Is there some sort of scale that ranks wetland quality?

I am looking for a standard way of ranking the quality of a wetland. I assume this would have something to do with Biological diversity within the wetland, water storage etc. Does anyone know of standards similar to this and if so where and who has created those standards.

I am doing a project that I hope will eventually lead to me quantifying the value of individual wetlands within the study area. I could come up with my own scale but would rather go with an industry standard if one exists.