Land use changes in the Min River basin and their impact on carbon storage

1 Introduction

The interplay between land use, people, and nature is crucial in tackling global sustainability issues. Human activities have extensively modified the Earth’s land surface, resulting in notable changes to carbon sources, biodiversity, and food security (Winkler et al., 2021). Approximately 75 % of the Earth’s terrestrial area has undergone human-induced modifications in the last century (Luyssaert et al., 2014). Alterations in the land use are a vital quantitative measure for assessing ecological environmental impacts. The alterations in the land use around aquatic systems/rivers are very observable due to the high frequency of human activity (Ghute et al., 2023). Human activities such as agriculture, urbanization, and construction of dams may lead to changes in land use within river basins. These changes have the potential to impact water resources, water quality, sediment loads, and ecosystem services. Implementing sustainable land management methods is essential for mitigating these consequences and safeguarding the well-being of river basin ecosystems (Chakraborty, 2021). Reducing carbon emissions and increasing carbon sinks have become essential components of economic development in China since the country committed to the “dual carbon” goals. Land use is one of the most crucial aspects of interaction between humans and nature, and it represents a significant carbon reservoir. The transition between various land use types affects terrestrial carbon cycling, thereby impacting human well-being (Chang et al., 2022; Li et al., 2020, 2022).

China has enacted several key regulations regarding land use change during the 1990s to combat land degradation and facilitate urbanization, resulting in notable effects. The land use change policy of the country consisted of converting agriculture to forests and grasslands was introduced in 1999 (Wang et al., 2018). Although the implementation of policy helped to expand the extent of forest, concerns regarding its cost-effectiveness and ability to target the greatest environmental objectives still exist. Land use change policies in the country have sought to achieve a harmonious equilibrium between environmental conservation and economic development, transitioning from a top-down regulatory approach to market-driven strategies. Nevertheless, there are still obstacles to enhancing the effectiveness and precision of these regulations to attain sustainable land use (Liu et al., 2014).

The transition among different land use classes could offer immediate economic advantages. The direct economic advantages of land use change might include improved economic expansion, increased investments, employment generation, and prospective cash gains (Harewan et al., 2023; Zhang et al., 2023). Nevertheless, possible trade-offs and consequences for food security, environmental sustainability, and local people must be considered when engaging in land use changes for economic reasons. The changes in the land use trigger significant changes or imbalance in ecosystem services, leading to alterations or degradation in areas such as water resources, air quality, disaster prevention, and biodiversity. This process influences the development of ecosystem service functions, thereby impacting human well-being (Dosdogru et al., 2020; Liu et al., 2021). Land use changes may have complex trade-offs and implications for food security, environmental sustainability, and the local population (Shi et al., 2021; Zhao et al., 2023). This highlights the need of careful planning, using sustainable approaches, and involving appropriate stakeholders to minimize negative consequences and promote sustainability (Padilha et al., 2024; Van Schmidt et al., 2023).

The Min River, with a length of around 577 km, is the biggest river in Fujian Province that flows into the sea. The basin area of this region comprises about 50 % of the whole area of Fujian Province (Lu, 2004). It satisfies 40 % of the province's overall water demand for commercial purposes and ensures the safety of drinking water for ∼ 33 % of the inhabitants. The river is often referred to as the 'Mother River' by the inhabitants of Fujian. To effectively regulate and safeguard the Min River basin (MRB), it is crucial to uphold the principle that mountains, rivers, forests, farmlands, lakes, grasslands, and sands constitute a community of life. The practical application of this principle can be seen via many forms of land use. Consequently, analyzing the transition between various land use classes within the MRB has immense importance in enhancing the ecological environment quality and transforming the Min River into a secure, thriving, ecologically balanced, aesthetically pleasing, and harmonic river of satisfaction. However, there is still relatively limited research on alterations in the land use in MRB, especially for the three periods of 2000, 2010, and 2020. This study determined the changes in land use categories in the MRB and their impact on the carbon storage. The major objective was to infer the land use changes from 2000 to 2020 in MRB and determine their impacts on carbon storage. It was hypothesized that the land use changes exerted negative impact on caron storage from 2000 to 2020. The results would help to understand the carbon storage changes and underlying reasons.

2 Materials and methods

2.1

2.1 Study area

The Min River is located in Fujian Province and regarded as the longest river in the region. It stretches from longitude 116°23′ to 119°35′ and latitude 25°23′ to 28°16′. The basin has an approximate size of 6.1 × 104 km² (Fig. 1). The topography of the basin mostly consists of mountains and characterized by a subtropical monsoon climate. The topography exhibits a gradient from the northwest to the southeast. The basin encompasses four cities in Fujian Province, i.e., Nanping, Ningde, Sanming, and Fuzhou, constituting ∼ 50 % of Fujian’s total land area. It functions as a crucial ecological buffer zone for the Fujian province. The Jianxi River, Futun River, and Shaxi River are the three main tributaries that flow into the upper parts of the basin. The Gutian River, Anren River, and Youxi River are the three principal tributaries in the middle reaches. There is a lot of vegetation in the upper and middle portions of the basin, mostly in the form of evergreen coniferous and broad-leaved forests. The Dazhang River, Qibu River, and Taojiang River are the three principal tributaries in the downstream region. The urban region of Fuzhou City is mostly dominated by the lower reaches. It divides into the Wulong River and the Minjiang River on Nantai Island. Human activity has a significant influence on land usage in this region.

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Fig. 1

Topographic map of Min River basin.

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3 Results

3.1

3.1 Spatial distribution of land use

Spatial distribution of land use in MRB from 2000 to 2020 is illustrated in Fig. 1. The main land use categories in the basin were forest land (FL), grassland (GL), and arable land (AL) (Fig. 2). The area is mostly covered by FL, which is in line with the overall condition of Fujian Province, known for its abundant mountains and huge forest cover. The basin has scattered AL and GL. Although their total size seems decreasing, they constitute a significant component of the land in the basin. The water areas are scattered throughout the basin and consistently increased with time. The area designated for construction witnessed the highest increase (704.93 km²) compared to the rest of the land use classes. The increase in the construction area (CA) was near the estuary of MRB, with dispersed increases in other parts. A significant decline (23.63 km²) was noted in unused land (UL) over this time, particularly from 2000 to 2010. Nevertheless, the decrease in UL from 2010 to 2020 was less evident.

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Fig. 2

Spatial distribution of land use in Min River Basin during 2000 (a), 2010 (b), and 2020 (c).

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3.4

3.4 Spatiotemporal variation in carbon storage

The highest carbon storage regions were concentrated in the southwestern mountainous and hilly areas of the MRB. These areas are covered by forests with high vegetation coverage. Medium carbon storage areas were mainly located in suburban areas of cities, as well as in mountainous/hilly regions and near water sources, land use types are cropland and grassland. Low carbon storage areas were distributed along both sides of the river and in urban areas, especially near the downstream estuary where extensive areas are classified as low carbon storage zones. Overall, decreasing trend was noted in carbon storage from 2000 to 2020. Carbon storage was 113.61 × 10⁷ tons during 2000, which slightly decreased to 113.31 × 10⁷ tons by 2010, representing a decrease of 0.3 × 10⁷ tons compared to 2000. Carbon storage further decreased to 113.05 × 10⁷ during 2020, reflecting a reduction of 0.26 × 10⁷ tons compared to 2010 and 0.56 × 10⁷ tons compared to 2000. The rate of decrease in carbon storage from 2010 to 2020 has slowed down compared to 2000 to 2010 (Fig. 3).

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Fig. 3

Carbon storage in Min River Basin during 2000 (a), 2010 (b), and 2020 (c).

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4 Discussion

Significant changes were recorded in the land use within the MRB from 2000 to 2020. The most noteworthy shift was in CL, which had a substantial increase of 704.93 km². The changes in AL, GL, and FL followed this trend. Overall, two land use classes witnessed an increase, whereas the rest of the four observed a decrease in total area during 2000 to 2020. The CL and WA were increased, whereas AL, FL, GL, and UL noted a decline during this period. Similarly, a substantial decline in AL, GL, and UL was noted between 2000 and 2010, whereas CL observed large increase. The decreasing trend of AL and GL was slowed down between 2010 and 2020; however, the decrease in unused land remained significant. Nevertheless, construction land witnessed is a large growth. The amount of AL, FL, GL, and UL in the MRB decreased between 2000 and 2020. However, the trend of decrease has been slowed down. This is associated with the government’s current efforts to protect the environment, which include advocating for programs like reforesting agricultural land and restoring meadows (Quan et al., 2023; Zhou et al., 2008; Zhu et al., 2016). There has been a notable expansion in both WA and CL. The conversion of AL and FL into WA is of particular significance, and it is directly linked with to the development of water conservation infrastructure, such as hydroelectric power plants in the basin, as well as the influence of agricultural water diversion and irrigation (Sun et al., 2023; Xiao et al., 2023; Zhen et al., 2023). A significant rise was noted in CL. A notable area (196.79 km²) of AL was transitioned to CL. Similarly, 152.8879 km² FL was turned into CL. These findings indicate that a substantial amount of forest and agricultural lands were converted into urban development during the study period.

The variations in land use types in the MRB displayed notable regional and geographical variability in temporal and spatial change features. A significant portion of UL was developed, with a considerable portion being transformed into a WA between 2000 and 2010. This is closely linked to the extensive water infrastructure development that occurred during this period, including the construction of hydroelectric plants, which significantly increased the size of water bodies (Sun et al., 2023; Xiao et al., 2023; Zhen et al., 2023). Furthermore, a substantial reduction in FL was recorded during 2010 and 2020. Most of the FL was converted into AL during this period. Geographically, there was a substantial expansion of CL in the lower part of the river, particularly in the areas around Fuzhou between 2000 and 2020. This aligns with the economic progress of Fuzhou during the respective period (Lin and Liu, 2022; Wu et al., 2008). Overall, there was a notable increase in the amount of land used for construction in the flat regions on both sides of the river. This aligns with the approach of promoting economic growth in waterfront areas. The alterations in FL and AL are mostly focused on the central and upper sections of MRB. The alterations exhibit a notable but somewhat dispersed nature, displaying a clear irregular pattern marked by small-scale fragmentation and large-scale concentration, which generally aligns with regions of high population density.

The alterations in land use types were mostly derived by a combination of natural and socio-economic factors between 2000 and 2020. The variations in land use types throughout this period were little influenced by natural factors, and they displayed a consistent regional stability (Ming et al., 2022; Niu et al., 2022; Wu et al., 2023). There were minor changes in land use types in high-altitude areas and forest land remained the dominating land type. The changes in land use during this period were primarily driven by social and economic forces, particularly in response to fast regional economic expansion. Population increases, increasing urbanization, and the emergence of port economies had a substantial influence on alterations in land use. This is clearly seen by the significant growth in the amount of land allocated for building between 2000 and 2020.

Urban development, rural construction, and the cultivation of new farmland in the MRB have been the leading factors contributing to the overall decline in carbon storage across the region from 2000 to 2020. Carbon storage has shown a decreasing trend year by year in Fujian Province, dropping from 113.61 × 10⁷ tons to 113.05 × 10⁷ tons, a decrease of 0.56 × 10⁷ tons. Forests and grasslands are the primary carbon reservoirs in Fujian Province, with forests alone accounting for 85.0 % of the total area. The major reason for the decline in carbon storage in the basin is the extensive conversion of forests and farmland into urban development areas.

Spatially, the distribution of carbon storage in the basin exhibits distinctive characteristics. Over the past 20 years, the lower reaches of the Min River in Fuzhou have been both a region with low carbon storage thresholds and the area experiencing the greatest loss of carbon storage. In contrast, the middle and upper reaches of the river, mainly in cities like Sanming and Nanping, represent high carbon storage threshold areas, although changes in carbon storage in these regions have been relatively minor. In summary, the dominant factors contributing to the decline in carbon storage in Fujian Province from 2000 to 2020 have been urban development, rural construction, and the cultivation of new farmland.

5 Conclusions

The MRB experienced notable shifts in land use between 2000 and 2020. Although there was minor decrease, forest land was the dominant land use category in the basin. Arable land and grassland recorded a significant decrease, and the lost area was converted to construction land or forest land. Construction land had the greatest growth, mostly in the areas next to the estuary and metropolitan regions. An expansion was recorded in water areas, accompanied by a reduction in the amount of unused land, particularly from 2000 to 2010. The decrease in arable land and grassland significantly decreased carbon storage. Although carbon storage had a general decrease, the rate of loss decreased between 2010 and 2020, which aligns with the stability seen in land use changes. Therefore, it is recommended that the conversion of land to construction areas should be monitored carefully to further decline the loss of carbon storage in the basin.

CRediT authorship contribution statement

Wenjia Jiang: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Gui Chen: Writing – review & editing, Visualization, Validation, Resources, Investigation, Formal analysis, Conceptualization. Ayesha Idrees: Writing – review & editing, Software, Formal analysis, Data curation, Conceptualization. Jingling Bao: Writing – review & editing, Visualization, Software, Methodology, Investigation, Data curation. Yuying Fu: Writing – review & editing, Visualization, Software, Investigation, Data curation, Conceptualization. Jingyan Chen: Writing – review & editing, Visualization, Investigation, Formal analysis, Data curation, Conceptualization. Zhimin Lin: Writing – review & editing, Visualization, Software, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Abdel-Rhman Z. Gaafar: Writing – review & editing, Visualization, Funding acquisition, Formal analysis, Conceptualization. Mohamed S Elshikh: Writing – review & editing, Validation, Methodology, Funding acquisition, Formal analysis, Conceptualization.