However, this approach is difficult to do in practice. Unit rent can also be estimated by using net price , where net price is meant to be the international price of a resource commodity minus all costs of production excluding tax, import duty and royalty, when royalty is considered as a cost of production. Defensive expenditure . Defensive expenditure is the executed expenses due to the activities to defend environment from damages or pollution created as the result of production process and consumption of society. Examples, are the expenditures to reduce air and water pollution, and to maintain soil fertility.
Depletion is a decrease in resource commodity to fulfil the needs of production and consumption.
For the nonrenewable resources, depletion means extraction of the available natural resources. For instance, a depletion of oil and natural gas for a certain year is equal to the production of oil and natural gas for the same year. For the renewable resources, depletion means the total value of deduction elements of the stock. For example, forest harvest or extraction of the forest products, deduction of forest stock due to forest conversion and forest damage. Aquifers To be decided later.