Timeline

  • Spring 2016 (Siphon on; stable isotope data collection)
  • Spring 2018 (Siphon off; field collections)
  • Spring 2019 (Siphon off; field collections)
  • Spring 2020 (Siphon on; no field collections)
  • Spring 2021 (Siphon on; anticipated field collections)

Summary Findings

Simarilities between created sites (LHA & LHB)
and reference sites (LHC & WPH2)


 

Insights from the last time the siphon was on in 2016

Ecopath modeling indicates that food web structure and ecosystem properties were similar between sites with different salinity regimes.

Insights from the last time the siphon was on in 2016

(Click to Enlarge)

Hydrology and Elevation Mapping

(Swenson/Polito)

Key Findings

  • Correlation among sites is high for all parameters, temperature, conductivity and marsh water level.
  • Most (70%) of the differences between the 2019 and 2018 elevation surveys were fairly small (<5 cm) with 74% of the 2019 elevations being higher
  • The percentage of the day that a marsh is flooded is correlated with the daily mean water level for CRMS3680.
  • The percent marsh flooding can be calculated from measured water level (in m NAVD88) using a logistic sigmoid growth model.

(Note: CRMS3680 is the index station)

View Station Map

 

Key Findings

Marsh elevation

  • LHA has the highest elevation (18.4 cm), the other sites are all similar (6.8-10 cm)
  • Reference marshes have a more uniform marsh surface (lower SE) compared to the created marshes.

Flooding duration

  • LHA is flooded the least (7.9 hrs d-1), the other sites are similar (12.1-13.5 hrs d-1).
  • Reference marshes have more uniform flooding across the landscape (lower SE) compared to the created marshes.

Primary Producers

(Roberts)

Field Work: May 2018 & 2019

  • 5 distances from edge (1, 10, 25, 50, 100 m)
  • 3 transects in 2018; 2 plots on single transect in 2019
  • Determine biomass (aboveground clip plot) and collect plants for biomarkers)
  • Sediment and water column chlorophyll
  • Ancillary data: organic matter, C and N, bulk density, water content, pore water salinity, pH)

Key Findings

  • Overall magnitude of aboveground biomass similar between years; no consistent pattern with distance.
  • Trend of decrease along salinity gradient in 2018, weaker in 2019.
  • Biomass lower in high elevation restored marsh (LHA) than natural marsh(LHC); Biomass in restored marsh (LHB) more similar to the natural marsh (LHC).
  • Overall aboveground richness similar between years.
  • Richness decreases with salinity.
  • Richness lower in restored marshes than control sites in 2018; species richness was similar at lower elevation restored marsh (LHB) and natural marsh (LHC) compared to the higher elevation restored marsh (LHA) site.
  • Many species in one of the restored marshes (LHA) were not typical of brackish wetlands.
  • No clear patterns in benthic chlorophyll by site or distance.
View Station Map

 

 

Key Findings

Aboveground Biomass

  • LHA has the lowest biomass (1319-1352 g/m2)
  • LHB (1571-1950 g/m2) is more like reference sites (LHC: 1814-1808 g/m2; WPH2: 1808-2665 g/m2).

Species Diversity (H’) & Similarity (SD)

  • Slightly higher diversity & species richness in created marshes.
  • Highest diversity at LHA with many species not typical of wetlands.
  • LHB is more similar to the reference marshes (88-90%) than it is to LHA (~66%).

Litter Bag Decomposition & Macroinvertebrates

(Lopéz-Duarte, Polito, Roberts)

Field Work: May & July 2019

  • 1 transect per site, 5 distances from edge (1,10,25,50,100*m)
  • 5 replicate Spartina alterniflora litter bags per distance deployed for 2 months

Key Findings

  • Spartina alterniflora decomposition is highest in marshes that are flooded more due to lower elevation and a larger tidal range
View Station Map

 

 

Key Findings

Soil Organic Matter (SOM) Content

  • Created sites (LHA &LHB) have lower soil organic matter content than reference marshes.

Spartina Litter Decomposition Rate

  • LHA has a lower decomposition rate relative to the other created site (LHB) and the two reference sites (LHC & WPH2)

Microbial Community

(Engel)

Key Findings

  • Created marsh soils are fundamentally different than natural soils: lack well-developed peatlayer, wider grain size distributions (and larger overall particle sizes), less organic carbon.
  • Distinct microbial communities within soils, which affect the types of metabolic processes and microbial community services that influence the marsh habitat through time.
  • Overall taxonomic diversity similar, but specific genetic groups differed between created & natural marshes
View Station Map
Sediment core collections. Left: from sandy dredge deposits at Lake Hermitage marsh creation site. Right: organic, mud rich sediments from natural marshes. Credit: Annette Engel.

 

Key Findings

  • Similar diversity (H’) between created and reference sites with some exceptions.
  • Operational taxonomic units (genetic units) used for comparisons
  • High community similarity across all sites.
  • LHA & LHB Bacteria & Archaea are slightly more like each other than reference sites.

Insects and Spiders

(Hooper-Bùi)

Field Work: May 2019

  • Emergence traps set Day 1, collected Day 8
  • 4 replicate sweeps at each site for biodiversity
  • 4 replicate sweeps at each site for isotopes

Key Findings

  • Not all works all the time. We placed emergence traps on the marsh platform on the first day. We collected insects via sweep net for biodiversity and community metrics. Another identical sweep sample was taken 5 m away for the insects for isotopes.
  • This is the second year (2019) we set the emergence traps. Last year (2018), there were a few insects – flies – in the emergence traps but not enough for isotope analyses. There were no insects in the emergence traps this year, likely because May may be too early in the year. One trap blew into the water on day 3 and was retrieved by the fish group. We added asecond collection of sweeping for isotopes to make up for the low numbers of insects in the emergence traps.
View Station Map

 

Key Findings

Species Diversity (H’)

  • Higher richness (78 morpho-species) in LHA and LHB (66) at LHB relative to reference sites (LHC: 50; WPH2: 48)

Community Similarity (SD)

  • ~52-64% community similarity between all sites



Benthic Infauna

(Rabalais)

Field Work: May 2018 and May 2019

  • 1 transect per site (middle), 2 distances from edge (10 m, 50 m)
  • 5 replicates infauna, TOC, grain size
View Station Map

 

 

Key Findings

  • Higher diversity (H’) in created marshes
  • ~50-60% community similarity between all sites, apart from LHB and LHC (~84.8%)



Trawl and Suction Sampling

(Martin)

Field Work: May 2018 and May and July 2019

  • 8 trawls/site in years 1 and 2
  • Year 1 suction, n = 10 at salinity gradient sites
  • Year 2 suction, n = 9/site

Key Findings

  • Trawl: Clear differences between years, sites
  • Nekton community varies among sub-habitats (ANOSIM, Global R=0.333 , p=0.001). Biodiversity is highest in ponds at natural marshes.
  • We identified a need to incorporate site-specific data (e.g., pond sizes, marsh height) to determine which drivers influence community structure in ponds, creeks, or edges, across sites
View Station Map

 

Key Findings

Species Diversity (H’)

  • No differences in diversity between the created & reference sites for both “on-marsh” & “off marsh” nekton communities

Community Similarity (SD)

  • High similarity across sites (~71-90%)
  • Nekton communities at created marshes are equally similar to communities at reference marsh as they are to each other.

 

Biomarkers

(Polito, Olin, Lopéz-Duarte)

Field Work: May 2019

  • Collected ~2000+ sample in 2018 & 2019
  • Fish, invert, plants, submerged aquatic vegetation, algae, benthic microalgae, soil organic matter, particulate organic matter

Lab Work

  • Processed 1800+ samples from 2018
  • C&N isotopes: 2016 & 2018 complete
  • Compound-specific: 2016 complete
  • Heads collected for otoliths

Key Findings

  • Aquatic basal carbon sources are more important than terrestrial at all sites.
  • Similar trophic level but slightly higher use of terrestrial carbon at natural sites relative to created sites.
View Station Map

 

Key Findings

Trophic Hypervolume Size

  • Reference sites (LHC & WPH2) have the smallest (24.1 & 26.1), LHA the largest (59.9) , and LHB is intermediate (30.6)

Food-Web Similarity (SD)

  • LHA is least similar to reference sites (18-33%)
  • LHB is nearly as similar to reference sites as created sites are to each other.
  • Created sites: wider trophic niches
  • Created sites: lower C4 plant contribution