Vol.11 No.1 - March 2003

The Waitaki River mouth, just north of Oamaru, South Island. Braided, gravel-bed rivers like the Waitaki are common in the South Island and feature in several areas of NIWA research. For example, techniques have been investigated for estimating the amount of gravel moved during floods. For more details see A bird’s eye assessment of gravel movement in large braided rivers .

In this issue

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    The key to climbing in koaro

    PDF of this article (106 KB)
    Bob McDowall
    Specially adapted fins in the koaro may help to explain why this fish is so good at climbing.
    Whitebait of the koaro climbing up the concrete walls of a velocity barrier in the Wairehu Canal, North Island. The barrier was constructed to prevent the upstream movement of fish. (Photo: E.J. Cudby)
    The climbing ability of the koaro, Galaxias brevipinnis, has become legendary over recent decades. This fish species is highly migratory and spends its larval/juvenile life in the sea, yet populations have been found upstream of high waterfalls.
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    Flow cytometry in aquatic science

    PDF of this article (99 KB)
    Julie Hall
    Andrea Cumming
    How many algal cells will mussels eat? What proportion of plankton in a sample will die if exposed to a toxic substance? To answer these kinds of questions, researchers have traditionally had to view tiny subsamples under a microscope and count individual cells. This is still the only practical option for some kinds of research.
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    Energy, industrial ecology and the cost of change

    PDF of this article (115 KB)
    Guy Penny
    NIWA is becoming involved in new research areas aimed at addressing the problem of how to restore the balance between society and nature.
    Industrial ecology is a relatively new, multi-disciplinary research area, which examines the relationship between economic activities, society and nature. It applies principles of ecology to contemporary society, treating society like an ecosystem with a defined boundary, inputs, outputs, components, regulators, internal flows, transformations and feedbacks of energy and materials.
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    What happens in estuaries during floods?

    PDF of this article (177 KB)
    Andrew Swales
    John Oldman
    John Radford
    Iain MacDonald
    An experiment in Auckland’s Mangemangeroa estuary is helping us understand what happens to sediment eroded from the land, how much accumulates and how much escapes during floods.
    Most sediment is washed into estuaries during floods. These events are difficult to record because they often only last a few hours and can happen any time.
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    A bird's eye assessment of gravel movement in large braided rivers

    PDF of this article (304 KB)
    Murray Hicks
    Richard Westaway
    Stuart Lane
    An experiment on the Waimakariri River has shown that remote sensing techniques could become very useful tools for estimating gravel movement.
    How much gravel from the riverbed – or bedload – do rivers transport during floods? Engineers and managers are interested in this for several reasons. First of all, knowledge of the gravel load is required to manage riverbed levels, so that, for example, the bed doesn’t build up and increase the risk of flood flows spilling out of the channel.
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    Spreading mangroves: a New Zealand phenomenon or a global trend?

    PDF of this article (159 KB)
    Anne-Maree Schwarz
    The spread of mangrove forests – currently seen by some as a problem in some North Island estuaries – is by no means a global trend.
    The value of mangrove (mānawa) ecosystems has recently been the topic of public debate in New Zealand, with discussions stimulated by the expansion of mangrove growth in some North Island estuaries.
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    NIWA news forum

    On this page
    NIWA identification workshops
    Science of waka kopapa
    Mangrove management guidelines
    Solutions to Pollution
    Australian bushfire effects
    NIWA identification workshops: just ask the experts!
    Have you ever had difficulty distinguishing respiratory lobes from sub-mental sclerites? Or wanted to know the difference between erect and sprawling emergent macrophytes?
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    How estuaries grow old

    PDF of this article (98 KB)
    Terry Hume
    Andrew Swale
    Have you ever wondered how estuaries have formed and if they will eventually fill up with sediment and die?
    Estuaries in New Zealand have not always looked like they do today. These semi-enclosed coastal water bodies, where land drainage mixes with the sea, began life about 6500 years ago, when climatic warming caused sea level to rise some 150 m to its present level. The sea level rise drowned an ancient and varied landscape.
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    Overfishing leads to loss of genetic diversity in Tasman Bay

    PDF of this article (56 KB)
    Peter Smith
    Lorenz Hauser
    Greg Adcock
    A collaborative study of Tasman Bay snapper suggests that there has been a loss of genetic diversity in this heavily fished stock over the past 50 years.
    Genetic diversity in a population is critical to a species’ ability to adapt to environmental changes, and to the continued productivity of a fish stock. The diversity is due to genetic differences between individuals. Rare genetic types, which are of little importance today, could be the key to adaptability in the future.
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    Stream vegetation and flow regimes

    PDF of this article (184 KB)
    Tenna Riis
    Barry Biggs
    What influences the growth of plant beds in streams? Surveys and experiments are helping to identify and quantify the important factors.
    Beds of water plants are a familiar sight in many lowland streams. These plants play a very important role as they influence nutrients, light, sediment stability, hydraulic conditions, and the abundance of micro-organisms, invertebrates and fish.