title: Physiological constraints on the latitudinal distribution of the mangrove Avicennia marina (Forsk.) Vierh. subsp. australasica (Walp.) J. Everett in New Zealand

authors: Beard, Catherine

subjects: Avicennia marina

abstract: ﻿New Zealand's only mangrove species, Avicennia marina (Forsk.) Vierh. subsp. australasica (Walp) Everett (Avicenniaceae), has a clearly defined southern natural limit around latitude 38° S. Historically, this has been attributed to the lethal effects of winter frosts (Chapman & Ronaldson, 1958) and, more recently to poor species dispersal and lack of suitable habitat south of the present species boundary ( de Lange & de Lange, 1994). 
A series of investigations of frost tolerance, leaf gas exchange, stomatal conductance, chlorophyll a fluorescence, water relations and stable carbon isotope analyses of New Zealand Avicennia were undertaken in the laboratory and field in order to characterise frost tolerance limits and photosynthetic performance under normal and stressed conditions. By so doing, the relative importance of winter frosts and low air temperatures in defining the range of Avicennia in New Zealand could then be determined. 
It was found that photosynthetic performance in Avicennia was increasingly depressed near its southern limits. Photosynthetic responses were consistent with those typical for cold-sensitive species after exposure to low temperatures. Large decreases in photosynthetic production, photoinhibition and chlorophyll loss were evident following exposure to night temperatures lower than 4°C, suggesting that critical damage occurred even at temperatures well above freezing. 
Frosts probably still play an important, additional and episodic role in defining the range of mangrove in New Zealand. The physiological stress effects of low temperatures were compounded by sub-zero temperatures and productivity in frostprone areas was significantly reduced by physical damage to leaves, branches and reproductive tissue. Freeze-injury of this form also reduced the likelihood of successful seedling establishment and long-term survival of saplings. 
These findings indicate that latitude 38° S acts as a physiological barrier for mangrove in New Zealand. Avicennia might persist further south than its present natural range if dispersal to suitable microclimates occurred. However, the probability of this occurring naturally is small, given the species poor dispersal abilities, and the reduced likelihood of survival in the face of damage and physiological stresses brought about by cold winter temperatures.

text: Physiological constraints on the latitudinal distribution of the mangrove Avicennia marina (Forsk.) Vierh. subsp. australasica (Walp.) J. Everett in New Zealand ﻿New Zealand's only mangrove species, Avicennia marina (Forsk.) Vierh. subsp. australasica (Walp) Everett (Avicenniaceae), has a clearly defined southern natural limit around latitude 38° S. Historically, this has been attributed to the lethal effects of winter frosts (Chapman & Ronaldson, 1958) and, more recently to poor species dispersal and lack of suitable habitat south of the present species boundary ( de Lange & de Lange, 1994). 
A series of investigations of frost tolerance, leaf gas exchange, stomatal conductance, chlorophyll a fluorescence, water relations and stable carbon isotope analyses of New Zealand Avicennia were undertaken in the laboratory and field in order to characterise frost tolerance limits and photosynthetic performance under normal and stressed conditions. By so doing, the relative importance of winter frosts and low air temperatures in defining the range of Avicennia in New Zealand could then be determined. 
It was found that photosynthetic performance in Avicennia was increasingly depressed near its southern limits. Photosynthetic responses were consistent with those typical for cold-sensitive species after exposure to low temperatures. Large decreases in photosynthetic production, photoinhibition and chlorophyll loss were evident following exposure to night temperatures lower than 4°C, suggesting that critical damage occurred even at temperatures well above freezing. 
Frosts probably still play an important, additional and episodic role in defining the range of mangrove in New Zealand. The physiological stress effects of low temperatures were compounded by sub-zero temperatures and productivity in frostprone areas was significantly reduced by physical damage to leaves, branches and reproductive tissue. Freeze-injury of this form also reduced the likelihood of successful seedling establishment and long-term survival of saplings. 
These findings indicate that latitude 38° S acts as a physiological barrier for mangrove in New Zealand. Avicennia might persist further south than its present natural range if dispersal to suitable microclimates occurred. However, the probability of this occurring naturally is small, given the species poor dispersal abilities, and the reduced likelihood of survival in the face of damage and physiological stresses brought about by cold winter temperatures.

year: 2006

title: Sedimentary processes building a tropical delta yesterday, today, and tomorrow: the Mekong System

authors: Nittrouer, Charles A.

abstract: River deltas are important for human habitation, commerce, food, and natural resources. Most terrestrial freshwater, dissolved substances, and suspended sediment supplied to the ocean pass through delta distributary channels. Transitions are complex as this river discharge moves through the serial environments of delta systems: tidal river, estuary, shoreline, continental shelf.

The bulk of Mekong sediment accumulates as a muddy clinoform deposit on the shallow continental shelf (<20–25 m water depth), which forms the foundation over which the subaerial delta surface has grown for the past ~8,000 years. The Song Hau distributary channel, the target of this investigation, receives ~40% of the Mekong discharge and transfers the majority of it to the adjacent shelf during high flow of the river (July–November). Some of the sediment is returned to the channel and to the mangrove shoreline during low flow of the river (December–April). The sediment reentering the channel is mostly mud, deposited by estuarine processes, that temporarily buries the channel bed and interrupts sand transfer to the coastal ocean.

Trapping of sediment supplied to the shoreline of the island, Cu Lao Dung, at the Song Hau mouth, is enhanced by the roughness from dense mangrove roots extending above the bed. Shoreline progradation is asymmetric with the most rapid sediment accumulation (~5 cm yr–1) in the southwestern portion of the island, and the distribution of mangroves is linked to this sedimentation pattern. About one-third of Mekong sediment discharge accumulates in the shelf clinoform near the mouths of the distributary channels, with the greatest accumulation rates (>10 cm yr–1) in the relatively steep foreset region. Intense landward and southwestward currents transport the other two-thirds of Mekong discharge during energetic shelf conditions (December–April). These sediments create a relatively shallow clinoform structure, cause the delta to grow asymmetrically toward the southwest, and form the Ca Mau Peninsula.

In the future, these same natural processes will operate under different conditions. Construction of many dams within the drainage basin (>200 constructed or approved) and the impacts of climate change (i.e., alterations in monsoonal conditions) will significantly decrease Mekong River discharge. In addition, the delta land surface will be flooded due to acceleration of eustatic sea level rise and local land subsidence. Together, loss of river discharge and rise of local sea level will cause many secondary impacts, including erosion of distributary channels, ocean shorelines, and the shelf seabed; saltwater intrusion farther into the channels, along with transfer of associated estuarine processes; and decreased supply of freshwater and solutes, including nutrients, to the coastal ocean. The collaborative research among international and Vietnamese scientists described in this special issue of Oceanography provides an integrated understanding of the Mekong Delta system, and could help formulate strategies to enhance the resiliency of the system and its ability to cope with future impacts.

text: Sedimentary processes building a tropical delta yesterday, today, and tomorrow: the Mekong System River deltas are important for human habitation, commerce, food, and natural resources. Most terrestrial freshwater, dissolved substances, and suspended sediment supplied to the ocean pass through delta distributary channels. Transitions are complex as this river discharge moves through the serial environments of delta systems: tidal river, estuary, shoreline, continental shelf.

The bulk of Mekong sediment accumulates as a muddy clinoform deposit on the shallow continental shelf (<20–25 m water depth), which forms the foundation over which the subaerial delta surface has grown for the past ~8,000 years. The Song Hau distributary channel, the target of this investigation, receives ~40% of the Mekong discharge and transfers the majority of it to the adjacent shelf during high flow of the river (July–November). Some of the sediment is returned to the channel and to the mangrove shoreline during low flow of the river (December–April). The sediment reentering the channel is mostly mud, deposited by estuarine processes, that temporarily buries the channel bed and interrupts sand transfer to the coastal ocean.

Trapping of sediment supplied to the shoreline of the island, Cu Lao Dung, at the Song Hau mouth, is enhanced by the roughness from dense mangrove roots extending above the bed. Shoreline progradation is asymmetric with the most rapid sediment accumulation (~5 cm yr–1) in the southwestern portion of the island, and the distribution of mangroves is linked to this sedimentation pattern. About one-third of Mekong sediment discharge accumulates in the shelf clinoform near the mouths of the distributary channels, with the greatest accumulation rates (>10 cm yr–1) in the relatively steep foreset region. Intense landward and southwestward currents transport the other two-thirds of Mekong discharge during energetic shelf conditions (December–April). These sediments create a relatively shallow clinoform structure, cause the delta to grow asymmetrically toward the southwest, and form the Ca Mau Peninsula.

In the future, these same natural processes will operate under different conditions. Construction of many dams within the drainage basin (>200 constructed or approved) and the impacts of climate change (i.e., alterations in monsoonal conditions) will significantly decrease Mekong River discharge. In addition, the delta land surface will be flooded due to acceleration of eustatic sea level rise and local land subsidence. Together, loss of river discharge and rise of local sea level will cause many secondary impacts, including erosion of distributary channels, ocean shorelines, and the shelf seabed; saltwater intrusion farther into the channels, along with transfer of associated estuarine processes; and decreased supply of freshwater and solutes, including nutrients, to the coastal ocean. The collaborative research among international and Vietnamese scientists described in this special issue of Oceanography provides an integrated understanding of the Mekong Delta system, and could help formulate strategies to enhance the resiliency of the system and its ability to cope with future impacts.

year: 2017

title: Rights to water an indigenous right?

authors: Toki, Valmaine

abstract: The United Nations Declaration on the Rights of Indigenous People ("the Declaration") was adopted by the United Nations General Assembly in September 2007 with a majority of 143 states in favour.  Since then Australia, New Zealand, Canada and the United States have also signalled their support for the Declaration.

text: Rights to water an indigenous right? The United Nations Declaration on the Rights of Indigenous People ("the Declaration") was adopted by the United Nations General Assembly in September 2007 with a majority of 143 states in favour.  Since then Australia, New Zealand, Canada and the United States have also signalled their support for the Declaration.

year: 2012