Fine‐scale spatial homogenization of microbial habitats: a multivariate index of headwater wetland complex condition

With growing public awareness that wetlands are important to society, there are intensifying efforts to understand the ecological condition of those wetlands that remain, and to develop indicators of wetland condition. Indicators based on soils are not well developed and are absent in some current assessment protocols; these could be advantageous, particularly for soils, which are complex habitats for plants, invertebrates, and microbial communities. In this study, we examine whether multivariate soil indicators, correlated with microbial biomass and community composition, can be used to distinguish reference standard (i.e., high condition) headwater wetland complexes from impacted headwater wetland complexes in central Pennsylvania, USA. Our reference standard sites existed in forested landscapes, while our impacted sites were situated in multi‐use landscapes and were affected by a range of land‐use legacies in the 1900s. We found that current assessment protocols are likely underrepresenting sampling needs to accurately represent site mean soil properties. On average, more samples were required to represent soil property means in reference standard sites compared to impacted sites. Reference standard and impacted sites also had noticeably different types of microbial habitats for the two multivariate soil indices assessed, and impacted sites were more homogenized in terms of the fine‐scale (i.e., 1 and 5 m) spatial variability of these indices. Our study shows promise for the use of multivariate soil indices as indicators of wetland condition and provides insights into the sample sizes and scales at which soil sampling should occur during assessments. Future work is needed to test the generalizability of these findings across wetland types and ecoregions and establish definitive links between structural changes in microbial habitats and changes in wetland soil functioning. Covering less than 9% of the world's land surface, wetlands provide a disproportionate percentage of ecosystem services to the larger landscape (Zedler and Kercher 2005, de Groot et al. 2012). As the public has become more aware of the importance of these systems, wetland managers and scientists have turned their attention toward promoting legislative wetland protections (e.g., legislative measures from the Ramsar Convention) and building inventories that describe the ecological condition of the wetlands that remain, such as the United States Environmental Protection Agency (USEPA) National Wetland Condition Assessment (NWCA) database and The Pennsylvania State University (PSU)