Vol.10 No.1 - March 2002

1 March 2002

A NIWA diver records information on submerged plants during a lake survey. These data are later added to NIWA’s Aquatic Plant Database. For more details on the database and how it is used, refer to Submerged plant data: answering the what, where and why.

Bugs 'n' mud - a sticky problem

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Sharon Stephens
Mal Green
Conrad Pilditch
The seabeds of our estuaries are inhabited by an array of organisms, including the more obvious crabs, worms and shellfish. But what about the bugs – or, more specifically, the microbes – and why should we be interested in them?
What do muddy water, shoreline erosion, mass kills of shellfish, and siltation of marinas and navigation channels have in common? No, it’s not bugs (they come soon), it’s sediment transport – the erosion, movement and deposition of sediments.

Why rivers get clearer as they flow downstream

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Ian Jowett
Robert Milhous
Settling sediment means that river water tends to clear as it flows downstream, but this is not always a good thing.
Some years ago, during construction of the Pukaki Dam in central South Island, a small amount of turbid glacial water from Lake Pukaki flowed down the Pukaki River. Immediately below the dam, the water was the blue-grey colour associated with the glacial lakes, but a kilometre or so farther downstream it was clear. The river bed was acting as a filter.

How often is New Zealand hit by tropical cyclones?

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Mark Sinclair
Recent NIWA research shows that northern New Zealand is hit by an average of a little over one storm of tropical origin each year. The severity of these storms depends on their location and on the phase of the El Niño/La Niña cycle.

Average distribution, motion and intensity for all tropical cyclones during 1970–1997.
top: Distribution.

Dealing with diversity dwarf galaxias style

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Richard Allibone
Biodiversity studies – whether they result in new species or not – can provide valuable information on how our native fish should be managed.
Over the last ten years the number of native freshwater fish recognised in New Zealand has increased by 33% – from 27 to 36 species. The nine new species have come about from new discoveries during surveys in remote areas, from natural colonisation by a diadromous eel and from detailed studies of some non-diadromous fish.
Non-diadromous fish spend all their life cycle in fresh water.

Claustrophobic fish: how do aquatic plants affect fish that feed on invertebrates?

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Ian Duggan
John Clayton
Mark James
David Rowe
Aquatic plants are important in fish–invertebrate interactions in lakes and both the species and density of these plants can affect their role.
Submerged aquatic plants – also known as macrophytes – are a familiar sight in lakes. Less well known is the importance of these plants in lake ecosystems. They are known to provide hiding places for small fish from larger predatory fish.

NIWA news forum

On this page

Giant squid discovery
Revamped NIWA website
Freshwater fish workshop
Wellington deluge
Underwater remotely operated vehicle
NIWA scientist in new international oceanographic programme
Teacher fellow at NIWA
River sedimentation survey
Tsunami Symposium New Zealand 2002
SOLAS: Surface Ocean–Lower Atmosphere Studies
Bluenose workshop

Giant squid discovery

One of the tiny giant squid juveniles (9–13 mm long).

A media conference to mark the first time giant squid had been captured and filmed alive was led by marine biologist Dr Steve O'Shea at NIWA’s Wellin

Ozone Table

Table 1. Correlation coefficients between daily ozone averages for the four Auckland ozone monitoring sites.

Sky Tower
Whangaparaoa
Musick Point
Pukekohe

Sky Tower
1

Whangaparaoa
0.75
1

Musick Point
0.70
0.74
1

Pukekohe
0.52
0.58
0.49
1

 
Table 2.

Ozone highs and lows in Auckland

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Farah Adeeb
David Shooter
From time to time ozone levels in Auckland can be quite high. What do these episodes indicate?

Contour map of weekly ozone concentration (in micrograms per cubic metre) at Pukekohe.

Mankind can be thankful for ozone in the upper atmosphere, which protects us from short-wavelength UV radiation. However, at ground level, ozone is a harmful air pollutant that can impact on community health (see Ozone as a pollutant, below). The gas forms over several hours when its air-pollution precursors accumulate in the atmosphere.

Submerged plant data: answering the what, where and why

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Mary de Winton
A database of submerged plant records can be used as a tool to describe lakes and to identify major influences on the composition and distribution of lake vegetation.
Plants growing within lakes integrate changes in environmental conditions over time, and so can tell us a lot more about a water body than “snapshot” measurements of physical or other biological parameters. Moreover, our understanding of how plants relate to lake condition is increasing.

Successful fish passage past weirs

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Eddie Bowman
David Rowe
An innovative fish-pass design allows small native fish to safely undertake their upstream migration yet does not interfere with hydrological measurements.
Many dams, culverts and weirs are barriers to upstream migration of native fish. Designing ways to allow fish to pass such obstacles is a significant area of research.

Whitebait can't jump

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Cindy Baker
Richard Allibone
Fish-pass design needs to take into account the abilities of the fish species likely to be using these structures to get past obstacles in rivers.

Proportion of inanga passing the weirs of different shapes with different vertical drops.

Proportion of inanga of different sizes found at the base of the weir and passing the weir for A 15-cm vertical drop and B 5-cm vertical drop.