- Morphoedaphic index (MEI) : - morphoedaphic index (MEI) : A morphoedaphic Index (MEI) is the ratio of Dissolved Solids (measured as total dissolved solids, alkalinity, or conductivity) to mean lake depth; MEI has been used to predict the total fish production, phytoplankton standing crop, and total phosphorus concentration of lakes not subject to cultural eutrophication.