The basis for any resource monitoring plan is a conceptual model of how the resource system operates. Mass balance is an appropriate conceptual model for the GBP. It is not the objective nor design of the monitoring plan in and of itself to determine definitive mass balances for selenium or other constituents; nevertheless, a mass balance approach to the GBP MP provides a valuable framework and philosophical rationale for various elements of the program. The mass balance approach will help to identify deficiencies and redundancies in data gathering, help to identify the need for adjustments to the monitoring program, and facilitate cooperation and coordination of data gathering and integration with related research or investigations that may be undertaken.

Review of data collected during the monitoring program, particularly if coupled with investigations that could be undertaken in conjunction with monitoring, will help develop a better understanding of the fate of selenium within and between the several media (sediment, water, biota) in the environment. The physical, chemical, biological and toxicity analyses will allow for the tracking of selenium input and output, and will provide a stronger scientific basis for predicting effects.

Use of the data base produced by the monitoring tasks, especially if coupled with data from other existing programs and related investigations that might be undertaken, will increase understanding of the mass balance of selenium throughout the study area. The data base will provide opportunities for further coordinated efforts to identify and understand the relevant components of a mass balance model including; 1. sources of selenium and salts to the SLD from surface and subsurface agricultural drainage and groundwater, 2. fluxes of selenium and salts among water, sediment, and biota in the GBP and receiving waters, 3. transport of selenium and salts in the SLD to receiving waters, and 4. fate and effect of selenium and salts in these receiving waters. Additionally, information from the monitoring program will be available and can be consulted by the GBD when interpreting the effect of irrigation events and other actions on drainage flows. An effort will be made to collect data during unusual events, such as storm-related flooding, which may or may not coincide with scheduled monitoring. Finally, an effort could also be made to determine the dominant selenium species within the study area, both temporally and spatially, as possible.

The defined tasks of the monitoring plan will provide some of this information, but it will need to be supplemented through separate, specifically focused investigations.