Evaluating Suaeda salsa restoration after micro-topography reconstruction in the coastal beach of the Yellow River Delta, China

Abstract: Coastal beaches are mostly distributed in the silt-type muddy coastal zone, particularly in the Yellow River Delta of China. The typical ecologically fragile areas have suffered from severe soil degradation, where the ground vegetation is scarce. Furthermore, the tides and evaporation have also posed great damage to forming bare beaches with dry surface and flat terrain. In this study, four types of micro-topography transformation modes were established in the flat terrain of the Yellow River Delta beach, in order to explore suitable vegetation restoration. Specifically, S-, strip-, pin-, and crescent-shaped topographies were selected in the bare land of the light beach. The specific parameters were then measured to analyze the engineering quantity in the four micro-terrain reconstructions, including the surface roughness, vegetation growth, and soil improvement. A principal component and fuzzy mathematics membership functions were used to comprehensively evaluate the vegetation restoration and soil improvement in the four micro-terrain reconstructions. The results showed that the surface roughness increased, but the wind speed reduced under the various micro-topography of bare land in the light beach. The probability of seed retention increased in this case, where a warm zone formed at the bottom of the pit, thereby to promoting seed germination and growth. It was found that the micro-topography significantly enhanced the physical and chemical properties of soil for the growth of vegetation (P<0.05). Meanwhile, the micro-topography significantly reduced the soil bulk density, salinity, and pH value, whereas, it increased soil nutrients, porosity, and water-holding capacity, compared with the bare land of the light beach. The indicators were systematically evaluated in the four micro-terrain reconstructions. The Crescent-shaped mode significantly reduced the soil salinity by 44.19% (P<0.05), indicating a much more excellent performance to promote the vegetation restoration, compared with the bare land in the four micro-terrain reconstructions. The content of soil organic matter in the striped transformation mode was 2.87 times of that in bare land (P<0.05), indicating a significant effect on the soil improvement, compared with the bare land of the bare beach. The pattern of the pin-shaped mode greatly increased the soil porosity, while reduced the soil bulk density by 15.24% (P<0.05), indicating a better improvement in the physical properties of soil. Nevertheless, the S-shaped pattern performed a relatively weak correlation on vegetation restoration and soil improvement. Therefore, four micro-topography modification modes were ranked in a descending order: crescent-shaped, strip-shaped, pin-shaped, S-shaped, and bare land, after the comprehensive evaluation on the plant growth and soil improvement. A strong recommendation was that the crescent-shaped should be considered firstly, when carrying out the micro-topography transformation on the beaches of the Yellow River Delta, followed by the stripe-shaped and pin-shaped ones, where the S-shaped one cannot be adopted. There were still some limitations here, where the moist area at the bottom of the pit was first used to promote the growth of Suaeda salsa. It is also expected to measure the environmental changes at the bottom of pits in a long term, due mainly to the short testing period here. The finding can provide insightful technical support to the vegetation restoration for the coastal beaches of the Yellow River Delta in China.