Although the concept of self-design is frequently employed in restoration, reestablishment of primary physical drivers does not always result in a restored ecosystem having the desired ecological functions that support system resilience and stability. We investigated the use of a primary environmental driver in coastal salt marshes, sediment availability, as a means of promoting the resilience and stability of submerging deltaic salt marshes, which are rapidly subsiding due to natural and human-induced processes. We conducted a disturbance-recovery experiment across a gradient of sediment slurry addition to assess the roles of sediment elevation and soil physico-chemical characteristics on vegetation resilience and stability in two restored salt marshes of differing age (a 15-year-old site and a 5-year-old site). Salt marshes that received moderate intensities of sediment slurry addition with elevations at the mid to high intertidal zone (2-11 cm above local mean sea level; MSL) were more resilient than natural marshes. The primary regulator of enhanced resilience and stability in the restored marshes was the alleviation of flooding stress observed in the natural, unsubsidized marsh. However, stability reached a sediment addition threshold, at an elevation of 11 cm above MSL, with decreasing stability in marshes above this elevation. Declines in resilience and stability above the sediment addition threshold were principally influenced by relatively dry conditions that resulted from insufficient and infrequent flooding at high elevations. Although the older restored marsh has subsided over time, areas receiving too much sediment still had limited stability 15 years later, emphasizing the importance of applying the appropriate amount of sediment to the marsh. In contrast, treated marshes with elevations 2-11 cm above MSL were still more resilient than the natural marsh 15 years after restoration, illustrating that when performed correctly, sediment slurry addition can be a sustainable restoration technique.
Addition of sediment slurries to restore submerging salt marshes -either 15% solids and 85% water by volume for the 15 yr old site or ;20–30% solids and 70–80% water by volume at the 5 yr old site -solids: 8.94% 6 0.20% sand, 42.89% 6 0.54% silt, and 47.21% 6 0.60% clay, and sediments in the reference zone contained 7.71% 6 2.55% sand, 34.88% 6 1.77% silt, and 49.74% 6 10.25% clay
|Climate change impacts
|Effect of Nbs on CCI
|Biomass cover loss
|Measure resilience and stability of vegetation in response to disturbance. (controls referred to below are plots that have not been subjected to disturbance, not the experimental control to detect effectiveness) Vegetation resilience defined as rate of recovery of vegetation canopy --> Percentage recovery = [percent cover disturbed / percent cover control] x 100 stability defined as: the ability of the vegetation to recover to within at least 95% of the disturbance control within one year.
The 15-year old Venice site (29812.310 N, 89826.230 W) was located within the Modern (Bird foot) Delta of the Mississippi River Delta Complex (Fig. 1A). The five-year old Fourchon site (29810.580 N and 90814.230 W) was located in the Terrebonne Basin, a part of the Mississippi River Deltaic Plain (Fig. 1B).