Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

This dataset contains measurements from discrete water samples collected for dissolved oxygen, dissolved inorganic carbon (DIC), and total alkalinity (TA) measurements during eleven instrument maintenance trips to recover and redeploy biogeochemical sensors at the SMIIL. Beginning in 2022, the SMIIL water quality monitoring program began discrete sample collection at 1) three Open Water Platforms (OWPs), named North, Gull, and South Platform, within the main salt marsh channel; 2) three salt ponds, named Ring West, Ring East, and Shark; and 3) five dredged sediment placement moorings. The monitoring program expanded over the next two years to three more salt ponds, named Long Reach, White, and Drum, and a second dredged sediment placement mooring system in 2023. During field maintenance trips that included discrete sample collection, samples were collected at the last measurement before removal of instruments for maintenance and again upon first available measurement once the sensors were re-deployed. Sample bottles were held by hand under ~0.2 m of seawater for 30 seconds to equilibrate with surrounding seawater before capping.

Dissolved Oxygen:

Samples were collected into volume-calibrated flasks and preserved for Winkler dissolved oxygen analysis following standard protocols (Langdon, 2010). After collection, samples were stored until laboratory analysis following the procedures of Zhang et al. (2002). All samples were titrated within one week of collection at the Boston College Marine Biogeochemistry Lab using a custom-built Winkler titrator with automated potentiometric end point detection (control software available here: Dnicholson et al., 2023). 

Precision of the sample collection and analysis procedure is determined by agreement between replicate measurements from the same location. Due to the need to preserve samples for short term storage, the majority of samples were collected in triplicate. After removal of outlier replicates in cases with triplicate sampling, median agreement among replicates was 0.18%. Larger discrepancies among replicates may reflect errors in sample collection and/or preservation; these results are reported for completeness but are flagged as questionable and/or bad (details of flagging scheme provided under “Problems/Issues” section).

Accuracy of sample measurements depends on standardization of the sodium thiosulfate titrant based on a reference standard. The sodium thiosulfate titrant used was determined by standardization with a 0.01N potassium iodate reference solution from Ocean Scientific International Ltd (OSIL). Lab-prepared potassium iodate standards, measured routinely throughout the monitoring period to verify titration accuracy and stability, were verified and adjusted by measurements against the OSIL standard.

Dissolved Inorganic Carbon and Total Alkalinity:

Samples were collected for dissolved inorganic carbon (DIC) and total alkalinity (TA) analysis following standard protocols (Dickson et al., 2007). Samples were collected into either 250 mL or 500 mL borosilicate glass bottles and preserved with saturated mercuric chloride (100 μL in 250 mL bottles, 200 μL in 500 mL bottles) for later analysis.

Samples were analyzed at the Boston College Marine Biogeochemistry Laboratory. DIC was analyzed using an Apollo SciTech AS-C6L DIC Analyzer and TA was analyzed using an Apollo SciTech AS-ALK2 TA Analyzer. Both DIC and TA were measured from each sample bottle. All DIC measurements were made on the day the bottle was opened for analysis, and TA measurements were made within the same week. DIC and TA instruments were calibrated daily and monitored throughout each analysis session by measuring Certified Reference Materials (Andrew Dickson, UCSD).

Analytical replicates were measured for all samples such that after analytical outliers (1 sigma) were removed, all samples for both DIC and TA retained at least two replicate measurements (median number of replicates for DIC = 3; median number of replicates for TA = 4). Analytical precision was determined for each sample as the standard deviation of analytical replicates. Mean analytical precision for all DIC samples in this dataset is 1.06 µmol/kg. Mean analytical precision for all TA samples in this dataset is 1.84 µmol/kg.

- Imported "SMIIL_DiscreteSampleOutput_all.xlsx" into the BCO-DMO system
- Converted datetime to ISO 8601 format YYYY-MM-DDTHH:MM
- Exported file as "971872_v1_smiil_discrete_sample.csv"

Salt marshes are highly productive, dynamic coastal environments that experience large fluctuations in biogeochemical parameters such as dissolved oxygen and pH in response to both natural forcings and anthropogenic impacts. At present, we have a limited understanding of the magnitude of biogeochemical variability in coastal habitats, hindering our ability to predict how they will respond in the future to episodic events and long-term change. This incomplete picture owes to a lack of sustained water quality measurements in coastal and estuarine systems worldwide.

This project investigates biogeochemical cycling in the Seven Mile Island Innovation Laboratory (SMIIL), a network of tidal marshes and channels in coastal New Jersey that is a site of historic and contemporary dredging and a testbed for marsh restoration techniques such as beneficial use of dredged sediment. It leverages multiple data sets of continuous, high-frequency (10-minute) measurements of physical and biogeochemical parameters, including water depth, temperature, salinity, dissolved oxygen, pH, chlorophyll a, and turbidity, as well as precipitation, wind speed, wind direction, temperature, relative humidity, and atmospheric pressure data. Two long-term biogeochemical sensor data sets, comprising a three-year time series at three sites in the main marsh channel (from June 2021–June 2024) and 1-2 year time series at six distinct salt ponds (August 2022–June 2024), were collected. Additionally, short-term (~months long) dredging and sediment placement monitoring data were collected at five different locations in 2022 and 2023. Data collection was designed to capture a variety of natural (diel, tidal, seasonal, storm-related) and human-created (sediment dredging and placement) conditions. Factory-calibrated biogeochemical sensors were field calibrated and maintained every 4 to 12 weeks. Discrete samples for dissolved oxygen, total alkalinity, and dissolved inorganic carbon were collected at the start and end of each sensor deployment for additional sensor calibration and validation. Altogether, our high-quality, multiyear dataset provides critical insights into the inherent variability of biogeochemical conditions in temperate salt marshes on diel and seasonal timescales, as well as how they may respond to transient events (e.g., storms, dredging activities) and over the longer term.