The Assessement of Estuarine Trophic Status (ASSETS) assessment method is a Pressure-State-Response model that has been used most recently to complete the update of the National Estuarine Eutrophication Assessment (NEEA), an examination of a decade of change in nutrient related impacts in 141 U.S. estuaries. It has also been applied to systems from Europe and Asia and shows that similar eutrophic symptoms occur in coastal waterbodies around the globe. The model includes three components: Influencing Factors which are a combination of natural system susceptibility and human-related nutrient loads, Overall Eutrophic Condition based on the combined staus of five indicators (chlorophyll a, macroalgae, dissolved oxygen, seagrass distribution, and nuisance/toxic blooms), and Future Outlook which examines how conditions will change in the future. The three components are then combined into a single rating for a system. The NEEA results show that eutrophication is a widespread problem in U.S. systems with 65% of assessed systems showing moderate to high level problems. The ASSETS synthesis can only be made if all three components are complete and because of inadequate data for many systems, an ASSETS rating could be made for only 48 systems. For those systems for which the synthesis could be made, 88% were rated as moderate to bad and for 50% the rating was poor or bad. Change analysis (early 1990s to early 2000s) shows that in systems where the analysis could be made, conditions have mostly remained the same (32 systems) though changes were observed in several smaller systems; 13 systems improved due to management efforts (primarily point source) and 13 systems worsened as a result of coastal population increases. Case studies for systems from Europe and Asia (e.g. Yangtze estuary) show that eutrophication is not restricted to U.S. waters and that management measures have worked to improve conditions in some systems.
The ASSETS eutrophication assessment method at the larger scale application provides a basis for prioritization of management. In combination with other models, the method can be used to maximize yield from aquaculture while minimizing water quality impacts. And analysis of specific indicators and hydrologic considerations provides information about the probability of nuisance/toxic bloom occurrences. Taken together, these results give important information for management of systems that are impacted as well as those which are not impacted now but are at risk due to long water residence times and expected population increases (and thus nutrient loads) in the future.