The size and distribution of tidal creeks affects salt marsh restoration.

Salt marshes are changeable and important ecosystems that currently face various threats, including global climate change and human activities. The influence of these factors can result in the degradation of salt marshes. Tidal creeks, which are an important source of nutrients and other substances for salt marsh vegetation, play an important role in the health of salt marshes. In this study, the morphological characteristics of tidal creeks and the characteristics of two typical plants, Suaeda glauca (SG) and Phragmites communis (PC), in the Yellow River Delta, China were investigated to determine the effect of tidal creeks on these plants. Aerial photography and field measurements of tidal creeks were carried out from May to July 2018 in the study area. At the same time, nine line-intercepts were set in the vertical direction of tidal creeks to investigate plants. The results showed that different grades of tidal creek exerted no significant influence on the growth of either S. glauca or P. communis. However, unlike grade, the size of a creek and the distance from it had marked effects on these plants. The cross-sectional area of a tidal creek had a significant positive impact on the density of S. glauca (r = 0.39, p = 0.02). For P. communis, the depth of a tidal creek had a strong correlation with this species' density (r = 0.51, p = 0.04) and height (r = 0.63, p = 0.01). Meanwhile, there was a negative relationship between the distance from tidal creeks and the height of S. glauca (r = -0.52, p = 0.02). Conversely, the height (r = 0 0.90, p = 0.00) and density (r = 0.62, p = 0.01) of P. communis were positively affected by its vertical distance from tidal creeks. We found that the subtidal zone near a tidal creek was more conducive to the recovery and growth of S. glauca, and that areas further away from a tidal creek, located in the intertidal and subtidal zones, were more conducive to the recovery and growth of P. communis. The parameters associated with tidal creeks in the subtidal zone (cross sectional area 4.55 m, distance 0-10 m) were beneficial for the growth of S. glauca. For P. communis, relevant features in the intertidal and subtidal zones (depth 0.40-0.45 m, distance 20-60 m) are useful. Our results suggest that attention should be paid to the effects of size and distribution of tidal creeks during the process of salt marsh restoration. This work also provides practical guidance for the restoration of native salt marshes in China.