Current Situation, Problems and Prospects of Land Use Research in Lake Basins

Qiuju WU, Zisheng YANG

Institute of Land & Resources and Sustainable Development, Yunnan University of Finance and Economics, Kunming 650221, China

Abstract Land use in lake basins has an important impact on the sustainable development of society, economy and ecology. Based on the literature induction method, this paper systematically summarized the current status of land use research in lake basins from six aspects: temporal and spatial changes, effects, driving factors, optimization research, and the application of remote sensing techniques in lake land use research. Correspondingly, three problems were proposed: lack of refined research on land use changes in lake basins, imperfect theoretical research on lake land use optimization research, and weak land type extraction techniques based on remote sensing images. It is believed that the future research on lake land use should focus on strengthening the refinement of land use change research in lake basins, further improving the theoretical and practical research on land use optimization in lake basins based on a variety of related theories, and further improving the interpretation algorithms of remote sensing images.

Key words Lake, Land use, Current situation, Problem, Prospect

1 Introduction

With a vast territory, China is one of the countries with the most types of lakes in the world[1]. However, since the 1950s, excessive lake reclamation and development activities around lakes have not only significantly reduced the area of lakes and the number of lakes, but also exacerbated the serious damage to ecosystems of lake basins. In lake basin ecosystems, lakes are the "sink" of materials and energy of watersheds, and watersheds are the "source" of materials and energy of lakes[2]. Therefore, ecosystem evolution of lakes is inextricably linked with the changes of natural elements in watersheds. Among them, the change of land use in lake basins is the most important factor affecting the ecological environments of lakes. With the continuous advancement of urbanization and industrialization, human activities in lake basins have increased, and the land cover in basins has gradually changed from natural vegetation to agricultural and urban land dominated by human activities. The use of a large number of chemical fertilizers and pesticides, the discharge of domestic wastewater and industrial sewage ultimately collected in lakes, the sharp reduction in the area of lakes due to changes in land use and cover, deterioration of water quality and aggravation of ecosystem degradation have greatly threatened the sustainable development of the economy and society. In 1995, the International Geosphere-Biosphere Program (IGBP) and the International Human Factors Program for Global Environmental Change (IHDP) jointly launched the scientific research projectLandUse/LandCoverChangeScientificResearchProgram, which aimed to study how human activities change land use cover types and the negative impact of these changes on the environment and human society[3]. Meanwhile, the International Geosphere-Biosphere Program (IGBP) included lake water resources and water environment issues into the key research topics of the global water resources program[4]. Since then, the deterioration of lake ecological environments caused by land use has become a hot issue in the study of global environmental change. Scholars in related fields at home and abroad have carried out a lot of research and produced many results. On the whole, scholars have carried out a series of research work in the aspects of lake basin land use change, lake basin land use optimization,etc., which have laid a certain theoretical foundation for the study of lake land use problems. On the basis of systematically summarizing the research status of land use in lake basins at home and abroad, this paper scientifically analyzed the main problems existing in the existing research, and put forward the research prospect of land use in lake basins accordingly, which is of great significance to further improving the theoretical system of land use research in lake basins and enriching the research content of sustainable development and utilization of water resources.

2 Research status of land use research in lake basins

2.1 Study on temporal and spatial variation of land use in lake basinsThe research on temporal and spatial changes of land use in lake basins is mainly to obtain land use data by collecting remote sensing images for a certain period of time and interpreting them or to directly obtain land use survey data from land management departments, and analyze lake land use changes from the two dimensions of time and space taking lakes and a certain range along their shores as the study area. The research results are often used as the basic data for the study on the relationship between lake environments and land use changes, the optimization of land use structures and spatial layout of watersheds, and the improvement of lake ecological environments.

At present, domestic research on land use changes is mainly concentrated in the scope of provinces, cities, counties and other administrative regions, and there are few researches on land use changes with natural boundaries as the research area. In the research on land use changes in lake basins in China, the research area is mainly in the middle and lower reaches of the Yangtze River. For example, scholars Lietal.[5]analyzed the temporal and spatial evolution laws of land use in Donghu District, Wuhan City from 1987 to 1999 using three-phase Landsat TM satellite remote sensing images at the end of the last century and the topographic map in 1981 and GIS technology. Except for urban land, other land use tends to be fragmented, and the urbanization of watersheds is directional. The results showed that in addition to urban land, other land tends to be fragmented, and the urbanization of watersheds is directional. Duetal.[6]analyzed the land use changes in shallow lake areas and their coasts in Wuhan City using the detailed survey data of urban land use from 1993 to 2004. The results showed that urban expansion has a significant impact on the land use of lakes and their shores in Wuhan, and the lakes and shallow water areas along their shores have been artificially transformed into urban building land, which further increases the possibility of lake environmental degradation. Liuetal.[7]developed a GIS-based integrated land use analysis system (IGAS) in urban fringe lake areas. Taking the Hanyang Lake area in the urban fringe areas of Wuhan City as an example, they studied the implementation of the system, predicted the potential land use changes from 2006 to 2020 under two scenarios, and designed stratified land use structures for protecting aquatic ecosystems. In addition, many scholars have systematically studied the evolution of land use patterns in other urban lakes in China, such as Poyang Lake[8], Dongting Lake[9], Taihu Lake[10], and Hulun Lake[11], and achieved rich results.

There are also studies related to land use cover changes in lake basins abroad. For example, Japanese scholars Matsushitaetal.[12]analyzed the changes in landscape patterns of land use in the Kusumigaura Lake Basin in Japan using landscape principles and GIS technology. The results indicated that the land cover and landscape pattern of the watershed tended to be fragmented. Scholars Mendozaetal.[13]integrated and interpreted the remote sensing image data of land cover in the Cuitzeo Lake Basin in Mexico from 1975 to 2003, found that the process of land use change in this region was not constant, and most land use changes occurred within 10 years. Hollenhorstetal.[14]monitored the land cover changes in the Superior Lake Basin from 1992 to 2001 and found that the land use cover changes in the entire lake basin were very dramatic, especially the reduction of coniferous forest land and the increase of mixed forest land. Wasigeetal.[15]analyzed land use/cover changes in the Kagera Basin in the Lake Victoria Basin, and the results showed that from 1901 to 2010, the area of farmland in the Kagera Basin increased significantly, while the area of grassland and woodland decreased significantly.

2.2 Study on land use effects in lake basinsSince the 1970s, the relationship between land use/cover changes and water environment quality has received extensive attention from scholars at home and abroad[16-18], and it has become one of the hotspots in the field of current resources and environmental sciences[19-21]. Studies have shown that land use changes have a great impact on water quality at scales such as point, river reach, and watershed[22-24]. For example, American scholars Basnyatetal.[19]found that forests and grasslands have a positive impact on the ecological environments of watersheds, but a negative impact on agricultural land and construction land. Scholars Rhodesetal.[25]have studied the impact of land use on water quality in different watersheds in New England through experiments. Japanese scholar Nakane[26]established the correlation between water quality and land use changes through empirical research, and proposed to improve water quality by optimizing land use structures. Although related research started late in China, it has also achieved rich results[27-29]. In recent years, the relationship between land use/cover changes and water quality has been paid more and more attention by Chinese scholars. Xuetal.[30]found that residential construction land is the type of land use that has the most significant impact on water quality. Pengetal.[31]found through research that the greater the degree of land use, the worse the water quality of rivers; and a larger proportion of wetlands, woodlands and grasslands led to less water pollution, and a larger proportion of construction land led to the condition that the river water quality was more likely to be polluted. Guoetal.[32]conducted empirical research by selecting four lakes in Wuhan as the research objects. The results showed that the heterogeneity of land use had a great impact on water quality, and when studying the relationship between land use and water quality, both land use structure and spatial layout should be considered.

2.3 Research on the driving factors of land use changes in lake basinsLand use changes are driven by both natural and human factors[33]. Human factors are the main driving factor for land use changes in most urban lake basins. However, in some lake basins with unique climate, topography and other conditions, natural factors will become the main driving factor of land use changes of lakes. In the research on the driving factors of land use changes in lake basins in China, representative Xiaoetal.[34]analyzed the humanistic driving factors of land use changes in the Taihu Lake Basin from 1998 to 2005 taking the amount of land use type conversion as the dependent variable and selected several humanistic, social and economic indexes as independent variables. The results showed that population increase, industrialization and urbanization and land management policies are the most important driving factors of land use changes in the Taihu Lake Basin. Lietal.[35]analyzed the driving force of land use changes in Fuxian Lake by principal component analysis and multiple regression analysis, and found that socioeconomic factors were the main driving factors of land use changes in the basin. However, in some typical plateau lake areas, a large number of studies have confirmed that lake land use changes are greatly affected by rainfall, temperature,etc.For example, the study of Yanetal.[36]showed that the land use changes in the Bojianghaizi watershed of the Ordos Plateau was driven by both climate and human activities, among which rainfall and temperature were the main climate driving factors, and ecological restoration projects and water conservancy project construction were the main human driving factors. Foreign studies on the driving factors of land use changes are not uncommon. Most of the research results show that lake land use changes are disturbed by both natural and human factors[37-38], and land use changes and climate changes interact and influence each other, and the two are inseparable[39-40]. Land use changes in urban lake basins are most affected by urbanization, and population growth is the most important reason[41]. In general, the research results of most scholars at home and abroad show that climate, population, economy, urbanization and industrialization are the main driving factors of land use changes in lake basins.

2.4 Research on dynamic monitoring of lake areas under the influences of land use changesSince the 1950s, in order to meet the needs of rapid economic development and rapid population growth, China’s lake shorelines and lakeside areas have been over-occupied and developed by people, and the area and number of lakes in China have changed dramatically over the past half century. Systematic and comprehensive analysis of the changes in the number and area of lakes in China and in-depth analysis of the impact mechanism of land use changes on lake changes is an urgent problem to be solved in China’s water environment governance, and it is also the top priority of scholars in the field of lake science. According to statistics, since the founding of the People’s Republic of China, the area of lakes in the middle and lower reaches of the Yangtze River has decreased by 13 000 km2due to reclamation, which is 1.3 times the total area of the five major freshwater lakes[42], and the total area of only Dongting Lake[43]and Poyang Lake has decreased by more than 4 000 km2. In the past 20 years, the satellite remote sensing technology has been widely used in the field of dynamic monitoring of land use and dynamic monitoring of lake area. Ma Ronghuaetal.[44]established a Chinese lake database using a large number of satellite remote sensing images. The research results showed that there were nearly 60 newly-born lakes in the Qinghai-Tibet Plateau, while the area of lakes in the middle and lower reaches of the Yangtze River has shrunk considerably. Scholar Xie[45]used long-term remote sensing image data to systematically study the dynamic change of lake area under the influence of land use changes in the middle and lower reaches of the Yangtze River in China. The results showed that from 1975 to 2015, the area of lakes in the middle and lower reaches of the Yangtze River shrank rapidly, and human activities such as reclaiming land around lakes and building houses around lakes were the main driving factors for the reduction of lake area. Similar studies have been carried out on the Qinghai-Tibet Plateau lake group[46]and the Hanjiang Lake group[47].

2.5 Research on land use optimization in lake basinsUrban lakes are most seriously disturbed by human activities, so the research on land use optimization in lake basins focuses on urban lakes. The idea of optimal allocation of land resources originated from the theory of urban location and its expansion theory[48]. The shrinking of lake area, the change of land use in lake basins, the deterioration of lake ecological environment and urban expansion are inextricably linked. Therefore, while people are concerned about the optimal allocation of urban land use space, they also face the problem of land use optimization of urban lakes. Land use optimization is a prerequisite for achieving certain goals. The early problems of land use optimization aimed at pure economic benefits. Due to the multiple attributes of land resources and the diversity of land structures and functions, current research has gradually changed from single-objective planning to multi-objective planning that takes into account economic, social and ecological benefits, and land use optimization has become a complex multi-objective optimization problem. Land use research in lake basins should take into account the organic combination of urban, agricultural and ecological benefits. For example, Zhaoetal.[49]took the Fuxian Lake Basin as the research area and used the MCR-CLUE-S model of 3S technology to study the land use optimization problem in the Fuxian Lake Basin, and proposed an urban-agricultural-ecological coordinated land use optimization zoning scheme. Zhu[48]introduced a differential evolution algorithm based on a systematic analysis of urban lake land use changes and dynamic changes in the lake area in Wuhan, and proposed a land use optimization scheme that takes into account the economic and ecological benefits of urban development. Fotakisetal.[50]innovated and optimized the cellular automata model, and proposed a multi-objective self-organization algorithm under the dual constraints of ecology and economy, which effectively solved the problems of land use and water resources allocation.

2.6 Application of remote sensing technology in land use research in lake basinsWith the rapid development of land satellite and aerial mapping technology, remote sensing (RS) has become an important supporting technical means in the fields of military, scientific research and meteorology. In the study of land use changes, the remote sensing technology is often used as one of the important means to obtain land cover information. At present, the remote sensing technology has been widely used in the fields of dynamic monitoring of land resources, land law enforcement and supervision, land resource survey, soil and water conservation,etc.In the existing research on land use of lake basins, obtaining basic data from remote sensing images is the technical method adopted by most scholars, such as the study on changes of lakes and watersheds in the Qinghai-Tibet Plateau and their influencing factors based on MSS images in the mid-1970s and ETM images in the late 1990s[51], the study on the changes of 22 lakes in the southeastern Qiangtang Plateau based on Landsat TM/ETM images and CBERSCCD images[52]and the study on dynamic monitoring of lake area in Dongting Lake which used 2005 Terra/MODIS satellite images to construct a time series dataset[53]. Among them, Landsat remote sensing images are widely used in land use research in lake basins. MODIS satellite images can better capture land use changes in lake basins due to their high temporal frequency.

3 Existing problems

3.1 Lack of refined research on land use changes in lake basinsExisting research on land use changes in lake basins mostly focuses on discussing land use changes in lake basins from a macro perspective and land classification based on remote sensing image interpretation is not precise enough. Therefore, most of the research on the driving factors and effects of land use changes in lake basins based on this basis remains in the qualitative stage, and it is difficult to reflect the unevenness of land use change in lakes at the micro level and the differences in drivers.. Meanwhile, in the study of lake land use changes, only the area change and type change of each land type can be reflected, and there are few analyses on the changes in spatial layout, and few studies that reflect the changes in spatial layout are only at the qualitative stage. Although the current research on land use changes in lake basins reflects the changes of land types within a certain period of time, it is limited to the comparison of two time points and cannot reflect the dynamic change process between the two time points. Moreover, because remote sensing images have quality differences, the interpretation accuracy will have a greater impact on the results. Most of the dynamic monitoring of lake area focuses on extracting past water area changes and predicting future lake area changes on this basis. However, the change in the area of a lake and the change of land use in its watershed are a coupled system change, and it is rare to study both as the object of discussion.

3.2 Imperfect theoretical research on lake land use optimization researchIn the research on optimal allocation of land use, economy, society and ecology are gradually taken as the ultimate goals of optimal allocation of land, but the research on optimal allocation of land use in lake basins is still in its infancy, and there are few studies on land use changes of lakes that take into account both economic development and lake protection. Since the changes of urban lakes and their surrounding land are a very complex system problem, and it is a very complex spatial coupling problem, which is reflected in the consideration of land use changes in lake basins and its interaction with other systems such as lake systems, which will put forward higher requirements for scholars engaged in this research. Although current scholars have optimized the land quantity structure by multi-objective programming and linear programming, some scholars have also combined the CA model, the Markov model,etc., with the geographic information system to open up new methods for the study of land use structure and spatial layout. However, in general, the current research on land use optimization in lake basins has not yet formed a systematic research framework, and there are few researches on lake land use optimization that take into account economic development and ecological protection. It is necessary to further enrich the theoretical and practical research on land use optimization in lake basins.

3.3 Weak land type extraction techniques based on remote sensing imagesRemote sensing images are the basic data for extracting land types. The quality of remote sensing images under different sensors is uneven, and the weather also greatly interferes with the quality of remote sensing images. The research on lake land use has higher requirements for basic remote sensing images. Because lake water levels are greatly disturbed by seasonal changes, the impact of seasonal changes in water levels on the interpretation of land use types in lake basins should also be considered when collecting basic data. Compared with general land use research, land use research in lake basins involves more water extraction techniques. At present, water extraction techniques at home and abroad have been well developed, and scholars have proposed algorithms with higher interpretation accuracy for remote sensing images based on different sensors. Nonetheless, there is still a lot of room for the improvement in water extraction techniques. In contrast, existing land type extraction techniques have more room for improvement. For example, the interference of clouds and mountain shadows will cause great difficulties in the interpretation of remote sensing images, while the accuracy of remote sensing interpretation determines the accuracy of the research results. Therefore, it is necessary to further improve the land type extraction techniques based on remote sensing images to promote the refined development of lake land use research.

4 Research prospect

4.1 Strengthening refined research on land use changes in lake basinsOn the basis of existing research, we should further strengthen refined research on land use changes in lake basins, establish lake land use change models from the micro level, and pay more attention to analyzing the changes in spatial distribution of lake land use while systematically analyzing changes in the quantity and structure of lake land use. Taking into account the spatial heterogeneity of land use changes, the research on land use changes at the micro level should be strengthened, and the research results will have more application value. In the research on driving factors and effects of lake land use changes, quantitative analysis should be further strengthened, and the impact of each driving factor on land use changes of lake basins should be further explored. Studying lake land use changes combining quantitative and qualitative research methods will become the main direction of future research.

4.2 Perfecting the theoretical research on land use optimization in lake basinsImproving the research on land use optimization in lake basins requires that the depth and breadth of the research should be improved. In terms of breadth, considering the dual goals of lake protection and rational utilization of land resources, it is necessary to strengthen the organic combination of related theories of land space planning, water resources protection, ecological protection and other related theories with research on land use optimization in lake basins. It is necessary to propose a lake basin land use optimization research plan that takes into account both social and economic development and lake ecological environmental protection, so as to enrich the theory and practice of lake basin land use optimization research. In terms of depth, it is necessary to further explore more perfect research methods on the existing basis, break through the shortcomings of existing models in the study of land use optimization in lake basins, and strive to make further breakthroughs in the research model algorithms to make the research results more reliable.

4.3 Improving methods for extracting land types based on remote sensing imagesRemote sensing images have been widely used in land use research and water resources monitoring. At present, water extraction techniques in China are already at the international leading level, and various water extraction techniques have achieved satisfactory accuracy. In contrast, the extraction accuracy of land types is difficult to reach an ideal level. Although the interpretation accuracy of most studies can reach more than 80%, a large-scale interpretation error of 20% can still have a decisive impact on the research results. As mentioned above, the land use of lake basins should be refined and developed, and improving the extraction methods based remote sensing techniques is also an indispensable part of refined research. In addition, in the selection of supervised classification algorithms, it should be noted that different interpretation algorithms have different degrees of applicability to remote sensing images from different sensors, and appropriate algorithms should be selected according to different images.

5 Conclusions

Based on the literature induction method, this paper collected a large number of literature on related topics with "lake land use" as the key word, and after screening and summarizing the literature, the status quo, problems and prospects of land use research in lake basins were summarized. This paper systematically summarized the current status of land use research in lake basins from six aspects: temporal and spatial changes, effects, driving factors, optimization research, and the application of remote sensing techniques in lake land use research. Correspondingly, three problems were proposed: lack of refined research on land use changes in lake basins, imperfect theoretical research on lake land use optimization research, and weak land type extraction techniques based on remote sensing images. On this basis, future research was prospected. It is believed that the future research on lake land use should focus on strengthening the refinement of land use change research in lake basins, further improving the theoretical and practical research on land use optimization in lake basins based on a variety of related theories, and further improving the interpretation algorithms of remote sensing images. The research provides reference materials for scholars engaged in lake research and land use research. However, due to the limitations of literature collection, the views drawn may be one-sided, and the content of the current situation, problems and prospects needs to be further enriched. Therefore, In the future, the above problems should be avoided as much as possible when sorting out the research status, existing problems and prospects of land use in lake basins.