As the runoff water passes, they retain excess nutrients and some pollutants.

随着径流水的流过，它们保留了多余的养分和一些污染物。

But sewage is still rife with dangerous contaminants, including billions of pathogens and microorganisms, trace chemicals, and excess inorganic nutrients that can pollute rivers and lakes.

但污水中仍然充斥着危险的污染物，包括数十亿的病原体和微生物、微量化学物质和过量的无机营养物质，这些都可能污染河流和湖泊。

Kelp is good for the environment, because it helps remove some of the excess nutrients that are in coastal ecosystems, often those nutrients are caused by human reasons, human sources.

海带对环境有好处，因为它有助于去除沿海生态系统中的一些多余营养物质，通常这些营养物质是由人类原因造成的。