The methodology is not yet ready for immediate application in many areas. The indicator needs to be measured using the mass balance principle through a technique called Regional Mass Flux Budgeting. First, system boundaries need to be established using the watershed, or drainage basin, as its horizontal extension. Vertical boundaries in the atmosphere and ground need to be selected. A time period of one year is usually selected for nutrient balances.
Additional information is needed to determine impacts.
The indicator relates to marine pollution. It is a Driving Force indicator in the DSR Framework. The indicator does not reflect the cumulative impact upon the water body. In some cases, it is difficult to distinguish between anthropogenic nutrient loading and environmental conditions. It would be appropriate for some countries which only border on one sea, to select either N or P as the indicator, depending on which is of primary influence.