Data from: Mechanisms and magnitude of dissolved silica release from a New England salt marsh
Data files
Jun 03, 2026 version files 25.88 KB
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Ge_Si_calculations.csv
3.34 KB
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README.md
6.94 KB
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SLP_DSi_SeasonalEbbFlood_NoOutlier.csv
2.28 KB
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SLP_DSiTemp_NoOutlier.csv
2.97 KB
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SLP_porewater_plus_Ge.csv
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tidal_cycle_avg_dsi.csv
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Abstract
Salt marshes are sites of silica (SiO2) cycling and export to adjacent coastal systems, where silica availability can exert an important control over coastal marine primary productivity. Mineral weathering and biologic fixation concentrate silica in these systems; however, the relative contributions of geologic versus biogenic silica dissolution to this export are not known. We collected water samples from the tidal creek of a relatively undisturbed New England (USA) salt marsh over 13 tidal cycles in the spring, summer, and fall of 2014 – 2016 to determine patterns of dissolved silica (DSi) concentration in the water entering and leaving the marsh. DSi concentrations in the tidal creek peaked in the summer and were at a minimum in the fall. Additionally, we analyzed DSi concentrations and Ge/Si ratios in marsh porewater and groundwater samples as a tracer of DSi origin. Ge/Si ratios in the porewater, subterranean estuary, and fresh groundwater averaged 6.3 ±0.31 µmol/mol, which is consistent with production via silicate weathering rather than biogenic silica dissolution. These results highlight a previously unstudied role marsh sediment plays in coastal biogeochemistry by supplying DSi to coastal ecosystems. This marsh exported 1170 mmol DSi m-2y-1, 85% of which originated from porewater exchange, with minor contributions from brackish groundwater discharge. Examining these values in the context of the other known DSi inputs to the estuary indicates that coastal marshes provide ~75% of the annual silica inputs into the adjacent estuary, Waquoit Bay.
https://doi.org/10.5061/dryad.zs7h44jdd
These data support the publication "Mechanisms and magnitude of dissolved silica release in a New England salt marsh," Williams et al, Biogeochemistry.
For additional methods and metadata, please see this publication and related datasets Brooks et al. 2021 and Mann et al. 2019. We conducted fieldwork at Sage Lot Pond marsh (41°33'13.73"N, 70°30'24.23"W), located within the Waquoit Bay National Estuarine Research Reserve (WBNERR) in Cape Cod, Massachusetts, USA.
The data presented here are only intended to supplement the data releases described above. These data have been formatted for ease of recreating the statistical analyses described in Williams et al. 2022. Please see Brooks et al. 2021 and Mann et al. 2019 for full data collection methods and comprehensive biogeochemical data for this site.
These data are in .csv (comma-separated text file) format.
Description of the Data
The following files are included in this data set:
- Ge_Si_calculations.csv (calculations of Ge/Si ratios from measurements of porewater and groundwater depth profiles)
- Sample_ID: Identifies date of sampling a depth profile (DP) or groundwater (GW) sample. Sites are numbered, and measurements from the same profile are numbered increasing with depth. E.g. 7/16 DP 4-3 is the 4th marsh porewater depth profile taken in July 2016 and the third depth within the profile.
- Ge_ppt: Germanium concentration in porewater in parts per trillion (measured unit)
- Ge_pmol/L: Germanium concentration converted to picomoles per liter
- Ge_umol/L: Germanium concentration converted to micromoles per liter
- SiO2_uM: Dissolved silica concentration in micromolar, or micromoles per cubic meter (measured unit)
- SiO2_mol/L: Dissolved silica concentration converted to moles per liter
- Ge/Si_umol/mol: The germanium/silicon ratio in micromoles per mole (conventionally reported unit)
- Sampling_Depth_cm: The depth in centimeters below the sediment surface of the measurement
- SLP_DSi_SeasonalEbbFlood_NoOutlier.csv (seasonal dissolved silica data from the tidal creek in micromolar, with outlier removed as discussed in manuscript; intended for seasonal statistical analysis)
- Empty cells have been filled with the value "null" to comply with Dryad formatting policies
- spring.flood.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from spring (March, April, May) flood tides
- spring.ebb.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from spring (March, April, May) ebb tides
- summer.flood.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from summer (June, July, August) flood tides
- summer.ebb.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from summer (June, July, August) ebb tides
- fall.flood.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from fall (September, October, November) flood tides
- fall.ebb.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from fall (September, October, November) ebb tides
- spring.total.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from spring (March, April, May), including both ebb and flood tides
- summer.total.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from summer (June, July, August), including both ebb and flood tides
- fall.total.dsi: Individual measurements of dissolved silica concentration in the marsh tidal creek in micromolar (uM) from fall (September, October, November), including both ebb and flood tides
- SLP_DSiTemp_NoOutlier.csv (tidal creek DSi data in uM, temperature in C, and chlorophyll concentration)
- Empty cells have been filled with the value "null" to comply with Dryad formatting policies
- DSi_uM: dissolved silica concentration measurements in micromolar
- Temp_C: accompanying tidal creek water temperature measurements in degrees Celcius
- Chl_ug/L: chlorophyll concentration in micrograms per liter
- SLP_porewater_plus_Ge.csv (porewater and groundwater samples listed with DSi and Ge concentrations, salinity, transect location, and depth)
- Empty cells have been filled with the value "null" to comply with Dryad formatting policies
- Date: Date of sampling
- Sample_ID: Identifies date of sampling a depth profile (DP) or groundwater (GW) sample. Sites are numbered, and measurements from the same profile are numbered increasing with depth. E.g. 7/16 DP 4-3 is the 4th marsh porewater depth profile taken in July 2016 and the third depth within the profile.
- Salinity_YSI: Salinity in practical salinity units (PSU)
- SiO2_uM: Dissolved silica concentration in micromolar
- Ge_pM: Germanium concentration in picomolar
- GeSi_ratio: Germanium/silicon ratio in micromoles per mol
- Transect_m: Sampling location in meters along transect (see Williams et al. 2022 for map)
- Depth_cm: Depth below sediment surface in centimeters
- Elevation_cmNAVD88: Elevation in centimeters
- tidal_cycle_avg_dsi.csv (ebb/flood dissolved silica ratio calculations for values averaged over individual tidal cycles)
- Year: year of tidal cycle
- Month: month of tidal cycle
- Flood Dsi: mean dissolved silica concentration of the flood tide in micromolar
- Ebb Dsi: mean dissolved silica concentration of the ebb tide in micromolar
- EbbFlood_Ratio: the straightfoward ratio between the ebb and flood DSi means for each tidal cycle
Funding & Conflict of Interest
The authors have no relevant financial or non-financial interests to disclose. This study was supported by the U.S. Geological Survey (USGS) Coastal and Marine Geology Program with support from the USGS Land Change Science Program’s LandCarbon program, U.S. National Science Foundation (OCE-1459521), NOAA Science Collaborative (NA09NOS4190153). Additional support was provided by ARCS Oregon, the Boston University (BU) Undergraduate Research Opportunities Program, and the BU Department of Earth and Environment. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Access Information
These data are available for public access and use. Please contact corresponding author Olivia Williams with further questions.
Data Collection (from Williams et al. 2022)
Tidal exchange at this site occurs through several interconnected man-made tidal creeks from the marsh into Sage Lot Pond, which in turn opens onto Waquoit Bay. We deployed a YSI EXO2 Sonde and a SonTek IQ Plus acoustic Doppler current profiler (ADCP) at the mouth of a single tidal creek to obtain measurements from a defined marsh drainage basin (4118 m2) and collected continuous data during the study period. The YSI EXO2 Sonde was used to measure salinity, dissolved oxygen concentration, pH, turbidity, temperature, and chlorophyll concentration every five minutes. The SonTek IQ Plus measured water flow velocity. More detailed methods may be found in Wang et al., 2016 and Chu et al., 2018.
During 13 field campaigns from 2014 to 2016, we collected tidal creek water samples roughly once per hour during each tidal cycle (10 to 12 times per ~12.5-hour tidal cycle). Field sampling occurred during four spring season tidal cycles, five summer tidal cycles, and four autumn tidal cycles between July 2014 and November 2016 for a total of 121 measurements (flood tide = 51 measurements, ebb tide = 70 measurements) over the 13 tidal cycles. Sampling occurred across a range of tidal amplitudes, or neap-spring tidal cycles.
Depth profiles of marsh porewater (n = 98) and subterranean estuary water (brackish water from the underlying sand aquifer below the marsh peat; n = 60) were collected from the marsh platform concurrently with tidal creek sampling during each season. To do this, we inserted an MHE Push-PointTM sampler into the subsurface, 15 to 162 cm depth, to capture a four- to five-point profile within the dynamic zones of biogeochemical activity within the vertical profile of the peat and underlying subterranean estuary. The boundary between the marsh peat (where porewater was sampled) and underlying sand aquifer (where subterranean estuary water was sampled) was determined by feel while the MHE sampler was inserted. During each sampling campaign, we collected at least one sample from each zone (peat and subterranean estuary), with typically three samples in each profile captured in the peat zone. In addition, we also collected depth profiles of fresh groundwater samples (n = 21) from the marsh-upland boundary from several depths (50 to 150 cm below surface) in each field campaign, which we refer to as “terrestrial groundwater.” All samples were filtered through a 0.22 µm polycarbonate filter (PALL AcroPak 200) with a peristaltic vacuum pump. Sample storage was the same as for tidal creek DSi samples.