Regional aquatic ecological security is an important indicator that presents the aquatic ecological state and can guide the aquatic environmental management. Here, an index system for the regional aquatic ecological security assessment was established based on the Pressure-State-Response Model and analytical hierarchy process. The system was applied in the city of Jinan in eastern China. The results indicated that the state of the aquatic ecological security is best in Changqing District which has relatively high vegetation coverage, a well-conserved ecological condition and a relatively smaller population density than other districts. Following were Lixia, Shizhong, Huaiyin, and Licheng Districts. The state of the aquatic ecological security is the poorest in Tianqiao District, mainly due to its over-exploitation of groundwater, declining landscape diversity and lower scientific and technical investment. The driving force test also demonstrated that economic development and population size are the dominant impact factors for the variation of aquatic ecological security. Environmental protection investment should be paid more attention as an important measure to improve the aquatic ecological security in Jinan. It was demonstrated that the index system can be effectively applied in an aquatic ecological security assessment to identify the primary impact factors that support decision-making on water resources management.
Serious worldwide water body pollution affects human productivity and standard of living as well as the total aquatic ecosystem (Millennium Ecosystem Assessment, 2005). To maintain sustainable development, consideration of water resources planning is necessary. The aquatic ecological security index, a critical indicator that can successfully represent the regional aquatic ecological state, has drawn considerable attention from some nations and international organizations (Ezeonu and Ezeonu, 2000; Rodriguez-Iturbe, 2000) and plays an important role in regional aquatic environmental planning and management.
Early studies on aquatic ecological security were focused simply on water volume, such as maximum and minimum stream flow (Sheail, 1997; Comer and Zimmermann, 1968). With the increasing interference by human activity, the functions of riverine ecological systems were destroyed and research associated with water body functions and aquatic environments were gradually developed. Ladson and Moore (1999) proposed an index system for representing stream state based on river hydrology, physical structural characteristics, riparian state, water quality and aquatic organisms that includes 22 indices. Chaves and Kojiri (2007) put forward a watershed health assessment method that combines hybrid optimization, fuzzy evaluation and genetic algorithm optimization. This approach revolves water culture, environmental value, water quality, and quantity simultaneously, bringing the ecological environment into the research scope of aquatic security. Yang and Zhang (2003) explored the temporal-spatial heterogeneity of water requirements in several types of ecosystems, and established a systematic assessment method for Huanghuai Lake Watershed to predict its ecological water requirements. Zhang and Yu (2005) established an index system to evaluate the ecological security in the reservoir region by considering three principles, namely the biological environment, the geological and climatic environment, and human engineering activity. The index system was applied in Huanglu Reservoir Region, integrated with analytic hierarchy process and fuzzy evaluation. Moreover, the groundwater table was identified as an important factor that affects the aquatic ecological security state (Koomey and Webber, 2001; Zhang et al., 2003; Hou et al., 2007). Aquatic ecological security of wetlands was also preliminarily discussed and the related studies were mainly focused on ecological health evaluation index system (Wang et al., 2003) and ecological water requirement (Cui and Yang, 2002). In conclusion, the index evaluation method provides a comprehensive way of assessing ecological security (Kwak, 2002; Bertollo, 2001; Zhao and Zhang, 2006). Nevertheless, there were few studies that deal with the regional aquatic ecological security. Regional aquatic ecological security refers not only to the ecology and environment, but also takes account of the social and economic development. It is a complicated system and places much emphasis on the interaction between humans and nature.
Jinan is the capital city and the political, economic and cultural center of Shangdong Province. With the rapid development of its urbanization and civilization, aquatic environment problems have become increasingly serious and are threatening the security of human productivity and well-being. The objective of this paper is to establish an index system for the regional aquatic ecological security state assessment, and apply it in Jinan to provide decision-making support for regional aquatic environment protection and water resources management.
Materials and Methods
Establishment of index system
According to the characteristics of regional aquatic ecosystems, in terms of society, economy and environment, this study adopted the Pressure–State–Response (PSR) framework model developed by Organisation for Economic Co-operation and Development (OECD, 1993; OECD, 1999) to establish the horizontal structure of the index system integrated with the landscape ecology method and Remote Sensing – Global Positioning System (RS-GPS). The detailed indicators can be categorized into three groups: (1) Pressure indicators that stand for the impact from human activity on aquatic ecology. These indicators are associated with production and consumption patterns and usually represent the pollutant discharge; (2) State indicators are related to the quantity and quality of natural resources and they ideally express the total state of aquatic ecology; (3) Response indicators that symbolize the response of the decision makers and policy constitutors to pressures, states, as well as to variations in these. They are designed to slow, remedy or control the negative effects of human activities on the environment.
Analytical hierarchy process (AHP) method (Barnhouse, 1992; Tran et al., 2002) was implemented to decompose the complicated issue into some related hierarchies for comparison. The indicators used in aquatic ecological security assessment consist of natural and social ones, static and active ones, as well as qualitative and quantitative ones. They can be simplified ito four hierarchy structure: (1) Objective hierarchy. It is represented by the regional aquatic ecological security comprehensive index and is designed to represent the regional aquatic ecological security state in turn. (2) Restriction hierarchy. It is the primary factor which confines the regional aquatic ecological security. (3) Element hierarchy. It includes the detailed indicative elements of restriction hierarchy and can express the characteristics of regional aquatic ecological security in term of society, economy and ecology. (4) Index hierarchy. It is the most fundamental hierarchy that is established by the directly measurable indice, such as groundwater mining rate and landscape diversity. In this study, four hierarchies were classified according to the subjective relation among factors. The degree of importance of each factor within one hierarchy was determined based on the relative importance of the same hierarchy. This method can quantify the empirical judgment of decision makers. In the consistency test, it was considered acceptable when the consistency ratio (CR) was less than 0.1.
The indices are standardized into dimensionless terms for comparison. There are three types of indices. For the first type, the aquatic ecology would be healthier with its increase (e.g. water resources quality), whereas for the second type the trend is opposite (e.g. water and soil loss degree). For the third type, the ecological state is the best when the value is intermediate (e.g. population density). In this paper, all the indices were transferred into the first type through standardization with the following equations.
Where xij and x′ij are the primitive value and standardized value of index j in i year, respectively;xjmax and xjmin are the maximum value and minimum value of index j, respectively.
After standardization, the index system of each hierarchy can be combined through calculation.
Where S is the comprehensive assessment value; wi is the weight of each index; A is an n × m order matrix, k= 1,2, …n; I= 1,2, …m; n is the number of assessment indices and m is the number of hierarchy. The aquatic ecological security state improves with the increase of S value.
Site description and available data
Jinan is located within Shandong Province, to the north of Tai Mountain and south of the Yellow River. It has a typical warm-temperate, semi-humid, continental monsoon climate and well-defined seasons (Kong and Nakagoshi, 2006). The research region of this study covers six districts, namely, Lixia, Licheng, Tianqiao, Changqing, Huaiyin and Shizhong Districts (Figure 1). This region is rich in surface and groundwater resources, with an annual precipitation of 617.2 mm. Nevertheless, the water resources exhibit a wide temporal-spatial heterogeneity that restricts the water usage. Moreover, with the industrial development in recent decades, the water resources in Jinan are reported to be severely polluted in quality and reduced in quantity. The data used in this study were available in the statistical yearbook and water recourses yearbook of Jinan in 2005 (Jinan Statistics Bureau, 2006a; 2006b).
Results and Discussion
Aquatic ecological security assessment index system
The aquatic ecological security index system and the weights of each index are listed in Table 1.
According to the CI, RI values and related weight of judgement matrix, the CR value can be obtained following equation:
Aquatic ecological security assessment results
The aquatic ecological security state is defined to be safer with the increase of index values, which has been explained in the Assessment method section. It can be seen from Figure 2 that the value of aquatic ecological pressure was the largest in Changqiang District; thus, it means Changqing District suffered the smallest aquatic ecological pressure actually. It also can be seen that Lixia Distruct has the lowest index value of aquatic ecological pressure; thus, this district experiences the highest aquatic ecological pressure actually. According to the index analysis, the aquatic ecological security pressure mainly comes from the population in Lixia district. And among the population pressures, the most important factor was the index of GDP per capita. In this district, the GDP per capita was 54.7 thousand yuan, less than one seventh of standard value in an ecologically-sound city (400 thousand yuan). For the other five districts, the pressure was primarily from the population and this was consistent with the fact that the population density in these districts has obviously exceeded the standard value (3500 km−2) in an ecological city.
Referring to the aquatic ecological state, Changqing District showed the best state, followed by Lixia District, whereas Licheng District was the poorest. Ecology was identified as the most important impact factor through the analysis. Among those ecological factors, the urban green land area per capita contributed most. The maximum value of urban green land area per capita in China was 16 m2, while the same index of the six districts in Jinan was less than 12 m2. This indeed demonstrated that the urban green land area per capita was a prominant factor for aquatic ecological security in Jinan.
In terms of aquatic ecological response, Huaiyin District exhibited the best response and Tianqiao District showed the poorest. Among the aquatic ecological response indicators, the social development was identified as the dominant one. In particular, the percentage of environmental protection investment in GDP showed the largest effect in Lixia and Shizhong Districts, while in the other four districts, percentage of scientific and technical personnel per ten thousand was the primary impact factor. According to the relevant data, it is estimated that a reasonable percentage of environmental protection investment should be 2.5%. However, the maximum value was just 1.2% in the six districts, and the percentage in Lixia Districts was even less than 0.03%. On the other hand, the number of scientific and technical personnel per ten thousand in an ecological city should be 1180, but the maximum number and minimum number among the six districts were only 536 and 65, respectively.
According to the aquatic ecological security comprehensive indices of these six districts, it is concluded that the state of aquatic ecological security was the best in Changqing District, followed by Lixia, Shizhong, Huaiyin and Licheng District, and was poorest in Tianqiao District.
Changqing District is located in the commanding point of the ecological landscape in Jinan. The vegetation coverage is up to 29.5%, a relatively high value. Biodiversity is well conserved with a good ecological condition. In terms of social pressure, the population density is relatively smaller and the land use is reasonable. Therefore, its aquatic ecological security state is the best among the six districts. For Lixia District, this area holds abundant groundwater resources and famous spring groups. However, water pollution is a severe issue here due to the age of the wastewater pipe network. Particularly, the Xiaoqing River has been seriously polluted by urban domestic wastewater containing large amounts of organic matter. The water quality of reservoirs can satisfy the demand of irrigation at present, but the flood control function of some tributaries has almost been lost. Thus, pollution discharge and flood control are the dominant issues threatening aquatic ecological security in Lixia District. For Shizhong District, the tributaries of the Xiaoqing River were mainly polluted by organic matter such as petroleum, ammonium nitrogen and COD (Chemical Oxygen Demand). With respect to flood control, there were several seasonal rivers subject to mountain torrent discharge from mountains. Nevertheless, the index of landscape diversity was relatively small, as was the percentage of environmental protection investment. Thus, the most important issues that affect the aquatic ecological security are water quality, landscape diversity and environmental protection investment. For Huaiyin District, the water resources are abundant, possessing the average annual natural surface water storage of 18031.2 m3, and a surface water usable amount of 13826.3 m3. However, it has a high population density, and the intensive fertilizer application and insufficient treatment of livestock manures has caused increasingly serious water pollution in this district. Thus, the most important impact factors of Huaiyin District are high density of population and domestic waste pollution affecting water quality. Licheng District suffers great aquatic ecological pressure due to the highest population density, the lowest water resources per capita among the total six districts. The well-developed industry has brought significant economic benefit, but the water quality of this area has been seriously contaminated and only a small proportion of industrial waste water has met the discharge standards. Thus, the dominant impact factor for aquatic ecological security is population density and industrial wastewater discharge in this district. For Tianqiao district, decades ago, the groundwater resources of northern part were abundant with springs and were not exploited in large scale. In the northern part, the water resource was also rich with shallow groundwater. Presently, groundwater has been over exploited and the impact of industrial pollution on water quality is serious due to the centralized industry in this area. Additionally, the indices of landscape diversity and vegetation coverage are comparatively lower. Moreover, the proportion of scientific and technical personnel is the smallest. Thus, the aquatic ecological security state is the poorest among the six districts. It can be concluded that the most importatant impact factors for aquatic ecological security are the groundwater table, landscape diversity and proportion of scientific and technical personnel in Tianqiao District.
Driving factor test for aquatic ecological security change
Driving factor test in six districts
The weight of each index was determined based on the AHP method. Five main impact factors for aquatic ecological security were identified through weight sequencing (Table 3), namely, daily water requirement per capita, water for agricultural irrigation per square meter, urban green land area per capita, population density, and wastewater load per GDP. It can be seen that economic development and population are the dominant factors that impact the aquatic ecological security. Meanwhile, the environmental protection investment should receive more attention as an important measure to improve the aquatic ecological security in Jinan.
Integrated with the analysis of aquatic ecological security state in each district, the primary driving factor of aquatic ecological security can be identified (Table 4), and it shows good consistency with the analysis section on Aquatic ecological security assessment results.
Driving factor test in Xiaoqing River
The Xiaoqing River watershed is an important center for industrial and agricultural production. There is a dense population and a large amount of wastewater discharge. Due to the landform and topography characteristics, the Xiaoqing River has become the only receiving channel for the wastewater and surface runoff in Jinan, and it also experiences great aquatic ecological pressure with flood diversion and storage. Therefore, the aquatic ecological security state of Xiaoqing River will directly influence that of entire Jinan. In this study, the driving factor of aquatic ecological security of each river reach was analyzed.
The upper reach of Xiaoqing River is 10.5 km long and connected with the Yufu River and the Lashan River. The water quality of this part is relatively good, as is the whole aquatic ecological security state. There are few large factories, and the dominant economy pattern is agriculture. Thus, the main driving factors for aquatic ecological security in the upper reach are domestic wastewater discharge, and fertilizer and pesticide application.
The middle reach of Xiaoqing River is 18.3 km in length and receives some tributaries. The water quality has been seriously polluted and lost considerable ecological function resulting in a very poor ecological security state. The human population density is large and most industrial and domestic wastewater converges here, which has caused extremely serious pollution in the river. Therefore, the dominant driving factors in the middle reach are population density and industrial wastewater discharge.
The lower reach stretches a length of 23.0 km with several tributaries. Due to the serious pollution in the middle reach and increasing pollutant load along the riverway in this part, the aquatic ecological security state is much poorer. This part of the Xiaoqing River has lost its self-purification ability and has been turned into a drainage ditch. Therefore, the primary driving factors of aquatic ecological security here is the proportion of environmental protection investment in GDP and the wastewater treatment rate.
This paper provides an efficient method for combining large quantities of data from various sources to arrive at simple indices for comparison. The establishment and application of the index system is a means of assessing the aquatic ecological security state and identifying the primary impact factors. In the city of Jinan, Changqing District has the best aquatic ecological security state with a relatively much higher vegetation coverage, well-conserved ecological condition and relatively smaller population density, whereas the aquatic ecological security state of Tianqiao District was the poorest mainly due to its over-exploitation of groundwater, decreasing landscape diversity, and lower scientific and technical investment. The driving force test also demonstrated that economic development and population are the dominant factors for the variation of aquatic ecological security and that the environmental protection investment should be paid more attention as an important measure to improve the aquatic ecological security in Jinan. It is proposed that the index system is helpful to assess the aquatic ecological security and identify the primary impact factors, which can support decision-making on water resources management in regional scales.
The aquatic ecological security state can represent the ecosystem function/biodiversity/ecological services to some extent, but as a comprehensive index proposed in this paper, it may be limited in some particular conditions. Thus, if combined with the independent measures of ecosystem function/ biodiversity/ecological services, it may reflect the total status of aquatic ecosystems in a more holistic way.
This work is supported by the Xiaoqing River Management Department in Jinan City.