鑽石舞台

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. 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.

在一年的大部分時間裡，墨西哥灣充斥着豐富的海洋生物，從微小的甲殼類動物到巨大的長鬚鯨。但每年夏天，災難都會降臨。大約在5月，動物們開始逃離該地區。很快，那些不會游泳或游得不夠快的生物開始窒息，甚至大量死亡。從春末到秋初，沿海數千平方公里的海域變成了海洋生命的死亡地帶——大多海洋生物無法生息。這每年一次的怪異詛咒，並非獨一無二。像這樣的死亡地帶已散布於世界各地。要想探尋導致這些致命環境形成的原因，我們先要了解一個健康的海洋生態系統是如何運作的。

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. 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.

在任何獲得足夠陽光的水體中，藻類和藍藻等類似植物的生物都會茁壯成長。深水區域的表面，有成群的水藻，在較淺的區域，大型海藻和海草覆蓋着海底的地面。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了海洋動物生存所需的氧氣。除了陽光和二氧化碳，水藻的生長也需要依賴於營養物質，例如磷和氮。這些資源經常短缺，有時周圍流域的營養物質會將沿海的水域淹沒。例如，一場大暴雨可能會把森林中富含營養物質的沉積物沖入湖中。

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.

這些額外的資源會導致藻類的生長大量增加，被稱為「富營養化」。但這種激增不僅沒有提供更多的食物和氧氣，反而造成了致命的後果。隨着更多藻類在水面生長，阻擋了海下植物生長所需的陽光。些因失去光照而死亡的植物，在分解的過程中進一步耗盡了海水中已經枯竭的氧氣供應。隨着時間的推移，這可能會使氧氣含量減少到每升不到2毫克的氧氣，形成一個不適合生息的死亡地帶。

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. American agriculture relies heavily on nitrogen and phosphate-based fertilizers.

有少數的水體要依賴天然的「富營養化」。像孟加拉灣這樣的地區就滿是底棲海洋生物，並已適應低氧條件。但人類活動已經使「富營養化」成了一種經常和廣泛發生的現象。污水處理系統和工業生產所致的富含營養物質的廢物，往往最終進入湖泊、河口和沿海水域。而墨西哥灣是地球上最大的傾倒區之一，它特定的污染物就是：化肥。美國農業嚴重依賴於氮肥和磷肥。

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.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. 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.

美國31個州，包括其頂級農業生產基地，都與密西西比河流域相連，它們的所有徑流通通流入墨西哥灣。農民在春季播種季節大量使用這種肥料，所以在不久之後會出現養分洪流。在墨西哥灣，分解掉的藻類會沉入接近海底冰冷的鹹水帶中。由於這些密集的低層水不與上面的較溫暖的淡水混合，熱帶風暴可能需要四個月的時間，才能完全使含氧水徹底循環到海灣中。目前，這個死亡海域每年給美國的海產品和旅遊業帶來高達8200萬美元的損失。而且這個損失只會隨着死亡海域的擴大而增加。

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.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.

平均而言，死亡海域大約為1萬5千平方公里，但在2019年，它增長到2萬2千多平方公里——大約相當於新澤西州的面積。人類活動同樣對世界各地死亡海域的增長負有責任。那麼我們能做些什麼呢？在短期內，各國可以對工業廢水制定更嚴格的法規，並禁止將未經處理的污水傾倒在海洋中。在農場，我們可以種植由樹木和灌木組成的緩衝區來吸收徑流。然而，長期的解決方案將需要徹底改變我們種植食物的方式。

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.

目前的農民因被鼓勵而使用的技術，會降低土壤健康，並嚴重依賴富含氮氣的肥料。但是我們未必那麼需要這些化肥，如果我們種植多樣化的作物管理好土壤的侵蝕和肥力，恢復土壤中的天然養分。希望我們能很快做出這些根本性的改變。因為如果不這樣做，我們海洋生態系統的未來可能就會消亡於水中。