Abstract
Abstract. Interaction studies of vegetation within flow environments are essential for the determination of bank protection, morphological characteristics and ecological conditions for wetlands. This paper uses the MIKE 21 hydrodynamic and salinity model to simulate the hydrodynamic characteristics and salinity transport processes in the Pink Beach wetlands of the Liao River estuary. The effect of wetland plants on tidal flow in wetland areas is represented by a varying Manning coefficient in the bottom friction term. Acquisition of the vegetation distribution is based on Landsat TM satellites by remote sensing techniques. Detailed comparisons between field observation and simulated results of water depth, salinity and tidal currents are presented in the vegetated domain of the Pink Beach wetlands. Satisfactory results were obtained from simulations of both flow characteristics and salinity concentration, with or without vegetation. A numerical experiment was conducted based on variations in vegetation density, and compared with the tidal currents in non-vegetated areas; the computed current speed decreased remarkably with an increase in vegetation density. The impact of vegetation on water depth and salinity was simulated, and the findings revealed that wetland vegetation has an insignificant effect on the water depth and salinity in this wetland domain. Several stations (from upstream to downstream) in the Pink Beach wetlands were selected to estimate the longitudinal variation of salinity under different river runoff conditions; the results showed that salinity concentration decreases with an increase in river runoff. This study can consequently help increase the understanding of favourable salinity conditions for particular vegetation growth in the Pink Beach wetlands of the Liao River estuary. The results also provide crucial guidance for related interaction studies of vegetation, flow and salinity in other wetland systems.
Highlights
Wetlands are transitional zones between terrestrial ecosystems and aquatic ecosystems, and have a variety of unique functions, which include the following: providing large amounts of food, raw materials and water resources for humans, and maintaining the ecological balance, biodiversity and resources for rare species
Based on the obvious spectral distinction of vegetation, a decision tree containing a number of decision rules is designed to classify different types of vegetation cover; the Liao River estuary is classified into water body, shoal, and major wetland vegetation types, (e.g. Phragmites communis and Suaeda heteroptera)
The model is tested by simulating the water level, tidal current and salinity concentration in Liao River estuary, and the results are consistent with the measured data
Summary
Wetlands are transitional zones between terrestrial ecosystems and aquatic ecosystems, and have a variety of unique functions, which include the following: providing large amounts of food, raw materials and water resources for humans, and maintaining the ecological balance, biodiversity and resources for rare species. Based on velocities from laboratory experiments for different water depths, discharges and aquatic vegetation densities, analyses were carried out for the resistance coefficient of vegetation (Li and Zhao, 2004). The two-dimensional numerical model was used to test the different flow conditions of Zhalong wetland, and the effect of reed vegetation on the process of storage and detention in wetlands was comprehensively evaluated (Gu et al, 2006). The majority of studies have focused on the effects of vegetation on fluid movement in flume experiments; few detailed field observations or salinity simulations exist in mudflat–salt marsh ecosystems, especially involving the typical wetland plants of the Liao River estuary. A two-dimensional hydrodynamic and salinity model is used to simulate flow patterns and salinity distribution in the wetland waters of the Liao River estuary.
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