การฟัง TOEFL

🎧 บทถอดเสียง

Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we’re going to talk about a surprising solution to water pollution: constructed wetlands. Now, these aren’t natural wetlands. They’re man-made systems that mimic the natural processes of marshes and swamps. The idea is simple—water, especially agricultural runoff, is full of nitrates and phosphates from fertilizers. When this water flows into rivers, it causes algal blooms that kill fish. But in a constructed wetland, we deliberately plant certain aquatic plants, like cattails and reeds, and their roots provide a home for bacteria. These bacteria break down the nitrates and phosphates, removing them from the water before it reaches the river. The process is passive—it doesn’t require energy or chemicals. And here’s the kicker: these wetlands also provide habitat for birds and other wildlife. So, they’re not just cleaning water; they’re restoring ecosystems. However, they do require land and time to mature. A well-designed wetland might take two to three years to reach full efficiency. But after that, it can operate for decades with minimal maintenance. So, the question is, why aren’t we using them everywhere?