Đề thi HSG Tiếng Anh 12 tỉnh Bà Rịa-Vũng Tàu năm học 2022-2023

PART 3: Read the passage EUTROPHICATION and CIRCLE the letter A, B, C or D to indicate the correct answer to each of the questions.

All plants need nutrients, but an excess of nutrients can be lethal to the ecosystem. Water bodies such as lakes or estuaries naturally have certain amounts of nutrients, and are rich in species. Species- rich ecosystems have a high level of biodiversity. However, when chemical nutrients infiltrate water in marine habitats, the plants will begin to grow without restraint and then decay rapidly. This process, known as eutrophication, can disturb the ecological balance and eventually result in severe reductions in water quality. Inspections of lakes and reservoirs around the world demonstrate that 54% of lakes in Asia are eutrophic; 53% in Europe; 48% in North America; and 28% in Africa. Today, eutrophication or what some call nutrient pollution is the number one water quality problem around the world.

In the 1950s, eutrophication was acknowledged as a waste problem in several lakes in Europe and North America although it was not immediately clear what the causes were. It had taken place over a short period of time in these lakes, and this shocked scientists because eutrophication had normally been known as a natural process that develops over thousands of years as a lake or river becomes

older. Scientists, who observed the excessive growth of plants and algae, often called an algal bloom, studied the phenomenon intensely from the 1960s to the 1970s. Their research pointed to the presence of large amounts of plant nutrients, including phosphorous, nitrogen and carbon, which are vital for life in the river and sea. The nutrients were traced to human activities: runoff from livestock waste, the release of domestic sewage and industrial wastewater. Moreover, in some ecosystems, nutrients had been deliberately added for purposes of enrichment. The large amounts of nutrients accumulated and their compounds acted as a stimulant to uncontrolled phytoplankton growth.

The unlimited growth of phytoplankton species provokes profound changes in the lake or river. Marine plants and plant particles breathe out oxygen during photosynthesis. When eutrophication occurs, however, the excessive amount of phytoplankton species spread over the surface of waters and block the sunlight, so the marine plants are not able to photosynthesize, then the amount of oxygen is reduced. When the dead plants and animals are decomposed, oxygen is consumed, therefore the dissolved oxygen is also reduced greatly. The lack of oxygen causes many organisms to suffocate and numbers of dead fish begin to appear in the water, and more animal species die out. The water loses its transparency, sometimes changing into a murky brown, red or orange color, and this phenomenon is called “red tide”. If the oxygen becomes completely depleted, bacteria called Clostridium botulinum becomes abundant and causes botulism, a disease of the nervous system that is often fatal. The bacteria poisons and kills birds and mammals that eat any existing phytoplankton in the water body. With so much death taking place, scientists call anaerobic waters “dead zones”. Ultimately, these effects have an impact on human beings.

The swift eutrophication in Lake Erie, one of the Great Lakes, was the subject of much concern and instigated experimental research. In 1968, the Experimental Lakes Area (ELA) was established as a field station and had been added various nutrients to determine which combination of nutrients was the key to controlling eutrophication. The most interesting experiment was a lake that was divided into two with a plastic curtain. One half was left alone while the other half was divided into three parts and each fed carbon, nitrogen and phosphorous. The lake was monitored for 8 years, and it was observed that the portion receiving phosphorous had eutrophic algal blooms. The parts containing carbon and nitrogen did not have those. The American government has since earmarked billions of dollars for a phosphate control program.