Evaluation of agro-ecosystem services and analysis of irrigation benefit in the North China Plain

Agro-ecosystem has become a hot research area in the field of ecology in recent years. One of the most important issues of agro-ecosystems is the strongly disturbance they have suffered from human activities. Agro-ecosystems not only provide critical services for human existence such as agricultural products, but could also have negative impacts on ecological environment which together comprise the negative services of agro-ecosystems. It is known that farmland irrigation is the main mode of groundwater depletion in the North China Plain. Although grain yields can be increased greatly under groundwater irrigation, over-exploitation of groundwater can lead to environmental problems including lowered underground water level. Therefore, it is essential to exactly measure the contribution of irrigation to agro-ecosystem production and to comprehensively evaluate the sustainability of the development of agro-ecosystems in the North China Plain. Based on the Millennium Ecosystem Assessment (MEA) framework developed by the United Nations Environment Programme and taking the typically high-yield farmlands in Luancheng District of Hebei Province in the North China Plain as the study area, we used emergy theory to analyze agro-ecosystem inputs. The study also analyzed both the positive and negative services of the agro-ecosystems in the three categories of service provision, service regulation and service support using statistical input/output data of the agro-ecosystems in Luancheng for the period from 1984 to 2008. Furthermore, irrigation efficiency was calculated by the sharing coefficient method and the development sustainability of agro-ecosystems was evaluated by the calculation and analysis of a series of emergy indicators. The results showed that annual emergy input of the agro-ecosystems in Luancheng was 1.00×10¹² sej·m^-2, over 90% of which were non-renewable industrial auxiliary emergy (6.81×10¹¹ sej·m^-2) and non-renewable environmental resource emergy (groundwater irrigation of 2.57×10¹¹ sej·m^-2). This indicated that agro-ecosystems consumed a huge portion of non-renewable resources. For agro-ecosystem output, the positive service (75.60% of the total output) was greater than the negative service (24.40% of the total output). While service provision (agricultural product supply, 1.07×10¹² sej·m^-2) was the main positive service (1.82×10¹² sej·m^-2), regulation service (greenhouse gas emission of 5.31×10¹¹ sej·m^-2) accounted for most of the negative service (5.87×10¹¹ sej·m^-2). The sharing coefficient of irrigation benefit of the agro-ecosystems was calculated as the lower value of 0.32, and the net irrigation benefit was determined to be 3.94×10¹¹ sej·m^-2, taking into consideration the negative services of the agro-ecosystems. The values of emergy sustainability index, emergy sustainability index of ecosystem service and emergy sustainability index of net ecosystem service in the study area were 0.10, 0.18 and 0.12, respectively. All the above three emergy sustainability indexes were far less than 1, suggesting that the agro-ecosystems of Luancheng largely depended on consumable resources. Therefore, a series of countermeasures were needed to be taken, including the conservation of groundwater, the promotion of alternative fertilizers and the development of low toxicity pesticides, the implementation of national policy and legal tools. These countermeasures ensured low-energy consumption and high-yield development in agriculture towards the realization of sustainable development of agro-ecosystems in the North China Plain.