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Article

Strategic Reduction Method for Energy Input and CO2 Emissions: Direct Supply of Underground Seawater for Land-Based Aquaculture Systems in South Korea

by
Seungyeop Baek
1,
Byungchil Jeon
2,
Sebong Oh
3,
Wontak Choi
4,
Seunggi Choi
4 and
Yonmo Sung
5,*
1
Institute of Marine Industry, Gyeongsang National University, Tongyeong-si 53064, Gyeongsangnam-do, Republic of Korea
2
Groundwater and Geological Technology Office, Korea Rural Community Corporation, Naju-si 58327, Jeollanam-do, Republic of Korea
3
Groundwater and Geology Department, Gyeongnam Regional Headquarter, Korea Rural Community Corporation, Tongyeong-si 53064, Gyeongsangnam-do, Republic of Korea
4
Graduate Program, Department of Energy and Mechanical Engineering, Gyeongsang National University, Tongyeong-si 53064, Gyeongsangnam-do, Republic of Korea
5
Department of Smart Energy and Mechanical Engineering, Gyeongsang National University, Tongyeong-si 53064, Gyeongdangnam-do, Republic of Korea
*
Author to whom correspondence should be addressed.
Energies 2025, 18(1), 177; https://doi.org/10.3390/en18010177
Submission received: 18 November 2024 / Revised: 24 December 2024 / Accepted: 31 December 2024 / Published: 3 January 2025
(This article belongs to the Special Issue Advances in Reduction Technologies of Gas Emissions (CO2, NOx, and SO2) in Combustion-Related Applications: 4th Edition)
Browse Figures
Figure 1
<p>Nationally determined contribution targets and annual greenhouse gas emissions trends of the EU, USA, and Republic of Korea [<a href="#B4-energies-18-00177" class="html-bibr">4</a>].</p> "> Figure 2
<p>Surface area of land-based fish cultivation in the Republic of Korea in 2021: (<b>a</b>) by region, (<b>b</b>) by fish species, and (<b>c</b>) monthly average surface water temperature in 2021. Note: the red line indicates the optimum rearing temperature for olive flounder.</p> "> Figure 3
<p>Current status of underground seawater boreholes in the Republic of Korea: (<b>a</b>) regional pumpage and (<b>b</b>) distribution of underground seawater boreholes by pumpage. Note: a full droplet refers to a pumpage of 10,000 m<sup>3</sup>/day.</p> "> Figure 4
<p>Annual and monthly required input energy comparison for olive flounder cultivation using surface water and underground seawater by region in the Republic of Korea.</p> "> Figure 5
<p>Monthly required input energy difference between surface water and underground seawater for olive flounder cultivation by region in the Republic of Korea.</p> "> Figure 6
<p>(<b>a</b>) Annual required input energy for heating or cooling seawater using surface water or underground seawater and (<b>b</b>) the estimation of CO<sub>2</sub> emissions.</p> "> Figure 7
<p>Classification of underground seawater utilization based on salinity levels and daily pumpage rate.</p> "> Figure 8
<p>Schematic diagram of land-based aquaculture systems utilizing underground seawater. (<b>a</b>) A traditional system with surface seawater heating; (<b>b</b>) an enhanced system with a heat pump and heat recovery for energy savings and reduced emissions.</p> ">
Versions Notes

Abstract

:
This study addresses the challenges of and opportunities for achieving the ambitious greenhouse gas emissions reduction target of the fishery sector of the Republic of Korea, set at 96% by 2030. We also focus on the current status of land-based aquaculture and underground seawater resource development, quantitatively compare energy inputs for land-based fish cultivation, and evaluate the potential of underground seawater to reduce CO2 emissions. Since 2010, 762 underground seawater boreholes have been developed, yielding a cumulative daily pumpage of 125,780 m3. Jeollanam-do was found to have the highest daily pumpage, with an annual energy requirement of 131,205,613 Mcal. Despite the fact that the energy demands for underground seawater are higher in some months, it provides a 22.6% reduction in total annual energy consumption compared to surface water. The use of underground seawater for heating or cooling resulted in a 24.1% reduction in the required input energy. However, energy requirements increase due to the relatively high surface water temperature in some regions and seasons. This study also highlights the utilization of underground seawater in heating or cooling surface water via indirect applications using geothermal heat pumps. This innovative research broadens the methods of greenhouse gas mitigation, particularly in the agriculture, livestock, and fisheries industries.

1. Introduction

Human-induced global greenhouse gas (GHG) emissions have increased since the industrial revolution. Despite a 3.7% decrease in global GHG emissions in 2020 from 2019, driven by the COVID-19 pandemic, it rebounded to a record-breaking 53.85 Gt CO2eq [1,2]. This implies that global GHG emissions are increasing. However, the Intergovernmental Panel on Climate Change 6th assessment report states that global GHG emissions should decrease by more than 45% by 2030 from 2010 levels to limit the increase in global average temperature within 1.5 °C, and carbon neutrality should be achieved by 2050 [3]. In response, countries have agreed to submit their nationally determined contribution (NDC) to the UN Framework Convention on Climate Change every five years to intensify efforts to curb GHG emissions. The data on GHG emissions from 1990 to 2018 and the declared NDC by country are shown in Figure 1. Almost all countries determined their 2030 NDC based on the reference year and did not provide any reason for it. Similarly, the Republic of Korea declared its 2030 NDC, considering the annual GHG emissions in 2018 as reference. The peak GHG emissions of EU, USA, and the Republic of Korea were 5648.0 MtCO2eq in 1990, 7416.5 MtCO2eq in 2007, and 727.6 MtCO2eq in 2018, respectively. The declared 2030 NDCs of the EU, USA, and Republic of Korea are 2541.6, 3622, and 436.6 MtCO2eq [4], with reductions of 55%, 51%, and 40%, respectively, compared to the peak GHG emissions of each country. To achieve the 2030 NDC of each country, the required annual reduction rates are 1.38%, 2.22%, and 3.33% for the EU, USA, and Republic of Korea, respectively. It is plausible that the relatively slower onset of economic growth in the Republic of Korea compared to the EU and the USA has contributed to its challenging annual reduction rate in GHG emissions.
As shown in Table 1, the Republic of Korea set its 2030 NDC goal based on the purpose of the Framework Act on Carbon Neutrality and Green Growth, international trends, etc. The sector that emits the largest amount of GHG is energy transformation, with 269.6 MtCO2eq, which is supposed to decrease to 44.4% based on 2018 emissions. Although the energy sector is a major source of GHG emissions, setting an ambitious reduction rate for this sector is supported by the development of diverse GHG-reduction technologies across various fields and approaches. For example, GHG emissions can be reduced by introducing renewable energy [5,6,7,8,9], fuel cells [10,11,12], hydrogen energy [13,14,15,16], nuclear power generation [17,18,19], and oil field extraction [20,21,22]. Ammonia combustion technology [23,24,25,26,27] has been extensively investigated for power generation because of its pivotal role in enabling carbon-free fuel combustion. In the cases of agriculture, livestock, and fisheries, the 2030 NDC was set at 27.1%, making it the second lowest sector after industry. Introducing innovative ideas or technologies capable of reducing GHG emissions across subsectors is essential. According to the 2050 carbon neutrality roadmap for the marine and fisheries sector by the Ministry of Oceans and Fisheries [28], the GHG emission of the sector was 4.06 MtCO2eq in 2018. With regard to the subsectors of fisheries and fishing villages, GHG emissions were set to 115,000 tCO2eq in 2050 from 3.042 MtCO2eq in 2018, i.e., a 96% reduction rate. This means that the GHG emissions from fisheries and fishing villages aim to achieve a net-zero carbon level, resulting in carbon neutrality. To accomplish this goal, diverse means of reduction should be introduced and utilized in these subsectors. We believe that underground seawater plays a role in reducing GHG emissions in fisheries and fishing villages.
Underground seawater, also known as subterranean seawater or subsurface seawater, refers to seawater that infiltrated the ground, typically in the pore spaces of sediments and rocks or within geological formations. This seawater can be located in various depths, from shallow subtidal zones to deeper isolated aquifers. It is a natural resource that has been used for various purposes, such as drinking water, agriculture, and industrial water. Underground seawater from a mixture of infiltrated seawater and freshwater percolating from land through aquifers tends to have lower salinity, but is characterized by high concentrations of minerals and nutrients. It also has high water quality and great sustainability, which can be continuously supplied for a long water retention time. Moreover, underground seawater is less affected by seasonal changes because it is less influenced by external environmental factors. Typically, underground seawater maintains a temperature range of 14–18 °C, making it an ideal resource for various applications. The Korea Rural Community Corporation (KRCC) has been developing 762 underground seawater boreholes since 2010. Leveraging these characteristics of underground seawater and developing underground seawater boreholes in land-based aquaculture can contribute to reducing GHG emissions in fisheries and fishing villages.
MacLeod [29] surveyed the world aquaculture production and calculated the global GHG emissions for 2017 by region. The global production of nine major aquaculture groups (bivalves, catfish, cyprinids, freshwater fish, Indian major carps, marine fish, salmonids, shrimps/pawns, and tilapias) was 74,855,000 tons of live weight. The total production of East Asia, which includes the Republic of Korea, was 57,633,000 tons of live weight, accounting for approximately 77% of the total global production. Out of the total global GHG emissions of 245.357 MtCO2eq, East Asia accounted for 193.319 MtCO2eq, representing approximately 79% of the total. Currently, in the Republic of Korea, there is an obvious trend of decreasing direct GHG emissions, largely due to reductions in fishing activities and improvements in fishing vessel technology. The government has supported this trend by encouraging fishermen to replace old fishery equipment with more energy-efficient options, such as electric or hybrid green fishing boats. In contrast, indirect GHG emissions are associated with electricity use in land-based aquaculture, which has increased since 1990 owing to higher fossil fuel prices for heating or cooling seawater, and the strengthening of environmental regulations. Therefore, to reduce GHG emissions in fisheries and fishing villages, it is essential to focus on reducing energy consumption in land-based aquaculture, particularly for cultivating major fish species.
Globally, countries are expected to reduce their GHG emissions to meet their 2030 NDC, and ultimately achieve carbon neutrality by 2050. However, meeting 2030 NDC targets is challenging, particularly for countries such as the Republic of Korea, which have experienced rapid economic growth in recent decades. In other words, late-industrialized countries are expected to face greater difficulties in reducing GHG emissions compared with previously industrialized countries, owing to the higher annual reduction rates required. Although the reduction rate of the agriculture, livestock, and fisheries sector is set to 27.1% in the 2030 NDC of the Republic of Korea, that of the fisheries and fishing village subsectors is set to 96%. Hence, to implement a reduction plan, it is crucial to introduce innovative and forward-looking methods across various industries. In this study, we examined the recent status of land-based aquaculture and the development of underground seawater resources and compared the input energy quantitatively for land-based fish cultivation in the Republic of Korea. Furthermore, we estimated the contribution of underground seawater to CO2 emissions in land-based aquaculture, with an emphasis on heating and cooling seawater.

2. Status of Land-Based Aquaculture and Underground Seawater Boreholes

The utilization of underground seawater is closely associated with energy consumption in land-based aquaculture in terms of CO2 emissions. Thus, it is essential to consider the cultivation conditions of major fish species when calculating the energy required for heating and cooling seawater. We used the latest data on the surface area of land-based fish cultivation in 2021 as the boreholes have been developed since 2010–2021. Figure 2a shows the surface area of land-based fish cultivation in the Republic of Korea. The areas marked in blue and gray indicate regions where fish are produced and not produced by land-based aquaculture, respectively. According to data from the Korean Statistical Information Service [30], the total surface area for land-based fish cultivation was 2,323,827 m2 in 2021 (Figure 2a). Jeju Island had the largest surface area for land-based fish cultivation (1,294,405 m2), followed by Jeollanam-do (812,025 m2). Figure 2c indicates that the monthly average surface water temperatures in Jeju Island during winter (typically from November to February) were higher compared to that in other regions despite a temperature difference of approximately 6 °C from the optimum rearing temperature for olive flounder. Land-based aquaculture targets fish species. As illustrated in Figure 2b, approximately 86% of the total surface area for land-based fish cultivation is dedicated to olive flounder (Paralichthys olivaceus), while approximately 12% is allocated to starry flounder (Platichthys stellatus). Hence, olive flounder was considered the primary fish species for the quantitative analysis of underground seawater CO2 emissions in this study.
The main fish species in this study was olive flounder; thus, the required input energy can be calculated using Equation (1).
Q = ρ × m ˙ × c p × ∆ T
where Q is the required input power; ρ is the density of seawater, given as 1025 kg/m3; m ˙ is the volume of seawater per day; cp is the specific heat of seawater, given as 0.932 kcal/kg∙°C; and ∆T is the temperature difference between the surface or underground seawater and the optimum rearing temperature of olive flounder. According to the standard manual for olive flounder culture published by the National Fisheries Research and Development Institute, the optimum rearing temperature for olive flounder ranges from 20 to 25 °C [31]. However, the optimum rearing temperature for olive flounder was determined to be 22 °C in this study.
Figure 3 shows the distribution of the underground seawater boreholes developed by the KRCC. The cumulative pumpage from these boreholes was 125,780 m3/day. Based on this pumpage, we calculated and compared the energy consumption associated with surface water and underground seawater. When considering the pumpage per underground seawater borehole, Jeollabuk-do exhibited the highest pumpage at 246 m3/day, whereas that of Chungcheongnam-do showed the lowest at 125.5 m3/day. Figure 3b depicts the distribution of pumpage across all underground seawater boreholes. Approximately 40% of underground seawater boreholes exhibited a pumpage of ~50 m3/day, while approximately 57% fall within the pumpage range of 51–1000 m3/day. Thus, the arithmetic mean pumpage of the underground seawater boreholes is 165.1 m3/day.
Table 2 presents a detailed overview of the conditions of the underground seawater boreholes and the properties of underground seawater. According to Equation (1), the primary considerations for underground seawater boreholes include not only the pumpage but also the temperature, which is crucial for estimating the required input energy. The temperature difference between the underground seawater and optimum rearing temperature for olive flounder is a key consideration. The arithmetic mean temperature of 762 underground seawater boreholes is 16.8 °C, with a standard deviation of 1.07 °C. This indicates that the temperature difference between the regions is relatively low compared to the difference in pumpage. As mentioned in the Introduction, underground seawater temperature is less susceptible to seasonal fluctuations. Consequently, in this study, the average temperature for each region was treated as a constant throughout the year. The monthly average surface water temperature for each region, as shown in Figure 2c, was used for the calculations in Equation (1).

3. Results and Discussion

3.1. Monthly Energy Requirements for Olive Flounder Cultivation by Region

Typically, land-based aquaculture systems extract surface water using water pumps from locations up to a kilometer from the shore, and utilize this water directly to cultivate olive flounder. In this study, we examined the direct use of underground seawater for olive flounder cultivation and compared the required input energy and carbon dioxide emissions from surface water and underground seawater. To facilitate this comparison, the input energies required for surface water and underground seawater were calculated using Equation (1). The temperature data for the surface water is provided in Figure 2c, and the data for the underground seawater is detailed in Table 2. Figure 4 illustrates the required annual absolute input energy for olive flounder cultivation using surface water and underground seawater, with cultivation maintained at an optimum rearing temperature of 22 °C. The required input energy for underground seawater is shown for only one month because a constant temperature is maintained throughout the year. Jeollanam-do consistently requires the highest input energy each month, except in August, with an annual requirement of 131,205,613 megacalories (Mcal). This elevated energy demand is primarily attributed to two factors. First, Jeollanam-do has the highest pumpage rate at 54,308 m3/day, which translates to greater energy consumption for heating or cooling seawater. Second, the relatively low average surface water temperature in the winter season increases the temperature differential between the surface water and optimum rearing temperature for olive flounder, thereby necessitating more energy than in other regions. In contrast, Gangwon-do had the lowest annual input energy requirement at 12,134,656 Mcal, which was 9.2% of that required by Jeollanam-do. Despite similar surface water temperatures between Gangwon-do and Jeollanam-do from spring to autumn, and the surface water temperature being approximately 5 °C higher in Gangwon-do during winter, the significant difference in the required input energy is primarily due to the lower pumpage in Gangwon-do. The daily pumpage in Gangwon-do was 6396 m3, representing 11.8% of the pumpage in Jeollanam-do, resulting in the lowest energy demand for heating or cooling surface water.
Figure 5 illustrates the monthly input energy required for olive flounder cultivation by comparing the surface water and underground seawater requirements. The difference in the required input energy from May to November was lower than that from December to April. In addition, the analysis revealed that the difference in the required input energy showed negative values from June to October, and in some regions into November, because of temperature variations. Surface water temperatures were closer to the optimum rearing temperature for olive flounder than the underground seawater temperatures. Consequently, energy demands are higher during specific months when underground seawater is used for heating or cooling seawater in olive flounder cultivation. Despite this seasonal disadvantage, the total annual required energy input for underground seawater across all regions was estimated to be 212,730,209 Mcal, while that for surface water was estimated at 274,779,302 Mcal. This indicates that utilizing underground seawater for heating or cooling can reduce the annual energy requirements by approximately 22.6% compared to surface water use throughout the year in the Republic of Korea.

3.2. Regional Required Input Energy and Estimation of CO2 Emission

In previous decades, land-based aquaculture facilities predominantly used boilers/electric heaters or chillers for heating or cooling seawater, respectively. Economic analyses of land-based aquaculture often emphasize fuel or energy costs [32,33,34]. According to the literature [35], the component contribution for salmon grows out and smolts (fuel and electricity) at the producer gate. The retailer shows the highest percentage of the estimated carbon footprint at approximately 47%, with a scenario applied to a land-based closed containment water recirculating aquaculture system in the US running on a typical electricity mix. However, in recent years, there has been a notable shift towards the use of heat pumps, which offer substantial benefits, including significant reductions in energy costs compared to fossil-fuel-based systems [36,37,38]. This study excludes the use of fossil-fuel-based boilers/electric heaters or chillers for heating or cooling seawater, focusing exclusively on heat pumps for CO2 emission estimation. Equation (2) was used to estimate the CO2 emissions (tCO2/year) from heat pumps.
E m i s s i o n s C O 2 e q = E ( G c a l ) ÷ C O P × 1.16 ( M W h / G c a l ) × 0.4747 ( t C O 2 / M W h )
where E represents the total required input energy over a year and COP denotes the coefficient of performance. COP is a measure of the efficiency of a heating or cooling system and is used in thermodynamics. Specifically, this is the ratio of useful output energy to the input energy required to produce that output. The COP varies with the heat pump operating mode, i.e., heating or cooling. A higher COP indicates a more efficient system. For instance, a COP of 4 can be interpreted as follows: for every 1 unit of work input, the system produces 4 units of heat or cooling. In this study, the COP values for heating and cooling were 6 and 4, respectively [39]. The carbon emission coefficient for electrical energy use was 0.4747.
Figure 6a illustrates the required input energy for the surface water and underground seawater used for heating or cooling annually, considering the seasonal surface water temperatures and COP. The total required input energy for surface water is 54,209 MWh, while for underground seawater is 41,128 MWh, which corresponds to a 24.1% reduction. Notably, the use of underground seawater had a significant impact in Chungcheongnam-do and Jeollanam-do, with both regions showing a reduction rate of approximately 31%. This result is attributed to the temperature differential between the surface water and underground seawater, particularly during winter, and the available daily pumpage. However, a negative effect was observed in Gangwon-do, where the required input energy increased by approximately 16% when switching from surface water to underground seawater. This can be explained by the lower underground seawater temperature compared to that in other regions, while the surface water temperature in winter was relatively higher. The temperature difference between the average annual surface water temperature and underground seawater in Gangwon-do is the smallest, with average annual temperatures of 16.5 °C and 15.6 °C, respectively. This results in an increased input energy when seawater is used for olive flounder cultivation in Gangwon-do. Overall, the use of underground seawater generally resulted in lower input energy requirements compared with surface water across most regions. These observations are consistent with the CO2 emissions estimates presented in Figure 6b, which show a similar trend.
Jeollanam-do accounts for nearly half of the total CO2 emissions among the regions without seawater sources. The total CO2 emissions for surface water amounted to 25,733 tCO2eq compared with the 19,523 tCO2eq for underground seawater, representing a 24.1% reduction. Jeollanam-do is estimated to emit 12,249 tCO2eq for surface water and 8399 tCO2eq for underground seawater, ranking it the highest among the regions in terms of emissions without considering the seawater source. In contrast, the region with the lowest emissions varied depending on the seawater source. For instance, Gangwon-do and Gyeongsangbuk-do showed a 38% difference in the available daily pumpage, with Gyeongsangbuk-do having a higher pumpage rate (10,223 m3/day) compared with Gangwon-do (6396 m3/day). Thus, the total CO2 emissions in Gyeongsangbuk-do are expected to be higher than that in Gangwon-do although the average surface water temperature is approximately 0.9 °C, which is 5.5% higher in Gyeongsangbuk-do. The total CO2 emissions of Gyeongsangbuk-do exceeded those of Gangwon-do by 416 tCO2eq. However, this trend was reversed when underground seawater was used. This is primarily because of the higher underground seawater temperature in Gyeongsangbuk-do. As indicated in Table 2, the temperature of underground seawater in Gyeongsangbuk-do is 18.6 °C, which is approximately 19% more than that in Gangwon-do. This resulted in lower CO2 emissions in Gyeongsangbuk-do despite the higher daily pumpage.

3.3. Further Exploration of Utilization of Underground Seawater

In the context of land-based aquaculture, the utilization of underground seawater is significantly influenced by daily pumpage rates and salinity levels. For underground seawater to be effectively used in land-based aquaculture, it must exhibit not only abundant pumpage rates but also high salinity levels sufficient to sustain fish growth, posing a considerable challenge in ensuring a reliable supply. This difficulty arises because coastal aquifers often contain a mixture of freshwater and seawater [40,41,42]. Consequently, the likelihood of encountering underground seawater with pure seawater salinity in coastal aquifer zones is relatively low. In aquifers where seawater infiltration occurs, the presence of sufficient salinity in underground seawater is more probable if the aquifer is located in a fractured zone, which facilitates seawater intrusion. Conversely, in fractured zones where freshwater infiltration occurs, the resulting underground water tends to be predominantly freshwater. This environmental dependence hinders the direct use of underground seawater, resulting in slow technological growth and spread of underground seawater utilization strategies for GHG mitigation. Although certain conditions may not always align with the requirements of land-based aquaculture, underground seawater can be used through multiple approaches, including direct use in fish cultivation. In this study, a comprehensive assessment of underground seawater utilization was conducted by classifying it according to daily pumpage rates and salinity levels. By exploring these classifications, we aim to provide insights into optimizing the use of underground seawater for diverse applications in aquaculture systems.
According to the literature [43], the utilization of underground seawater can be classified based on salinity levels and daily pumpage rates, as shown in Figure 7. A survey conducted with fishermen establishes the criteria for optimal salinity and daily pumpage as 20% and 100 m3, respectively. As illustrated in Figure 7, underground seawater utilization can be classified into direct and indirect applications. The PS type represents conditions characterized by high salinity and sufficient daily pumpage rate. This type is advantageous for reducing energy costs associated with heating or cooling seawater and enables year-round fish growth, regardless of seasonal variations. Similarly, the Ps1 type involves an adequate daily pumpage rate but an intermediate salinity level. For this type, blending surface water with underground seawater is recommended to meet the requirements for direct use. In contrast, Ps2 and ps types are more appropriate for indirect applications because their salinity and daily pumpage rates do not meet the conditions necessary for optimal fish cultivation.
Figure 8 illustrates the practical applications of these types. The Ps2 and Ps types can be employed for energy savings using ground seawater and geothermal heat pumps, respectively. Specifically, land-based aquaculture systems generally follow the approach depicted in Figure 8a. Seawater should be supplied to the rearing tanks within the optimum rearing temperature range for fish cultivation. If the temperature of the supplied seawater exceeds or is below the optimum rearing temperature, fish production decreases drastically. For this reason, in the case of olive flounder, surface water (6–9 °C) typically is heated (13–25 °C) by a boiler before being supplied, as depicted in Figure 8a. Once the heated surface water is supplied to the fish-rearing tanks, its temperature decreases by a certain amount because the heated surface water is directly exposed to the surroundings. Then, the cooled surface water was discharged near the coast through a filter tank. In this system, low-temperature surface water is extracted and supplied to aquaculture tanks via boilers, which typically use fossil fuels for heating. This process results in GHG emissions and increases energy costs. To mitigate GHG emissions and recover waste heat, a heat pump system with heat recovery was introduced, as shown in Figure 8b. This system efficiently heats surface water using heat pumps that leverage the underground seawater temperature and supply it to the aquaculture tanks. Wastewater is then discharged through heat recovery equipment, reducing energy costs by approximately 70–80%, particularly during winter. In summary, this direct and indirect method broadens the role of underground seawater, regardless of its daily pumpage, temperature, and salinity, and provides insight for other countries that struggle to mitigate GHG emissions and reduce energy consumption in agriculture, livestock, and fisheries. It is recommended that the greater the development of underground seawater boreholes, the greater their contribution to GHG reduction.

4. Conclusions

The authors evaluated the current status of GHG emissions and analyzed the challenges in meeting the 2030 NDC targets. The fisheries and fishing village sector in the Republic of Korea has an ambitious reduction target of 96% by 2030, compared with the overall agriculture, livestock, and fisheries sector reduction target of 27.1%. Achieving these goals requires innovative and forward-looking strategies. In this study, we focused on the current status of land-based aquaculture and underground seawater resource development, quantitatively compared energy inputs for land-based fish cultivation in the Republic of Korea, and evaluated the potential of underground seawater to reduce CO2 emissions, particularly in the context of heating and cooling. The main conclusions of this study are as follows:
  • The daily pumpage from underground seawater boreholes totals 125,780 m3. Regional differences in pumpage were also reflected in the average pumpage per borehole, which ranges from 246 m3/day to 125.5 m3/day. Approximately 40% of the underground seawater boreholes have a pumpage of approximately 50 m3/day, and 57% have a pumpage between 51 and 1000 m3/day, resulting in an arithmetic mean pumpage of 165.1 m3/day. The average temperature of the underground seawater is 16.8 °C with a standard deviation of 1.07 °C, indicating minimal regional variation in temperature compared to the differences in pumpage.
  • Jeollanam-do exhibited the highest annual energy demand at 131,205,613 Mcal, driven by its substantial daily pumpage rate of 54,308 m3 and the pronounced temperature differential between the colder surface water in winter and the desired rearing temperature. Despite having a similar surface water temperature profile to that of Jeollanam-do from spring to autumn and a marginally higher winter temperature, the lower daily pumpage of 6396 m3 in Gangwon-do significantly reduced its energy needs for heating or cooling.
  • The energy required for surface water is closer to the optimum rearing temperature during warmer months, resulting in reduced energy requirements compared to underground seawater. Although underground seawater requires more energy in some months owing to temperature differences, it offers a substantial reduction in the total annual energy consumption, indicating a potential annual energy savings of approximately 22.6% when utilizing underground seawater for heating or cooling in olive flounder aquaculture across the Republic of Korea.
  • The total required input energy for surface water was 54,209 MWh, while that for underground seawater was 41,128 MWh, reflecting a 24.1% reduction. Although Gyeongsangbuk-do had a higher pumpage rate, its CO2 emissions exceeded those of Gangwon-do by 416 tCO2eq when using surface water. However, this trend reverses with underground seawater owing to the higher underground seawater temperature in Gyeongsangbuk-do (18.6 °C) compared with Gangwon-do (15.6 °C), resulting in lower CO2 emissions despite the higher pumpage rate.
  • Direct application of underground seawater is feasible with high salinity and high pumpage types (PS), which support year-round fish growth and reduce energy costs for temperature regulation. Intermediate salinity types (Ps1) with adequate pumpage require blending with surface water to meet aquaculture requirements. Conversely, types with insufficient salinity or pumpage (Ps2 and Ps) are better suited for indirect uses, such as energy savings.

Author Contributions

Investigation, W.C.; data curation, S.C.; writing—original draft, S.B.; writing—review and editing, Y.S.; supervision, B.J.; project administration, S.O. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Research Resurgence under the Glocal University 30 Project at Gyeongsang National University in 2024.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

Authors Byungchil Jeon and Sebong Oh were employed by Korea Rural Community Corporation, KRC. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Energies 18 00177 g001
Figure 1. Nationally determined contribution targets and annual greenhouse gas emissions trends of the EU, USA, and Republic of Korea [4].
Figure 1. Nationally determined contribution targets and annual greenhouse gas emissions trends of the EU, USA, and Republic of Korea [4].
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Figure 2. Surface area of land-based fish cultivation in the Republic of Korea in 2021: (a) by region, (b) by fish species, and (c) monthly average surface water temperature in 2021. Note: the red line indicates the optimum rearing temperature for olive flounder.
Figure 2. Surface area of land-based fish cultivation in the Republic of Korea in 2021: (a) by region, (b) by fish species, and (c) monthly average surface water temperature in 2021. Note: the red line indicates the optimum rearing temperature for olive flounder.
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Figure 3. Current status of underground seawater boreholes in the Republic of Korea: (a) regional pumpage and (b) distribution of underground seawater boreholes by pumpage. Note: a full droplet refers to a pumpage of 10,000 m3/day.
Figure 3. Current status of underground seawater boreholes in the Republic of Korea: (a) regional pumpage and (b) distribution of underground seawater boreholes by pumpage. Note: a full droplet refers to a pumpage of 10,000 m3/day.
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Figure 4. Annual and monthly required input energy comparison for olive flounder cultivation using surface water and underground seawater by region in the Republic of Korea.
Figure 4. Annual and monthly required input energy comparison for olive flounder cultivation using surface water and underground seawater by region in the Republic of Korea.
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Figure 5. Monthly required input energy difference between surface water and underground seawater for olive flounder cultivation by region in the Republic of Korea.
Figure 5. Monthly required input energy difference between surface water and underground seawater for olive flounder cultivation by region in the Republic of Korea.
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Figure 6. (a) Annual required input energy for heating or cooling seawater using surface water or underground seawater and (b) the estimation of CO2 emissions.
Figure 6. (a) Annual required input energy for heating or cooling seawater using surface water or underground seawater and (b) the estimation of CO2 emissions.
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Figure 7. Classification of underground seawater utilization based on salinity levels and daily pumpage rate.
Figure 7. Classification of underground seawater utilization based on salinity levels and daily pumpage rate.
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Figure 8. Schematic diagram of land-based aquaculture systems utilizing underground seawater. (a) A traditional system with surface seawater heating; (b) an enhanced system with a heat pump and heat recovery for energy savings and reduced emissions.
Figure 8. Schematic diagram of land-based aquaculture systems utilizing underground seawater. (a) A traditional system with surface seawater heating; (b) an enhanced system with a heat pump and heat recovery for energy savings and reduced emissions.
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Table 1. Greenhouse gas emissions by sector in the Republic of Korea for 2018 and their 2030 nationally determined contribution target.
Table 1. Greenhouse gas emissions by sector in the Republic of Korea for 2018 and their 2030 nationally determined contribution target.
TypeSectorGHG Emissions in 2018 [Unit: MtCO2eq]2030 NDC [Reduction from 2018]
EmissionsEnergy transformation269.6149.9 [44.4%]
Industries260.5222.6 [14.5%]
Buildings52.135 [32.8%]
Transportation98.161 [37.8%]
Agriculture, livestock, and fisheries24.718 [27.1%]
Waste17.19.1 [46.8%]
Hydrogen(-)7.6
Others (omissions, etc.)5.63.9
Absorption and removalCarbon sinks−41.3−26.7
CCUS(-)−10.3
Oversea reduction(-)−33.5
Emission amount727.6436.6 [40%]
Table 2. Characteristics of ground seawater by region.
Table 2. Characteristics of ground seawater by region.
RegionDepth (m)Pumpage (m3/day)Temperature (°C)Salinity (‰)pH
Gyeonggi-do129224.615.35.97.3
Gangwon-do122.9177.715.611.96.8
Chungcheongnam-do146.1125.516.410.17.5
Jeollabuk-do123.624616.620.17.1
Jeollanam-do139.5146.817.18.37.3
Gyeongsangbuk-do168.3200.518.67.27.2
Gyeongsangnam-do146.5174.817.79.37.5
Arithmetic mean value139.4185.116.810.47.2
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Baek, S.; Jeon, B.; Oh, S.; Choi, W.; Choi, S.; Sung, Y. Strategic Reduction Method for Energy Input and CO2 Emissions: Direct Supply of Underground Seawater for Land-Based Aquaculture Systems in South Korea. Energies 2025, 18, 177. https://doi.org/10.3390/en18010177

AMA Style

Baek S, Jeon B, Oh S, Choi W, Choi S, Sung Y. Strategic Reduction Method for Energy Input and CO2 Emissions: Direct Supply of Underground Seawater for Land-Based Aquaculture Systems in South Korea. Energies. 2025; 18(1):177. https://doi.org/10.3390/en18010177

Chicago/Turabian Style

Baek, Seungyeop, Byungchil Jeon, Sebong Oh, Wontak Choi, Seunggi Choi, and Yonmo Sung. 2025. "Strategic Reduction Method for Energy Input and CO2 Emissions: Direct Supply of Underground Seawater for Land-Based Aquaculture Systems in South Korea" Energies 18, no. 1: 177. https://doi.org/10.3390/en18010177

APA Style

Baek, S., Jeon, B., Oh, S., Choi, W., Choi, S., & Sung, Y. (2025). Strategic Reduction Method for Energy Input and CO2 Emissions: Direct Supply of Underground Seawater for Land-Based Aquaculture Systems in South Korea. Energies, 18(1), 177. https://doi.org/10.3390/en18010177

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