Bacterial community composition of soils in created freshwater mitigation wetlands as affected by soil chemistry and site hydroconnectivity

Background/Question/Methods

Soil bacterial communities are intricately involved in biogeochemical cycles in natural wetlands.  They play a role in energy flows and nutrient transformation as constituents of detrital food webs, yet are rarely examined in assessing ecosystem development of created wetlands.  It is known that bacterial communities respond to environmental changes, which may then affect biogeochemical cycles.  To understand the possible effects, it is necessary to understand the make-up of these bacterial communities.   In this regard, the use of molecular techniques has shown great diversity of microbial communities in many natural systems, however, there is significantly less known about the role bacterial communities in created wetlands play in the development a functional wetland.  We use amplicon length heterogeneity polymerase chain reaction (LH-PCR) of 16S ribosomal DNA to generate ‘fingerprints’ of the bacterial communities in soil samples collected during the beginning and the end of growing season from two created and two natural (reference) wetlands in Virginia's Piedmont physiographic province.  LH-PCR profiles along with physicochemical data (%moisture, C:N, %N, %C, pH and SOM) were used to identify community level differences within and between these wetlands specifically in terms of age and hydrologic connectivity to a water body.

Results/Conclusions

Multidimensional scaling and analysis of similarity showed clustering and significant differences in soil bacterial community profiles (global R= 0.45, p= 0.001) between sites and (global R= 0.17, p= .05) between seasons.  Further ordination of the biotic data as influenced by the environmental data using canonical correspondence analysis showed a clear association between soil moisture and bacterial community structure.  The diversity of soil bacterial community (Shannon's H') differed between sites with a slightly higher diversity observed in a relatively older created wetland with relatively high hydrologic connectivity to a surrounding water body.  The association between physicochemistry and bacterial community patterns of soils, suggests that soil bacterial community dynamics may serve as an indicator for physicochemical changes in soils, which has a practical implication for post-construction monitoring of ecosystem development in created wetlands.  Sequencing as well as amplification of nitrite reductase genes (nirK and nirS) is in progress in order to identify the structural makeup of these sites' bacterial communities and to link to known functional characteristics of certain guilds.