The amount of salt carried in rivers, streams, groundwater or surface runoff, in a given time period, is called the salt load. The salt load is calculated from data on salinity and stream flow and is often expressed as:
Salt load estimates are vital because they indicate the amount of salt stored in the landscape, washed from land, or entering the system from groundwater. If we only used salt concentration (measured as EC) as an indicator of salinity, we would not have a sense of the total quantity of salt in the system.
For example, if a river has high flows, salt concentration (EC) can be low, but the salt load can still be very high. Salt loads also indicate the potential rate of salt build up in places where salt might accumulate, such as wetlands and depressions on floodplains.
Salt load estimates are also important in predicting the impacts of salinity further downstream in the system.