Salt marsh establishment in poorly consolidated muddy systems: effects of surface drainage, elevation, and plant age

Abstract

Conservation and restoration of salt marsh ecosystems are becoming increasingly important because of the many ecosystem services they provide. However, the processes controlling salt marsh establishment and persistence, especially on bare tidal flats in muddy areas, remain unclear. As muddy sediments typically experience a restriction of soil drainage, we expect that a surface drainage relief due to a heterogeneity topography, as might occur on the edge of tidal channels, can facilitate the establishment of salt marsh vegetation on muddy tidal flats. By means of a manipulative field experiment, using "Mega-Marsh Organ" mesocosms, we investigated the impact of surface drainage and elevation relative to mean sea level on (1) the survival of Spartina anglica seedlings from three different age classes: 1-yr, 3-month, and 1-week; and (2) the growth performance of mature S. anglica marsh tussocks. S. anglica seedling survival, especially in the establishment phase, was positively affected by better surface drainage, increases of seedling age, and higher elevation relative to mean sea level. That is, the survival rate of S. anglica seedlings at the end of 6th week increased from 0% (at surface water undrained, 1-week, 0 cm elevation) to 94.44% (at surface water drained, 1-yr, 90 cm elevation). In contrast, surface drainage did not affect the performance of large S. anglica marsh tussocks, as only increased elevation relative to mean sea level was shown to affect S. anglica tussock growth in terms of plant height, shoot numbers, and dry biomass. Based on our findings, we proposed a conceptual model to understand how surface drainage-driven feedbacks in a heterogeneous topography may be reinforced to induce salt marsh establishment in muddy systems. Further testing of present hypothesized model would be beneficial for insights into salt marsh establishment on tidal mudflats.

A probabilistic framework for windows of opportunity: the role of temporal variability in critical transitions

“…Bivalves are also known to become less vulnerable to predation by crustaceans once a size threshold is surpassed [ 10 ]. Becoming larger can even increase an organism's ability to tolerate toxic conditions [ 19 , 20 ]. In the above examples, the size or biomass of an organism is thus directly linked to its tolerance, especially in the earliest stages of life, underlining the key concept of stage-dependent tolerance.…”

Drainage-Improved Sediment Strength Enhances Saltmarsh Seedling Establishment Chance

“…In our mesocosm experiment, neither drainage nor sediment were observed to affect seedling growth and survival. This is surprising, because drainage in earlier studies was found to facilitate saltmarsh seedling survival and growth by relieving anoxic toxicity to root layers (Redelstein et al, 2018;Fivash et al, 2020;Cao et al, 2021). Although there were certain differences in soil water content showing that our drainage treatments were effective in dewatering all sediments, we note that drainage had no overall effects on redox potential of sediments.…”

“…Seedling establishment is a crucial phase that determining the success of saltmarsh restoration attempts (Friess et al, 2012;Balke et al, 2014;Hu et al, 2021). Whereas recent studies highlight drainage is a critical factor in facilitating saltmarsh seedling establishment (Fivash et al, 2020;Cao et al, 2021), much less is known on the underlining mechanisms for the effects of drainage. Using Spartina anglica as an example, present study demonstrates that drainage could enhance saltmarsh seedling stability indirectly by improving sediment strength during the windows of opportunity for seedling establishment.…”

“…Recent studies highlight that enhanced drainage condition can facilitate seedling establishment for different saltmarsh species (Fivash et al, 2020;Cao et al, 2021). Drainage is common features in saltmarsh, which can be generally caused by surface sheet flow towards channels during ebbing when the tidal area become exposed (Fagherazzi et al, 2004;Perillo et al, 2009).…”

“…By water recirculation, drainage is able to inject oxygen-rich water into anoxic sediments via porewater flow in them by a pressure head developing at low tide (Jansen et al, 2009), and thereby alleviate anoxic saline conditions (Rabouille et al, 2003;Lamers et al, 2013) that are toxic to salt marsh root layers (Redelstein et al, 2018). This process is suggested to be vital for the establishment of earlystage saltmarsh seedlings (Fivash et al, 2020;Cao et al, 2021), whose aerenchyma is underdeveloped (Burdick and Mendelssohn, 1987;Jung et al, 2008). Nevertheless, it is largely unknown to what extent drainage may affect saltmarsh seedling growth and stability, and whether these effects would dictate the availability of WoOs in determining the ultimate seedling establishment.…”