title: Investigating groundwater derived nutrient fluxes within Tauranga harbour, New Zealand

authors: Stewart, Benjamin Thomas

subjects: Submarine groundwater discharge (SGD)

abstract: Submarine groundwater discharge (SGD) is one of the key pathways that connects land and ocean, delivering freshwater, nutrients, carbon, metals, and other chemical constituents to coastal waters. In New Zealand, local Māori have had a strong cultural connection to this natural process for centuries. Recently, it has been recognised that this process is important in global hydrological and biogeochemical cycles. Due to the large coastline to land area ratio, steep topography, permeable sediments and high rainfall, oceanic islands, may have the potential for disproportionally large SGD fluxes into the ocean compared to river inputs. Since SGD is driven under different timescales and processes (saline porewater through sediments and fresh groundwater from aquifers), it can provide a continual source of nutrients to coastal water bodies. This has previously received very little attention in New Zealand despite its potential importance, mainly due to the difficulty in measuring this diffuse process. 
Regional system scale studies among oceanic islands are poorly quantified and understood, especially in the South Pacific region.  Population increases have placed added stresses on hydrological cycles and subsequent land use changes, particularly agriculture, have resulted in excess nutrient loading and nitrogen pollution in coastal systems. Radium isotopes were used to quantify SGD and related nutrient fluxes into Tauranga Harbour, a coastal lagoon system, on the largely volcanic North Island of New Zealand. A ²²⁶Ra mass balance quantified SGD fluxes at the harbour scale, resulting in a range of SGD flux rates between 0.53 cm d⁻¹ and 3.09 x10⁶ m³ d⁻¹. When compared to other freshwater discharges (rivers and streams) into the harbour this was between ~1 – 2.8 times greater in flow. SGD inputs were also calculated to be ~5 times (for nitrogen) and ~8 times (for phosphorus) greater than the input from surrounding rivers and streams. Over the past decades the harbour has suffered reduced water quality and has inter-annual macro-algal blooms of Ulva spp. (sea lettuce). Harbour waters had a N:P ratio of ~17:1 with a positive relationship between radium isotopes (assumed groundwater related) and N:P ratios. This demonstrated that SGD has major implications for primary production, including recurrent algal bloom events which commonly occur in the harbour.
While higher loads of inorganic and organic nitrogen from surrounding water catchments are important for water quality, the physical processes that control estuarine flushing, such as tides, wind, rainfall, and freshwater discharge are equally as important. To better understand how future changes in climate over the coming century will impact coastal systems a numerical model was developed and combined with machine learning techniques to ‘emulate’ dilution rates based on time series of historical hydro-metrological data. A 22-year hind cast revealed the spatial variability of flushing times over short term ‘event’ and long range inter annual timescales. A significant relationship (r² 0.43 p =<0.001) between flushing rates and the southern oscillation index (SOI) was also established, highlighting direct and indirect implications of climate on water quality by altering flushing rates, nutrient availability, storage and transport across different regions. Using these data driven tools will be important into the future for monitoring water movement and ‘estuarine forecasting’. 
Finally, I present a study that assessed the effects of spring-neap tidal variations on estuarine connectivity over multiple spatial scales. Being a tidally dominated system, variations in tidal amplitudes can alter the movement of water and associated chemical exchanges between the harbours sub estuaries and coastal shelf. A combination of numerical modelling and artificial tracer experiments were used together with field-based measurements of naturally occurring radioactive tracers (radium). The modelled flushing times across all harbour regions (~4 – 20 days) agreed well with calculated apparent Ra ages. The average apparent radium water ages were revealed to be younger on spring tide at the harbour scale, suggesting tidal pumping of radium rich water from sub regions. Waters at the harbour scale were also well mixed from other sub regions. Nutrients and other chemical constituents varied substantially with the tide and were up to 4 times greater at the sub estuary scale on ebb tides. This demonstrated the important role of spring-neap tidal cycles in water transport, mixing and biogeochemical behaviour within sensitive coastal lagoon systems.

text: Investigating groundwater derived nutrient fluxes within Tauranga harbour, New Zealand Submarine groundwater discharge (SGD) is one of the key pathways that connects land and ocean, delivering freshwater, nutrients, carbon, metals, and other chemical constituents to coastal waters. In New Zealand, local Māori have had a strong cultural connection to this natural process for centuries. Recently, it has been recognised that this process is important in global hydrological and biogeochemical cycles. Due to the large coastline to land area ratio, steep topography, permeable sediments and high rainfall, oceanic islands, may have the potential for disproportionally large SGD fluxes into the ocean compared to river inputs. Since SGD is driven under different timescales and processes (saline porewater through sediments and fresh groundwater from aquifers), it can provide a continual source of nutrients to coastal water bodies. This has previously received very little attention in New Zealand despite its potential importance, mainly due to the difficulty in measuring this diffuse process. 
Regional system scale studies among oceanic islands are poorly quantified and understood, especially in the South Pacific region.  Population increases have placed added stresses on hydrological cycles and subsequent land use changes, particularly agriculture, have resulted in excess nutrient loading and nitrogen pollution in coastal systems. Radium isotopes were used to quantify SGD and related nutrient fluxes into Tauranga Harbour, a coastal lagoon system, on the largely volcanic North Island of New Zealand. A ²²⁶Ra mass balance quantified SGD fluxes at the harbour scale, resulting in a range of SGD flux rates between 0.53 cm d⁻¹ and 3.09 x10⁶ m³ d⁻¹. When compared to other freshwater discharges (rivers and streams) into the harbour this was between ~1 – 2.8 times greater in flow. SGD inputs were also calculated to be ~5 times (for nitrogen) and ~8 times (for phosphorus) greater than the input from surrounding rivers and streams. Over the past decades the harbour has suffered reduced water quality and has inter-annual macro-algal blooms of Ulva spp. (sea lettuce). Harbour waters had a N:P ratio of ~17:1 with a positive relationship between radium isotopes (assumed groundwater related) and N:P ratios. This demonstrated that SGD has major implications for primary production, including recurrent algal bloom events which commonly occur in the harbour.
While higher loads of inorganic and organic nitrogen from surrounding water catchments are important for water quality, the physical processes that control estuarine flushing, such as tides, wind, rainfall, and freshwater discharge are equally as important. To better understand how future changes in climate over the coming century will impact coastal systems a numerical model was developed and combined with machine learning techniques to ‘emulate’ dilution rates based on time series of historical hydro-metrological data. A 22-year hind cast revealed the spatial variability of flushing times over short term ‘event’ and long range inter annual timescales. A significant relationship (r² 0.43 p =<0.001) between flushing rates and the southern oscillation index (SOI) was also established, highlighting direct and indirect implications of climate on water quality by altering flushing rates, nutrient availability, storage and transport across different regions. Using these data driven tools will be important into the future for monitoring water movement and ‘estuarine forecasting’. 
Finally, I present a study that assessed the effects of spring-neap tidal variations on estuarine connectivity over multiple spatial scales. Being a tidally dominated system, variations in tidal amplitudes can alter the movement of water and associated chemical exchanges between the harbours sub estuaries and coastal shelf. A combination of numerical modelling and artificial tracer experiments were used together with field-based measurements of naturally occurring radioactive tracers (radium). The modelled flushing times across all harbour regions (~4 – 20 days) agreed well with calculated apparent Ra ages. The average apparent radium water ages were revealed to be younger on spring tide at the harbour scale, suggesting tidal pumping of radium rich water from sub regions. Waters at the harbour scale were also well mixed from other sub regions. Nutrients and other chemical constituents varied substantially with the tide and were up to 4 times greater at the sub estuary scale on ebb tides. This demonstrated the important role of spring-neap tidal cycles in water transport, mixing and biogeochemical behaviour within sensitive coastal lagoon systems.

year: 2021

title: Obituary − Emeritus Professor Dr John Davidson McCraw (1925−2014) MBE, MSc NZ, DSc Well, CRSNZ, FNZSSS.

authors: Tonkin, Philip J.

abstract: John McCraw was an Earth scientist who began working as a pedologist with Soil Bureau, DSIR, then became the Foundation Professor of Earth Sciences at the University of Waikato in Hamilton, inspiring a new generation to study and work in Earth sciences . In retirement, John McCraw was an author and historian with a special emphasis on Central Otago as well as the Waikato region. Throughout his career, marked especially by exemplary leadership, accomplished administration, and commitment to his staff and students at the University of Waikato, John McCraw also contributed to the communities in which he lived through public service organizations and as a public speaker. He received a number of awards including an MBE, fellowship, and companionship, and, uniquely, is commemorated also with a glacier, a fossil, and a museum-based research room named for him. Emeritus Professor John McCraw passed away on the 14th of December, 2014. An obituary, entitled “Dedicated to earth science and his students”, was published in the Waikato Times on the 10th of January, 2015.

text: Obituary − Emeritus Professor Dr John Davidson McCraw (1925−2014) MBE, MSc NZ, DSc Well, CRSNZ, FNZSSS. John McCraw was an Earth scientist who began working as a pedologist with Soil Bureau, DSIR, then became the Foundation Professor of Earth Sciences at the University of Waikato in Hamilton, inspiring a new generation to study and work in Earth sciences . In retirement, John McCraw was an author and historian with a special emphasis on Central Otago as well as the Waikato region. Throughout his career, marked especially by exemplary leadership, accomplished administration, and commitment to his staff and students at the University of Waikato, John McCraw also contributed to the communities in which he lived through public service organizations and as a public speaker. He received a number of awards including an MBE, fellowship, and companionship, and, uniquely, is commemorated also with a glacier, a fossil, and a museum-based research room named for him. Emeritus Professor John McCraw passed away on the 14th of December, 2014. An obituary, entitled “Dedicated to earth science and his students”, was published in the Waikato Times on the 10th of January, 2015.

year: 2015-03-06

title: Indigenous-washing and colonial amnesia: how New Zealand’s nation brand depoliticizes climate change

authors: Hellmann, Olli

abstract: New Zealand’s nation brand has drawn ever louder accusations of “greenwashing” the country’s image in recent years. Through a visual discourse analysis of Air New Zealand’s Tiaki & The Guardians safety briefing video, this article shows that brand managers have responded with a strategy of “Indigenous-washing,” appropriating the Māori worldview to deflect attention from intensive farming’s carbon footprint and other environmentally unfriendly activities. More broadly, this article makes an important contribution to the growing critical-cultural literature on nation branding by revealing how New Zealand’s latest marketing initiative contributes to the depoliticization of climate change. The “Tiaki” campaign not only positions New Zealand as an “untouched land,” but also closes the space for democratic debate about climate change by obscuring the role of colonialism in causing the planet’s ecological crisis and by silencing alternative socioecological futures proposed by Indigenous peoples.

text: Indigenous-washing and colonial amnesia: how New Zealand’s nation brand depoliticizes climate change New Zealand’s nation brand has drawn ever louder accusations of “greenwashing” the country’s image in recent years. Through a visual discourse analysis of Air New Zealand’s Tiaki & The Guardians safety briefing video, this article shows that brand managers have responded with a strategy of “Indigenous-washing,” appropriating the Māori worldview to deflect attention from intensive farming’s carbon footprint and other environmentally unfriendly activities. More broadly, this article makes an important contribution to the growing critical-cultural literature on nation branding by revealing how New Zealand’s latest marketing initiative contributes to the depoliticization of climate change. The “Tiaki” campaign not only positions New Zealand as an “untouched land,” but also closes the space for democratic debate about climate change by obscuring the role of colonialism in causing the planet’s ecological crisis and by silencing alternative socioecological futures proposed by Indigenous peoples.

year: 2023-07-27