Can the ocean run out of oxygen? - Kate Slabosky

譯者: Lilian Chiu 審譯者: Pui-Ching Siu

For most of the year, the Gulf of Mexico is teeming with marine life,

一年中大部分的時候， 墨西哥灣裡滿是海洋生命，

from tiny crustaceans to massive baleen whales.

從小型的甲殼綱動物 到大型的長鬚鯨都有。

But every summer, disaster strikes.

但每到夏天，災難就會來襲。

Around May, animals begin to flee the area.

大約五月時，動物開始逃離該地區。

And soon, creatures that can’t swim or can’t swim fast enough

很快地，不會游泳 或游泳不夠快的生物

begin to suffocate and die off in massive numbers.

就會開始大量窒息死亡。

From late spring to early autumn,

從晚春到初秋，

thousands of square kilometers along the coast become a marine dead zone—

沿岸會有數千平方公里的面積 變成海洋死亡區——

unable to support most forms of aquatic life.

無法提供海洋生命形式的維生所需。

This strange annual curse isn’t unique;

這種每年一次的奇特詛咒 並非獨一無二的；

dead zones like this one have formed all over the world.

全世界各地都有像這樣的死亡區。

But to explore what’s creating these lethal conditions,

但若要探究是什麼原因 造成這些致命的條件，

we first need to understand how a healthy marine ecosystem functions.

我們得先了解

健康的海洋生態系統如何運作。

In any body of water that receives sufficient sunlight,

在任何有足夠陽光的水體中，

plant-like organisms such as algae and cyanobacteria thrive.

類似植物的生物，

例如水藻和藍綠細菌會很繁盛。

Clouds of algae streak the surface of deep waters,

深水區域的表面會有成群的水藻，

and in shallower regions, large seaweeds and seagrass cover the ground.

在比較淺的區域，

大型海藻和海草覆蓋地面。

Not only do these organisms form the foundation of local food chains,

這些生物不僅形成了 當地食物鏈的基礎，

their photosynthesis provides the oxygen necessary for aquatic animals to survive.

它們的光合作用也提供

海洋動物生存所需的氧氣。

Besides sunlight and C02,

除了陽光和二氧化碳，

algae growth also depends on nutrients like phosphorus and nitrogen.

水藻的生長也要仰賴營養物，

如磷和氮。

While such resources are typically in short supply,

雖然這些資源經常供應不足，

sometimes the surrounding watershed can flood coastal waters with these nutrients.

有時周圍的分水嶺可以

讓岸邊的水域充滿這類營養。

For example, a large rainstorm might wash nutrient-rich sediment

比如，

一場暴雨可能會將森林裡

營養豐富的沉積物沖到湖中。

from a forest into a lake.

These additional resources lead to a massive increase in algae growth

這些額外的資源

會讓水藻的生長大大增加，

known as eutrophication.

就是所謂的「優養化」。

But rather than providing more food and oxygen,

但這種激增的狀況 並沒有提供更多食物和氧氣，

this surge of growth has deadly consequences.

反而有致命的後果。

As more algae grows on the surface, it blocks sunlight to the plants below.

隨著表面長出更多水藻，

水藻下方的植物就無法取得陽光。

These light-deprived plants die off and decompose

這些被剝奪陽光的植物 會死亡，接著分解，

in a process which uses up the water’s already depleted oxygen supply.

這個過程會用掉

水中已經快耗盡的氧氣供應。

Over time, this can reduce the oxygen content

隨時間，這個現象 可能會把水中的含氧量

to less than 2 milligrams of oxygen per liter,

減少到低於每公升二毫克的氧氣，

creating an uninhabitable dead zone.

造成不適居住的死亡區。

There are rare bodies of water that rely on natural eutrophication.

有很少數的水體

要仰賴天然的優養化。

Regions like the Bay of Bengal are full of bottom-dwelling marine life

像孟加拉灣這樣的地區

就滿是底棲海洋生物，

that has adapted to low-oxygen conditions.

這些生物已適應低氧的條件。

But human activity has made eutrophication a regular and widespread occurrence.

但人類活動讓優養化

變成經常且廣泛發生的現象。

Nutrient-rich waste from our sewage systems and industrial processes

我們污水系統和工業製造過程

會產生一些富含營養的廢棄物，

often end up in lakes, estuaries and coastal waters.

它們通常最後會進入 湖泊、河口，及沿岸水域。

And the Gulf of Mexico is one of the largest dumping zones on earth

墨西哥灣是世界上 最大的傾倒區之一，

for one particular pollutant: fertilizer.

它特定的污染物是：肥料。

American agriculture relies heavily on

美國農業極度仰賴

nitrogen and phosphate-based fertilizers.

氮肥料和磷肥料。

31 states, including America’s top agricultural producers,

三十一個州，包括美國 最大的農業製造者，

are connected to the Mississippi River Basin,

和密西西比河流域相連，

and all of their runoff drains into the Gulf of Mexico.

它們的逕流通通流入墨西哥灣。

Farmers apply most of this fertilizer during the spring planting season,

農民施肥的時間 通常是春天的播種季，

so the nutrient flood occurs shortly after.

所以沒多久之後就會出現營養洪流。

In the Gulf,

在墨西哥灣，分解掉的水藻

decomposing algae sinks into the band of cold saltwater near the seafloor.

會沉入接近海底冰冷的鹹水帶。

Since these dense lower waters don’t mix with the warmer freshwater above,

因為這些高密度且位置較低的水

不會和上方較溫暖的淡水混在一起，

it can take four months for tropical storms

熱帶暴風雨可能要花四個月的時間

to fully circulate oxygenated water back into the gulf.

才能將帶氧的水透過循環 完全帶到墨西哥灣。

This dead zone currently costs U.S. seafood and tourism industries

目前，這片死亡區 每年會讓美國的海鮮產業

as much as $82 million a year,

和觀光產業損失 高達八千兩百萬美金，

and that cost will only increase as the dead zone gets bigger.

且隨著死亡區越來越大， 損失也只會越來越多。

On average the gulf dead zone is roughly 15,000 square kilometers,

墨西哥灣的死亡區面積

平均約為一萬五千平方公里，

but in 2019 it grew to over 22,000 square kilometers—

但在 2019 年，

它成長到超過兩萬兩千平方公里——

approximately the size of New Jersey.

接近新澤西州的大小。

Human activity is similarly responsible for growing dead zones around the world.

同樣地，人類的活動 導致世界各地的死亡區不斷擴大。

So what can be done?

所以，能怎麼辦？

In the short term, countries can set tighter regulations on industrial run-off,

短期來說，

國家可以針對工業逕流 設定更嚴格的規定，

and ban the dumping of untreated sewage into ocean waters.

並禁止將未處理的污水 傾倒進海洋水域。

On farms, we can plant buffer zones

農田方面，我們可以 種植樹木和灌木，

composed of trees and shrubs to absorb runoff.

形成緩衝區來吸收逕流。

However, long term solutions will require radical changes to the way we grow food.

然而，長期的解決方案

會需要從根本上改變 我們栽種食物的方式。

Farmers are currently incentivized to use techniques

目前，農民被鼓勵使用的技術

that reduce the health of the soil

會對土壤健康有不良影響，

and rely heavily on nitrogen-rich fertilizers.

且非常仰賴氮肥。

But there would be less need for these chemicals

但我們未必那麼需要這些化肥，

if we restore the soil’s natural nutrients

倘若我們種植多樣性的作物，

by planting diverse crops that manage soil erosion and fertility.

來管理土壤侵蝕和肥沃， 恢復土壤中的天然養份。

Hopefully we can make these fundamental changes soon.

希望我們能盡快實現 這些根本上的改變。

Because if we don’t,

因為如果不快點，

海洋生態系統的未來 可能就會沉淪水中。

the future of our marine ecosystems may be dead in the water.