Using indicators of community structure and ecosystem function to assess the biological integrity and recovery of restored prairie wetlands

I assessed ecological integrity and recovery in recently (6-8 yrs) restored prairie wetlands in eastern South Dakota, USA, by examining three ecological indicators: (1) diatom species assemblages, (2) the relationship between diatom production and diatom community structure, and (3) community respiration:biomass ratios. Integrity of eight restored wetlands was based on comparisons with eight reference wetlands. Diatoms were collected from artificial substrates which allowed communities to be transplanted from restored to reference wetlands and vice versa. Diatom production was estimated from cell volumes and abundances. Respiration was estimated from biological oxygen demand and biomass was estimated from phytoplankton chlorophyll concentration and from seston carbon mass. Species richness, diversity and equitability at restored and reference sites were similar but seasonal differences were apparent. Based on multidimensional scaling results, restored and reference sites could not be distinguished by species assemblages. Transplanted diatom species assemblages became similar to those in the wetlands to which they were transferred suggesting a strong environmental control over diatom communities. Diatom production was negatively related to the number of functional groups at restored but not at reference wetlands. Communities transplanted from reference to restored wetlands exhibited a diversity-production relationship like that observed among control samples in restored wetlands. Likewise, communities transplanted from restored to reference wetlands apparently lost any such relationship after being relocated. Wetland sites possessing a unique combination of three functional groups had higher production than sites having any other combination. Restored sites exhibited high production as a function of N-fixing diatoms. No difference was observed in respiration:biomass ratios in restored and reference wetlands. However, high variability in respiration:biomass ratios was observed among sampling periods and wetlands. Diatom species assemblages alone may not be appropriate ecological indicators of recovery because diatoms may be adapted to the drought-like conditions imposed by drainage. Respiration:biomass ratios may be insensitive indicators of disturbance because plankton communities may recover quickly after restoration and/or plankton species are redundant with respect to production and respiration. Restored and reference wetlands could be distinguished by their respective diversity-function relationships but knowledge of species composition revealed the mechanisms connecting diversity and function.