The Green Zone with David Suzuki
NARRATOR: New Brunswick's Meremashee is a world famous Atlantic salmon river. It's also one of the world's last large accessible watersheds that has not been altered by development. Hydrologist Bob Newberry comes regularly to the Meremashee. Known internationally for his work on river restorations, he has a special appreciation of the importance of rivers and watersheds.
BOB NEWBERRY: They play a tremendous cultural, historical role. But even more importantly they probably are esntial for our survival. The river gives you transportation. It gives you the mature forests. It gives you cool water. It gives you drinking water. It gives you fertile soils. All of tho things that for our species are important to survive are in fact wrapped up in the corridors of river valleys.
NARRATOR: (1)Water is a basic element of life. And where water flows, it creates varied and complex habitats. The strip of vegetation along a waterway is called a riparian zone. The riparian zone plays a vital role, protecting the structure of the stream and maintaining w
ater quality. Streams with clean, fresh water are esntial for fish like Pacific salmon. Fish in turn attract a host of predators. Becau it supports such a diversity of species, many scientists believe a riparian area is as vital as the stream itlf.
(A) Riparian areas are relatively small compared to other habitats, but their importance far exceeds their size. However, the vital areas are often damaged or destroyed by urban development, industry, logging and agriculture. And the loss of the green zones bears enormous cost.
NARRATOR: Riparian vegetation paysshades the stream, keeping the water cool. The plants provide food and shelter for many animals隔墙有耳英文. Hordes of incts attract predators like spiders and birds. This caterpillar us elaborate camouflage for protection. The tree frog wears a leaf on its back to blend in with the vegetation. Numerous aquatic animals provide food for many species such as wading birds. A stream and its riparian area are really a single entity. Without riparian vegetation, a stream can support very little life. In cities, the destruction of riparian areas contributes to vere water pollution. Without vege
tation acting as a filter, urban waterways become open 2011山东高考英语答案wers. A large percentage of all the commercial fish caught in the world depend on streams for reproduction. The dwindling number of pacific salmon is a direct result of the destruction of the streams where the fish hamimelonspawn. In recent years there has been an increa in vere flooding worldwide. The destruction is caud in part becau people ignore the way rivers work.
BOB NEWBERRY: When we say a "rious flood", we mean a rious flood for our civilization. For the river, it's just a normal event. It's just we've intruded so cloly on the river that when the normal events happen in the river, in fact we think it's some new destructive force we haven't en before.
NARRATOR: Running water is often associated with fertility and the rippling sound of a flowing stream is one of the most soothing in nature.
DAVID SUZUKI: A stream is almost like a living organism. As it flows, it's constantly varying its form, providing different opportunities for plants and animals. The force that drives this stream is one of the most basic in nature — gravity.
NARRATOR: Water is a restless substance. When it moves, it shapes the landscape. It's natural for a stream to twist and turn as it flows. This meandering is regulated by the riparian vegetation. Bob Newberry us a plastic ribbon to demonstrate how flowing water is constantly moving back and forth across a stream. The dimensions of this curving create a highly predictable pattern. The distance for the flow to cross from one side to the other is always six times the width of the stream. Wherever water flows on earth, it will take this path. It's the force of the water moving back and forth across the channel that creates the meandering pattern. Like a wave, this pattern is constantly moving.
BOB NEWBERRY: The wave shape is established on the landscape by the river, by the hydraulic forces. But it's also translatinghe is just kidding itlf down the valley much the same way as a wave goes down a skipping牛津书虫系列 rope when you snap it, and so the whole wave form is travelling down the valley, planing off this valley bottom surface and defining the outer limits of the riparian zone.
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NARRATOR: At any one time a river will only occupy a small portion of a valley bottom. But as it meanders and periodically overflows, it can dramatically shift within its flood plain. When it moves, the stream leaves behind rich diments that create fertile soil. Riparian vegetation acts as a regulator of this movement by buffering the rate of erosion. A obd是什么意思curving tree is one sign of a healthy riparian area.
BOB NEWBERRY: When you e the trees that are curving upwards like this, it means the river is moving at a rate that is slow enough to allow the trees to correct the vertical growth on the tree. Now if you saw straight trees that were falling into the river, you'd know there was an unnatural amount of erosion but in fact this river moves at this pace of a tree's growth.
