Land and Water Use
AP Environmental Science Topic 5 13:36 English narration · English + 中文 subtitles burned in
Chapters
Transcript
Three ordinary places.
三个平常的地方。
A logging truck carrying trees that stood here this morning.
一辆运材车，拉走今早还站着的树。
A pit so wide you could see it from space.
一个大坑，宽得从太空都能看见。
A city spreading over the farmland.
一座城市铺过农田，一直延伸到地平线。
Nobody here is a villain.
照片里没有坏人。
Each is somebody taking what they need — wood, metal, a home.
每一个都只是有人在取自己需要的东西——木材、金属、住处。
So why does that keep ending like this?
那为什么这样做，总是这样收场？
Here is one field, shared by everyone.
这是一片田，大家共用。
Add one more animal, and the whole gain is yours.
多放一头牲畜，好处全归你。
The cost — less grass for every herder — is split between all of you.
代价——每个牧民的草都变少——由所有人分摊。
So for each herder, adding one is always the clever move.
所以对每个牧民来说，再多放一头永远是聪明的选择。
Watch what that does to the grass.
看看草地会变成什么样。
Every herder was right, and they all lose anyway.
每个牧民都没做错，可他们最后都输了。
That is one question, asked six ways.
这是同一个问题的六种问法。
First the commons, and why sharing fails.
先是公地，以及共享为什么会失败。
Then farming and food.
然后是农业与粮食。
Then irrigation and water.
然后是灌溉与水。
Then pests, and the poison problem.
然后是虫害，以及农药带来的问题。
Then harvesting forests, fish and rock.
然后是森林、渔业和矿产的开采。
And last, cities, footprints, and what sustainable really means.
最后是城市、生态足迹，以及可持续到底是什么意思。
Look at the shape of the problem.
看清这个问题的形状。
The resource is open to all — nobody owns it.
资源对所有人开放——没有人拥有它。
The gain from one extra user goes to that one user.
多用一份带来的好处全归那一个人。
The cost is shared by everybody.
代价却由所有人分摊。
Both halves matter, so write both.
两半都重要，答题时都要写。
Once you see the shape, the fix follows: regulation — a catch limit, a quota — or private ownership, because an owner protects what they own.
看清形状之后，对策就出来了：管制——捕捞限额、配额——或者私有制， 因为所有者会保护属于自己的东西。
From the nineteen sixties, the Green Revolution changed farming: high-yield seeds, synthetic fertilizer, irrigation, machines, and one single crop across a whole field — monoculture.
从二十世纪六十年代起，绿色革命改变了农业：高产种子、化肥、灌溉、机械， 以及整块田里只种一种作物——单一栽培。
Look at the field: one crop, edge to edge.
看这片田：从这头到那头只有一种作物。
It fed billions of people.
它养活了几十亿人。
But every gain carried a cost — nutrients in the rivers, dry land turning to desert, worn-out soil, and less variety in what we grow.
但每一分收益都有代价——养分流进河里， 干旱地区退化成沙漠，土壤耗尽，我们种的作物种类也变少了。
Fertilizer is the heart of it, and the exam wants three elements.
化肥是核心，考试要考三种元素。
Nitrogen builds leaves and stems.
氮让叶和茎长起来。
Phosphorus builds strong roots.
磷让根系强壮。
Potassium builds flowers and fruit — the three letters on every bag.
钾让开花结果——每袋化肥上的那三个字母就是它们。
But plants take up only part of what we spread.
但作物只吸收我们撒下去的一部分。
The rest washes off with the next rain, and that is where the trouble starts.
剩下的会随下一场雨冲走，问题就从这里开始。
Follow that fertilizer into the water.
跟着这些化肥进入水里。
This is eutrophication, and it is one of the impacts of agricultural practices the exam asks about.
这就是富营养化，也是考试会问到的农业活动影响之一。
Nitrogen and phosphorus feed algae just as well as they feed a crop.
氮和磷喂养藻类，就像喂养作物一样有效。
The algae bloom across the surface and cut off the light.
藻类在水面大量繁殖，把光挡住。
The plants underneath die.
下面的水生植物死掉。
Bacteria rot them, and the rotting burns up the dissolved oxygen.
细菌分解它们，分解过程会耗掉溶解氧。
Watch the oxygen fall.
看着氧气下降。
The fish suffocate.
鱼窒息而死。
Now water.
现在说水。
Irrigation is by far the largest human use of fresh water — about seventy percent of it worldwide.
灌溉是人类淡水使用中最大的一项——全球大约占七成。
Three methods, and they are not equal.
三种方法，效果并不一样。
Flooding the field is cheapest and wastes the most: much of the water evaporates or runs off, so only about half reaches the crop, and the saturated ground suffers waterlogging.
漫灌最便宜，浪费也最多：大量水蒸发或流走， 只有大约一半到达作物，而且饱和的土壤会发生渍水。
Spraying does better, about seventy percent.
喷灌好一些，大约七成。
Drip lays water at the roots and reaches ninety percent.
滴灌把水送到根部，能达到九成。
Drip beats flood.
滴灌胜过漫灌。
But watering has a sting.
但浇水也有后患。
Flood a dry field again and again, and the sun evaporates the water off the surface.
一片干旱的田反复漫灌，太阳会把地表的水蒸发掉。
The salt dissolved in that water stays behind.
原本溶在水里的盐留了下来。
Year after year it builds up, until crops stop growing.
年复一年越积越多，直到作物无法生长。
That is salinization.
这就是土壤盐碱化。
And there is a second cost.
还有第二笔代价。
Pump water from an aquifer faster than rain can refill it, and the water table falls, until the well is dry.
从含水层抽水比雨水补充得更快，地下水位就会下降，直到井里没水。
Now pests.
现在说虫害。
Spray a field with pesticides and almost every insect dies — almost.
往田里喷药，几乎所有昆虫都会死——几乎。
A few happen to carry a gene that lets them survive.
少数昆虫刚好带有一个基因，让它们活下来。
Those survivors are the ones that breed, and their young inherit it.
活下来的正是繁殖的那一批，后代也继承了这个基因。
Next season a bigger share of the pests is resistant, so you spray again, and stronger.
下一季，抗药的害虫占比更高，于是你再喷一次，而且更浓。
More poison, same pests.
药更多，害虫照旧。
That is the pesticide treadmill.
这就是农药的恶性循环。
So what should a farmer do instead?
那农民应该怎么做？
There are two approaches.
有两条路。
Chemical control is fast, but it breeds resistance and kills species that were never the target.
化学防治见效快， 但会培养出抗药性，还会杀死本来不是目标的物种。
Biological control uses the pest's own natural predators — slower, but no poison.
生物防治利用害虫自己的天敌——慢一些，但没有毒。
Integrated pest management puts them together: watch the pest numbers first, use crop rotation and predators, and spray only when you must.
综合虫害管理把两者结合起来：先监测虫口数量，使用轮作和天敌， 只在必须时才少量喷药。
Monitor first, spray last.
先监测，最后才喷药。
Forests, fish and rock follow one rule: take a renewable resource no faster than it grows back.
森林、渔业和矿产遵循同一条规则：可再生资源的取用速度不能超过它再生的速度。
That is the sustainable yield.
这就是可持续产量。
Selective cutting keeps a forest working.
择伐能让森林继续发挥作用。
Clearcutting takes every tree at once — cheap, but the bare soil erodes into the streams.
皆伐一次砍光所有树——便宜，但裸露的土壤会侵蚀进河流。
Overfishing pulls fish out faster than they breed; the cod fishery collapsed that way.
过度捕捞把鱼捞得比它们繁殖还快；鳕鱼渔场就是这样崩溃的。
And mining tears the land open, with acid drainage and tailings.
采矿把土地撕开，带来酸性废水和尾矿。
Meat production is expensive in land, and the ten percent rule is why.
肉类在土地上非常昂贵，原因就是百分之十定律。
Start with ten thousand units of energy in the plants.
从植物中的一万单位能量开始。
Only a tenth of that energy reaches the cattle that eat them, and only a tenth of that again reaches you.
只有十分之一的能量到达吃它们的牛， 而其中又只有十分之一到达你。
Ninety percent is lost as heat at every step, so the same field feeds far fewer people through an animal than it would directly.
每一步都有百分之九十以热的形式损失， 所以同一块地通过动物养活的人，远少于直接种植。
Most of that meat comes from concentrated animal feeding operations, or CAFOs, which use large amounts of land, water, feed and energy, and concentrate the waste.
大部分肉来自集中动物饲养场，也就是CAFO， 它们消耗大量土地、水、饲料和能源，并把废物集中在一起。
Cattle also belch methane, a powerful greenhouse gas.
牛还会打嗝排出甲烷，一种强效温室气体。
Out on open range the problem is different.
在开阔牧场上问题不同。
Overgrazing lets livestock eat the vegetation faster than it regrows, stripping the soil of its protective cover; on dry land that drives desertification, where a low-rainfall region degrades until it becomes desert.
过度放牧让牲畜吃草的速度超过草再生的速度， 剥去土壤的保护层；在干旱地区这会导致荒漠化， 即低降水地区退化成沙漠。
Rotational grazing is the answer: move the animals between pastures so no area is ever grazed bare.
轮牧是答案： 让牲畜在牧场之间轮换，使任何一块地都不会被啃光。
Overfishing takes fish out faster than they can reproduce, and a population that is fished that way can collapse and fail to return.
过度捕捞把鱼捞得比它们繁殖的速度还快，被这样捕捞的种群可能崩溃并且无法恢复。
But the damage is wider than the target species, because the net comes down on everything in its path.
但危害远不止目标物种，因为网会罩住路径上的一切。
Bycatch is the unwanted catch — the wrong species, the young, the turtles and dolphins — hauled up and thrown back, usually dead.
副渔获是不想要的捕获物——错误的物种、幼鱼、海龟和海豚—— 被拖上来又扔回去，通常已经死了。
Bottom trawling is worse still: the gear is dragged across the seabed and scrapes the habitat itself bare.
底拖网更糟：渔具在海底拖行，把栖息地本身刮得精光。
And because nobody owns the open ocean, every fleet has a reason to take its share before someone else does.
而且因为没有人拥有公海，每支船队都有理由抢在别人之前拿走自己那份。
That is the tragedy of the commons at sea.
这就是海上的公地悲剧。
Mining takes the land from the top down.
采矿从上往下取走土地。
Surface mining, also called strip mining, cuts benches that get wider and deeper until the ore is reached, and the habitat that was there is simply gone.
露天开采，也叫剥采， 切出越来越宽、越来越深的台阶，直到挖到矿石，原来的栖息地就此消失。
Where the coal sits under a ridge, the method is mountaintop removal: the summit is blasted off and pushed into the valley below.
当煤层位于山脊之下时，方法是山顶移除：把山顶炸掉，推入下面的山谷。
When the deposits near the surface are exhausted, the shaft goes underground to subsurface mining, which is far more expensive and far more dangerous — and the same pattern applies to coal as its accessible reserves shrink.
当靠近地表的矿藏耗尽，竖井就转入地下开采， 它昂贵得多，也危险得多——随着易采储量减少，煤炭也遵循同样的模式。
The impact that outlives the mine is acid mine drainage: exposed rock reacts with air and water to make acid that carries metals into the streams, alongside the toxic tailings left in heaps at the surface.
比矿山寿命更长的影响是酸性矿山废水： 暴露的岩石与空气和水反应生成酸，把金属带进河流， 还有留在地表堆积的有毒尾矿。
Cutting a forest down does four things at once, and the exam wants all four.
砍掉一片森林，会同时造成四件事，考试四件都要。
Habitat disappears, so biodiversity falls and species are lost.
栖息地消失，生物多样性下降，物种消失。
With no roots to hold it, the soil washes away.
没有树根抓住土壤，土壤被冲走。
Rain runs straight off the bare ground, so flooding gets worse.
雨水直接从裸地上流走，洪水更严重。
And the carbon the trees were holding goes back into the air as carbon dioxide.
树里原本储存的碳，又以二氧化碳的形式回到空气中。
Ways to mitigate deforestation pull the other way: reforestation, reused wood, and the prescribed burn that clears fuel before a wildfire can.
缓解森林砍伐的做法往相反方向用力：重新造林、重复利用木材， 以及在野火来临前先烧掉可燃物的计划烧除。
Urbanization changes the ground itself.
城市化改变了地面本身。
Roads and roofs are impervious surfaces — water cannot soak through.
道路和屋顶是不透水面——水渗不下去。
Runoff and flooding rise, groundwater is never recharged, and dark surfaces hold heat: the urban heat island.
径流和洪水增加，地下水得不到补充，深色表面积聚热量：这就是城市热岛。
Sprawl eats farmland at the edge.
城市扩张吞掉边缘的农田。
A dense city also strains the hydrologic cycle: it depletes the local water, and heavy pumping near a coast pulls seawater into the aquifer — that is saltwater intrusion, and it can ruin a freshwater supply for good.
密集的城市还会给水循环带来压力： 它耗尽当地的水，海岸附近的大量抽水会把海水引进含水层—— 这就是海水入侵，它可能永久毁掉一处淡水水源。
The fixes let water back in: permeable pavement, rain gardens, green roofs.
各种对策都是让水重新渗下去：透水路面、雨水花园、绿色屋顶。
And one line here points at the last idea of this unit.
这里还有一行字，指向本单元最后一个概念。
Now the calculation.
我们来算一算。
An ecological footprint measures the land and water one person needs.
生态足迹衡量一个人需要多少土地和水。
Earth supplies about one point six global hectares of biocapacity per person.
地球为每个人提供大约一点六全球公顷的生物承载力。
The average person uses two point seven.
而平均每人实际使用二点七。
How many Earths would that take?
这要用掉几个地球？
The rule is a single division: footprint, divided by biocapacity per person.
规则只有一次除法：生态足迹除以人均生物承载力。
Two point seven divided by one point six is about one point seven.
二点七除以一点六，约等于一点七。
We live as if we had one point seven planets.
我们过得就像拥有一点七个地球。
Now a high-income country, at eight hectares each: eight divided by one point six is five.
再算一个高收入国家，人均八公顷：八除以一点六等于五。
Five Earths.
五个地球。
And notice — a footprint is per person.
注意——生态足迹是按人计算的。
So what does sustainability mean?
那么可持续性到底是什么意思？
Meeting our needs today without taking away the ability of future generations to meet theirs, and using resources no faster than they can be replaced.
满足我们今天的需要，同时不损害后代满足他们需要的能力， 并且使用资源的速度不超过它们被补充的速度。
It balances three things: a healthy environment, an economy that works, and fairness between people.
它平衡三件事：健康的环境、能运转的经济，以及人与人之间的公平。 具体来看就是这样。
In practice: energy that does not run out, and farming that holds its soil — crop rotation, cover crops, contour plowing, terraces.
用不完的能源。 以及守得住土壤的农业：轮作、覆盖作物、等高耕作、梯田。
Seal a city under roads and roofs and the rain has nowhere to go: it runs straight off those impervious surfaces, picks up oil and grit, and arrives at the stream all at once as a flood.
把一座城市用道路和屋顶封起来，雨水就无处可去： 它直接从这些不透水面上流走，卷起油污和沙砾， 一次性涌进河流，形成洪水。
The fix is to give the water somewhere to go on the way.
办法是在途中给水找地方去。
Permeable pavement lets it pass through the surface instead of across it.
透水路面让水穿过地面，而不是从上面流过。
Rain gardens and green roofs hold it in soil and plants.
雨水花园和绿色屋顶把水留在土壤和植物里。
Retention ponds catch the peak and release it slowly.
滞留池截住洪峰，再慢慢放出。
Each one lets water soak in, which filters the pollutants out and recharges the groundwater instead of flooding the stream.
每一种都让水渗下去，既过滤掉污染物，又补充地下水，而不是淹没河流。
Sustainable agriculture starts from one fact: a bare slope loses its soil with every rain, and soil is the one input a farm cannot buy back quickly.
裸露的坡地每下一场雨就流失一次土壤，而土壤是农场唯一无法迅速买回来的投入。
Terracing cuts the slope into level steps so the water stops instead of running, and the soil stays on the hill where the crop needs it.
梯田把坡面切成水平的台阶，水就停下来而不是流走， 土壤留在作物需要它的山坡上。
The other practices work the same way.
其他做法原理相同。
Crop rotation changes what is grown each season so pests and nutrient demands never settle in.
轮作每季更换种植的作物， 使害虫和养分需求都无法固定下来。
Cover crops keep roots in the ground between harvests.
覆盖作物在两次收获之间让根系留在土里。
Contour plowing follows the curve of the land instead of cutting straight down it.
等高耕作顺着地形的曲线走，而不是直着往下切。
And agroforestry grows trees among the crops, holding the soil and adding a second harvest.
农林间作在作物之间种树，既固定土壤，又多一份收成。
Together they cut erosion, maintain fertility, and reduce the chemical inputs the field needs.
它们合起来减少侵蚀、保持肥力，并降低农田所需的化学投入。
Aquaculture is fish farming, and it is genuinely efficient — fish convert feed far better than cattle do.
水产养殖就是养鱼，它确实高效——鱼把饲料转化成肉的效率远高于牛。
Because the fish on the plate was raised in a pen, it takes pressure off the wild stock, which is exactly what an overfished ocean needs.
因为盘子里的鱼是在网箱里养大的，它减轻了野生种群的压力， 而这正是被过度捕捞的海洋所需要的。
But the pressure is moved rather than removed.
但压力只是被转移，而不是被消除。
Thousands of fish in one pen means the waste has to go somewhere, and it goes into the water along with the antibiotics used to keep crowded fish healthy.
成千上万条鱼挤在一个网箱里，废物必须有去处， 它们连同用来让密集养殖的鱼保持健康的抗生素一起进入水中。
Disease spreads from the pen to the wild population swimming past.
疾病从网箱传播到游过的野生种群。
And the ponds have to be built somewhere: shrimp farming has cleared vast areas of mangrove, which was nursery habitat and coastal storm protection at the same time.
而且池塘必须建在某个地方： 养虾业已经清除了大片红树林，而红树林同时是育幼场和海岸风暴屏障。
Sustainable forestry is how a forest is worked without being erased, and the exam wants the methods by name.
森林可以被利用而不被抹去，考试要求你说出这些方法的名称。
Selective cutting takes marked trees and leaves the canopy standing, so the forest keeps shading, holding and sheltering while it regrows.
择伐只取走做了标记的树，让林冠保持完整， 森林在恢复的同时继续遮荫、固土、提供庇护。
Leave a buffer strip of untouched trees along every stream, and the sediment never reaches the water.
沿每条溪流留下一条不动的缓冲带，泥沙就到不了水里。
Replant, and give it time — long rotations let the stand recover its structure rather than being cut again as soon as the trunks are merchantable.
重新种植，并给它时间——较长的轮伐期让林分恢复其结构， 而不是一旦树干可以出售就再次砍伐。
Reforestation regrows what was already lost.
重新造林让已经失去的森林重新长出来。
Do all of that and the forest keeps providing its services: habitat kept, erosion stopped, and the carbon still stored in the wood instead of in the atmosphere.
做到这些，森林就能继续提供它的服务： 保住栖息地、阻止侵蚀，碳仍然储存在木材里而不是大气中。
Four things that win marks.
四件能拿分的事。
First, in any commons answer, say who gains and who pays — gain to one user, cost shared by all.
第一，凡是公地题，都要说清谁得利、谁付出代价： 好处归一个使用者，代价由所有人分摊。
Second, a footprint answer is one division — footprint over biocapacity per person — and it is per person.
第二，生态足迹题就是一次除法， 足迹除以人均生物承载力，而且是按人算的。
Third, learn the four harms of deforestation: lost habitat, erosion, flooding, and more carbon dioxide.
第三，记住森林砍伐的四个危害： 栖息地丧失、土壤侵蚀、洪水加剧、二氧化碳增加。
And fourth, when a question says evaluate, give the cost and the fix in one sentence.
第四，题目要求评价时，请在同一句话里给出代价和对策。