Trends in Surface Elevation and Accretion in a Retrograding Delta in Coastal Mississippi, USA from 2012 – 2016

The Grand Bay estuary is in the north-central Gulf of Mexico and lacks riverine sediment input for marsh elevation maintenance. This study quantified trends in surface elevation change and accretion along an elevation gradient within the estuary. Elevation change rates were compared to short (13.71 mm/yr; 95% CI: -2.38 – 29.81), medium (6.97 mm/yr; 95% CI: 3.31 – 10.64), and long-range (3.50 mm/yr; 95% CI: 2.88 – 4.11) water level rise (WLR) rates for the region. Elevation change rates ranged from 0.54 mm/yr (95% CI: -0.63 – 1.72) to 5.45 mm/yr (95% CI: 4.27 – 6.62) and accretion rates ranged from 0.82 mm/yr (95% CI: -0.16 – 1.80) to 3.89 mm/yr (95% CI: 2.90 – 4.89) among marsh zones. Only the elevation change rate at a Juncus roemerianus marsh located high in the tidal frame was lower than long- ( P <0.001) and medium-range WLR rates ( P <0.01). The elevation change rate at a lower elevation J. roemerianus marsh was higher than the long-range WLR rate ( P <0.05). No marsh zones had elevation change rates that were significantly different from short-range WLR. These results suggest that J. roemerianus marshes higher in the tidal frame with limited sediment delivery are the most vulnerable to increases in sea level. Lower elevation marshes had higher rates of elevation change driven by sediment accretion and biogenic inputs. Other local research suggests that shoreline erosion is a threat to marsh persistence but provides elevation capital to interior marshes. Marsh migration is potential solution for marsh persistence in this relatively undeveloped area of the Gulf Coast.

Fungal Biodiversity in Salt Marsh Ecosystems

This review brings together the research efforts on salt marsh fungi, including their geographical distribution and host association. A total of 486 taxa associated with different hosts in salt marsh ecosystems are listed in this review. The taxa belong to three phyla wherein Ascomycota dominates the taxa from salt marsh ecosystems accounting for 95.27% (463 taxa). The Basidiomycota and Mucoromycota constitute 19 taxa and four taxa, respectively. Dothideomycetes has the highest number of taxa, which comprises 47.12% (229 taxa), followed by Sordariomycetes with 167 taxa (34.36%). Pleosporales is the largest order with 178 taxa recorded. Twenty-seven genera under 11 families of halophytes were reviewed for its fungal associates. Juncus roemerianus has been extensively studied for its associates with 162 documented taxa followed by Phragmites australis (137 taxa) and Spartina alterniflora (79 taxa). The highest number of salt marsh fungi have been recorded from Atlantic Ocean countries wherein the USA had the highest number of species recorded (232 taxa) followed by the UK (101 taxa), the Netherlands (74 taxa), and Argentina (51 taxa). China had the highest number of salt marsh fungi in the Pacific Ocean with 165 taxa reported, while in the Indian Ocean, India reported the highest taxa (16 taxa). Many salt marsh areas remain unexplored, especially those habitats in the Indian and Pacific Oceans areas that are hotspots of biodiversity and novel fungal taxa based on the exploration of various habitats.

Vegetative Community Diversity Assessment of a Beneficial Use Salt Marsh Restoration

Restoration of lost marsh platforms can include de-novo construction using dredged sediments. Two restoration projects constructed with beneficial use material in 2004 and 2015 were planted with native vegetation in the anticipation they would function similarly to adjacent Juncus roemerianus (Black needlerush) dominated salt marshes. Planted J. roemerianus, however, failed to establish and exists sparsely in the restored marsh. To better understand potential sources of failure, this study assessed vascular plant diversity in Spring and Fall of 2017 through 2019 and demonstrated establishment of both planted and naturally recruited vegetation. The two constructed sites were found to have higher species richness and plant diversity (Shannon-Wiener H’, and Simpson’s D) than the natural reference marsh, in part due to the higher elevations of the two constructed sites. The plant diversity metrics indicated the two beneficial use restorations did not meet the species composition of the reference marsh. Further monitoring should be conducted to observe the species development over the long term with considerations given to the potential future marsh change.

New insights into the influence of plant and microbial diversity on denitrification rates in a salt marsh

Coastal salt marshes are some of the most productive ecosystems on Earth, providing numerous services such as soil carbon storage, flood protection and nutrient filtering, several of which are mediated by the sediment microbiome associated with marsh vegetation. Here, nutrient filtering (nitrate removal through denitrification) was examined by determining microbial community structure (16S rRNA gene iTag sequencing), diversity, denitrification rates and metabolic potential (assembled metagenomic sequences) in collocated patches of Spartina alterniflora (Spartina) and Juncus roemerianus (Juncus) sediments. The iTag data showed that diversity and richness in Spartina and Juncus sediment microbial communities were highly similar. However, microbial community evenness differed significantly, with the most even communities observed in Juncus sediments. Further, denitrification rates were significantly higher in Juncus compared to Spartina, suggesting oscillations in microbial abundances and in particular the core microbiome identified herein, along with plant diversity influence marsh nitrogen (N) removal. Amplicon and assembled metagenome sequences pointed to a potentially important, yet unappreciated Planctomycetes role in N removal in the salt marsh. Thus, perturbations, such as sea-level rise, that can alter marsh vegetation distribution could impact microbial diversity and may ultimately influence the ecologically important ecosystem functions the marsh sediment microbiome provides.