现代集约农业下基塘系统的退化与生态恢复

基塘系统是珠江三角洲地势低洼地貌类型的一种独特的传统人工生态系统。随着现代集约农业的推行和经济的高速发展，基塘系统地区的土地利用方式发生改变，传统的基塘系统严重退化。许多基塘系统种养分离、过度集约化养殖，养殖水体水质恶化，成为区域环境的重点污染源；大量污染物汇集和积蓄在基塘系统，导致有毒有害物质经食物链富集而危及水产养殖和人类健康；由于农业比较利益低下，农民经营基塘系统的积极性下降，部分基塘疏于管理，塘基崩塌、塘泥严重淤积，使不少基塘丧失正常功能，成为生产力很低的退化基塘。在充分调查分析基塘系统退化原因和机理的基础上，根据恢复生态学的原理，提出应用食物链和生态位原理对退化基塘系统进行生态恢复。其主要措施有鱼塘的水体恢复、基面的土壤恢复、环境污染的治理以及基塘面积的合理配比等。

The dike-pond system in the Pearl River Delta: degradation following recent land use alterations and measures for their ecological restoration

The traditional dike pond system (DPS) that has been developed and practiced in the Pearl River Delta for centuries is a sustainable agro ecosystem in low lying area. It has an obvious land water interaction and remarkable eco economical effect. In general, a DPS consists of fish ponds surrounded by crop dikes (mulberry, sugar cane, grass, flowers or vegetables). Most of the crops are used to feed the silkworms or livestock (ducks, geese, pigs etc.) and the manure from these animals are added to the pond as part of the fish feeds. The bottom mud of the pond are periodically excavated and added on the dike to increase soil fertility. A DPS is a particular artificial ecosystem of land water interaction, and also a special crop fish animal production system, so it has the characteristics of both terrestrial ecosystem and freshwater ecosystem. The system has a comprehensive structure and multi levels. The input and output of material and energy in the dike pond system are basically balanced. The sections of the system coordinate and benefit each other. Each unit of the DPS can give various agricultural and aquatic products with high productivity. However, severe environmental pollution and land degradation has occurred since the late 1980s. Following the replacement of mulberry by other crops in dike and the decline of traditional Chinese carps production in ponds, a more intensive monoculture has emerged. The dike pond system was mismanaged and the degradation of the system has happened. Rapid urbanization and industrialization of the Pearl River Delta have triggered the degradation of DPS in the recent two decades. A great quantity of contaminants, especially organic and heavy metal pollutants accumulated in the system, resulting in the loss of the normal function of many dike pond systems. Too much pesticides and heavy metal rich feed are used in many DPS, leading to the concentration of contaminants along the food chain, eventually endangered human health and aquatic life. Because of the relatively low profit, many farmers did not want to run the dike pond system anymore, so that the dike dilapidated, the bottom mud of the pond filled up there, the DPS degraded and the system productivity became lower. The degradation of the DPS and the pollution of low lying land always promote each other, which have affected the agriculture and the regional environment, and become the trouble of the sustainable development. The environmental pollution, market oriented, over intensive mono cultural systems which are focusing primarily on expanding pond surface to raise production value per unit area, are becoming threats to the sustainability of the dike pond system. It is necessary to understand that the DPS has important social, ecological and economic impacts on the region. Based on the theory of restoration ecology and ecological engineering design, a series of ecological safe models with economic feasibility were put forward in this paper. The main countermeasures to restore the degraded DPS include the water restoration of the pond, the rehabilitation of the dike soils, the remediation of environmental pollution, and the appropriate combination of dikes and ponds.