华北平原农田生态系统服务评价及灌溉效益分析

农田生态系统为人类提供农产品等服务的同时,对生态环境也产生负面影响。本文基于千年生态系统评估(MA)框架,以华北平原典型高产农田区域——河北省石家庄市栾城区为研究对象,应用能值理论分析农田生态系统投入,从供给、调节和支持3方面分析农田生态系统正、负服务产出;应用分摊系数法求解农田灌溉净效益,计算能值指标并评价农田生态系统可持续发展状况。结果表明:研究期间栾城农田生态系统能值年均总投入(1.00×1012 sej·m~(-2))中,不可更新工业辅助能(6.81×1011 sej·m~(-2))与不可更新环境资源(灌溉用地下水,2.57×1011 sej·m~(-2))投入之和占总能值投入的90%以上,说明农田生态系统消耗了大量不可更新资源;农田提供的正服务(1.82×1012 sej·m~(-2))主要是农产品供给(1.07×1012 sej·m~(-2)),负服务(5.87×1011 sej·m~(-2))以温室气体排放(5.31×1011 sej·m~(-2))为主;考虑农田生态系统环境负效益,计算栾城农田灌溉效益分摊系数为0.32,灌溉净效益为3.94×1011 sej·m~(-2),灌溉效益偏低;栾城区能值可持续发展指标取值为0.10~0.18,属于典型的消费型农田生态系统,迫切需要探索出一条低能耗,高产出的真正意义上的高质量农田发展之路,实现农田生态系统健康可持续发展。

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.