Komado Wetland in Fukushima Prefecture is a nationally protected ecosystem composed of three peatlands of differing ages: Oyachi, Shirakabayachi, and Mizunashiyachi, surrounded by areas formerly used for agriculture. In the late 1990s, increased sediment and nutrient inflow from these cultivated lands raised concerns about impacts on peatland ecosystems, leading to the protection of the entire catchment in the early 2000s. Today, past-crop areas remain visible as sparse-vegetation patches, and field observations show slow vegetation recovery on sandy to clayey reddish soils.
To assess the current influence of these past-crop areas on peatland soil ecosystems, we applied two complementary approaches, both relying on microbial functional diversity (Biolog Ecoplate assays: AWCD, SR, SCMD), soil chemical properties (TC, TN, C/N ratio, EC, pH), and, in the second approach, elemental composition.
The first approach examined 1‑m depth profiles (20‑cm intervals) across the three peatlands, assuming differing hydrological influences based on topography. Oyachi, located directly downslope from former crop fields, showed strong declines in microbial functional diversity and organic carbon with depth. Shirakabayachi displayed similar but weaker trends, whereas Mizunashiyachi maintained relatively stable microbial activity. These results support a disturbance gradient aligned with expected hydrological connectivity.
The second approach involved a transect from the past-crop area into Oyachi, with sampling of surface and deep soils at six locations. Microbial diversity decreased from peatland toward former agricultural land, accompanied by preferential use of lighter aliphatic-like organic carbon. The intermediate site showed reduced diversity, indicating sensitivity to sediment inflow. Notably, the revegetated past-crop area exhibited moderately rich microbial functional diversity, similar to undisturbed hillslope soils, suggesting that 25-30 years of recovery may suffice for microbial functions to re-establish. However, the continued difficulty of vegetation regrowth in some patches raises new questions.
Overall, past agricultural activity and natural environmental features influence microbial functional diversity among the three peatlands. Yet, transect-scale observations alone may not fully capture proximity effects despite clear evidence of soil incursions. A broader, wetland-scale analysis is likely needed to better assess ecosystem-level responses. Future work will investigate vegetation composition, distribution, and long-term dynamics.