Assessing ecosystem integrity of restored prairie wetlands from species production-diversity relationships

We assessed ecosystem integrity in restored prairie wetlands in eastern South Dakota, U.S.A., by examining the relationship between and diatom diversity and production. We asked three questions: (1) Is production related to species diversity? (2) Can production-diversity relationships be used to distinguish between restored and reference wetlands with the purpose of assessing ecological integrity? (3) Are production-diversity relationships influenced by species composition? Eight undisturbed, unrestored wetlands were chosen as references to compare to eight wetlands restored after drainage. Diatoms were collected from artificial substrates that allowed communities to be transplanted from restored to reference wetlands and visa versa. Production was measured as total cell biovolume and diversity as species richness. Neither diversity nor production alone differed between restored and reference wetlands. However, production was negatively related to diversity at restored wetlands, whereas production at reference wetlands was not. Communities transplanted from reference to restored wetlands exhibited a production-diversity relationship like that observed among control samples in restored wetlands. Likewise, communities transplanted from restored to reference wetlands apparently lost any such relationship after they were relocated. Production was dependent on species composition. Furthermore, production of some species differed by restored and reference wetland type. The negative relationship observed between diversity and production was strongly influenced by Rhopalodia gibba and Epithemia species, suggesting that these species were superior competitors under the conditions found in some restored wetlands. We consider restored wetlands displaying the highest production:diversity ratio to be the most impaired sites, based on the extreme deviation from reference wetlands. We conclude that the relationships between diversity and production provided a rapid measure of restored wetland integrity with respect to baseline conditions observed in reference sites.