Dataset on Environmental Parameters and Greenhouse Gases in Port and Harbor Seawaters of Jeju Island, Korea

Abstract

This dataset presents environmental observations collected in August 2021 from 18 port and harbor sites located around Jeju Island, Korea. It includes physical, biogeochemical, and greenhouse gas (GHG) variables measured in surface seawater, such as temperature, salinity, dissolved oxygen, nutrients, chlorophyll-a, pH, total alkalinity, and dissolved inorganic carbon. Concentrations and air–sea fluxes of nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) were also quantified. All measurements were conducted following standardized analytical protocols, and certified reference materials and duplicate analyses were used to ensure data accuracy. Consequently, the dataset revealed that elevated nutrient accumulation in port and harbor waters and GHG concentrations tended to be higher at sites with stronger land-based influence. During August 2021, most sites functioned as sources of N₂O, CH₄, and CO₂ to the atmosphere. This integrated dataset offers valuable insights into the influence of anthropogenic and hydrological factors on coastal GHG dynamics and provides a foundation for future studies across diverse semi-enclosed marine systems.

Dataset: https://zenodo.org/records/15625306

Dataset License: CC-BY

1. Summary

While greenhouse gases such as CH₄ and CO₂ have been increasingly utilized in industrial applications [1,2], their controlled use has emerged as a critical issue in terms of environmental sustainability. In addition, greenhouse gases are naturally emitted from coastal waters through biogeochemical processes that are often intensified by anthropogenic nutrient inputs. Despite the importance of quantifying natural GHG fluxes for climate change assessments, coastal port and harbor systems have often been overlooked, even though they are highly susceptible to anthropogenic pressures and restricted hydrodynamics. These conditions, particularly during the summer season, with stratified water columns caused by surface warming and freshwater inputs, can promote GHG enrichment in surface waters, potentially increasing air–sea GHG fluxes [3]. While a few studies have reported elevated N₂O and CH₄ fluxes from stagnant port and harbor environments [4,5], no prior dataset has comprehensively quantified GHG concentrations and fluxes in these environments. This effort was driven by the need to quantitatively characterize not only GHG variability but also the physical and biogeochemical properties of semi-enclosed coastal systems. This is also the first high-resolution dataset systematically documenting GHG distributions in port and harbor seawaters. By enabling comparisons across regional and global coastal systems, the dataset serves as a valuable resource for future studies. A related research article based on this dataset has been published [6], supporting ongoing efforts to examine greenhouse gas budgets across diverse coastal environments.

2. Data Description

2.1. Study Sites

The study area was Jeju Island in the East China Sea, located south of the Korean Peninsula. According to the Korea Fisheries Infrastructure Public Agency (FIPA), many ports and harbors are distributed along its coastline, supporting diverse coastal activities. Port and harbor environments are highly vulnerable to the accumulation of land-based pollutants due to their limited water exchange with offshore waters [6]. To ensure comprehensive spatial coverage, we selected 4 ports and 14 harbors distributed along the entire coastline of Jeju Island (Figure 1A). The selection was based on the diversity of surrounding anthropogenic activities, including logistics operations, aquaculture, and tourism infrastructure. In addition, structural characteristics such as port size and the degree of enclosure were also taken into account. As a result of these factors, each site exhibits distinct environmental conditions, primarily influenced by terrestrial inputs rather than offshore waters. The precise geographical coordinates of each sampling site are shown in Figure 1B.

2.2. Environmental Parameters

This dataset comprises measurements of physical, biogeochemical, and GHG parameters collected in August 2021 from 18 selected port and harbor stations distributed along the coastline of Jeju Island. The data are provided in an Excel file (.xlsx), containing 558 records arranged in 18 rows and 31 columns. Each row corresponds to a seawater sample collected from an individual station. The columns include temporal information (year, month, and day), spatial information (station number and name, latitude, and longitude), and environmental variables categorized into four groups: physical properties, biogeochemical parameters, GHG concentrations, and air–sea GHG fluxes.

Physical parameters such as temperature (T, °C), salinity (S, PSU), and dissolved oxygen concentration (DO, mg L⁻¹) were measured on site using a calibrated YSI ProDSS multi-parameter probe. The biogeochemical parameters consist of dissolved inorganic nutrients, chlorophyll–a (Chl–a) concentrations, and carbonate system variables. Laboratory analyses of dissolved nutrients, including ammonium (NH₄⁺, mg L⁻¹), nitrite (NO₂⁻, mg L⁻¹), nitrate (NO₃⁻, mg L⁻¹), phosphate (PO₄³⁻, mg L⁻¹), and silicate (SiO₂, mg L⁻¹), were carried out using a QuAAtro39 autoanalyzer. Chl–a concentrations (μg L⁻¹) were measured using a Trilogy Fluorometer, with duplicate measurements conducted to ensure analytical reproducibility. The carbonate system variables include pH on the total scale at 25 °C (pH_T^25°C), total alkalinity (TA, μmol kg⁻¹), pH_T at in situ temperature (pH_T in situ), and dissolved inorganic carbon (DIC, μmol L⁻¹). Among these, pH_T and TA were directly measured using an Agilent 8453 spectrophotometer and Apollo AS-ALK2 titrator, respectively. Using the CO2SYS MATLAB tool (Version 3), pH_T in situ and DIC were calculated. The GHG parameters include the concentrations of nitrous oxide (N₂O, nmol L⁻¹), methane (CH₄, nmol L⁻¹), as well as the partial pressure of carbon dioxide (pCO₂, μatm). N₂O and CH₄ were analyzed using a CRDS (Picarro G2308), also with duplicate measurements. Although the partial pressure of CO₂ (pCO₂, μatm) is derived from the carbonate system and calculated using the CO2SYS program, it is classified as a GHG parameter in this dataset due to its role in quantifying air–sea CO₂ fluxes. pCO₂ at 25 °C (pCO₂ 25 °C), calculated based on measurements at 25 °C, provides a standardized reference value for cross-sample comparison, while pCO₂ at in situ temperature (pCO₂ in situ) was used for estimating air–sea CO₂ fluxes, as it reflects the actual thermodynamic conditions. Air–sea fluxes of GHG were estimated as the average of four gas transfer velocity models.

3. Methods

3.1. Sampling and Measurements of Physical Parameters

In August 2021, surface water T, S, and DO were measured at each site using a pre-calibrated portable multi-parameter water quality meter (YSI ProDSS; YSI Inc., Yellow Springs, OH, USA). Measurements were conducted at approximately 1 m depth after allowing the probe to stabilize for about 10 min to ensure accurate readings. Calibration was carried out in accordance with the manufacturer’s guidelines prior to field survey. The measurement accuracies were ±0.2 °C for T, ±0.1 psu for S, and ±0.1 mg L⁻¹ for DO.

Discrete surface water samples (~1 m depth) were collected for subsequent laboratory analysis of nutrients, Chl–a, pH_T, TA, and dissolved N₂O and CH₄ concentrations. For Chl–a and dissolved N₂O, CH₄ concentrations, duplicate sampling was conducted. For nutrient measurements, samples were filtered through a 0.2 μm syringe filter and then stored in 15 mL tubes at −20 °C before laboratory analysis. For Chl–a concentration analysis, 1–2 L of surface seawater was filtered through 47 mm Whatman GF/F filters, and the filters were frozen at −80 °C until analysis. Samples for pH_T, TA, and dissolved N₂O and CH₄ concentrations were collected in 125 mL acid-rinsed bottles, and 100 μL of saturated HgCl₂ solution was added to prevent biological activity. Bottles were sealed using rubber stoppers and aluminum caps and maintained at room temperature until laboratory analysis [7,8]. All discrete samples were transported to the laboratory and analyzed as soon as possible.

3.2. Laboratory Analysis of Biogeochemical Variables

Inorganic nutrient concentrations including NH₄⁺, NO₂⁻, NO₃⁻, PO₄³⁻, and SiO₂ were quantified using a QuAAtro39 autoanalyzer (Seal Analytical, Germany). Analytical precision was maintained below 1% by following standard operating procedures.

Chl–a concentrations were determined fluorometrically using a Trilogy Fluorometer (Model # 7200-002, Turner Designs, Sunnyvale, CA, USA), with an estimated measurement uncertainty of ±0.05 μg L⁻¹ [9]. Filters were first extracted in 90% acetone at 4 °C for 24 h and then sonicated for 10 min to ensure uniform pigment extraction from the filter. After sonication, the samples were centrifuged at 4000 rpm for 20 min, and the supernatant was used for fluorescence measurement.

Spectrophotometric pH_T measurements were carried out using unpurified meta cresol purple (mCP) dye. Prior to the measurements, all seawater samples were maintained at 25 °C using a thermostatic water bath. Seawater from glass bottles was transferred to a 10 cm long–path length spectrophotometric cell (5061–3392, Agilent Technologies, Waldbronn, Germany) via a peristaltic pump. After adding 80 μM of unpurified mCP dye, it equilibrated into acid (HI⁻) and base (I₂⁻) species depending on the proton concentration. The absorbance was recorded at 434 nm and 578 nm (the acidic and basic peaks of mCP) and 730 nm for dye impurity correction, using a UV–Vis spectrophotometer (Agilent 8453, Agilent Technologies, Waldbronn, Germany). The absorbance values obtained at these three wavelengths were then substituted into the published equation at a fixed temperature of 25 °C and each sample’s salinity [10]. The resulting pH_T^25°C measurements had an analytical precision of ±0.004 pH units [10].

TA was analyzed by open-cell potentiometric titration at 25 °C using an automated Apollo titrator (AS-ALK2, Newark, NJ, USA). A titrant solution of 0.7 mol L⁻¹ HCl solution, which was prepared in NaCl solution, was used to maintain ionic strength. When seawater reached the equivalence point, TA was calculated using the Gran function. The equivalence point was determined using a pH meter (Orion Star A211, Thermo Fisher Scientific, Waltham, MA, USA) calibrated with standard buffer solutions (pH 4, 7, and 10) prior to the measurements. The concentration of the HCl solution used to prepare the titrant was determined using certified reference materials (CRMs) from A. Dickson’s laboratory (Scripps Institution of Oceanography, San Diego, CA, USA), with a relative standard deviation (RSD) of less than 0.08%. In addition, the CRM was repeatedly measured before seawater sample measurements to maintain an uncertainty of ±2 μmol kg⁻¹.

pH_T in situ, pCO₂, and DIC were derived by inputting measured pH_T^25°C and TA values into the CO2SYS program in MATLAB [11]. The calculations involved in situ temperature, salinity, PO₄³⁻, and SiO₂ concentrations. Carbonic acid dissociation constants (K₁ and K₂) derived by the authors of [12] as refitted by the authors of [13]. KSO₄ dissociation was accounted for using constants from the study of [14].

Cavity ring-down spectrometer (CRDS; Model G2308, Picarro Inc., Santa Clara, CA, USA) was used to measure dissolved N₂O and CH₄ concentrations in seawater samples following the headspace equilibration technique. In total, 40 mL of seawater from the glass bottles was transferred into 100 mL gas-tight syringe, and then 40 mL of high-purity zero gas was injected. This subsample was equilibrated for 8 min using a shaker (ASA–026–12, Asia Testing Machine Co., Gwangju, Republic of Korea). Before and during measurements, the CRDS was calibrated using certified reference materials from the Korea Research Institute of Standards and Science (KRISS). Equilibrated headspace gas concentration (ppb) of the syringe, which was injected into the CRDS, was converted into nmol L⁻¹ units based on the calculation described in Equation (1):

$$N_2{O\&{CH}_4}_{conc.}=\left(\beta ·x·P·V_w+{\displaystyle \frac{x·P}{R·T_K}}·V_{hs}\right)∕V_w,$$

(1)

In this equation, N₂O_conc. and CH_4conc. refer to the dissolved N₂O and CH₄ concentration of seawater sample (nmol L⁻¹); β is the Bunsen solubility coefficient (nmol L⁻¹ atm⁻¹), which was determined based on the room temperature and the salinity of each seawater sample. Solubility was calculated using the formulations by the study of [15] for N₂O and by [16] for CH₄; x represents the N₂O and CH₄ dry mole fraction (ppb) in the headspace; P is the atmospheric pressure (1 atm); V_w is the volume of the seawater sample (40 mL); V_hs is the volume of the headspace phase (40 mL); R is the gas constant (0.082057 L atm K⁻¹ mol⁻¹); and T_K represents the equilibration temperature in Kelvin (K), which was maintained at constant room temperature [8].

3.3. Greenhouse Gas Flux Estimation

The air–sea fluxes of GHGs were estimated based on the concentration gradient across the air–sea interface. A positive air–sea flux represents emission from the ocean to the atmosphere, whereas a negative flux indicates uptake from the atmosphere into the ocean. N₂O and CH₄ fluxes were calculated based on the difference between the measured surface water concentration and the air-equilibrated concentrations, using the following Equation (2):

$$\left.{N_{2}O\&{CH}_4}_{flux}=k_w·\left({\left[Gas\right]}_{measured}^{surface}-{\left[Gas\right]}_{eq}\right.\right),$$

(2)

where ${\left[Gas\right]}_{measured}^{surface}$ represents the measured concentrations of N₂O and CH₄ (nmol L⁻¹) in surface water, ${\left[Gas\right]}_{eq}$ represents the air-equilibrated concentration of N₂O and CH₄, estimated based on in situ temperature and salinity of each seawater sample using empirical solubility equations [15,16]. Atmospheric concentrations of N₂O and CH₄ were obtained from meteorological stations operated by the Korea Meteorological Administration (KMA) on Jeju Island. In August 2021, the monthly average atmospheric concentrations recorded at the Gosan station were 336.37 ppb (N₂O) and 1909.09 ppb (CH₄).

For CO₂, air–sea fluxes were derived using the difference in partial pressure between seawater and the atmosphere as follows in Equation (3):

$${{CO}_2}_{flux}=k_w·K_0·\left({pCO}_{2w}-{pCO}_{2a}\right),$$

(3)

K₀ is the solubility coefficient of CO₂ (mol L⁻¹ atm⁻¹), calculated based on the study of [17]. pCO_2w represents the partial pressure of CO₂ (μatm) in surface seawater, which was estimated from measured pH_T and TA at in situ temperature using the CO2SYS program. This corresponds to the pCO₂ in situ values reported in the Data Description section. Atmospheric CO₂ concentrations in August 2021, obtained from the KMA, were 414.75 ppm. These values were converted into atmospheric partial pressure (pCO_2a, μatm) using barometric pressure and water vapor pressure, estimated from the in situ temperature and salinity [18].

k_w is the gas transfer velocity (cm s⁻¹), which was parameterized as a function of wind speed and the Schmidt number. Although region-specific models are generally recommended, due to the lack of previous studies investigating GHG fluxes in Jeju Island, we adopted the average k_w values from four commonly used models [19,20,21,22]. Wind speed is a key factor influencing air–sea fluxes, as it affects the stability of the air–sea interface. Given the considerable spatial variability in wind conditions across Jeju Island, we applied three different wind speeds observed at three KMA meteorological stations (Jeju, Seogwipo, and Gosan). We used the logarithmic wind speed method to convert them to wind speeds at a 10 m height (U₁₀) [23]. U₁₀ values of 2.40 m s⁻¹ (Jeju), 1.56 m s⁻¹ (Seogwipo), and 4.05 m s⁻¹ (Gosan) were applied to stations 1–5 and 18, 6–11, and 12–17, respectively. Further details on the wind speeds used for flux calculations can be found in the related publication [6].

This dataset, generated from a relatively understudied environment, provides an integrated assessment of three GHG concentrations and air–sea fluxes in semi-enclosed port and harbor waters. By characterizing the environmental conditions of such anthropogenically influenced systems, this dataset may serve as a valuable reference for future comparative studies and modeling efforts in similar coastal settings.