title: Assessment of the Waikato River estuary delta for whitebait habitat management: field survey, GIS modelling and hydrodynamic modelling

authors: Jones, Hannah Frances Emily

abstract: The University of Waikato was contracted by Waikato Regional Council to develop a hydrodynamic model of the Waikato River delta to aid with the assessment of whitebait spawning habitat, and to help inform restoration plans for the area. The Waikato River estuary and delta cover the lowest reaches of the Waikato River, less than c. 15 km from the sea. The estuary is classed as a tidal river mouth and is mostly subtidal, whilst the delta is the widest part of the river and estuary and extends from 6 to 15 km from the entrance. The most common whitebait species in the lower Waikato River is juvenile īnanga, Galaxias maculatus, a diadromous fish species that matures in freshwater and then migrates downstream to spawn in a tidal estuary. īnanga spawn close to the interface between fresh and saltwater, in bankside vegetation that is inundated only on spring tides, and spawning sites in the lower Waikato River have mostly been found in and around the delta. As there have been few published studies on the physical or ecological characteristics of the Waikato River estuary or delta, there is currently limited understanding of the impact of tidal state and river flow on salinity distributions and water levels, which will likely exert significant influence on the location of īnanga spawning sites.
Whilst collating available data it was found that there was limited bathymetry, and little data on water levels, temperature and salinity in the estuary and delta. These data are required for the calibration and validation of hydrodynamic models of water transport and mixing. To address this paucity of data a field survey (measuring spatial and temporal variability in parameters such as temperature and salinity) was conducted by the University of Waikato, and Waikato Regional Council contracted Discovery Marine Ltd to conduct a hydrographic survey of the estuary and delta region. Bathymetry data from the hydrographic survey was used in hydrodynamic modelling of the estuary and delta, and GIS modelling of potential floodplain inundation. This report details the results of the field survey and GIS modelling, as well as the hydrodynamic model simulations, as these studies provide significant insight into spatial and temporal variability in ecologically relevant parameters and potential whitebait spawning habitat.
A field survey was conducted in the Waikato River estuary and delta over a spring-neap tidal cycle in April 2013. Data loggers measuring water level, temperature, conductivity, and other water quality parameters, such as dissolved oxygen and turbidity, were deployed at several locations in the estuary and delta over a 16-day period. In addition, boat surveys used a Conductivity-Temperature-Depth (CTD) probe and a towed horizontal profiler to map spatial variability in temperature and conductivity, and to determine the extent of saltwater intrusion into the estuary under neap tide and spring tide conditions. The surveys indicated that there was considerable variability in temperature and salinity distributions in the estuary and delta, both laterally and longitudinally. In contrast, there was little vertical variation, as the water column was typically well-mixed, except in the very lowest reaches of the estuary where a distinct salt wedge was sometimes observed. The limit of saltwater intrusion into the estuary and delta was found to be in the mid-islands region, c. 10 km from the entrance, on the neap tide survey and in the upper islands, c. 13 km from the entrance, on the spring tide survey, which is further than has previously been reported. Water level loggers revealed marked tidal asymmetry at sites upstream of the entrance, caused by bottom friction and the interaction of the tidal wave with freshwater discharge. There was substantial temporal variability in variables such as temperature, salinity and dissolved oxygen, related to diurnal and tidal cycles, and river flow, and these also provided critical data that was then used in calibration and validation of the hydrodynamic model.

text: Assessment of the Waikato River estuary delta for whitebait habitat management: field survey, GIS modelling and hydrodynamic modelling The University of Waikato was contracted by Waikato Regional Council to develop a hydrodynamic model of the Waikato River delta to aid with the assessment of whitebait spawning habitat, and to help inform restoration plans for the area. The Waikato River estuary and delta cover the lowest reaches of the Waikato River, less than c. 15 km from the sea. The estuary is classed as a tidal river mouth and is mostly subtidal, whilst the delta is the widest part of the river and estuary and extends from 6 to 15 km from the entrance. The most common whitebait species in the lower Waikato River is juvenile īnanga, Galaxias maculatus, a diadromous fish species that matures in freshwater and then migrates downstream to spawn in a tidal estuary. īnanga spawn close to the interface between fresh and saltwater, in bankside vegetation that is inundated only on spring tides, and spawning sites in the lower Waikato River have mostly been found in and around the delta. As there have been few published studies on the physical or ecological characteristics of the Waikato River estuary or delta, there is currently limited understanding of the impact of tidal state and river flow on salinity distributions and water levels, which will likely exert significant influence on the location of īnanga spawning sites.
Whilst collating available data it was found that there was limited bathymetry, and little data on water levels, temperature and salinity in the estuary and delta. These data are required for the calibration and validation of hydrodynamic models of water transport and mixing. To address this paucity of data a field survey (measuring spatial and temporal variability in parameters such as temperature and salinity) was conducted by the University of Waikato, and Waikato Regional Council contracted Discovery Marine Ltd to conduct a hydrographic survey of the estuary and delta region. Bathymetry data from the hydrographic survey was used in hydrodynamic modelling of the estuary and delta, and GIS modelling of potential floodplain inundation. This report details the results of the field survey and GIS modelling, as well as the hydrodynamic model simulations, as these studies provide significant insight into spatial and temporal variability in ecologically relevant parameters and potential whitebait spawning habitat.
A field survey was conducted in the Waikato River estuary and delta over a spring-neap tidal cycle in April 2013. Data loggers measuring water level, temperature, conductivity, and other water quality parameters, such as dissolved oxygen and turbidity, were deployed at several locations in the estuary and delta over a 16-day period. In addition, boat surveys used a Conductivity-Temperature-Depth (CTD) probe and a towed horizontal profiler to map spatial variability in temperature and conductivity, and to determine the extent of saltwater intrusion into the estuary under neap tide and spring tide conditions. The surveys indicated that there was considerable variability in temperature and salinity distributions in the estuary and delta, both laterally and longitudinally. In contrast, there was little vertical variation, as the water column was typically well-mixed, except in the very lowest reaches of the estuary where a distinct salt wedge was sometimes observed. The limit of saltwater intrusion into the estuary and delta was found to be in the mid-islands region, c. 10 km from the entrance, on the neap tide survey and in the upper islands, c. 13 km from the entrance, on the spring tide survey, which is further than has previously been reported. Water level loggers revealed marked tidal asymmetry at sites upstream of the entrance, caused by bottom friction and the interaction of the tidal wave with freshwater discharge. There was substantial temporal variability in variables such as temperature, salinity and dissolved oxygen, related to diurnal and tidal cycles, and river flow, and these also provided critical data that was then used in calibration and validation of the hydrodynamic model.

year: 2014

title: Terrestrial ecosystems, increased solar ultraviolet radiation and interactions with other climatic change factors

authors: Caldwell, Martyn M.

subjects: terrestrial ecosystem

abstract: Based on research to date, we can state some expectations about terrestrial ecosystem response as several elements of global climate change develop in coming decades. Higher plant species will vary considerably in their response to elevated UV-B radiation, but the most common general effects are reductions in height of plants, decreased shoot mass if ozone reduction is severe, increased quantities of some phenolics in plant tissues and, perhaps, reductions in foliage area. In some cases, the common growth responses may be lessened by increasing CO2 concentrations. However, changes in chemistry of plant tissues will generally not be reversed by elevated CO2. Among other things, changes in plant tissue chemistry induced by enhanced UV-B may reduce consumption of plant tissues by insects and other herbivores, although occasionally consumption may be increased. Pathogen attack on plants may be increased or decreased as a consequence of elevated UV-B, in combination with other climatic changes. This may be affected both by alterations in plant chemistry and direct damage to some pathogens. Water limitation may decrease the sensitivity of some agricultural plants to UV-B, but for vegetation in other habitats, this may not apply. With global warming, the repair of some types of UV damage may be improved, but several other interactions between warming and enhanced UV-B may occur. For example, even though warming may lead to fewer killing frosts, with enhanced UV-B and elevated CO2 levels, some plant species may have increased sensitivity to frost damage.

text: Terrestrial ecosystems, increased solar ultraviolet radiation and interactions with other climatic change factors Based on research to date, we can state some expectations about terrestrial ecosystem response as several elements of global climate change develop in coming decades. Higher plant species will vary considerably in their response to elevated UV-B radiation, but the most common general effects are reductions in height of plants, decreased shoot mass if ozone reduction is severe, increased quantities of some phenolics in plant tissues and, perhaps, reductions in foliage area. In some cases, the common growth responses may be lessened by increasing CO2 concentrations. However, changes in chemistry of plant tissues will generally not be reversed by elevated CO2. Among other things, changes in plant tissue chemistry induced by enhanced UV-B may reduce consumption of plant tissues by insects and other herbivores, although occasionally consumption may be increased. Pathogen attack on plants may be increased or decreased as a consequence of elevated UV-B, in combination with other climatic changes. This may be affected both by alterations in plant chemistry and direct damage to some pathogens. Water limitation may decrease the sensitivity of some agricultural plants to UV-B, but for vegetation in other habitats, this may not apply. With global warming, the repair of some types of UV damage may be improved, but several other interactions between warming and enhanced UV-B may occur. For example, even though warming may lead to fewer killing frosts, with enhanced UV-B and elevated CO2 levels, some plant species may have increased sensitivity to frost damage.

year: 2007

title: Traditional plant harvesting in contemporary fragmented and urban landscapes

authors: Wehi, Priscilla M.

subjects: ethnobiology

abstract: Ecosystem fragmentation and destruction can lead to restrictive administration policies on traditional harvesting by indigenous peoples from remaining ecosystem tracts. In New Zealand, concerns about endangered species and governmental policies that focus on species and ecosystem preservation have resulted in severely curtailed traditional harvesting rights. Although provision has been made for limited gathering of traditional plants from government-administered conservation lands, it is unclear how much harvesting is undertaken on these lands and elsewhere and what this harvest might consist of. We interviewed seven expert Maori elders from the Waikato, New Zealand, to identify plant species they currently harvested and from where. We compared these data with the data we collected on permits issued for plant collecting on conservation lands in the same region. We sought to gain information on indigenous plant harvesting to determine the extent of permitted harvesting from conservation lands in the Waikato and to identify issues that might affect plant harvesting and management. Elders identified 58 species they harvest regularly or consider culturally important; over 50% of these species are harvested for medicinal use. Permit data from 1996 to 2006 indicated no apparent relationship between species of reported cultural significance and the number of permits issued for each of these species. Currently, few plant species are harvested from conservation lands, although some unofficial harvesting occurs. Elders instead reported that medicinal plants are frequently collected from urban and other public areas. They reported that plant species used for dyeing, carving, and weaving are difficult to access. Elders also discussed concerns such as spraying of roadsides, which resulted in the death of medicinal species, and use of commercial hybrids in urban planning. Local government may have an increasingly important role in supporting native traditions through urban planning, which takes account of cultural harvesting needs while potentially reducing future harvesting pressure on conservation lands. We suggest that active participation by the Māori community in the development and management of urban harvesting resources will result in positive outcomes.

text: Traditional plant harvesting in contemporary fragmented and urban landscapes Ecosystem fragmentation and destruction can lead to restrictive administration policies on traditional harvesting by indigenous peoples from remaining ecosystem tracts. In New Zealand, concerns about endangered species and governmental policies that focus on species and ecosystem preservation have resulted in severely curtailed traditional harvesting rights. Although provision has been made for limited gathering of traditional plants from government-administered conservation lands, it is unclear how much harvesting is undertaken on these lands and elsewhere and what this harvest might consist of. We interviewed seven expert Maori elders from the Waikato, New Zealand, to identify plant species they currently harvested and from where. We compared these data with the data we collected on permits issued for plant collecting on conservation lands in the same region. We sought to gain information on indigenous plant harvesting to determine the extent of permitted harvesting from conservation lands in the Waikato and to identify issues that might affect plant harvesting and management. Elders identified 58 species they harvest regularly or consider culturally important; over 50% of these species are harvested for medicinal use. Permit data from 1996 to 2006 indicated no apparent relationship between species of reported cultural significance and the number of permits issued for each of these species. Currently, few plant species are harvested from conservation lands, although some unofficial harvesting occurs. Elders instead reported that medicinal plants are frequently collected from urban and other public areas. They reported that plant species used for dyeing, carving, and weaving are difficult to access. Elders also discussed concerns such as spraying of roadsides, which resulted in the death of medicinal species, and use of commercial hybrids in urban planning. Local government may have an increasingly important role in supporting native traditions through urban planning, which takes account of cultural harvesting needs while potentially reducing future harvesting pressure on conservation lands. We suggest that active participation by the Māori community in the development and management of urban harvesting resources will result in positive outcomes.

year: 2010