In situ experiment on groundwater control of the ecological zonation of salt marsh macrophytes in an estuarine area

Abstract

Tides and river water affect the groundwater vertical flow in the shallow soil in estuary areas, which in turn determines the ecological zonation of the salt marsh macrophytes. The groundwater vertical flow under the influence of the interaction of saltwater and freshwater is very complicated and includes upward porewater flow driven by evapotranspiration and downward groundwater drainage. In this study, in situ experiments were conducted to investigate the groundwater vertical flow direction and rate in four macrophytes zones of salt marsh macrophytes in the Yellow River Estuarine Nature Reserve. This study found that there are significant differences in groundwater vertical flow among these four macrophytes zones. (1) In the Bare flat zone, the downward drainage of groundwater and the upward porewater movement process frequently alternate. The processes of accumulation of and reduction in shallow soil salinity frequently alternate, and it is difficult for salt to accumulate continuously. (2) The Suaeda heteroptera Kitag. zone is mainly affected by tides. There are long periods of continuous porewater upward movement or groundwater downward drainage, and salinity in the shallow soils continues to accumulate or decrease during these periods. (3) In the Chinese tamarisk zone, the groundwater table is deep, and the moisture content of the shallow soil is low. The groundwater vertical flow is mainly an upward porewater process caused by evapotranspiration, and the shallow soil salinity accumulates gradually. (4) In the Staggered growth zone, the groundwater vertical flow characteristics of both the Bare flat zone and the Chinese tamarisk zone are evident. In general, in the salt marshes of the Yellow River Estuary, the tides and the Yellow River recharge affect the characteristics of the salt marsh groundwater. The salt marsh macrophytes are affected by the interactions of water and salt in the shallow soil, which form band-shaped macrophytes zones.