Metadata

Description
For FCE_1250_AltStableState_HydroGeo:
A field survey was conducted to characterize hydrogeomorphic variability across the study site, initiated in November 2019 and completed in January 2020. The survey was conducted along three, 300 m transects, spaced 100 m apart, with survey points positioned roughly every 30 m and stratified across three ecosystem states: Emergent (EMG), submerged (SUB), and open-water (OW). Percent cover of > 75% of Cladium jamaicense within a 1-m2 plot was used to identify the EMG state. Presence of Chara sp. and absence of C. jamaicense was used to identify the SUB state. The OW state was identified based on the absence of any vegetation. Measurements at each survey point included geomorphic measurements of soil surface elevation and soil depth, and hydrologic measurements of porewater salinity and surface water depth. For EMG and SUB points, soil surface elevation was measured by placing the survey rod on the soil surface. Surface water depth was measured simultaneously via centimeter markings on the survey rod. For OW points, there was generally a thick layer of flocculent, unconsolidated sediment, making the soil surface difficult to discern. To standardize measurements, the survey rod was allowed to gently fall through this flocculent layer until resistance was met. The point at which resistance was met was identified as the soil surface and subsequent measurements of elevation and surface water depth were taken. Soil depth was measured at each point using a stainless-steel soil probe by driving the probe through the soil profile to the bedrock. Porewater salinity was measured at a soil depth of 15 cm using a YSI Model 600 XL (Xylem, Inc., Yellow Springs, OH, USA).

References:
Gillins, D.T., D. Kerr, and B. Weaver. 2019. Evaluation of the online positioning user service for processing static GPS surveys: OPUS-Projects, OPUS-S, OPUS-Net, and OPUS-RS. Journal of Surveying Engineering 145: 1-14.

Description
Methods that pertain to FCE_1250_AltStableState_Bio:
To estimate C. jamaicense aboveground (ABG) biomass, we used a non-destructive, phenometric technique developed and validated in the Florida Everglades (Childers et al. 2006). Measurements were initiated in November 2019 and completed in January 2020. Within 1 m2 plots (n = 29), we counted all live individual C. jamaicense culms and randomly selected 1/3 of all individual plants, or a minimum of 15 when the total culm density was less than 45. For this subset, we measured: (1) length of longest leaf, (2) culm diameter at the base, and (3) inflorescence height, if present. Biomass estimates for each individual C. jamaicense plant measured was then estimated using a multiple regression model developed and described in Childers et al. (2006). Total ABG biomass (g m-2) for each plot was then estimated by multiplying culm density per m2 by mean plant biomass (g dw). Soil surface elevation, soil depth, water depth, and porewater salinity were surveyed at three points within each plot to obtain plot-level averages. Methods for these geomorphic and hydrologic methods can be found in the methods description for the FCE_1250_AltStableState_HydroGeo dataset.
Methods that pertain to FCE_1250_AltStableState_Bio_LongTerm:
ABG biomass, water depth, and porewater salinity measurements were taken across a subset of the EMG aboveground biomass plots, with three plots positioned along each transect, for a total of nine, 1-m2 plots. Six plots were established in November 2019 with an additional three plots established in January 2020. Measurements continued bi-monthly from Nov 2019/Jan 2020 - July 2022. Plot locations were selected to cover the range of soil surface elevation and C. jamaicense aboveground biomass based on the initial field survey. Specific methods for ABG biomass, water depth, and porewater salinity can be found in the methods description for the FCE_1250_AltStableState_HydroGeo and FCE_1250_AltStableState_Bio datasets. For each time point, ABG biomass was averaged across all plots while water depth and porewater salinity were averaged for each plot, then averaged across all plots. Additionally, we estimated dry days water depth was continuously measured in a permanent well at 30-minute intervals and calibrated monthly for the duration of the study using an AquaTroll 200 (In-Situ Inc., Fort Collins, CO). These data were averaged to the daily scale before calculating the number of dry days. To calculate dry days for EMG plots, we referenced water depth to NAVD88 and subtracted the difference between the soil surface elevation at the well and the mean soil surface elevation of the EMG state (-0.09 ± 0.05 m rel. NAVD88). To obtain soil surface elevation at the well, we measured the elevation of top of the well using real-time kinematic surveys (0.61 m rel. NAVD88) and subtracted the height of the well above the soil surface (0.76 m).
References:
Childers, D. L., Iwaniec, D., Rondeau, D., Rubio, G., Verdon, E., & Madden, C. J. (2006). Responses of sawgrass and spikerush to variation in hydrologic drivers and salinity in Southern Everglades marshes. Hydrobiologia, 569(1), 273-292.

Description
Methods that pertain to FCE_1250_AltStableState_SETMH:

Soil elevation change and vertical accretion were monitored from June 2018 – May 2023 using the rSET-MH approach. Three rSETs were established in May 2017 at the study site within the SUB state following standard methods. The rSETs were installed ~10 meters apart on alternating sides of a permanent, wooden boardwalk at the edge of the study site adjacent to a major road. The boardwalk was built prior to rSET installation and provided direct access to the plots from the road without disturbing rSET plots. Following an 11-month equilibration period, baseline soil elevation measurements were made by attaching the rSET instrument to the benchmark, leveling the rSET, and lowering fiberglass pins (n = 9) to the soil surface at four fixed azimuths per rSET plot, for n = 36 measurements per plot, and 108 measurements total across rSET plots (Fig. 3a). Soil elevation change measurements were made bi-monthly from June 2018 – June 2019, and seasonally from October 2019 – May 2023, except for one additional measurement made in in June 2021. All rSET plots were in locations that were covered by submerged mats of Chara spp that formed during the wet season. We removed any Chara sp. that was deposited on the soil surface during the dry season so that pin height reflected elevation changes solely from the soil profile. We followed this method for all dry season measurements except in March 2021, when measurements were made shortly after a prescribed fire was conducted that impacted the majority of the study site. Ash deposition and a thick mat of Chara sp. made it difficult to remove material without disturbing the soil surface, so pins were lowered on top of the deposited material. We established five MH plots to monitor vertical accretion at locations characterized by the SUB state along the wooden boardwalk adjacent to rSET plots in May 2017. Marker horizons were established by pouring a white feldspar clay onto the soil surface within a circular bucket with the bottom cut out (circumference = 0.25 m; height of MH layer ~ 5 cm). Feldspar was allowed to settle for one month to form an identifiable layer before the bucket was removed. During each soil elevation measurement, MH plots were examined for accreted material. When accretion was observed, a small soil core was extracted and the depth of vertical accretion above the MH was measured in triplicate. When the soil surface was dry, a serrated knife was used to cut out a core. When the soil surface was inundated, liquid nitrogen was used to “cryo-core” the MH plot.