Beavers - Test 1

C1 Advanced · Gapped Text · Cambridge English Advanced 3, Cambridge University Press

You are going to read a magazine article about the ecological importance of the semi-aquatic animal, the beaver. Six paragraphs have been removed from the article. Choose from the paragraphs A–G the one which fits each gap (1–6). There is one extra paragraph which you do not need to use.

Beavers

Beavers play an important role in keeping Rhode Island's waters clean

These results have interesting implications. According to Julia Lazar, who was involved in conducting some of the work as part of her doctoral dissertation and is now working as an environmental consultant, it might change our attitude to beavers and their ponds.

At the same time, the specimens were also sufficiently small to be easily replicated, managed and measured for numerous changes. The scientists then added a special type of nitrogen to the soil that allowed them to tell if the nitrogen levels were altered and how.

'Streamside wetlands are one example of such elements,' said Professor Gold, who studies these types of features in his research. But nobody had ever documented the role beaver ponds might play.

Found in agricultural fertilizers, nitrogen is often introduced to such areas by runoff, eventually travelling to estuaries where rivers meet the sea. Once in the water system, it has been known to cause what is known as eutrophication. This is where a sudden increase in nutrients can cause blooms of algae to grow.

This process is known as de-nitrification and means the nitrogen is no longer stored within the stream or pond, and thus can no longer degrade water quality further downstream. However, some of the nitrogen is not changed to gas, but instead is stored in organic soils.

They are a species whose numbers crashed after widespread hunting 150 years ago, but with their return they are helping solve one of the major problems of the 21st century and that should not be underestimated. It is important to remember that those ponds would not be there without the beavers.

When the team set out to conduct their research, they quickly realized the water retention time and organic matter build-up within beavers' ponds lead to the creation of ideal conditions for eliminating nitrogen. They then wanted to see how effectively this was done.

In time these plants die and decompose, consuming the oxygen from the waters, creating low oxygen levels that kill fish. While these dead zones are common in the Gulf of Mexico, they are also becoming a problem along northeastern U.S. coastlines. However, according to the study findings of Professor Arthur Gold and colleagues of the University of Rhode Island, this problem is less common where there are beavers.

Thanks to a naturally occurring bacterium present in the soil of beaver ponds, 5% to 45% of nitrogen in the water can be removed, depending on the pond and the amount of nitrogen present, the study found. This bacterium is able to transform nitrogen in the water into nitrogen gas.

This transformative power was tested by taking samples from the beds of beaver ponds, and adding nitrogen to them. These samples were large enough to incorporate the factors that generate the chemical and biological processes that take place in the pond.

The experiments also found that 12% of the nitrogen gases created in the samples were nitrous oxide, a very potent greenhouse gas and air pollutant. To put this into perspective, considered over a 100-year period, nitrous oxide is calculated to have between 265 and 310 times more impact than carbon dioxide does. However, the scientists pointed out that the high amount was likely to be a result of some unique laboratory conditions and that it is unlikely these ponds would release that much of the gas in nature.

Most of these semi-aquatic animals are in areas with small streams, rather than big rivers, and the beaver dams in these smaller streams are usually the first to be removed. They are considered a nuisance because they block the waterways. This causes a decrease in beaver populations. It is therefore important that these areas remain untouched so they can positively affect nitrogen levels downstream. Professor Gold now hopes to study the ponds over a longer period and to investigate abandoned ponds to see if the nitrogen-retaining qualities remain after the beavers have gone.

In addition, these areas of water also attract other wildlife such as insects and birds which are vital to the ecosystem. Studies like the one carried out by Professor Gold may well give people a new-found appreciation for the beaver.

There are an estimated 50 million beavers across North America. As a keystone species, beavers enrich ecosystems around them. By building dams, they control water moving through their habitat, retaining the flow during times of drought and slowing it down during heavy rain and floods. This also creates beaver ponds – areas several meters deep they use for sleeping and eating. However, a study by the American Society of Agronomy says beavers are doing something more: they are now helping to remove nitrogen that has moved its way through soil into ground water and lakes and streams. ___ In time these plants die and decompose, consuming the oxygen from the waters, creating low oxygen levels that kill fish. While these dead zones are common in the Gulf of Mexico, they are also becoming a problem along northeastern U.S. coastlines. However, according to the study findings of Professor Arthur Gold and colleagues of the University of Rhode Island, this problem is less common where there are beavers. ___ Thanks to a naturally occurring bacterium present in the soil of beaver ponds, 5% to 45% of nitrogen in the water can be removed, depending on the pond and the amount of nitrogen present, the study found. This bacterium is able to transform nitrogen in the water into nitrogen gas. ___ This transformative power was tested by taking samples from the beds of beaver ponds, and adding nitrogen to them. These samples were large enough to incorporate the factors that generate the chemical and biological processes that take place in the pond. ___ The experiments also found that 12% of the nitrogen gases created in the samples were nitrous oxide, a very potent greenhouse gas and air pollutant. To put this into perspective, considered over a 100-year period, nitrous oxide is calculated to have between 265 and 310 times more impact than carbon dioxide does. However, the scientists pointed out that the high amount was likely to be a result of some unique laboratory conditions and that it is unlikely these ponds would release that much of the gas in nature. ___ Most of these semi-aquatic animals are in areas with small streams, rather than big rivers, and the beaver dams in these smaller streams are usually the first to be removed. They are considered a nuisance because they block the waterways. This causes a decrease in beaver populations. It is therefore important that these areas remain untouched so they can positively affect nitrogen levels downstream. Professor Gold now hopes to study the ponds over a longer period and to investigate abandoned ponds to see if the nitrogen-retaining qualities remain after the beavers have gone. ___ In addition, these areas of water also attract other wildlife such as insects and birds which are vital to the ecosystem. Studies like the one carried out by Professor Gold may well give people a new-found appreciation for the beaver.

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