title: Contrasting hydrodynamic regimes of submerged pinnacle and emergent coral reefs.

authors: Galbraith, Gemma F.

subjects: Animals

abstract: Hydrodynamics on coral reefs vary with depth, reef morphology and seascape position. Differences in hydrodynamic regimes strongly influence the structure and function of coral reef ecosystems. Submerged coral reefs on steep-sided, conical bathymetric features like seamounts experience enhanced water circulation as a result of interactions between currents and the abrupt physical structure. There may also be similar interactions between smaller pinnacles and regional water currents in offshore locations (crests > 10 m), while shallow reefs (crests <10 m) may be more subject to surface currents driven by wind, waves and tide. Here we tested whether coral pinnacles experienced stronger and more variable currents compared to emergent reefs at the same depth in both nearshore and offshore positions. Current speeds and temperature were monitored for 12 months at 11 reefs, representing the three different reef categories: submerged offshore pinnacles, emergent offshore reefs and emergent nearshore reefs. We found different patterns in current speeds and temperature among reef types throughout the year and between seasons. Submerged pinnacles exhibited stronger, more variable current speeds compared to both near and offshore emergent reefs. We found seasonal changes in current speeds for pinnacle and nearshore reefs but no variation in current strength on offshore reefs. Whilst instantaneous current directions did reflect the seascape position of individual sites, there was no difference in the directional variability of current speeds between reef types. Annual daily average temperatures at all reef types were not strongly seasonal, changing by less than 2 °C throughout the year. Daily temperature ranges at specific sites however, exhibited considerable variability (annual range of up to 6.5 °C), particularly amongst offshore emergent reefs which experienced the highest temperatures despite greater exposure to regional-scale circulation patterns. Additionally, we found a consistent mismatch between satellite sea surface temperatures and in-situ temperature data, which was on average 2 °C cooler throughout the annual study period. Our results suggest that distinct hydrodynamic processes occur on smaller submerged structures that are physically analogous to seamounts. Our findings highlight important nuances in environmental processes that occur on morphologically distinct coral reef habitats and these are likely to be important drivers for the community dynamics of organisms that inhabit these reefs.

text: Contrasting hydrodynamic regimes of submerged pinnacle and emergent coral reefs. Hydrodynamics on coral reefs vary with depth, reef morphology and seascape position. Differences in hydrodynamic regimes strongly influence the structure and function of coral reef ecosystems. Submerged coral reefs on steep-sided, conical bathymetric features like seamounts experience enhanced water circulation as a result of interactions between currents and the abrupt physical structure. There may also be similar interactions between smaller pinnacles and regional water currents in offshore locations (crests > 10 m), while shallow reefs (crests <10 m) may be more subject to surface currents driven by wind, waves and tide. Here we tested whether coral pinnacles experienced stronger and more variable currents compared to emergent reefs at the same depth in both nearshore and offshore positions. Current speeds and temperature were monitored for 12 months at 11 reefs, representing the three different reef categories: submerged offshore pinnacles, emergent offshore reefs and emergent nearshore reefs. We found different patterns in current speeds and temperature among reef types throughout the year and between seasons. Submerged pinnacles exhibited stronger, more variable current speeds compared to both near and offshore emergent reefs. We found seasonal changes in current speeds for pinnacle and nearshore reefs but no variation in current strength on offshore reefs. Whilst instantaneous current directions did reflect the seascape position of individual sites, there was no difference in the directional variability of current speeds between reef types. Annual daily average temperatures at all reef types were not strongly seasonal, changing by less than 2 °C throughout the year. Daily temperature ranges at specific sites however, exhibited considerable variability (annual range of up to 6.5 °C), particularly amongst offshore emergent reefs which experienced the highest temperatures despite greater exposure to regional-scale circulation patterns. Additionally, we found a consistent mismatch between satellite sea surface temperatures and in-situ temperature data, which was on average 2 °C cooler throughout the annual study period. Our results suggest that distinct hydrodynamic processes occur on smaller submerged structures that are physically analogous to seamounts. Our findings highlight important nuances in environmental processes that occur on morphologically distinct coral reef habitats and these are likely to be important drivers for the community dynamics of organisms that inhabit these reefs.

year: 2022-08-12

title: Making positive use of the fibrillation of lyocell fibres in composite materials

authors: Graupner, Nina

abstract: The present study investigates the influence of surface fibrillation of lyocell fibres on the adhesion and resulting properties of short fibre-reinforced polypropylene (PP) and polylactide (PLA) composites. Fibrillation was shown to reduce the tensile strength and elongation at break of the fibres, while not affecting Young's modulus. It was demonstrated that fibrillation improved adhesion significantly compared to non-fibrillated (untreated) fibres, and the critical fibre length determined by microbond tests was reduced. Despite the reduced tensile strength of the fibrillated lyocell fibres, the tensile strength of the composites was increased by a factor of 1.15 for PP and 1.62 for PLA compared to composites produced with untreated fibres. The Young's modulus of the composites was increased using fibrillated fibres by a factor of 1.41 for PP and 1.20 for PLA. The impact strength was also improved by using fibrillated fibres by a factor of 1.38 for PP-based and 1.23 for PLA-based composites. Surface fibrillation of lyocell offers interesting application possibilities, particularly for short fibre-reinforced materials, as the higher specific fibre surface reduces the critical fibre length of lyocell, leading to improved stress transfer from the matrix to the fibre. These fibres seem particularly promising to enhance the mechanical properties of short-fibre reinforced composites for 3D printing applications.

text: Making positive use of the fibrillation of lyocell fibres in composite materials The present study investigates the influence of surface fibrillation of lyocell fibres on the adhesion and resulting properties of short fibre-reinforced polypropylene (PP) and polylactide (PLA) composites. Fibrillation was shown to reduce the tensile strength and elongation at break of the fibres, while not affecting Young's modulus. It was demonstrated that fibrillation improved adhesion significantly compared to non-fibrillated (untreated) fibres, and the critical fibre length determined by microbond tests was reduced. Despite the reduced tensile strength of the fibrillated lyocell fibres, the tensile strength of the composites was increased by a factor of 1.15 for PP and 1.62 for PLA compared to composites produced with untreated fibres. The Young's modulus of the composites was increased using fibrillated fibres by a factor of 1.41 for PP and 1.20 for PLA. The impact strength was also improved by using fibrillated fibres by a factor of 1.38 for PP-based and 1.23 for PLA-based composites. Surface fibrillation of lyocell offers interesting application possibilities, particularly for short fibre-reinforced materials, as the higher specific fibre surface reduces the critical fibre length of lyocell, leading to improved stress transfer from the matrix to the fibre. These fibres seem particularly promising to enhance the mechanical properties of short-fibre reinforced composites for 3D printing applications.

year: 2023-07-01

title: Current state of the Rotorua Lakes

authors: Hamilton, David P.

abstract: The Rotorua Te Arawa Lakes’ programme of restoration has arguably been the most ambitious and effective of any for a group of lakes around the world. It has been characterised by willingness to ‘try things’, to be guided closely by scientific input, and to
now have excellent structures for monitoring and implementation of actions. Still, major challenges remain. One of these is the potential for a sense of complacency, particularly when some lakes have responded extremely positively to in-lake treatments (e.g. Rotorua) or major one-off actions (e.g. Rotoiti). It is essential that these improvements in lake water quality, some of which may not be able to be maintained indefinitely in their current mode, not delay further catchment management actions.
Another challenge is exotic oxygen weeds, particularly where it is difficult to harvest large accumulations. The final challenge relates to climate. Recent years have been characterised by droughts and intense rainfall events that challenge land management practices. Further, surface water temperatures in the lakes in 2015 have been greater than at any time in the past. If these changes are symptomatic of a future climate, then there will need to be greater effort put into building resilience in the lakes and their catchments.

text: Current state of the Rotorua Lakes The Rotorua Te Arawa Lakes’ programme of restoration has arguably been the most ambitious and effective of any for a group of lakes around the world. It has been characterised by willingness to ‘try things’, to be guided closely by scientific input, and to
now have excellent structures for monitoring and implementation of actions. Still, major challenges remain. One of these is the potential for a sense of complacency, particularly when some lakes have responded extremely positively to in-lake treatments (e.g. Rotorua) or major one-off actions (e.g. Rotoiti). It is essential that these improvements in lake water quality, some of which may not be able to be maintained indefinitely in their current mode, not delay further catchment management actions.
Another challenge is exotic oxygen weeds, particularly where it is difficult to harvest large accumulations. The final challenge relates to climate. Recent years have been characterised by droughts and intense rainfall events that challenge land management practices. Further, surface water temperatures in the lakes in 2015 have been greater than at any time in the past. If these changes are symptomatic of a future climate, then there will need to be greater effort put into building resilience in the lakes and their catchments.

year: 2015