DOI: 10.5061/dryad.v41ns1s5x
title: Data from: Contrasting CO2 dynamics in seagrass meadows between organic carbon (OC)-rich reef and OC-poor terrestrial sediments: Implications for enhanced alkalinity production

description: This dataset covers the carbonate chemistry of seawater and porewater,
 sediment carbon content, and benthic alkalinity fluxes and carbon dioxide
 removal (CDR) in two distinct seagrass meadows: one situated in organic
 carbon (OC)–rich reef sediments and the other in OC–poor terrestrial
 sediments. Seawater carbonate chemistry parameters include
 temperature, salinity, pH, pCO2, dissolved inorganic carbon
 (DIC), total alkalinity (TA), bicarbonate (HCO3-), carbonate (CO32-), and
 aragonite saturation state. Porewater parameters include pH, DIC,
 TA, pCO2, aragonite saturation state, and calcium ion
 concentration. Sediment characterization covers total organic carbon
 (TOC), total inorganic carbon (TIC), and total nitrogen (TN). The benthic
 flux data include measurements taken during the daytime, nighttime, daily,
 and annually. The carbon dioxide removal capacity of seagrass was
 calculated from the measured total alkalinity.
description: <strong>A. Sample collection</strong>
 Seawater samples for TA, DIC, and pH analyses were collected at
 specific intervals. At the DS site, samples were taken at 06:00, 12:00,
 and 18:00 daily, while at the KT site, samples were collected at 4-hour
 intervals. Discrete seawater samples were obtained using a 9-L Nalgene™
 HDPE carboy. Within 30 minutes of collection, the seawater samples were
 transferred into pre-cleaned 350-mL borosilicate bottles upon arrival at
 the laboratory in Dongsha or Kenting. To arrest biological activity, each
 sample received an injection of 200 μL of saturated HgCl2 solution, after
 which they were sealed and transported to the laboratory at the National
 Taiwan Ocean University. Subsequently, these samples underwent analysis
 for DIC, TA, and pH measurements. Porewater samples
 were acquired using porewater wells, following a modified methodology
 described by Falter and Sansone (2000). At various sediment depths (2, 4,
 6, 8, 12, 16, and 20 cm), 25 mL of pore water was extracted from each well
 using a Luer-Lok syringe. The sampling procedure and preservation of
 porewater samples followed the methods outlined in Kindeberg et al.
 (2020). These porewater samples were also subjected to analysis for DIC,
 TA, and pH measurements, with additional determination of calcium ion
 concentrations. Sediment samples were collected using
 an acrylic push core (7 cm diameter; 1 m long) and stored in a -20°C
 freezer until subsequent analysis. Subsamples, taken at 5 cm intervals
 from top to bottom, underwent microscopic examination using a Leica WILD
 M8 microscope and EOS Utility software. The semi-quantitative analysis of
 major minerals in surface sediment was conducted using X-ray powder
 diffraction (XRD) with a Bruker D2 Phaser instrument, following methods
 outlined in previous studies (Chen et al., 2011; Lo et al., 2017).
 Additionally, each core section was analyzed for total organic carbon
 (TOC), total inorganic carbon (TIC), and total nitrogen (TN) contents,
 providing a comprehensive assessment of sediment composition and organic
 matter content. Benthic metabolism incubations were
 conducted within seagrass meadows using specialized benthic chambers
 positioned at a depth of 1 meter, facilitating the differentiation between
 light and dark fluxes of total alkalinity (TA) and dissolved inorganic
 carbon (DIC). The benthic chambers, made of polymethyl methacrylate
 cylinders with dimensions of 35 cm in diameter and 40 cm in height, were
 carefully inserted approximately 10 to 15 cm into the sediment. These
 chambers were equipped with autonomous sensors capable of capturing
 critical parameters. Within each chamber, individual water circulation
 pumps ensured representative water sampling while minimizing chemical
 gradients. Furthermore, the chambers were designed with two sampling ports
 to facilitate a controlled collection of biological and chemical samples.
 On average, the chambers held a water volume ranging from 24 to 29 liters.
 The HOBO U26, with a precision of 0.02 mg L<sup>-1</sup> and
 accuracy of ± 2%, was used to record DO levels, temperature, and light
 intensity at 10-minute intervals at each site. Complementing this data
 collection, temperature and light loggers (HOBO Pendant® Temperature/Light
 64K Data Loggers) were deployed. <strong>B.
 Sample analysis</strong> The following methods
 were used to analyze seawater, porewater, and sediment samples:
 DIC was analyzed using the Non-dispersive infrared
 method on DIC Analyzer (AS-C3, Apollo SciTech Inc.).
 TA was analyzed using the Gran Titration Method (TA titrator, AS
 AS-ALK2, Apollo SciTech Inc.). pH was analyzed using
 a spectrophotometer at 25 °C. Partial pressure of
 CO<sub>2</sub> (<em>p</em>CO<sub>2</sub>) and aragonite saturation state (Ω<sub>Ar</sub>) in both seawater and porewater were calculated using DIC, TA, temperature, and salinity data, utilizing the CO2SYS program (Pelletier et al. 2011). The dissociation constants for carbonic acid used in these calculations were derived from the dataset of Mehrbach et al. (1973) and refined by Dickson and Millero (1987), providing accurate and validated results for <em>p</em>CO<sub>2</sub> or Ω<sub>Ar </sub>determinations (Wanninkhof et al. 1999). Calcium ion concentration was quantified using an inductively coupled plasma mass spectrometry (ICP-MS) system (Agilent 7700×, Agilent Technologies). TOC, TIC, and TN were measured using an elemental analyzer (Elementar, Soil TOC<sup>®</sup> cube, Germany). Carbon dioxide removal (CDR) was calculated from the TA benthic fluxes <strong>C. Instrument precision and uncertainty error</strong> The calibration of both the alkalinity titrator and DIC analyzer was conducted using certified reference materials (CRMs) sourced from Dr. A. Dickson's laboratory at the Scripps Institution of Oceanography. The accuracy and precision of the TA and DIC measurements were equal to or exceeded ±0.15%. The measurement of pH at 25 °C is performed with a precision of 0.005 on the total hydrogen ion concentration scale. The uncertainty (error) of <em>p</em>CO<sub>2</sub> and Ω<sub>Ar</sub> was determined using the Seacarb package in R, following the methodology outlined by Gattuso et al. (2024). <strong>D. Statistical analysis</strong> The study used Wilcox's robust ANOVA (WR-ANOVA) to account for the heteroscedasticity among habitat groups. Given the skewed distribution of carbonate chemistry observations within seagrass habitats, comparisons between medians, as suggested by Baldry et al. (2020), were used over means. This statistical approach was applied to assess differences in the medians of pH<sub>25</sub>, pCO<sub>2 in situ</sub>, DIC, and TA at the DS and HK sites across different seasons. The WR-ANOVA analysis was executed using the "med1way" function from the R package "WRS2" (Mair and Wilcox, 2020). All statistical analyses were conducted in R software v4.1.1 (R Core Team, 2021) with a confidence level of 95%.
description: GENERAL INFORMATION 1. TITLE OF DATASET: Contrasting CO2 Dynamics in
 Seagrass Meadows between Organic Carbon (OC)-Rich Reef and OC-Poor
 Terrestrial Sediments: Implications for Enhanced Alkalinity Production 2.
 GEOGRAPHICAL LOCATION OF DATA COLLECTION: Dongsha Island (DS), Taiwan, and
 Kenting (KT), Taiwan 3. FUNDING INFORMATION Funding Agency: National
 Science and Technology Council (NSTC) Funding No.: #112-2611-M-019 -005
 and #112-2119-M-019 -008 4. CITATION OF THIS DATA: Chou, W-C, L.-F. Fan,
 M. B. Natividad, J.-J. Chen, Z.-W. Tang, H.-F. Chen, P.-C. Chen, E.-C.
 Kong, Y.-Y. Shih, W.-J. Huang, C.-C. Hung. 2024. Contrasting CO2 Dynamics
 in Seagrass Meadows between Organic Carbon (OC)-Rich Reef and OC-Poor
 Terrestrial Sediments: Implications for Enhanced Alkalinity Production. 5.
 DATA AND FILE OVERVIEW **A. DS-KT_Water.csv** Seawater carbonate chemistry
 parameters include temperature, salinity, pH, pCO2, dissolved inorganic
 carbon(DIC), total alkalinity (TA), bicarbonate (HCO3-), carbonate
 (CO32-), and aragonite saturation state (WAr). **B.
 DS-KT_Porewater_and_Sediment.csv** Porewater parameters include pH, DIC,
 TA, pCO2, aragonite saturation state, and calcium ion concentration.
 Sediment characterization covers total organic carbon (TOC), total
 inorganic carbon (TIC), and total nitrogen (TN). **C.
 DS-KT_Benthic_flux_CDR.csv** The benthic flux data include measurements
 taken during the daytime, nighttime, daily, and annually. The carbon
 dioxide removal capacity (CDR) of seagrass was calculated from the
 measured total alkalinity. 6. VARIABLE LISTS: **A. DATA SPECIFIC
 INFORMATION FOR: DS-KT Water.csv** 1. Number of variables: 15 (Columns
 A-O) 2. Number of rows: 94 3. Variable list: * Year: The year the study
 was conducted (2021-2022) * Month of the sampling period 1: January 5: May
 9: September 10: October * Date: Day of the month when sampling occurred *
 Site: Location of the study sites DS - Dongsha Island, Taiwan KT -
 Kenting, Taiwan * Season: Wet season and dry season * Time: Specific time
 interval during which the sample was collected. * Temperature: Temperature
 measured in degrees Celsius (°C) * Salinity: Salinity is measured in PSU
 (Practical Salinity Units) * pH at 25: pH measured spectrophotometrically
 at 25 (°C) * pCO2(µatm): Partial pressure of Carbon Dioxide (units of
 microatmospheres, µatm) * DIC(µmol kg-1) Dissolved Inorganic Carbon
 (micromoles per kilogram, µmol/kg) * TA(µmol kg-1) : Total Alkalinity
 (micromoles per kilogram, µmol/kg) * HCO3-(µmol kg-1): Bicarbonate values
 (micromoles per kilogram, µmol/kg) * CO32-(µmol kg-1): Carbonate values
 (micromoles per kilogram, µmol/kg) * WAr: Aragonite saturation state 4.
 Summary rows for statistics: * Rows 11-13: Mean, SD (Standard Deviation),
 and Uncertainty for DS, dry season * Rows 26-28: Mean, SD (Standard
 Deviation), and Uncertainty for DS, wet season * Rows 52-54: Mean, SD
 (Standard Deviation), and Uncertainty for KT, wet season * Rows 92-94:
 Mean, SD (Standard Deviation), and Uncertainty for KT, dry season **B.
 DATA SPECIFIC INFORMATION FOR: DS-KT Porewater and Sediment.csv** 1.
 Porewater data Number of variables: 10 (Columns A-J) Number of rows  56
 Variable list for Porewater data * Site : Location of the study sites DS -
 Dongsha Island, Taiwan KT - Kenting, Taiwan * Season : Wet season and dry
 season * Year/Month: Year and month of the sampling period (2021-2022) *
 Depth : Depth of sediment where porewater was sampled (0cm - 20cm) * pH :
 acidity of the porewater * DIC(µmol kg-1) : Dissolved Inorganic Carbon
 (micromoles per kilogram, µmol/kg) * TA(µmol kg-1) : Total alkalinity
 (micromoles per kilogram, µmol/kg) * pCO2(µatm) : Partial pressure of
 carbon dioxide in porewater (units of microatmospheres, µatm) * WAr :
 Aragonite saturation state (WAr) * Ca2+ : Calcium ion concentration in
 porewater (millimolar, mM) Summary rows for statistics: * Rows 12-14:
 Mean, SD (Standard Deviation), and Uncertainty for DS, dry season * Rows
 26-28: Mean, SD (Standard Deviation), and Uncertainty for DS, wet season *
 Rows 40-42: Mean, SD (Standard Deviation), and Uncertainty for KT, wet
 season * Rows 54-56: Mean, SD (Standard Deviation), and Uncertainty for
 KT, dry season 2\. Sediment data Number of variables: 7 (Columns M-S)
 Number of rows: 8 for DS, 7 for KT Variable List for Sediment Data * Site
 : Location of the study sites DS - Dongsha Island, Taiwan KT - Kenting,
 Taiwan * Season : one season sampling only for each site. DS sediment was
 sampled in dry season KT sediment was sampled in wet season * Year/Month:
 Year and month of the sampling period DS: January 2021 KT: March 2023 *
 Depth (cm) : Depth of sediment where porewater was sampled (in
 centimeters, 0cm - 20cm) * TOC(wt %) : Total organic carbon (percentage of
 dry weight) * TIC(wt %) : Total inorganic carbon (percentage of dry
 weight) * TN(wt %) : Total nitrogen (percentage of dry weight **C. DATA
 SPECIFIC INFORMATION FOR: DS-KT Benthic flux_CDR.csv** 1. Original benthic
 fluxes * Number of variables: 9 (Columns A-I) * Number of rows  18 (Rows
 1-19) * Variable list * Year: Year of the sampling period (2021-2022) *
 Month : the month of the sampling period 1: January 5: May 9: September
 10: October * Date: Day of the month when sampling occurred * Site:
 Location of the study sites DS: Dongsha Island, Taiwan KT: Kenting, Taiwan
 * Season: Dry and wet season * Period  Benthic flux measurement during
 daytime and nighttime * Replication: Number of collections during daytime
 and nighttime * TA flux (mmol m-2 h-1): Total Alkalinity flux (millimoles
 per meter square per hour, mmol m-2 h-1) * DIC flux (mmol m-2 h-1):
 Dissolved Inorganic Carbon flux (millimoles per meter square per hour,
 mmol m-2 h-1) 2. Daytime- and nighttime fluxes * Number of variables: 9
 (Columns A-J) * Number of rows: 9 (Rows 21-30) * Variable list * Year of
 the sampling period (2021-2022) * Month: Month of the sampling period 1:
 January 5: May 9: September 10: October * Site: Location of the study
 sites DS: Dongsha Island, Taiwan KT: Kenting, Taiwan * Season: Dry and wet
 season * Peri : Bethic flux measurement during daytime and nighttime * TA
 flux (mmol m-2 h-1): Total Alkalinity flux on an hourly basis (millimoles
 per meter square per hour, mmol m-2 h-1) * TA_SD: Total Alkalinity
 Standard Deviation values * DIC flux (mmol m-2 h-1): Dissolved inorganic
 carbon flux on an hourly basis (millimoles per meter square per hour, mmol
 m-2 h-1) * DIC_SD  Dissolved Inorganic Carbon Standard Deviation values
 Daily fluxes * Number of variables : 8 (Columns A-B, D-E, G-J) * Number of
 rows : 5 * Variable list * Year : Year of the sampling period (2021-2022)
 * Month : Month of the sampling period 1: January 5: May 9: September *
 Site : Location of the study sites DS: Dongsha Island, Taiwan KT: Kenting,
 Taiwan * Season : Dry and wet season * TA flux (mmol m-2 d-1): Total
 Alkalinity flux on a daily basis between dry and wet season (millimoles
 per meter square per day, mmol m-2 d-1) * TA_SD : Total Alkalinity
 Standard Deviation values * DIC flux (mmol m-2 d-1): Dissolved Inorganic
 Carbon flux on a daily basis between dry and wet season (millimoles per
 meter square per day, mmol m-2 d-1) * DIC_SD : Dissolved inorganic carbon
 Standard Deviation values Annual Fluxes * Number of variables : 6 (Columns
 A, D, G-J) * Number of rows : 3 * Variable list * Year : Year of the
 sampling period (2021-2022) * Site : Location of the study sites * DS:
 Dongsha Island, Taiwan * KT: Kenting, Taiwan * TA flux (mmol m-2 d-1):
 calculated TA flux on an annual basis (millimoles per meter square per
 day, mmol m-2 d-1) * TA_SD : Total Alkalinity Standard Deviation values *
 DIC flux (mmol m-2 d-1): calculated DIC flux on an annual basis
 (millimoles per meter square per day, mmol m-2 d-1) * DIC_SD : Dissolved
 inorganic carbon Standard Deviation values Annual CDR * Number of
 variables : 3 (Columns D, G-H) * Number of rows : 3 * Site : Location of
 the study sites DS: Dongsha Island, Taiwan; KT: Kenting, Taiwan * CDR
 (tCO2eq ha-1 y-1): Calculated Carbon Dioxide Removal tons of carbon
 dioxide per hectare (ha) per year (y)