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w orldwatch n Groundwater tracked via satellite: Scientists at Stanford University in California have developed a technique for accurately monitoring the volume of groundwater in aquifers in agricultural regions using satellite data.

With aquifers around the world rapidly becoming depleted due to the widespread use of groundwater, primarily for irrigation, regulation is vitally important. Levels can fluctuate seasonally due to changing patterns of rainfall, snowmelt and extraction, but regulators can only make direct measurements from wells drilled directly into the aquifers. Such wells are rare, compared to the size of most groundwater systems.

atellite data can be used to measure the movement of the ground above the aquifer as water levels rise and fall, but these data can be rendered inaccurate by the presence of plants, particularly crops, whose heights change on an almost daily basis.

he scientists analysed a decade’s worth of surface-elevation data from the San Luis Valley in Colorado. They produced maps of satellite measurements and found a regular pattern of high- and low-quality data. By overlaying Google Earth images of the farmland, they found that the high-quality data corresponded with dry, crop-free areas. By comparing data from these areas with data collected from local wells, they showed that the satellite results provided an accurate picture of groundwater levels in the aquifers below.

he scientists suggest that this technique can be used in agricultural regions around the world, including areas that lack modern infrastructure such as wells.

Maori fires transformed New Zealand shut terstock

New Zealand’s early settlers used fire to rapidly transform the South Island’s ecosystems, according to new research.

n international team led by Dave McWethy and Cathy Whitlock of Montana State University used pollen records, charcoal fragments and algae and midge remains to reconstruct the environmental history of 16 small lakes. The results indicated that several high-intensity fire events occurred within two centuries of the arrival of Maoris during the 13th century.

Previous research has shown that prior to Maori arrival, closed forest covered 85–90 per cent of New Zealand, but by the mid-19th century, when the first Europeans arrived, grass and shrubs had replaced more than 40 per cent of the South Island’s forests. Archaeological evidence suggests that in the cooler southern areas, the Maori relied on the rhizomes of bracken fern, which replaced the burnt forests.

The team used new records of past climate to disprove the hypothesis that the increase in fire frequency was due to unusual climatic conditions. Before human arrival, forest fires were generally rare, occurring only once every 1,000–2,000 years.

‘What is remarkable is that small mostly subsistence-based groups of people were able to burn large tracts of forests throughout the relatively large South Island in only a few decades,’ McWethy said.

The authors suggest that a better understanding of the history of fire and people in New Zealand will improve the development of strategies for forest-fire management and conservation.

In brief

ATLANTIC OCEAN The spread of areas of low oxygen in the Atlantic Ocean is restricting the range of fish such as marlin, forcing them into shallower waters, where they are more likely to be caught, according to new research. Rising ocean temperatures are expected to exacerbate the problem, as they reduce the amount of oxygen dissolved in water.

INDONESIA Six years after the Boxing Day tsunami struck, the German–Indonesian Tsunami Early Warning System for the Indian Ocean has been completed. Comprising 300 stations made up of tide gauges, seismometers, GPS stations and buoys, the system is designed to provide a warning within five minutes of a submarine earthquake taking place.

GLOBAL Tiny larval fish can settle long distances – in some cases more than 150 kilometres – from where they were spawned, according to a new study. The findings give weight to the idea that marine reserves can help to rebuild fish stocks in unprotected areas.

CANARY ISLANDS The establishment of a population of Egyptian vultures on the Canary Islands was apparently made possible by the arrival of humans 2,500 years ago, according to a study by Spanish researchers. Genetic analysis demonstrated that the birds arrived at the same time as the humans, whose livestock would have provided the vultures with a food source.

UK The past decade has been the best for the UK’s rivers since the Industrial Revolution, according to the Environment Agency. Wildlife is returning in record numbers to many rivers, and incidents of serious water pollution have more than halved since 2001.

february 2011 www.geographical.co.uk 11

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