Academic Reading — Test 99

Reading passage

Across the windswept uplands of the Scottish Highlands lie vast expanses of peat bog, a type of wetland that has quietly shaped the region's landscape for thousands of years. To the casual observer these tracts of soft, waterlogged ground may seem unremarkable, even bleak. Yet beneath their surface lies one of the planet's most efficient natural systems for locking away carbon. Peatlands cover a substantial proportion of Scotland and, although they occupy only a small fraction of the world's land area, they hold far more carbon than all of the planet's forests combined. Understanding how these soggy environments achieve this has become a pressing concern for scientists studying the changing climate. Peat forms through an unusually slow process of partial decay. In most environments, when plants die their remains are broken down rapidly by bacteria, fungi and other organisms, releasing carbon dioxide back into the atmosphere. In a bog, however, decomposition is dramatically suppressed. The ground is permanently saturated with water, which prevents oxygen from reaching the dead plant material. Because the microbes responsible for decay depend on oxygen to function, they cannot operate effectively in such conditions. The result is that dead vegetation accumulates faster than it rots, building up layer upon layer over many centuries. A bog typically grows in thickness by around one millimetre each year, meaning that a peat deposit several metres deep may represent the accumulated remains of thousands of years of plant growth. The principal builder of these landscapes is a group of plants known as sphagnum, or bog moss. Sphagnum possesses several remarkable properties that make it ideally suited to its role. It can hold many times its own weight in water, helping to keep the bog permanently wet, and it actively releases acids that lower the pH of its surroundings. This acidity further hampers the microbes that would otherwise consume the moss, creating conditions in which the plant's own remains are preserved rather than destroyed. As living sphagnum grows upward towards the light, the older parts beneath it die and are compressed into peat. In this way the moss is both the architect of the bog and the raw material from which it is constructed. The same chemistry that preserves dead plants can also preserve other organic material with extraordinary fidelity. The cold, acidic and oxygen-starved water of a bog acts as a natural preservative, halting the processes that would normally cause flesh, leather and wood to break down. Over the years, archaeologists working in peatlands across northern Europe have recovered objects that have survived for millennia, including wooden tools, woollen garments and even the remarkably well-preserved bodies of people who died long ago. These so-called bog bodies often retain their skin, hair and facial features, offering researchers a rare and intimate window into the distant past. Although the most famous examples have been found outside Scotland, Highland bogs have yielded their own share of preserved artefacts, and each discovery adds to our knowledge of how earlier communities lived. In recent decades, the value of peat bogs has come to be understood in an entirely new light. Healthy, intact peatland continues to absorb carbon from the atmosphere and store it safely underground, making it a powerful ally in efforts to limit global warming. When a bog is damaged, however, this benefit can be reversed. Draining peatland for agriculture or forestry allows oxygen to penetrate the soil, which reawakens the dormant microbes and causes the stored carbon to escape as carbon dioxide. Cutting peat for fuel, a practice with deep roots in the Highlands, has a similar effect. A degraded bog can therefore switch from being a store of carbon to being a source of it, releasing in a few years what took centuries to accumulate. Recognising this, conservation bodies in Scotland have launched ambitious programmes to repair damaged peatlands. The work typically involves blocking the drainage channels that were dug in earlier generations, raising the water table once more and encouraging sphagnum to recolonise bare ground. Restoration of this kind is neither quick nor cheap, and the benefits may take decades to become fully apparent. Nevertheless, scientists broadly agree that protecting and restoring these landscapes is among the most cost-effective measures available for keeping carbon out of the atmosphere. The quiet bogs of the Highlands, long dismissed as wasteland, are now valued as a natural resource of national and even global significance.