Are there dead zones in the ocean? Find out on this Moment of Science.

Well, as if we needed one more reason to get our environmental act together, a recent U.N. report warns that the number and size of dead zones in the ocean is increasing.

Dead zones are regions of oxygen-deprived water, where nothing can live. They’re caused by an excess of nutrients–usually nitrogen(氮)–released into the water. When sewage, farm fertilizers, and emissions from vehicles and factories get washed into the ocean, you get what experts call a “nitrogen cascade(氮容器)”. Tiny free- floating organisms known as plankton(浮游生物) feed on all that untreated nitrogen, and multiply to such an extent that they (1)deplete the oxygen supply in the water.

While fish may be able to swim away and avoid (2)suffocation, slower-moving and (3)bottom-dwelling creatures like lobsters(龙虾), clams(蛤蚌), and oysters(牡蛎) often can’t. Also, the ocean might be a large place, but right now there are 146 known dead zones, some of which span tens of thousands of square miles. One of the worst is where the Mississippi River (4)drains into the Gulf of Mexico, and dumps fertilizer (5)runoff from the Midwest.

Oh,no.Is there anything we can do? We can reduce nitrogen emissions from cars and factories, and implement better sewage treatment. We can plant new forest and grasslands to (6)soak up extra nitrogen and keep it out of the water. And we can develop alternative energy sources(替代能源) that aren’t based on burning fossil fuels(化石燃料).

(1)deplete [di\'pli:t] vt.耗尽，用尽;使衰竭，使空虚

The fire had depleted the game in the forest.

那场大火使森林里的鸟兽濒临绝迹。

(2)suffocation [,s?f?\'kei??n] n.窒息;闷死

A target that makes her save is immune to suffocation from that elemental for 24 hours.

豁免成功的目标在24小时内免疫这个火元素造成的窒息效果。

(3)bottom-dwelling 底栖生物

marine eellike mostly bottom-dwelling fishes of northern seas.

北部海洋中大多数底栖的似鳗海鱼。

(4)drain into 流入，排入，泄入

The river drains into the sea.

河流向大海。

(5)runoff n.径流;决赛;流走的东西 adj.决胜的

So, it is practical to use the sequential clustering and Markov model to forecast the river runoff.

这说明运用马尔可夫模型进行河径流量的丰枯状态预报是有效可行的。

(6)soak up v.吸收

Soak the spilt tea up with a cloth.

用块布把洒了的茶水吸干