Great Lakes tributary phosphorus bioavailability

Information on phosphorus bioavailability can provide water quality managers with the support required to target point source and watershed loads contributing most significantly to water quality conditions. This study presents results from a limited sampling program focusing on the five largest sources of total phosphorus to the U.S. waters of the Great Lakes. The work provides validation of the utility of a bioavailability-based approach, confirming that the method is robust and repeatable. Chemical surrogates for bioavailability were shown to hold promise, however further research is needed to address site-to-site and seasonal variability before a universal relationship can be accepted. Recent changes in the relative contribution of P constituents to the total phosphorus analyte and differences in their bioavailability suggest that loading estimates of bioavailable P will need to address all three components (SRP, DOP and PP). A bioavailability approach, taking advantage of chemical surrogate methodologies is recommended as a means of guiding P management in the Great Lakes.