Effect of anthropogenic loadings of nutrient and mineral from groundwater on the distribution of hummocks of Sphagnum subnitens var. nitidum in poor fen

The purpose of this study is to clarify the effect of anthropogenic load via groundwater on the appearance of Sphagnum subnitens var. nitidum hummock. In August 2014, in the Yufutsu mires in Hokkaido, a loaded area with upland fields and a control area were established. Next, we investigated the hydrochemical environments of groundwater, and analyzed the relationship between the appearance of S. subnitens and the environmental variables. The precipitation contribution ratios of Ca2＋, Mg2＋, and K＋ in the groundwater of the loaded area were lower than the control area, indicating the anthropogenic load of these ions. In non-metric multidimensional scaling (nMDS), the S. subnitens community distribution showed a negative relationship with pH, concentrations of minerals (Na＋, Ca2＋, Mg2＋, K＋, and Cl－) and inorganic nitrogen (IN). Logistic regression analysis showed that the appearance of S. subnitens was negatively related to pH, minerals, IN, competitive species, and water level, which was in generally good agreement with nMDS. The estimated ranges of appearance of S. subnitens were pH≦6.5, Na＋≦7.8 mg L－1, K＋≦2.6 mg L－1, Mg2＋≦3.0 mg L－1, Ca2＋≦13.9 mg L－1, Cl－≦6.6 mg L－1, IN≦0.4 mg L－1, water level≦＋3.2 cm, and competitive species≦103.9 % in coverage. Some of S. subnitens also appeared in the higher outside the range of appearance, suggesting that the water quality inside the hummock is different from that of groundwater. As a result of path analysis, the effect of each variable on the appearance of S. subnitens was higher in the direct effect than in the indirect effect through the exclusion by competitive species. Therefore, it is important to maintain the hydrochemical environments within the range of the occurrence and to control competitive species in order to conserve S. subnitens.