the farmers use large amount of substance P in the field to increase the crop yield.The excess of P dissolves in water and runs into Lake. the substance P causes Rapid growth of tiny green water plants Q in the lake which covers the whole lake like a green sheet. when the plants Q die , the organism called R decompose them by utilising S dissolved in water .the amount of dissolved S in water decreases too much due to which the fish living in lake suffocate and water P Q R and S name the process​