GroundWaterSpatio-temporal characteristics of land use change in the black soil region 

Summary

As one of the four major black soil regions in the world, the northeast black soil region is distributed with fertile and rare black soil resources, and its protection and utilization have always attracted much attention. Land use/cover change affects the structure, function and health of ecosystems, and is of great significance to the sustainable use of land resources. This paper selects four periods of land use/cover data in 1970, 1995, 2010 and 2020, and uses methods such as land use transition matrix, comprehensive dynamic degree, and spatial change model to analyze the temporal and spatial characteristics of land use change in the black soil region of Northeast China in the past half century. , found that: ①In the past half century, the area of ​​construction land, cultivated land, and grassland in the black soil region of Northeast China has generally increased, while the area of ​​wetland, forest land, and unused land has generally decreased. region; ② the change of each region is dominated by alternating variables, and there is a large number of spatial location shifts; ③ the degree of land use shows a slight increase year by year, but it is still lower than the national level, and the potential for land development and utilization is huge. In the future, we should further study the temporal and spatial characteristics and mechanism of land use change in the black soil region of Northeast China and its impact on the ecological environment, ecological service functions, and carbon balance, so as to optimize the spatial layout of the land and realize "good use and maintenance of black soil".

 

Key words: black soil area; land use; transfer matrix

 

Abstract

As one of four major black soil areas in the world, the black soil area in northeast China boasts fertile and rare black soil resources, and its protection and utilization have always attracted much attention. The changes in land uses/cover affect the structure, function , and health of the ecosystem and thus are greatly significant for the sustainable utilization of land resources. Based on the data on the land uses/cover in 1970, 1995, 2010, and 2020, this study analyzed the spatio-temporal characteristics of the change in the land uses of the black soil area in northeast China over the past half century using the methods, such as transfer matrix, comprehensive dynamic degree, and spatial change model. The results are as follows. ①The areas of construction land, cultivated land,and grassland in the black soil area of ​​northeast China generally increased over the past half century, whereas the areas of wetland, woodland, and unused land generally decreased. The changes in land types mainly occurred in the Sanjiang Plain, the northwestern Songnen Plain, and the Xiliaohe Plain. ②The change in each land type was dominated by the alternating quantity, with a large amount of spatial position shift occurring. ③The degree of land utilization slightly increased yearly but is still lower than the national level, suggesting considerable land development potential for and utilization. Therefore, further studies should focus on the spatio-temporal characteristics and mechanisms of the change in the land uses of the black soil area in northeast China, as well as their impacts on the habitats, ecological service functions,and balance of carbon budget, to fully utilize and protect the black soil area and optimize the national spatial layout.

 

Keywords: black soil area; land use; transfer matrix

0 Preface

As one of the most fertile soils in the world [ 1 ] , black soil is known as the "king of soil". The natural black soil is under suitable climate, hydrology and vegetation coverage conditions, with loose sediments such as loess-like clay, diluvial deposits, alluvial deposits, glacial moraines and aeolian deposits as soil-forming parent materials. After a long period of development, a soil type with unique natural attributes has been formed. The topsoil layer has a large amount of black or dark black humus and high organic matter content. It is a precious and scarce land resource with good properties, strong fertility, and suitable for farming [ 2-3 ] . In the past, farmers could only distinguish fertile black soil based on the color of the soil, soil fertility, and whether the thickness was more than one plow [ 4 ] . , rich in organic matter, suitable bulk density, good aggregate structure, high base saturation and suitable pH value, etc. [ 3 ] . At present, the total area of ​​the global black soil area accounts for about 7% of the earth's land surface, and is mainly distributed in the four major black soil areas in the world: Russia-Ukraine Great Plains, Mississippi River Basin in North America, Northeast China Plain, and Pampas Grassland in South America[ 5 ] ] . The Chinese government has always paid close attention to the protection and utilization of black land. In 2020, when General Secretary Xi Jinping inspected the Northeast, he instructed that "the black land, the 'giant panda in cultivated land', should be well protected and utilized, so that it will benefit the people forever" [ 6 ] .

 

Land use includes the use of land and its socio-economic attributes [ 7 ] . With the rapid development of the global economy, the explosive growth of population, and the increasingly severe pressure on ecological resources, due to the comprehensive influence of natural conditions and human activities, the use pattern of more than 30% of the world's land is undergoing drastic changes [ 8 ] . Land use/cover change can easily lead to changes in soil microorganisms and soil carbon storage [ 9⇓ - 11 ] , thereby changing the structure and function of the ecosystem [ 12-13 ] , and affecting the health of the ecological environment and the value of ecological services [ 14 ] . According to research, 1/3 of the carbon dioxide emitted by global human activities is caused by land use/cover change, second only to the burning of fossil fuels [ 15 ] . Land use/cover change is the most significant manifestation of human activities on the Earth's surface system and one of the most closely related links between man and nature [ 16-17 ] . It is also a key topic in the field of contemporary global change research [ 18 ].

 

1 Overview of the study area

According to the "Black Soil White Paper" released by the Chinese Academy of Sciences in 2021, the black soil region in Northeast China includes Heilongjiang Province, Jilin Province, northeast Liaoning Province and the "Eastern Four League" region of Inner Mongolia. It borders Russia to the east, North Korea to the southeast, and Mongolia to the west. , reaching the Liaohe River in the south, including 246 counties (cities, banners), with an area of ​​1.09 million km 2 , accounting for 12% of the total black soil area in the world [ 5 ] . The Northeast Black Soil Region is located in the eastern part of the Asian continent at mid-latitudes, and has a temperate monsoon climate with four distinct seasons, with rain and heat in the same season [ 19 ] . The black soil in Northeast China is a soil type formed under the interaction of its unique climatic conditions and vegetation with gravel and loess-like clay as the main parent materials [ 4 , 20 ] . The vegetation that grows vigorously in summer dies in autumn and winter, and the low temperature inhibits the microbial activity in the soil, causing the plant residues to decompose slowly. Over time, a thick humus layer accumulates on the surface of the soil, and eventually develops into fertile black soil [ 3 , 19 ] .

 

The Northeast black soil region is one of the most arable regions in the world, and it is also the largest commercial grain production base in China [ 2 ] , the output of corn and soybean accounts for 38.2% and 45.8% of the country [ 21 ] , and the total grain output accounts for a quarter of the country. The amount of grain exported accounts for one-third of the country's total [ 22 ] , and the per capita grain possession is more than twice that of the country's per capita amount [ 23 ] . ] . According to the "National Main Functional Area Planning" issued by the State Council in 2010, the Northeast Black Soil Area covers the Greater and Lesser Khingan Mountains Forest Ecological Functional Area, the Sanjiang Plain Wetland Ecological Functional Area, the Changbai Mountain Forest Ecological Functional Area, the Hulun Buir Grassland Meadow Ecological Functional Area and part of Horqin Grassland ecological functional area [ 26 ] ; As an important old industrial base in China, the Northeast Black Soil Region is an important production base of energy, timber and metallurgy in China. It has experienced the process of economic development, decline and revitalization for decades [ 13 ] .

 

2 Data sources

The land use/cover data required for this study were obtained from the Data Center for Resources and Environment Science of the Chinese Academy of Sciences (http://www.resdc.cn), respectively select land use/land cover data at a scale of 1:100,000 in the 1970s (according to 1970 statistics), the mid-1990s (according to 1995 statistics), 2010, and 2020. The reconstruction of data in the 1970s mainly used Landsat-MSS remote sensing images, the remote sensing interpretation of data in the mid-1990s and 2010 mainly used Landsat-TM/ETM remote sensing images, and the update of land use/cover data in 2020 mainly used Landsat 8 remote sensing images. According to the "National Land Classification Standard" [ 27 ] , combined with the specific conditions of the study area and the definition of wetlands [ 28 ] , the natural resources of 25 land resources in China's 1:100,000 scale land use/land cover remote sensing monitoring database (LUCC) Attributes and Utilization Attributes are divided into six types of land use: cultivated land, forest land, grassland, wetland, construction land, and unused land ( Table 1 ). Here, wetland refers to natural wetland, excluding artificial wetland.

3 Research methods

3.1 Land use transfer matrix

The land use transfer matrix (Markov model) reflects the changes of various land use types at the beginning and end of a certain period of time in a certain region [ 29-30 ] . In Table 2 , P represents the percentage of a certain land type in the regional area, P ii represents the percentage of the unchanged area of ​​the i-th land type in the regional area, P i + represents the percentage of the initial area of ​​the i- th land type in the regional area , P + i represents the percentage of the period-end area of ​​the i-th land type in the regional area, P ij represents the percentage of the area converted from the i-th land type to the j-th land type in the regional area, and the sum of row elements in the table represents a certain The percentage of the area at the beginning of the period to the area of ​​the land type, and the sum of the elements in the column represents the percentage of the area at the end of the period to the area of ​​the area.gentle    

A 1         A 2         …            A j          …            An _      

A 1         P 11       P12 _     …            P 1 j       …            P 1 n      P 1+       P 1+ - P 11

A 2         p 21       p 22       …            P 2 j       …            P 2 n      P 2+       P 2+ - P 22

…           …            …            …            …            …            …            …            …

A i          P i 1       P i 2       …            P ij          …            pin _      P i +       P i + - P ii

…           …            …            …            …            …            …            …            …

An _       P n 1      P n 2      …            P _         …            P nn       P n +      P n + - P n

Ending area        P +1       P +2       …            P + j       …            P + n      1             -

increase the area             P +1 - P 11           P +2 - P 22           …            P + j - P jj             …            P + n - P nn -              -

3.2 Net land change

The net land change reflects the absolute change of a certain land type area in a certain period of time [31-32 ] , because it cannot reflect the transfer of land use types in spatial position, it is easy to underestimate the degree of transformation between land types . The calculation formula of net land change B1 is:

 

B1=m a x(Pi +−Pi _,P+ i−Pi _) −m i n(Pi +−Pi _,P+ i−Pi _) = |Pi +−P+ i|

.

(1)

3.3 Land transfer change

The land exchange change reflects the change in the spatial position of a certain land use type within a certain period of time, and it is added to the net land change to form the total land change [ 31-32 ] . The calculation formula of land exchange change B2 is:

 

B2= 2 ×m i n(Pi +−Pi _,P+ i−Pi _)

.

(2)

3.4 Land use type transfer network

Based on the land use type transition matrix, the index of "land use transfer flow" is introduced to measure the "transfer flow" and "inflow" of each land use type, and the land use type transfer network will be obtained[8], which can intuitively show The mutual conversion between land use types in a period helps to reveal the transfer direction and spatial evolution process of land use types. The calculation formula of land use transfer flow B 3 and net value of land transfer flow B 4 is:

 

B 3 = P out + P in ,

(3)

B 4 = P in - P out ,

(4)

In the formula: P out is the transfer-out flow, and P in is the transfer-in flow. When the value of B4 is positive, it means net inflow, and when its value is negative, it means net outflow .

 

3.5 Area change rate of individual land types

The area change rate of a single land type indicates the ratio of the changed area of ​​a certain land type to the initial area within a certain period of time. Calculating the area change rate of a single land type in each district on the basis of partitions will help reveal the intensity of land use changes in different land types. Spatial distribution features [ 31 ] . The formula for calculating the area change rate B5 of a single land type is:

 

B5= (P+ i−Pi +) /Pi +

.

(5)

3.6 Dynamic degree of a single land use type

The dynamic degree of a single land use type can quantitatively describe the change speed of land use types in the study area within a certain time interval [ 7 , 29 ] . If the result is positive, it is the degree of land use development (LUD), which represents the degree of actual new development of a certain type of land use per unit time (unused land is not applicable), and if the result is negative, it is the degree of land use depletion (LUC), refers to the degree of actual consumption of a certain type of land use per unit time [ 33 ] . The calculation formula is:

 

B6=P+ i−Pi +Pi +x1T× 100 %

(6)

In the formula: B6 is the dynamic degree of a single land use type of the i-th land type; T is the research period, where the unit is year.

 

3.7 Comprehensive dynamic degree of land use

The comprehensive dynamic degree of land use reflects the dynamic degree of the total land activity in the study area [ 31 ] . When the driving force of land use evolution is dominated by human factors, it can reflect the comprehensive impact of human activities on the degree of land use [ 34 ] . The formula for calculating the comprehensive dynamic degree of land use B7 in a certain period of time in the study area is:

 

B7= 1 −∑i = 1Pi _no

.

(7)

3.8 Comprehensive index of land use degree

The comprehensive index of land use degree reflects the comprehensive change of land use intensity in the study area caused by the change of land use type and mode in the study area [ 16 , 29 ] . The calculation formula is:

 

B8= { ∑Ai(Si/ S) }/n×100%

(8)

In the formula: B 8 is the comprehensive index of land use degree in the study area; A i is the grading index of the i- level land use degree; S i is the land use area of ​​the i- level; S is the total land area in the area; n is the total land use area number of categories.

 

3.9 Spatial change model of land use

Based on the common principle of population distribution center of gravity in population geography, by comparing the distribution center of gravity of different land types in the study area at the beginning and end of the period, the spatial change model of land use was finally obtained [ 7,35 ] .

 

X B =∑i = 1no(Ct ixxi)

/∑i = 1no

C ti ,

(9)

Y B =∑i = 1no(Ct ixYi)

/∑i = 1no

C ti .

(10)

In the formula: X B , Y B represent the longitude and latitude coordinates of the center of gravity of a certain land type distribution in year t ; C ti represents the area of ​​the i-th land type in the study area in year t ; X i , Y i represent the research area The latitude and longitude coordinates of the geometric center (or the location of Banner County) of the i-th small area in the district .

 

4 Results and analysis

4.1 Spatial change and area change of land use

4.1.1 Area change

In the past half century, the area of ​​various types of land use in the black soil region of Northeast China has changed to varying degrees and trends ( Fig. 1 ). Among them, the overall area of ​​wetlands has decreased significantly. In 2020, the area of ​​wetlands in the black soil area has decreased by 41.2% compared with that in 1970. Except for the significant increase in the area of ​​wetlands during the period from 1995 to 2010, the area of ​​wetlands in 1970 to 1995 and 2010 to 2020 has continued to decrease; The overall area of ​​cultivated land (including paddy fields and dry fields) increased by 24.88%, except for the impact of the policies of returning farmland to forest, returning farmland to grassland, and returning farmland to wetlands, the delineation of ecological protection red lines, and the rapid expansion of urban construction land in 2010-2020, and the area of ​​cultivated land decreased slightly Except for this period, all other periods showed an increasing trend; the forest area in the black soil area decreased by 6.94% compared with the beginning of the period in the 50 years, and the changes in each period showed a continuous downward trend in the past half century; the grassland area in the black soil area increased by 9.75% in the 50 years. From 2010 to 2010, the area showed a downward trend, and the area of ​​other periods increased on average; the area of ​​construction land in the black soil area increased by 25.69% in 50 years, and each period showed a continuous growth trend; the area of ​​unused land in the black soil area decreased by 7.69% in 50 years. Except for the increase in the area from 1995 to 2010, the area in other periods showed a downward trend.

4.1.2 Spatial variation

From 1970 to 2020, the spatial transfer of land use in the black soil region was mainly concentrated in the northern Sanjiang Plain, the northwestern Songnen Plain, and the West Liaohe Plain ( Figure 2 ). Among them, grassland is mainly transformed into cultivated land and forest land, and the transformation of grassland into cultivated land is mainly distributed in the Sanjiang Plain, the middle and upper reaches of Nenjiang River, the surrounding areas of Hulunbuir City, the south of Songyuan City, and the west of Tongliao City; In the south of the grassland, the south of the Hulunbuir grassland, and the Greater and Lesser Khingan Mountains; cultivated land was mainly transformed into woodland and grassland. Among them, the transformation of cultivated land into forest land was mainly distributed in the northwest of Qiqihar City, the north of Baicheng City, the east of Tongliao City, and the surrounding areas of Yanji City. Grassland is mainly distributed in the northern part of the Hulun Buir Grassland and the West Liaohe Plain; the forest land is mainly converted to cultivated land and grassland, among which, the conversion of forest land to cultivated land is mainly distributed in the southern part of the Greater and Lesser Khingan Mountains, parts of the Sanjiang Plain and parts of the Changbai Mountains, and the conversion of forest land to grassland is mainly distributed In the southwest of Xing'an League and the south of Hulun Buir Grassland; wetlands are mainly converted to cultivated land and grassland, among which, the conversion of wetlands to cultivated land is mainly distributed in the Sanjiang Plain and the surrounding areas of Nenjiang River, and the conversion of wetlands to grasslands is mainly distributed in the Greater and Lesser Khingan Mountains and the Hulun Buir Grassland; construction land It is mainly converted to cultivated land and distributed scatteredly; the unused land is mainly converted to grassland, mainly distributed in the 

4.2 Land use transfer matrix and various changes

4.2.1 Land use transfer matrix

According to the land use transfer matrix ( Table 3 and Table 4 ), in the past half century, the area of ​​cultivated land in the black soil region of Northeast China accounted for 20.3%, the area of ​​cultivated land converted to other land types accounted for 2.58%, and the area of ​​other land types converted to cultivated land accounted for 20.3%. Accounted for 8.26%; the unchanged area of ​​forest land accounted for 38.92%, the area of ​​forest land converted to other land types accounted for 7.08%, and the area of ​​other land types converted to forest land accounted for 3.87%; the area of ​​grassland unchanged accounted for 10.53%, and the area of ​​grassland converted to other land types The total area accounted for 6.17%, and the area converted from other land types to grassland accounted for 7.74%; the area of ​​wetland remained unchanged accounted for 4.33%, the area converted from wetland to other land types accounted for 6.18%, and the area converted from other land types to wetland accounted for 1.85%; The unchanged area of ​​construction land accounted for 1.4%, the conversion of construction land to other land types accounted for 0.36%, and the conversion of other land types to construction land accounted for 0.82%; the unchanged area of ​​unused land accounted for 1.23%, and the conversion of unused land to other types The converted area of ​​land use types accounted for 0.91%, and the converted area of ​​other land types to unused land accounted for 0.75%.