How hydrological connectivity regulates the plant recovery process in salt marshes

Abstract

1. Designing effective restoration strategies is a priority in recovering salt marsh plants. Hydrological connectivity is a main driver underpinning the success of the plant recovery process and can regulate life-history process-based restoration strategies. However, the relationship between these is unclear.2. Plant recovery needs to go through a whole life-history process, from seed to adult. Common restoration strategies are seed addition (SA) or seedling transplantation (ST), which start from seed germination and seedling growth stage.Besides these two strategies, another strategy starting from seed retention stage, microtopographic adjustment (MA), was designed to study the relationship with hydrological connectivity. A framework was also constructed to assess a gradient of hydrological connectivity between marsh plain and sea. We conducted several field experiments to test their relationships.3. The composite measurement of hydrological connectivity with five geomorphic variables can well represent the variation of environmental factors. Soil moisture, inundation frequency and sediment deposition were positively correlated, while soil salinity and hardness were negatively correlated with hydrological connectivity.4. The success of different restoration strategies varied with hydrological connectivity. MA showed a monotone decreasing trend, while SA and ST showed a unimodal trend as hydrological connectivity increased. Importantly, each strategy occupies a non-overlapping optimum range along the hydrological connectivity gradient.There is low hydrological connectivity for MA (0-0.28), middle hydrological connectivity for SA (0.28-0.55) and high hydrological connectivity for ST (0.55-1). Synthesis and applications.Our findings expand the quantification of the hydrological environment beyond elevation, distance or other single index to include a range of elements of hydrological connectivity, thus illustrating the underlying mechanisms of hydrological connectivity which regulate restoration strategies based on different life stages. The results provide a reliable framework to assess hydrological connectivity and offer guidance to select the optimum restoration strategy under different hydrological connectivities or to regulate the hydrological connectivity variables (topography on marsh plain and morphology of tidal | 1315

Effects of roots systems on hydrological connectivity below the soil surface in the Yellow River Delta wetland

“…There have been surprisingly multiple studies reporting hydrological connectivity above the soil surface for managers or governments to restore wetlands or create new wetlands (Chen et al, 2016; Jiang et al, 2021; Zhao et al, 2019). For example, high hydrological connectivity above the soil surface will disrupt the survival of the autochthonous producers in coastal salt marshes and damage wetland ecosystem services (Yin et al, 2020), whereas Wang et al (2021) found that hydrological connectivity above the soil surface could improve soil physical and chemical properties, such as reducing soil compactness and soil salinity and increasing soil water content. However, our understanding of hydrological connectivity below the soil surface remains an extreme gap in our recent works.…”

Quantifying the Impact of Hydrological Connectivity on Salt Marsh Vegetation in the Liao River Delta Wetland

“…Above 6 m can be correspondingly expressed as poor and worst hydrological connectivity strength. Vegetation growth in different cycles also has different hydrological requirements (Wang et al 2021 ). The next step will also be to further quantify the relationship between vegetation response to hydrological connectivity in different growth cycles to provide more detailed suggestions for wetland hydrological connectivity restoration.…”

Self-organized mud cracking amplifies the resilience of an iconic “Red Beach” salt marsh

“…The high marsh has a low tidal flood frequency of 1 to 15% in terms of number of days per year ( 69 ). The soils are characterized by a hypersaline condition with salinity of up to 25 parts per thousand and present accumulated salts on the surfaces regularly ( 69 , 70 ). The salt marshes are primarily dominated by the annual succulent plant species Suaeda .…”

“…Salicornia europaea , Phragmites australis , Tamarix chinensis , and the invasive cordgrass Spartina alterniflora are also found in the Yellow River Delta ( 71 ). The vegetation in our study site is monospecific ( Suaeda ), presenting a sparse vegetation cover around 5% ( 70 ). Regular spatial patterning of Suaeda vegetation following self-organized mud cracking is clearly observed in the field (Fig.…”