Effects of saline conditions and hydrologic permanence on snail assemblages in wetlands of Northeastern China

Invertebrate community structure in wetlands is determined by a complex suite of environmental factors and biotic interactions. Hydrology (i.e. hydroperiod and water permanence) is considered the paramount environmental control of freshwater wetlands, with temporary drying being a major constraint on biota. However, factors controlling invertebrate assemblages in saline-alkaline wetlands remain poorly investigated. Moreover, most previous studies analyzing environmental filtering on wetland invertebrates have focused on local scales, and cross-regional studies are rare. In this study, the snail fauna was used to evaluate environmental filtering across saline-alkaline intermittently inundated and perennially inundated marshes in Songnen Plain and freshwater intermittently inundated and perennially inundated marshes in Sanjiang Plain, of Northeastern China. Multivariate analyses showed snail assemblages were concurrently being influenced by saline conditions (Sanjiang, for freshwater versus Songnen, for saline), and hydrologic conditions (intermittently inundated wetlands versus perennially inundated wetlands in Songnen and Sanjiang). Snail abundance and richness were significantly higher in freshwater wetlands of the Sanjiang Plain than in saline-alkaline wetlands of the Songnen Plain. Snail abundance of perennially inundated wetlands was higher than intermittently inundated wetlands in Sanjiang Plain, as predicted, but the reverse was true in Songnen Plain wetlands, contrary to prediction. Across Northeastern China, salinity was a more important control on snail assemblages than hydroperiod, a pattern previously unreported, and salinity mediated the impacts of hydroperiod. In regions where saline wetlands occur, the unique relationships between saline conditions and hydroperiod need to be considered for the assessment and conservation of threatened wetland resources.