title: Morphodynamics of embayed beaches: The effect of wave conditions

authors: Daly, C.J.

subjects: parabolic bays

abstract: Embayed beaches are abundant along many coastlines of the world, yet our understanding of the role of wave conditions on their morphodynamics still needs to be furthered in order to better predict their dynamics. In this paper, a numerical modeling approach was used to determine the response of embayed beaches to varied wave forcing. The process-based numerical model, Delft3D, was used to simulate 16 wave conditions. Results indicate that complex flow patterns develop within the bay which drive long-shore and cross-shore currents. These currents actively interact to promote the formation of a stable bay shape. The resulting bathymetry in the bay is highly dependent on the incident wave conditions. It is also shown that beach rotation can occur for the same mean wave direction due to changes in the directional spreading. The numerical modeling approach has given agreeable results, and can be further used to explore the importance of other factors affecting embayed beach morphology, such as nearshore processes and bay geometry.

text: Morphodynamics of embayed beaches: The effect of wave conditions Embayed beaches are abundant along many coastlines of the world, yet our understanding of the role of wave conditions on their morphodynamics still needs to be furthered in order to better predict their dynamics. In this paper, a numerical modeling approach was used to determine the response of embayed beaches to varied wave forcing. The process-based numerical model, Delft3D, was used to simulate 16 wave conditions. Results indicate that complex flow patterns develop within the bay which drive long-shore and cross-shore currents. These currents actively interact to promote the formation of a stable bay shape. The resulting bathymetry in the bay is highly dependent on the incident wave conditions. It is also shown that beach rotation can occur for the same mean wave direction due to changes in the directional spreading. The numerical modeling approach has given agreeable results, and can be further used to explore the importance of other factors affecting embayed beach morphology, such as nearshore processes and bay geometry.

year: 2011

title: Exploring the mānuka phyllosphere microbiome

authors: Noble, Anya Sophia

subjects: manuka

abstract: The surface of plant leaves, termed phyllosphere, is a ubiquitous microbial habitat that harbours diverse communities of microorganisms. Although a growing body of experimental evidence demonstrates that these microorganisms can have an influential role in host physiology, the ecological processes that drive the assembly of natural phyllosphere communities remain poorly understood.

Leptospermum scoparium (mānuka) is an indigenous New Zealand tea tree widely known for the non-peroxide antibacterial properties of its honey. However, the host physiological traits associated with these properties exhibit variation that remain unexplained despite decades of research. Considering a preliminary study that identified spatially persistent host association in the mānuka phyllosphere microbiome with patterns congruent with those of a microbial community under strong host selection, the primary objective of this research was to generate a holistic understanding of the ecological processes underpinning community assembly in the natural mānuka phyllosphere.

Since the host specificity of the mānuka phyllosphere microbiome was unquantified, this PhD thesis research began with a multi-species, spatially hierarchical survey of a native forest to understand the relative influence of host species identity versus distance on the phyllosphere microbiome of mānuka and ecologically similar, adjacent native plant species. The results revealed that the relative influence of host species identity on the phyllosphere microbiome was quantitatively stronger in mānuka compared to other plant species, and mānuka species-specificity was not associated with leaf morphological traits.

Using a pair of morphologically indistinguishable and naturally co-occurring plant species (mānuka and Kunzea ericoides [kānuka]), I then explored the relative influence of host species identity and leaf morphology on inter-host dispersal. Specifically, I addressed a longstanding yet under-examined hypothesis that the relative strength of the phyllosphere microbiome as a source of dispersing microorganisms (i.e., source-strength) is contingent on leaf morphology. The results revealed considerable spatial heterogeneity among morphologically indistinguishable leaves at small spatial scales and suggested that mānuka may act as a stronger source of phyllosphere microorganisms than kānuka. These findings suggest that source-strength is determined by the quantitative difference in the relative strength of host selection among plant species.

To contextualise this apparent spatial stability and host species-specificity of the mānuka phyllosphere microbiome, temporal variation was investigated by replicate sampling in three different seasons. My results revealed that the relative influence of individual host trees was larger than the season, and specific phyllosphere taxa persisted across time. Additionally, my results revealed an increased core microbiome during summer flowering, suggesting an association between host selection strength and host phenology.

Lastly, I explored the relationship between the mānuka phyllosphere microbiome and mānuka honey quality. I sampled trees and honey from three adjacent mānuka populations known to exhibit visually discrete phenological traits (i.e., flowering time). My results revealed correlations between phyllosphere community composition and chemical properties of mānuka honey, including the primary constituent of mānuka’s non-peroxide antibacterial properties (i.e., methylglyoxal).

Through the incorporation of spatial and temporal sampling designs, as well as a multi-disciplinary case study, this thesis provides a holistic understanding of the relative influence of host selection (abiotic and biotic), dispersal (short- and long-distance), and climate, on the assembly of the mānuka phyllosphere microbiome. These results also provide new perspectives on prevailing controversies (e.g., host selection vs. dispersal), address unverified hypotheses (e.g., source-strength), and illustrate a path forward that will allow the emergence of a coherent and generalisable understanding of phyllosphere microbial ecology.

text: Exploring the mānuka phyllosphere microbiome The surface of plant leaves, termed phyllosphere, is a ubiquitous microbial habitat that harbours diverse communities of microorganisms. Although a growing body of experimental evidence demonstrates that these microorganisms can have an influential role in host physiology, the ecological processes that drive the assembly of natural phyllosphere communities remain poorly understood.

Leptospermum scoparium (mānuka) is an indigenous New Zealand tea tree widely known for the non-peroxide antibacterial properties of its honey. However, the host physiological traits associated with these properties exhibit variation that remain unexplained despite decades of research. Considering a preliminary study that identified spatially persistent host association in the mānuka phyllosphere microbiome with patterns congruent with those of a microbial community under strong host selection, the primary objective of this research was to generate a holistic understanding of the ecological processes underpinning community assembly in the natural mānuka phyllosphere.

Since the host specificity of the mānuka phyllosphere microbiome was unquantified, this PhD thesis research began with a multi-species, spatially hierarchical survey of a native forest to understand the relative influence of host species identity versus distance on the phyllosphere microbiome of mānuka and ecologically similar, adjacent native plant species. The results revealed that the relative influence of host species identity on the phyllosphere microbiome was quantitatively stronger in mānuka compared to other plant species, and mānuka species-specificity was not associated with leaf morphological traits.

Using a pair of morphologically indistinguishable and naturally co-occurring plant species (mānuka and Kunzea ericoides [kānuka]), I then explored the relative influence of host species identity and leaf morphology on inter-host dispersal. Specifically, I addressed a longstanding yet under-examined hypothesis that the relative strength of the phyllosphere microbiome as a source of dispersing microorganisms (i.e., source-strength) is contingent on leaf morphology. The results revealed considerable spatial heterogeneity among morphologically indistinguishable leaves at small spatial scales and suggested that mānuka may act as a stronger source of phyllosphere microorganisms than kānuka. These findings suggest that source-strength is determined by the quantitative difference in the relative strength of host selection among plant species.

To contextualise this apparent spatial stability and host species-specificity of the mānuka phyllosphere microbiome, temporal variation was investigated by replicate sampling in three different seasons. My results revealed that the relative influence of individual host trees was larger than the season, and specific phyllosphere taxa persisted across time. Additionally, my results revealed an increased core microbiome during summer flowering, suggesting an association between host selection strength and host phenology.

Lastly, I explored the relationship between the mānuka phyllosphere microbiome and mānuka honey quality. I sampled trees and honey from three adjacent mānuka populations known to exhibit visually discrete phenological traits (i.e., flowering time). My results revealed correlations between phyllosphere community composition and chemical properties of mānuka honey, including the primary constituent of mānuka’s non-peroxide antibacterial properties (i.e., methylglyoxal).

Through the incorporation of spatial and temporal sampling designs, as well as a multi-disciplinary case study, this thesis provides a holistic understanding of the relative influence of host selection (abiotic and biotic), dispersal (short- and long-distance), and climate, on the assembly of the mānuka phyllosphere microbiome. These results also provide new perspectives on prevailing controversies (e.g., host selection vs. dispersal), address unverified hypotheses (e.g., source-strength), and illustrate a path forward that will allow the emergence of a coherent and generalisable understanding of phyllosphere microbial ecology.

year: 2024

title: Turning a negative into a positive: Aquatic weed harvesting Lake Rotoehu

authors: Mallinson, Richard

abstract: The submerged aquatic weed hornwort (Ceratophyllum demersum) has become widespread through Lake Rotoehu since its establishment in the lake around 2000. This exotic pest plant is surface reaching in large parts of this shallow lake making it a perfect candidate for mechanical harvesting.
As part of the Te Arawa - Rotorua Lakes Programme the Lake Rotoehu Action Plan sets out nutrient reduction targets for nitrogen and phosphorus. Realising these targets is integral if lake water quality is to be restored to the trophic level index (TLI) target for Lake
Rotoehu. Restoration measures have included land use management efforts to arrest nutrient inputs, phosphorus locking through alum dosing, floating wetlands, and most recently the deployment of two aerators. To date the most successful in-lake nutrient reduction method has been mechanical harvest of hornwort.
Aquatic weed harvesting has resulted in reaching a significant portion of the annual nutrient target for the lake catchment. Attaining this level of nutrient removal has manifested in tangible water quality gains in the past few years. Most noticeable is the reduction in cyanobacterial (blue-green) algal blooms which had been prevalent in the lake in summer months. We discuss the practicalities and problems of submerged lake weed harvesting, disposal options, and impacts of this activity on the lake.

text: Turning a negative into a positive: Aquatic weed harvesting Lake Rotoehu The submerged aquatic weed hornwort (Ceratophyllum demersum) has become widespread through Lake Rotoehu since its establishment in the lake around 2000. This exotic pest plant is surface reaching in large parts of this shallow lake making it a perfect candidate for mechanical harvesting.
As part of the Te Arawa - Rotorua Lakes Programme the Lake Rotoehu Action Plan sets out nutrient reduction targets for nitrogen and phosphorus. Realising these targets is integral if lake water quality is to be restored to the trophic level index (TLI) target for Lake
Rotoehu. Restoration measures have included land use management efforts to arrest nutrient inputs, phosphorus locking through alum dosing, floating wetlands, and most recently the deployment of two aerators. To date the most successful in-lake nutrient reduction method has been mechanical harvest of hornwort.
Aquatic weed harvesting has resulted in reaching a significant portion of the annual nutrient target for the lake catchment. Attaining this level of nutrient removal has manifested in tangible water quality gains in the past few years. Most noticeable is the reduction in cyanobacterial (blue-green) algal blooms which had been prevalent in the lake in summer months. We discuss the practicalities and problems of submerged lake weed harvesting, disposal options, and impacts of this activity on the lake.

year: 2015