological model to test management options for restoration of lakes Onoke and Wairarapa

authors: Allan, Mathew Grant

abstract: This report describes a modelling and remote sensing study of lakes Onoke and Wairarapa that seeks to determine water quality and ecological effects of specific management scenarios, and therefore inform the Ruamāhanga Whaitua Committee of potential water quality management options for lakes Onoke and Wairarapa.
The study applied both one dimensional (1-D) and three dimensional (3-D) ecologically coupled hydrodynamic models to simulate current and scenario-based water quality variables. The Baseline model (calibration) simulates “current conditions” including management practices between 1992 and 2014. Business As Usual (BAU), SILVER and GOLD scenarios were all run using representative data catchment inflow and nutrients for mitigation taking effect in 2025, 2040 and 2080. Additional hydrodynamic scenarios were modelled (which also include catchment mitigations above). They were: deepening both lakes by 1 m, Ruamāhanga diversion back into Lake Wairarapa, and Lake Onoke summer outlet closed scenarios. These scenarios were provided by the Ruamāhanga Whaitua Committee.
Within Lake Wairarapa, catchment mitigation-based scenarios showed considerable potential for the improvement of water quality. These mitigations simulated that the trophic state of the lake could change from the current supertrophic category, to the top of the eutrophic category (GOLD and SILVER mitigations). However, this still indicates poor water quality and high turbidity/low water clarity. In addition, these catchment mitigations did not move the lake from a NOF D category for total phosphorous (TP). Simulations indicated that larger reductions in TP (60%) (with SILVER2080 mitigations of other nutrients) could achieve a NOF C category for TP. Simulations that included the re-establishment of macrophytes also indicated NOF C category for TP (under SILVER2080), however only under a 1 m depth increase scenario, and under Ruamāhanga diversion scenario. These simulations indicated that the trophic status could move to the mid-eutrophic category. However, this is still indicative of poor water quality.
Catchment scenarios had a greater influence on Lake Onoke trophic status compared to Wairarapa, due to the shorter residence time and low internal load (from the sediments) relative to external load. In effect, the composition of Onoke aligns closely with that of its inflows. Water quality in Lake Onoke is susceptible to changes in water quality in Lake Wairarapa, particularly in relation to chlorophyll a (chl a) and total suspended solids (TSS). High sediment resuspension events in Lake Wairarapa transport increased levels of suspended sediment to Lake Onoke. The very low residence time in Onoke does not allow adequate time for significant phytoplankton growth within the lake. However, 3-D simulations show higher phytoplankton concentrations at times in the western lake, relating to flushing and transport effects. The outlet-closed scenario in Lake Onoke simulated increased water quality in both 1-D and 3-D models However, we note that the risk of cyanobacteria blooms was low, but marginally increased. Also 1-D models suggested that the simulated TLI under SILVER2080 was almost identical to outlet closed SILVER2080. The 3-D model simulated lower chlorophyll concentrations and higher TSS under SILVER2080 outlet closed (compared to SILVER2080 and Baseline), largely due to changes in hydrodynamics and flushing. Therefore, these results show no conclusive evidence that water quality would be significantly increased or decreased in comparison to SILVER2080 under an outlet closed scenario. However, we note that in situ monitoring and expert opinion has indicated that under outlet closed conditions the lake is more susceptible to eutrophication.

text: A coupled hydrodynamic-ecological model to test management options for restoration of lakes Onoke and Wairarapa This report describes a modelling and remote sensing study of lakes Onoke and Wairarapa that seeks to determine water quality and ecological effects of specific management scenarios, and therefore inform the Ruamāhanga Whaitua Committee of potential water quality management options for lakes Onoke and Wairarapa.
The study applied both one dimensional (1-D) and three dimensional (3-D) ecologically coupled hydrodynamic models to simulate current and scenario-based water quality variables. The Baseline model (calibration) simulates “current conditions” including management practices between 1992 and 2014. Business As Usual (BAU), SILVER and GOLD scenarios were all run using representative data catchment inflow and nutrients for mitigation taking effect in 2025, 2040 and 2080. Additional hydrodynamic scenarios were modelled (which also include catchment mitigations above). They were: deepening both lakes by 1 m, Ruamāhanga diversion back into Lake Wairarapa, and Lake Onoke summer outlet closed scenarios. These scenarios were provided by the Ruamāhanga Whaitua Committee.
Within Lake Wairarapa, catchment mitigation-based scenarios showed considerable potential for the improvement of water quality. These mitigations simulated that the trophic state of the lake could change from the current supertrophic category, to the top of the eutrophic category (GOLD and SILVER mitigations). However, this still indicates poor water quality and high turbidity/low water clarity. In addition, these catchment mitigations did not move the lake from a NOF D category for total phosphorous (TP). Simulations indicated that larger reductions in TP (60%) (with SILVER2080 mitigations of other nutrients) could achieve a NOF C category for TP. Simulations that included the re-establishment of macrophytes also indicated NOF C category for TP (under SILVER2080), however only under a 1 m depth increase scenario, and under Ruamāhanga diversion scenario. These simulations indicated that the trophic status could move to the mid-eutrophic category. However, this is still indicative of poor water quality.
Catchment scenarios had a greater influence on Lake Onoke trophic status compared to Wairarapa, due to the shorter residence time and low internal load (from the sediments) relative to external load. In effect, the composition of Onoke aligns closely with that of its inflows. Water quality in Lake Onoke is susceptible to changes in water quality in Lake Wairarapa, particularly in relation to chlorophyll a (chl a) and total suspended solids (TSS). High sediment resuspension events in Lake Wairarapa transport increased levels of suspended sediment to Lake Onoke. The very low residence time in Onoke does not allow adequate time for significant phytoplankton growth within the lake. However, 3-D simulations show higher phytoplankton concentrations at times in the western lake, relating to flushing and transport effects. The outlet-closed scenario in Lake Onoke simulated increased water quality in both 1-D and 3-D models However, we note that the risk of cyanobacteria blooms was low, but marginally increased. Also 1-D models suggested that the simulated TLI under SILVER2080 was almost identical to outlet closed SILVER2080. The 3-D model simulated lower chlorophyll concentrations and higher TSS under SILVER2080 outlet closed (compared to SILVER2080 and Baseline), largely due to changes in hydrodynamics and flushing. Therefore, these results show no conclusive evidence that water quality would be significantly increased or decreased in comparison to SILVER2080 under an outlet closed scenario. However, we note that in situ monitoring and expert opinion has indicated that under outlet closed conditions the lake is more susceptible to eutrophication.

year: 2018

title: Colin George Vucetich (1918–2007)—pioneering New Zealand tephrochronologist

authors: Lowe, David J.

subjects: New Zealand

abstract: Many Quaternarists, tephrochronologists, and soil scientists mourned the passing in New Zealand of Colin Vucetich—gentle mentor, pedologist, and pioneering tephrochronologist—on 25 April (Anzac Day), 2007. Colin was in his 89th year. As well as forming a 25-year partnership with W.A. “Alan” Pullar, with whom he published three classic papers on tephrostratigraphy based on field work undertaken by the pair largely in their own time, Colin inspired and mentored numerous postgraduates in his later career as an academic at Victoria University of Wellington. There he taught pedology, soil stratigraphy, and tephrochronology until his retirement as Reader (Associate Professor) in 1982. In retirement he was an honorary lecturer and supervisor at Massey University (Palmerston North) until 1991 (Fig. 1, Fig. 2 and Fig. 3).

text: Colin George Vucetich (1918–2007)—pioneering New Zealand tephrochronologist Many Quaternarists, tephrochronologists, and soil scientists mourned the passing in New Zealand of Colin Vucetich—gentle mentor, pedologist, and pioneering tephrochronologist—on 25 April (Anzac Day), 2007. Colin was in his 89th year. As well as forming a 25-year partnership with W.A. “Alan” Pullar, with whom he published three classic papers on tephrostratigraphy based on field work undertaken by the pair largely in their own time, Colin inspired and mentored numerous postgraduates in his later career as an academic at Victoria University of Wellington. There he taught pedology, soil stratigraphy, and tephrochronology until his retirement as Reader (Associate Professor) in 1982. In retirement he was an honorary lecturer and supervisor at Massey University (Palmerston North) until 1991 (Fig. 1, Fig. 2 and Fig. 3).

year: 2008

title: Whakatautika: Generating balance in the business and activity of fishing at Moana New Zealand - A case study on Indigenising the blue economy in Aotearoa

authors: Mika, Jason

abstract: This report sets out the results of a case study on Moana New Zealand, an iwi (tribal) owned fishing company formed out of the Treaty of Waitangi fisheries settlement and a whānau (family) owned inshore fishing enterprise known as The Rawlinson Group (TRG). The research is part of an Indigenising the blue economy project funded by Ngā Moana Whakauka Sustainable Seas National Science Challenge. This case study draws on the knowledge and experience of Moana New Zealand and TRG to understand relationships between iwi and whānau scale enterprises in the Māori marine economy (MME). TRG is a Māori-owned family inshore fishing business which has been operating for 30 years. As first-generation fishers, the Rawlinson whānau have prioritised both strategic and family decisions that have established their business and assured their role in Aotearoa New Zealand’s commercial fishing industry. The case study sought to learn how Māori marine-based enterprises apply mātauranga Māori to achieve multidimensional wellbeing, human potential, and relational balance with Tangaroa.

text: Whakatautika: Generating balance in the business and activity of fishing at Moana New Zealand - A case study on Indigenising the blue economy in Aotearoa This report sets out the results of a case study on Moana New Zealand, an iwi (tribal) owned fishing company formed out of the Treaty of Waitangi fisheries settlement and a whānau (family) owned inshore fishing enterprise known as The Rawlinson Group (TRG). The research is part of an Indigenising the blue economy project funded by Ngā Moana Whakauka Sustainable Seas National Science Challenge. This case study draws on the knowledge and experience of Moana New Zealand and TRG to understand relationships between iwi and whānau scale enterprises in the Māori marine economy (MME). TRG is a Māori-owned family inshore fishing business which has been operating for 30 years. As first-generation fishers, the Rawlinson whānau have prioritised both strategic and family decisions that have established their business and assured their role in Aotearoa New Zealand’s commercial fishing industry. The case study sought to learn how Māori marine-based enterprises apply mātauranga Māori to achieve multidimensional wellbeing, human potential, and relational balance with Tangaroa.

year: 2024