Earth’s LAKES ARE UNDER THREAT - IELTS Reading Answers & Explanations

Earth's LAKES ARE UNDER THREAT

Lake Poopo used to be Bolivia's second largest lake. Situated in the Altiplano Mountains at an altitude of around 3,700m, the lake in winter would cover an area of some 2,700 square kilometres as it was fed by swollen rivers. With very little rainfall during summer, this reduced to around 1,000, still a remarkable size. This was the pattern in previous centuries, but in December 2015, satellites confirmed the reports of local people that the lake had gone. While scientists had suspected that Poopo would eventually run dry, they didn't expect that this would occur for at least another thousand years. The local mining industry had already contributed to the pollution of the lake, but scientists believe global warming, drought and irrigation projects are all responsible for its disappearance. Today the consequences of Lake Poopo's disappearance are dramatic; many people who lived in the villages around it have left, since there are no more fish to be caught. Environmentalists also point to the fact that the lake had been the stopover point for thousands of birds as they migrated to other regions. Their numbers will certainly fall now the lake has gone.

Lake Poopo is not the only vast are of water to have disappeared. The Aral Sea in Central Asia was once the world's fourth largest lake but then it began to shrink in the 1960s. As a shallow lake, it depended on rivers to keep its level up. But then water from these rivers was diverted for irrigation purposes. Rice is a crop that needs huge quantities of water to survive in desert areas. Fields planted with cotton also require a regular supply. Now thee water level is so low that fishing has stopped altogether. And it is not just the immediate are that is affected. Because the floor of the lake is now exposed, the salt that lies there is often carried by the wind across a radius of 300 kilometres. This impacts on agriculture as it damages growing plants and is absorbed by the soil.

For some lakes, the biggest threat is form climate change. On average, the surface water of the world's lakes has gone up in temperature by 0.34° C every ten years since 1985. Lake Tanganyika in East Africa is a lake where this trend has been observed, although it is by no means the most extreme example. This would be Lake Fracksjön in Sweden, where an increase of 1.35° C per decade has been observed - a figure which is estimated to rise. For Lake Tanganyika, however, the consequences have been severe. Warming has disrupted its ecosystem, and fish numbers have dropped sharply. In turn, this decline in fish stocks has impacted on families living in villages and towns around the lake, since they have no other source of protein. Furthermore, around 100,000 people depend on the fisheries established around the Lake Tanganyika. These companies provide them with regular employment, without which communities will not survive.

In Iran, Lake Urmia's waters have also been affected by unusually hot summers, but dams and irrigation projects have also played a part. In the past, people admired its beautiful green-blue colour. However, the water now has a red tint. The reason for this is that bacteria quickly multiply in the warm waters of a shallow lake. Now local communities are understandably concerned about the future. One of their concerns is that Lake Urmia is no longer seen as a place where people can bathe to improve their health. As a result, in the last decade, there has been a downturn in tourism in the area, an industry many people depended on.

In some cases, it can be a challenge for scientist to predict outcomes for a lake or to recognise the factors that threaten it. Take, for example, Lake Waiau in Hawaii, a lake that was used in healing rituals by native Hawaiians. It is a fairly small lake, approximately 100m across, with some variation as the water level rises and falls. However, in early 2010, the lake began to decrease in size. By September 2013, it could only be described as a pond. The cause of the lake's decline has not yet been established, but drought is among the suspects. Then there is Scott Lake in central Florida. In June 2006 a massive sinkhole opened up beneath the lake - acting like a plug hole in a bath. It only took two weeks for the water to drain away. Local residents called meetings to decide what action to take, but in the end, nature took care of the problem. Clay, sand and other fine material plugged the hole and the lake started to fill with water again. Nevertheless, as geologists point out, sinkholes can occur with some frequency in Florida so there is a chance that Scott Lake will drain away again.