基于生态流方法的土地整治项目对农田生态系统的影响研究

将土地整治活动作为外界对农田生态系统(项目区)集中性的外部激励,以陕西关中凤翔县典型土地整治项目为例,分析了项目实施前后生态流(物质流、能量流、信息流)变化状况,建立了土地整治生态影响概念性模型,明确了相应生态流的流向与路径关系,使用可用能法和能值法测算项目区外部输入及生态产品输出,应用生态流分析法,对土地整治项目生态流和系统效率进行了定量计算。根据设定的土地整治工程使用年限,评估了项目实施后区域净生态价值、自然资源依赖度、可更新资源依赖度、生态产出率、生态承载力和生态可持续度等指标的时间变化过程。得到以下研究结果:(1)可用能法和能值法测算出的系统生态效益均呈现由项目建设初期陡降为负值,而后指数增加,再趋于平稳的过程;(2)可用能法测算出项目实施后的第29年,生态效益由亏转盈,体现出系统从被扰乱后恢复自然平衡状态的过程;(3)能值法测算出项目实施后的第4年,生态系统趋于平衡状态;(4)研究区土地整治项目的经济效益为负,于项目实施3a后趋于平稳,总投资中农业生产年投入占资金总额的78.35%。通过可用能和能值方法的结合,可以定量计算系统稳定性,为土地整治项目的物质、劳动力和资金投资选择等提供借鉴。

Determining the effect of the land consolidation project on the cropland ecosystem based on the ecological flow method

Ecological flows reflect the relationships among metabolism, energy conversion, information exchange, and so forth. A quantitative analysis of the development of ecological flow patterns of various parameters was performed. Based on existing exergy accounting, ecological flow networks in a typical semi-natural cropland ecosystem were analyzed, with five ecological indicators being used to evaluate the ecological effectiveness of these networks. Exergy buffers the capacity and environmental impact on cropland ecosystems. Previous studies have examined exergy effectiveness in a variety of fields, but exergy analysis has rarely been applied to assess cropland ecosystems. Research time is significant because ecosystem stability varies in different periods;hence, ecological flow results will differ. In the cropland ecosystem used for this study, we chose the time period from planting to harvest to determine eco-flows based on the life-cycle theory, and set the land consolidation project edge as the boundary. This study only considered crop growth and the impacts of human-assisted primary production. As a sudden short-term external incentive of the project cropland ecosystem area, land consolidation activities influenced ecological flow changes after land consolidation project implementation (LCPI), which included material, energy, and information flow changes. A land consolidation ecological conceptual model was built and reflected ecological flow direction and path. It used exergy and emergy accounting methods to study the external input, output, and ecological products. The study used a land consolidation project in Fengxiang County of Shaanxi Province as a case study, and applied ecological flow analysis to it to determine the intensity of ecological flow and system efficiency. Using different land consolidation project terms, this study evaluated net ecological value, natural resource dependency, renewability dependency, ecosystem productivity, ecological capacity, and ecological sustainability after LCPI. The exergy and emergy accounting methods presentedchanges to the ecological benefits process as a steep negative decline at the preliminary stage, followed by an exponential increase, and finally leveled off. Second, the exergy accounting method traced the ecological benefit losses and profit over the 29 years after LCPI in the study area was initiated, and manifested the system process recovery from chaos to natural balance. Third, the emergy accounting method demonstrated that, in the fourth year after LCPI, the ecosystem tended toward a state of relative balance, with an increase in ecological productivity and potential investment demands. Fourth, the economic benefits of the land consolidation project were negative and leveled off after 3 years, reflecting an annual agricultural production investment of 78.35%. Through the combination of exergy and emergy, the system stability was quantified and calculated. This study can be used as a reference for deciding input material, labor, capital, etc. for use in future land consolidation project planning.