title: Review of sand extraction impacts for Miller’s Bank, Kaipara Harbour

authors: de Lange, Willem P.

abstract: A review of the monitoring reports for resource consent MCO623701 (CON20030623701) involving sand extraction near Millers Bank, and additional reports relating to sediment transport within the Kaipara Harbour was undertaken. The available data indicates that the Waikeri Bank and surrounding channels are mobile, and while occupying approximately the same position since the first full survey in 1852, they are not fixed features. The adjacent shoreline between Ru Point and Tauhara Creek, have undergone phases of erosion and accretion since 1852, with variable behaviour along the coast. Overall this section of coast is tending to erode. Monitoring since sand extraction began indicates that natural phenomena, particularly episodic storm conditions from the northeast quadrant, are the dominant cause of shoreline erosion. No quantitative data are available prior to sand extraction, so it is difficult to determine if there has been any change in the rate of erosion since extraction began. Limited current data, and numerical modelling, suggest that Five Fathom Channel is ebb dominated, and the channel between Waikeri Bank and the shore may be flood dominated. This would cause a recirculation of sediment around Waikeri Bank, and the morphology suggests that sediment tends to accumulate at the northern and southern junctions of the two channels. Bathymetric surveys indicate that the supply of sediment to this region is sufficient to replenish sand extracted. However, the surveys completed to date do not have sufficient resolution and datum controls to quantify volumetric changes. The variations recorded by monitoring are minor compared to historic changes, so it is unlikely that the sand extraction is having any measurable effect on flow through either channel or sedimentation in the vicinity.

text: Review of sand extraction impacts for Miller’s Bank, Kaipara Harbour A review of the monitoring reports for resource consent MCO623701 (CON20030623701) involving sand extraction near Millers Bank, and additional reports relating to sediment transport within the Kaipara Harbour was undertaken. The available data indicates that the Waikeri Bank and surrounding channels are mobile, and while occupying approximately the same position since the first full survey in 1852, they are not fixed features. The adjacent shoreline between Ru Point and Tauhara Creek, have undergone phases of erosion and accretion since 1852, with variable behaviour along the coast. Overall this section of coast is tending to erode. Monitoring since sand extraction began indicates that natural phenomena, particularly episodic storm conditions from the northeast quadrant, are the dominant cause of shoreline erosion. No quantitative data are available prior to sand extraction, so it is difficult to determine if there has been any change in the rate of erosion since extraction began. Limited current data, and numerical modelling, suggest that Five Fathom Channel is ebb dominated, and the channel between Waikeri Bank and the shore may be flood dominated. This would cause a recirculation of sediment around Waikeri Bank, and the morphology suggests that sediment tends to accumulate at the northern and southern junctions of the two channels. Bathymetric surveys indicate that the supply of sediment to this region is sufficient to replenish sand extracted. However, the surveys completed to date do not have sufficient resolution and datum controls to quantify volumetric changes. The variations recorded by monitoring are minor compared to historic changes, so it is unlikely that the sand extraction is having any measurable effect on flow through either channel or sedimentation in the vicinity.

year: 2010

title: Long-term variations in fish assemblage, macrophyte community, and water quality in Lake Rotoroa (Hamilton Lake)

authors: Law, Duncan Robert Mckenzie

abstract: Lake Rotoroa (37º48’S, 175º16’E) is a small, shallow, polymictic lake located on the western side of Hamilton City. The lake covers an area of 0.54 km2 with a mean depth of 2.4 m, catchment and riparian margins have been significantly modified into a suburban park-like setting. Due to its urban location and recreational value, exotic flora and fauna have been intentionally and unintentionally introduced. This has resulted in fluctuations in water quality and changes in phytoplankton, fish, and macrophyte assemblages over the past 60 years. The overall aim of this thesis is to summarise the fluctuations in water quality and macrophyte community of Lake Rotoroa associated with introduction of exotic species, and to develop a general understanding of the ecosystem response. This study involved collating and analysing available information on fish assemblages, macrophyte community, and water quality in Lake Rotoroa. Data from nine fish surveys undertaken between 1976 and 2012 has been combined. Water quality and macrophyte data was supplied by NIWA, who have undertaken monitoring for Hamilton City Council as part of the national lakes monitoring programme.

Fishing methods have varied from gill, trap, and fyke netting between 1976 and 2001, with boat electrofishing surveys between 2003 and 2012. Lake Rotoroa has a relatively diverse freshwater fish fauna, comprising two native and six exotic fish species. The fish assemblage is now dominated by the native shortfin eel (Anguilla australis), European perch (Perca fluviatilis), brown bullhead catfish (Ameiurus nebulosus), and tench (Tinca tinca), with low densities of rudd (Scardinius erythrophthalmus) and goldfish (Carassius auratus). Fish density and biomass have varied throughout the survey period, to some extent related to the environmental conditions and macrophyte cover. 

Macrophyte coverage and water quality have undergone considerable changes in the last 30 years, with the collapses of macrophytes stimulating decreases in water quality and increased perch abundance. In 1990, the macrophyte community collapsed with an associated release of nutrients into the water column, causing the lake to become supertrophic. Between 1992 and 2010, water quality improved, with a decrease phosphorus concentrations that apparently limited phytoplankton biomass and improved water clarity. This allowed macrophytes to recolonise the lake to 30% lake bed coverage in 2005 and a consequent improvement from supertrophic to a eutrophic state. Since 2009, the macrophyte community has undergone another collapse, with only a few clumps of native charophytes and Egeria densa present in 2011. The reduction of macrophytes has been accompanied by a decrease in water clarity. The collapse has been attributed to disturbance by grazing from the herbivorous rudd and foraging benthic feeding fish, although other stresses such as decreased water clarity and microcystins may also have had an influence. 

Further research is needed on the selectivity between passive and active fish capture methods used to allow accurate comparisons between the two methods. This will allow for density and biomass estimates to be made for the passive fishing methods previously used and allow greater insight into changes in abundance of fish populations in Lake Rotoroa.

text: Long-term variations in fish assemblage, macrophyte community, and water quality in Lake Rotoroa (Hamilton Lake) Lake Rotoroa (37º48’S, 175º16’E) is a small, shallow, polymictic lake located on the western side of Hamilton City. The lake covers an area of 0.54 km2 with a mean depth of 2.4 m, catchment and riparian margins have been significantly modified into a suburban park-like setting. Due to its urban location and recreational value, exotic flora and fauna have been intentionally and unintentionally introduced. This has resulted in fluctuations in water quality and changes in phytoplankton, fish, and macrophyte assemblages over the past 60 years. The overall aim of this thesis is to summarise the fluctuations in water quality and macrophyte community of Lake Rotoroa associated with introduction of exotic species, and to develop a general understanding of the ecosystem response. This study involved collating and analysing available information on fish assemblages, macrophyte community, and water quality in Lake Rotoroa. Data from nine fish surveys undertaken between 1976 and 2012 has been combined. Water quality and macrophyte data was supplied by NIWA, who have undertaken monitoring for Hamilton City Council as part of the national lakes monitoring programme.

Fishing methods have varied from gill, trap, and fyke netting between 1976 and 2001, with boat electrofishing surveys between 2003 and 2012. Lake Rotoroa has a relatively diverse freshwater fish fauna, comprising two native and six exotic fish species. The fish assemblage is now dominated by the native shortfin eel (Anguilla australis), European perch (Perca fluviatilis), brown bullhead catfish (Ameiurus nebulosus), and tench (Tinca tinca), with low densities of rudd (Scardinius erythrophthalmus) and goldfish (Carassius auratus). Fish density and biomass have varied throughout the survey period, to some extent related to the environmental conditions and macrophyte cover. 

Macrophyte coverage and water quality have undergone considerable changes in the last 30 years, with the collapses of macrophytes stimulating decreases in water quality and increased perch abundance. In 1990, the macrophyte community collapsed with an associated release of nutrients into the water column, causing the lake to become supertrophic. Between 1992 and 2010, water quality improved, with a decrease phosphorus concentrations that apparently limited phytoplankton biomass and improved water clarity. This allowed macrophytes to recolonise the lake to 30% lake bed coverage in 2005 and a consequent improvement from supertrophic to a eutrophic state. Since 2009, the macrophyte community has undergone another collapse, with only a few clumps of native charophytes and Egeria densa present in 2011. The reduction of macrophytes has been accompanied by a decrease in water clarity. The collapse has been attributed to disturbance by grazing from the herbivorous rudd and foraging benthic feeding fish, although other stresses such as decreased water clarity and microcystins may also have had an influence. 

Further research is needed on the selectivity between passive and active fish capture methods used to allow accurate comparisons between the two methods. This will allow for density and biomass estimates to be made for the passive fishing methods previously used and allow greater insight into changes in abundance of fish populations in Lake Rotoroa.

year: 2012

title: Local values and the promotion and restoration of wetlands and their ecosystem services in Aotearoa-New Zealand: a case study of Tauranga’s planning regime

authors: Peat, Helen Ann

subjects: Environmental planning

abstract: Aligning wetlands restoration planning mechanisms with public perceptions and values can help gain support for and assistance with restoration. Using Tauranga as a case study, this thesis is an exploratory study that applies the Millennium Ecosystem Assessment (MEA) framework to examine the extent to which New Zealand's planning regime incorporates local values in the promotion and restoration of wetlands and their ecosystem services.

This thesis used multiple qualitative research methods in a two-pronged process. A narrative literature review and systematic statutory analysis in phase one helped identify values associated with wetland ecosystem services and how New Zealand’s, and more specifically Tauranga’s, resource management system promotes and enables the restoration of wetlands and their ecosystem services. A case study approach with analysis of primary and secondary data in phase two helped identify what Tauranga local residents value as important wetland ecosystem services and the extent to which the local policy mechanisms reflect these values. 

Through thematic analysis of semi-structured interviews and summaries of submissions, this thesis identifies six dimensions that represent values towards wetland ecosystem services and their restoration in Tauranga. Other than one dimension that consists of a single value on education from the cultural services category of the MEA framework, the remaining five dimensions comprise services from within and between the framework categories. These dimensions are wetlands as nutrient- and mineral-rich areas that support biodiversity and provide habitat; that regulate water, act as natural flood plains and sequester carbon to help protect against climate change and natural hazards; that maintain Māori cultural practices; that remove nutrients and contaminants in water; and provide recreational and aesthetic experiences. Therefore, identified dimensions could form the basis of educational programmes and toolkits that promote wetlands restoration.

The systematic policy analysis and cross-comparison with the results of the thematic analysis found that Tauranga’s planning regime partially provides for each of the six dimensions. However, the nuances and complexities of the values, including the interconnected nature of wetlands values and services, are not captured. This means Tauranga’s planning regime does not fully incorporate local values in the promotion and restoration of wetlands and their ecosystem services. Bridging the gap between wetlands restoration provisions and wetland ecosystem service values is likely to be supported by enacting the current resource management reforms. Enacting the reforms would help reduce the number of policies and plans, implement regional spatial planning, and develop outcomes-based policy mechanisms that encompass ecological, social, cultural and spiritual values, including those associated with wetlands.

text: Local values and the promotion and restoration of wetlands and their ecosystem services in Aotearoa-New Zealand: a case study of Tauranga’s planning regime Aligning wetlands restoration planning mechanisms with public perceptions and values can help gain support for and assistance with restoration. Using Tauranga as a case study, this thesis is an exploratory study that applies the Millennium Ecosystem Assessment (MEA) framework to examine the extent to which New Zealand's planning regime incorporates local values in the promotion and restoration of wetlands and their ecosystem services.

This thesis used multiple qualitative research methods in a two-pronged process. A narrative literature review and systematic statutory analysis in phase one helped identify values associated with wetland ecosystem services and how New Zealand’s, and more specifically Tauranga’s, resource management system promotes and enables the restoration of wetlands and their ecosystem services. A case study approach with analysis of primary and secondary data in phase two helped identify what Tauranga local residents value as important wetland ecosystem services and the extent to which the local policy mechanisms reflect these values. 

Through thematic analysis of semi-structured interviews and summaries of submissions, this thesis identifies six dimensions that represent values towards wetland ecosystem services and their restoration in Tauranga. Other than one dimension that consists of a single value on education from the cultural services category of the MEA framework, the remaining five dimensions comprise services from within and between the framework categories. These dimensions are wetlands as nutrient- and mineral-rich areas that support biodiversity and provide habitat; that regulate water, act as natural flood plains and sequester carbon to help protect against climate change and natural hazards; that maintain Māori cultural practices; that remove nutrients and contaminants in water; and provide recreational and aesthetic experiences. Therefore, identified dimensions could form the basis of educational programmes and toolkits that promote wetlands restoration.

The systematic policy analysis and cross-comparison with the results of the thematic analysis found that Tauranga’s planning regime partially provides for each of the six dimensions. However, the nuances and complexities of the values, including the interconnected nature of wetlands values and services, are not captured. This means Tauranga’s planning regime does not fully incorporate local values in the promotion and restoration of wetlands and their ecosystem services. Bridging the gap between wetlands restoration provisions and wetland ecosystem service values is likely to be supported by enacting the current resource management reforms. Enacting the reforms would help reduce the number of policies and plans, implement regional spatial planning, and develop outcomes-based policy mechanisms that encompass ecological, social, cultural and spiritual values, including those associated with wetlands.

year: 2022