Diatom communities along pH and hydrological gradients in three montane mires, central China

The distribution patterns of epiphytic diatom assemblages in three montane mires in central China were investigated to examine their relationships with selected environmental variables (pH and depth to water table, DWT). Two of the mires are considered to be in good ecological condition (Dajiuhu and Qizimeishan Mires) while Erxianyan Mire is extensively affected by acid deposition and human activities. A total of 206 taxa belonging to 56 genera were found in 44 Sphagnum samples. Multivariate analysis revealed that pH and DWT were significantly correlated with diatom distribution. In Erxianyan Mire, the characteristic taxa (Eunotia minor and Eunotia intermedia) had lower pH optima and may therefore be useful indicators of highly-acidic conditions. In Dajiuhu Mire, the dominant species had higher pH optima, and abundant xerotolerant taxa (Hantzschia amphioxys, Pinnularia borealis, Luticola mutica and Diadesmis contenta) were observed. In the partial canonical correspondence analyses with mire location as a covariable, the correlation between diatom data and pH was insignificant, likely because pH differences between mires were greater than those within mires. In contrast, diatom data were significantly correlated with DWT, suggesting that diatoms are good sensors of hydrological variability along the hollow to hummock gradient. Together, these data can expand current autecological information for these potential diatom indicator species, which is critical for refining our interpretations of bio-monitoring and palaeolimnological studies in montane mires.