title: Coupled flow-wave numerical model in assessing the impact of dredging on the morphology of Matakana Banks

authors: Ramli, Andi Yulianti

subjects: ebb-tidal delta

abstract: The short- and long-term impacts of dredging on the Matakana Banks ebb-tidal delta was investigated by numerical modelling using Delft3D. The model covered dredging locations inside Tauranga Harbour and the offshore areas around the Matakana Banks ebb-tidal delta, and was calibrated by an extensive field programme to measure hydrodynamic processes and sediment characteristics, and high resolution bathymetric surveys. The impacts of dredging was then investigated by modelling three different conditions: (1) before dredging started in 1968, using 1967 bathymetry; (2) the present situation using 2013 bathymetry with existing dredging and dumping; and (3) future scenarios using 2013 bathymetry with alternative offshore disposal locations. 
The field data and hydrodynamic model results showed that the ebb-tidal delta can be separated into two main regions that are dominated by tidal processes or wave processes. Overall, the wave influence becomes more dominant as the distance from the entrance channel (main ebb jet) increases, and vice versa for tidal processes. Sediment transport pathways were inferred using spatial patterns of erosion and accretion from bathymetric surveys and cross-sectional profiles along the shoreline. The pathways reflected the interactions between the identified wave and tide processes. 
A month-long time series of wave conditions were used to force a wave model coupled with the hydrodynamic model for the 2013 bathymetry to simulate the present day situation. The results showed that the sediment volume of the ebb-tidal delta fluctuated with tidal range; accretion occurred during neap tides and erosion during spring tides. To assess the long term impact, the morphological factor (morfac) tool in Delft3D was used. Morfac of 60 was applied for 12 days simulation time and the results will be presented in this paper

text: Coupled flow-wave numerical model in assessing the impact of dredging on the morphology of Matakana Banks The short- and long-term impacts of dredging on the Matakana Banks ebb-tidal delta was investigated by numerical modelling using Delft3D. The model covered dredging locations inside Tauranga Harbour and the offshore areas around the Matakana Banks ebb-tidal delta, and was calibrated by an extensive field programme to measure hydrodynamic processes and sediment characteristics, and high resolution bathymetric surveys. The impacts of dredging was then investigated by modelling three different conditions: (1) before dredging started in 1968, using 1967 bathymetry; (2) the present situation using 2013 bathymetry with existing dredging and dumping; and (3) future scenarios using 2013 bathymetry with alternative offshore disposal locations. 
The field data and hydrodynamic model results showed that the ebb-tidal delta can be separated into two main regions that are dominated by tidal processes or wave processes. Overall, the wave influence becomes more dominant as the distance from the entrance channel (main ebb jet) increases, and vice versa for tidal processes. Sediment transport pathways were inferred using spatial patterns of erosion and accretion from bathymetric surveys and cross-sectional profiles along the shoreline. The pathways reflected the interactions between the identified wave and tide processes. 
A month-long time series of wave conditions were used to force a wave model coupled with the hydrodynamic model for the 2013 bathymetry to simulate the present day situation. The results showed that the sediment volume of the ebb-tidal delta fluctuated with tidal range; accretion occurred during neap tides and erosion during spring tides. To assess the long term impact, the morphological factor (morfac) tool in Delft3D was used. Morfac of 60 was applied for 12 days simulation time and the results will be presented in this paper

year: 2015

title: The role of Chaetopterus sp. in reshaping sediment characteristics and benthic communities in Queen Charlotte Sound

authors: Scott-Simmonds , Thomas

abstract: Soft-sediment habitats are critical to marine ecosystems, supporting diverse benthic communities and key processes such as nutrient cycling, sediment stabilisation, and energy transfer. Among these habitats, tube-building polychaetes like Chaetopterus act as ecosystem engineers, modifying sediment properties and influencing community structure and functioning. This study investigated the ecological impacts of Chaetopterus in East Bay, Queen Charlotte Sound, focusing on its role in sediment modification, macrofaunal biodiversity, and functional group composition. 

Field surveys were conducted across ten paired Chaetopterus and control sites, selected to capture a gradient in tube mat density and depth. At each site, five sediment and macrofaunal samples were collected using coring techniques, enabling a robust comparison of Chaetopterus-modified and unmodified habitats. 

Results showed significantly higher organic content (3.1% ± 0.2 vs. 2.0% ± 0.1) and mud content (19.8% ± 2.0 vs. 7.7% ± 0.5) in Chaetopterus habitats, highlighting its role in sediment enrichment and stabilisation. Macrofaunal communities exhibited significantly greater species richness (20.0 ± 0.8 vs. 14.5 ± 0.7 species per core) and diversity (Shannon diversity: 2.48 ± 0.05 vs. 2.16 ± 0.06), driven by increased structural complexity and organic matter retention. 

Functional group analysis revealed a shift towards surface-oriented taxa in Chaetopterus habitats, including increased surface-feeding deposit feeders (e.g., amphipods) and scavengers (e.g., Halicarcinus cookii), alongside a relative reduction in deeper-burrowing taxa such as bioturbating polychaetes (Prionospio multicristata) and burrowing bivalves (Tawera spissa). This suggests that Chaetopterus tube mats promote surface-associated processes like organic matter turnover and detritus retention, while potentially suppressing sediment-mixing and oxygenation functions. 

Chaetopterus habitats exhibited significantly lower dispersion (PERMDISP), indicating more functionally homogeneous assemblages compared to control sites, where greater within-group variability reflected a broader range of functional traits, including suspension feeders and opportunistic burrowers (e.g., Phoxocephalidae amphipods). Chaetopterus density was significantly correlated with macrofaunal community composition, reinforcing the role of tube mats as a key driver of functional trait distributions. However, the extent of these effects varied across sites, suggesting that local environmental factors, particularly sediment properties (mud content, organic matter) and Chaetopterus density, mediate its influence on benthic communities. 

These findings advance understanding of habitat-modifying polychaetes by demonstrating that Chaetopterus effects are highly context-dependent, shaped by habitat × site interactions and environmental conditions. While previous studies have identified Chaetopterus as a biodiversity enhancer, this study highlights its dual role as both a facilitator of surfacedominated processes and a potential suppressor of deeper sediment functions. These findings provide critical insights into its ecological role within New Zealand's coastal ecosystems and underscore the need for site-specific management strategies that balance local biodiversity benefits with broader ecosystem functions.

text: The role of Chaetopterus sp. in reshaping sediment characteristics and benthic communities in Queen Charlotte Sound Soft-sediment habitats are critical to marine ecosystems, supporting diverse benthic communities and key processes such as nutrient cycling, sediment stabilisation, and energy transfer. Among these habitats, tube-building polychaetes like Chaetopterus act as ecosystem engineers, modifying sediment properties and influencing community structure and functioning. This study investigated the ecological impacts of Chaetopterus in East Bay, Queen Charlotte Sound, focusing on its role in sediment modification, macrofaunal biodiversity, and functional group composition. 

Field surveys were conducted across ten paired Chaetopterus and control sites, selected to capture a gradient in tube mat density and depth. At each site, five sediment and macrofaunal samples were collected using coring techniques, enabling a robust comparison of Chaetopterus-modified and unmodified habitats. 

Results showed significantly higher organic content (3.1% ± 0.2 vs. 2.0% ± 0.1) and mud content (19.8% ± 2.0 vs. 7.7% ± 0.5) in Chaetopterus habitats, highlighting its role in sediment enrichment and stabilisation. Macrofaunal communities exhibited significantly greater species richness (20.0 ± 0.8 vs. 14.5 ± 0.7 species per core) and diversity (Shannon diversity: 2.48 ± 0.05 vs. 2.16 ± 0.06), driven by increased structural complexity and organic matter retention. 

Functional group analysis revealed a shift towards surface-oriented taxa in Chaetopterus habitats, including increased surface-feeding deposit feeders (e.g., amphipods) and scavengers (e.g., Halicarcinus cookii), alongside a relative reduction in deeper-burrowing taxa such as bioturbating polychaetes (Prionospio multicristata) and burrowing bivalves (Tawera spissa). This suggests that Chaetopterus tube mats promote surface-associated processes like organic matter turnover and detritus retention, while potentially suppressing sediment-mixing and oxygenation functions. 

Chaetopterus habitats exhibited significantly lower dispersion (PERMDISP), indicating more functionally homogeneous assemblages compared to control sites, where greater within-group variability reflected a broader range of functional traits, including suspension feeders and opportunistic burrowers (e.g., Phoxocephalidae amphipods). Chaetopterus density was significantly correlated with macrofaunal community composition, reinforcing the role of tube mats as a key driver of functional trait distributions. However, the extent of these effects varied across sites, suggesting that local environmental factors, particularly sediment properties (mud content, organic matter) and Chaetopterus density, mediate its influence on benthic communities. 

These findings advance understanding of habitat-modifying polychaetes by demonstrating that Chaetopterus effects are highly context-dependent, shaped by habitat × site interactions and environmental conditions. While previous studies have identified Chaetopterus as a biodiversity enhancer, this study highlights its dual role as both a facilitator of surfacedominated processes and a potential suppressor of deeper sediment functions. These findings provide critical insights into its ecological role within New Zealand's coastal ecosystems and underscore the need for site-specific management strategies that balance local biodiversity benefits with broader ecosystem functions.

year: 2025

title: Te Mātaiaho as curricular justice?

authors: Shafer, Derek

abstract: Te Mātaiaho produces a version of curricular justice which aims to give effect to Te Tiriti and address long-standing inequities in education in Aotearoa New Zealand. We examine Te Mātaiaho’s vision for subject English and its construction of students’ identities as fundamental to a curriculum that advances both bicultural nationhood and just outcomes for all students. We draw on Raewyn Connell’s (2010) model of curricular justice, and Nancy Fraser's (2017) notion of progressive neoliberalism to explore the opportunities and implications for subject English within Te Mātaiaho's vision. How might these frameworks for justice help to critique the development of educational policy and support the implementation of Te Mātaiaho's vision for biculturalnationhood and just outcomes for all students.

text: Te Mātaiaho as curricular justice? Te Mātaiaho produces a version of curricular justice which aims to give effect to Te Tiriti and address long-standing inequities in education in Aotearoa New Zealand. We examine Te Mātaiaho’s vision for subject English and its construction of students’ identities as fundamental to a curriculum that advances both bicultural nationhood and just outcomes for all students. We draw on Raewyn Connell’s (2010) model of curricular justice, and Nancy Fraser's (2017) notion of progressive neoliberalism to explore the opportunities and implications for subject English within Te Mātaiaho's vision. How might these frameworks for justice help to critique the development of educational policy and support the implementation of Te Mātaiaho's vision for biculturalnationhood and just outcomes for all students.

year: 2023-11-22