Analysis on trade-offs and synergies of ecosystem services in arid inland river basin

Abstract: Ecosystem services (ES) are the benefits that humans received from the natural environment, which are closely related to the environmental process and human activities. With the deepening understanding on ES, their relationships and integrated effects between different ES have been paid more and more attention both at spatial and temporal dimensions. Due to the complex relationships between diverse ES, there is likely to be a contradictory mutual relationship between various ES, which is mainly shown as reciprocal trade-offs or mutual gain synergies. Trade-offs occur when the provisions of several ES are in the opposite trend, while synergies occur when the provisions of several ES gather. Scientific understanding and weighing trade-offs and synergies relationship of ES makes contribution to ecosystem management and decision-making. What's more, this also has great significance on realizing "win-win" policies of the economic development and ecological protection. In recent decades, serious eco-environmental problem have occurred in most areas of the arid inland river basin, such as vegetation degradation in the upper reaches, the descending of water conservation capacity, the declining of groundwater level in middle reaches, the outstanding of water conflicts and the desertification in the lower reaches. These problems of fragile ecological environment have influenced the basins' sustainable development. Jiayuguan-Jiuquan region (JJR), a typical representative of arid inland river basin, was taken as an example. Several models were used to estimate the value of four key ES in 2000 and 2010, including food supply, water retention, soil conservation and carbon storage. Besides, trade-offs and synergies among ES and the characteristics of spatial distribution of ES were also discussed by using the correlation analysis and hot cartography of space. Conclusions were as follows: 1) The annual average value of food supply per unit area in cultivated land decreased from 2 522.42 kJ/(m2·a) in 2000 to 2 115.35 kJ/(m2·a) in 2010. The annual average value of food supply per unit area in grass land increased from 15.75 kJ/(m2·a) to 24.49 kJ/(m2·a), and that in water areas increased from 6.05 kJ/(m2·a) to 6.50 kJ/(m2·a). From 2000 to 2010, the annual average value of carbon storage per unit area, the annual average value of soil retention per unit area and the annual average value of water retention per unit area increased by 0.38%, 84% and 147.5%, respectively. 2) From the perspective of space, the high value regions of food supply were distributed in oasis areas of Suzhou, Jinta and Dingxin. The overall trend of carbon storage distribution was stronger in the central and southeastern regions of JJR, but weaker in the north of JJR. The high value regions of soil conservation were concentrated in Yanchi, Yema River, and Dang River of Subei County. While, the high value regions of water retention distributed in Dashui river basin of Subei County, Haller Teng river basin of Aksay County, and Heihe and Taolai river basin of Jinta County. 3) The correlation analysis displayed that synergy was the dominant relationship among ES, and the synergy degree of carbon storage with food supply and water retention was more obvious. Along with the change of scale, the trade-off and synergy of ES had obvious dependence. In the county scale, there were trade-off between soil retention and carbon storage in Jigyuguan City and Suzhou District. And there were synergy between carbon storage and soil retention in Aksay County, Subei County and Yumen City. In regional scale, trade-offs between food supply and soil conservation, as well as water retention and soil conservation were significant in 2010. Carbon storage with food supply and soil retention showed significant synergies. 4) The hot cartography of space indicated that service areas of type 0 were the largest, accounting for 58.50% of the total area of JJR; and service areas of type 1, type 2, type 3 and type 4 accounting for 25.20%, 11.68%, 4.59% and 0.03% of the total area of JJR, respectively. The results have implications for the planning and management of natural capital and ES, and provide a scientific basis for sustainable development in JJR.