explain why the north and the south poles of a needle always align with North and South poles of Earth respectively?

Its led to migrationits led to death 

When a lake, river or other aquatic  system  becomes  eutrophic, it can have serious negative effects on other organisms like fish, birds and even people.if an algal bloom is so bad that it causes wide-spread death  in  the  water, the organisms that die will all sink to the bottom and start to decompose.