For most of the year, the Gulf of Mexico is teeming with marine life, from tiny crustaceans to massive baleen whales. But every summer, disaster strikes. Around May, animals begin to flee the area. And soon, creatures that can’t swim or can’t swim fast enough begin to suffocate and die off in massive numbers. From late spring to early autumn, thousands of square kilometers along the coast become a marine dead zone— unable to support most forms of aquatic life.
一年中大部分的時候, 墨西哥灣裡滿是海洋生命, 從小型的甲殼綱動物 到大型的長鬚鯨都有。 但每到夏天,災難就會來襲。 大約五月時,動物開始逃離該地區。 很快地,不會游泳 或游泳不夠快的生物 就會開始大量窒息死亡。 從晚春到初秋, 沿岸會有數千平方公里的面積 變成海洋死亡區—— 無法提供海洋生命形式的維生所需。
This strange annual curse isn’t unique; dead zones like this one have formed all over the world. But to explore what’s creating these lethal conditions, we first need to understand how a healthy marine ecosystem functions.
這種每年一次的奇特詛咒 並非獨一無二的; 全世界各地都有像這樣的死亡區。 但若要探究是什麼原因 造成這些致命的條件, 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, plant-like organisms such as algae and cyanobacteria thrive. Clouds of algae streak the surface of deep waters, and in shallower regions, large seaweeds and seagrass cover the ground. Not only do these organisms form the foundation of local food chains, their photosynthesis provides the oxygen necessary for aquatic animals to survive.
在任何有足夠陽光的水體中, 類似植物的生物, 例如水藻和藍綠細菌會很繁盛。 深水區域的表面會有成群的水藻, 在比較淺的區域, 大型海藻和海草覆蓋地面。 這些生物不僅形成了 當地食物鏈的基礎, 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, algae growth also depends on nutrients like phosphorus and nitrogen. While such resources are typically in short supply, sometimes the surrounding watershed can flood coastal waters with these nutrients. For example, a large rainstorm might wash nutrient-rich sediment from a forest into a lake. These additional resources lead to a massive increase in algae growth known as eutrophication. But rather than providing more food and oxygen, this surge of growth has deadly consequences. As more algae grows on the surface, it blocks sunlight to the plants below. These light-deprived plants die off and decompose in a process which uses up the water’s already depleted oxygen supply. Over time, this can reduce the oxygen content to less than 2 milligrams of oxygen per liter, creating an uninhabitable dead zone.
除了陽光和二氧化碳, 水藻的生長也要仰賴營養物, 如磷和氮。 雖然這些資源經常供應不足, 有時周圍的分水嶺可以 讓岸邊的水域充滿這類營養。 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。 這些額外的資源 會讓水藻的生長大大增加, 就是所謂的「優養化」。 但這種激增的狀況 並沒有提供更多食物和氧氣, 反而有致命的後果。 隨著表面長出更多水藻, 水藻下方的植物就無法取得陽光。 這些被剝奪陽光的植物 會死亡,接著分解, 這個過程會用掉 水中已經快耗盡的氧氣供應。 隨時間,這個現象 可能會把水中的含氧量 減少到低於每公升二毫克的氧氣, 造成不適居住的死亡區。
There are rare bodies of water that rely on natural eutrophication. Regions like the Bay of Bengal are full of bottom-dwelling marine life that has adapted to low-oxygen conditions. But human activity has made eutrophication a regular and widespread occurrence. Nutrient-rich waste from our sewage systems and industrial processes often end up in lakes, estuaries and coastal waters. And the Gulf of Mexico is one of the largest dumping zones on earth for one particular pollutant: fertilizer.
有很少數的水體 要仰賴天然的優養化。 像孟加拉灣這樣的地區 就滿是底棲海洋生物, 這些生物已適應低氧的條件。 但人類活動讓優養化 變成經常且廣泛發生的現象。 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, 它們通常最後會進入 湖泊、河口,及沿岸水域。 墨西哥灣是世界上 最大的傾倒區之一, 它特定的污染物是:肥料。
American agriculture relies heavily on nitrogen and phosphate-based fertilizers. 31 states, including America’s top agricultural producers, are connected to the Mississippi River Basin, and all of their runoff drains into the Gulf of Mexico.
美國農業極度仰賴 氮肥料和磷肥料。 三十一個州,包括美國 最大的農業製造者, 和密西西比河流域相連, 它們的逕流通通流入墨西哥灣。
Farmers apply most of this fertilizer during the spring planting season, so the nutrient flood occurs shortly after. In the Gulf, decomposing algae sinks into the band of cold saltwater near the seafloor. Since these dense lower waters don’t mix with the warmer freshwater above, it can take four months for tropical storms to fully circulate oxygenated water back into the gulf.
農民施肥的時間 通常是春天的播種季, 所以沒多久之後就會出現營養洪流。 在墨西哥灣,分解掉的水藻 會沉入接近海底冰冷的鹹水帶。 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, 熱帶暴風雨可能要花四個月的時間 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 as much as $82 million a year, and that cost will only increase as the dead zone gets bigger. On average the gulf dead zone is roughly 15,000 square kilometers, but in 2019 it grew to over 22,000 square kilometers— approximately the size of New Jersey.
目前,這片死亡區 每年會讓美國的海鮮產業 和觀光產業損失 高達八千兩百萬美金, 且隨著死亡區越來越大, 損失也只會越來越多。 墨西哥灣的死亡區面積 平均約為一萬五千平方公里, 但在 2019 年, 它成長到超過兩萬兩千平方公里—— 接近新澤西州的大小。
Human activity is similarly responsible for growing dead zones around the world. So what can be done? In the short term, countries can set tighter regulations on industrial run-off, and ban the dumping of untreated sewage into ocean waters. On farms, we can plant buffer zones composed of trees and shrubs to absorb runoff. However, long term solutions will require radical changes to the way we grow food. Farmers are currently incentivized to use techniques that reduce the health of the soil and rely heavily on nitrogen-rich fertilizers. But there would be less need for these chemicals if we restore the soil’s natural nutrients by planting diverse crops that manage soil erosion and fertility. Hopefully we can make these fundamental changes soon. Because if we don’t, the future of our marine ecosystems may be dead in the water.
同樣地,人類的活動 導致世界各地的死亡區不斷擴大。 所以,能怎麼辦? 短期來說, 國家可以針對工業逕流 設定更嚴格的規定, 並禁止將未處理的污水 傾倒進海洋水域。 農田方面,我們可以 種植樹木和灌木, 形成緩衝區來吸收逕流。 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。 目前,農民被鼓勵使用的技術 會對土壤健康有不良影響, 且非常仰賴氮肥。 但我們未必那麼需要這些化肥, 倘若我們種植多樣性的作物, 來管理土壤侵蝕和肥沃, 恢復土壤中的天然養份。 希望我們能盡快實現 這些根本上的改變。 因為如果不快點, 海洋生態系統的未來 可能就會沉淪水中。