State the Variety of chemical and biological reactions

Variety of chemical and biological reactions takes place leading to the formation of the solution phase. If we analyse the solution phase by  separating it from the solid phase, we get information about the nutrient content of the solution phase at that time. The solid phase may be allowed to equilibrate with fresh water and the solution phase analysed again. This may be repeated for many times  till no more nutrient comes into water. The sum of the amounts of nutrients present in successive solution phases may be assumed to represent the quantity of available nutrients.