A variety of methods can be used to sample populations to determine their size and density, depending up whether the organism is

Mobile or Stationary

Explanation:

This is often plants (stationary) and animals (mobile). The two most common methods are the mark and recapture method and the Quadrat method.

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affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.