Ecological engineering for traditional Chinese agriculture—A case study of Beitang

Beitang is an ecologically engineered constructed wetland dominated by human activities and is composed of paddy fields, ponds, ditches, courtyards and other related ecological infrastructure with the functions of agricultural production, hydrological regulation, environmental cleanup and ecological agricultural regulation. The history of Beitang extends back more than 2500 years in China, and it plays a very important role in China's agricultural development. This paper first reviews the history of the development of Beitang; then according to the historical structural features of Beitang, it summarizes Beitang as a pond–ditch–courtyard–farmland ecological engineering composed of constructed breakwaters, sluice gates, and water intakes; courtyards; and farmland and irrigation ditches with the functions of water collection, storage and conveyance. Under different terrain conditions, Beitangs exhibit different characteristics. For example, in flat areas featuring a larger pond capacity, longer shoreline and larger area of farmland, a Beitang can serve more rural areas; in hilly areas featuring a smaller pond capacity and smaller area of farmland, ditches serve as a very important structural unit that can connect ponds for water volume regulation between ponds, increase the irrigated area, and achieve gravity irrigation to as great an extent as possible. Moreover, the paper analyzes the hydrological, nutrient cycling and biological processes as well as other ecological processes associated with this type of pond–ditch–courtyard–farmland-system. The paper also proposes five ecosystem services of Beitang: hydrological regulation, ecological purification, soil and water conservation, production functions and biological diversity protection. Finally, the paper analyzes the reasons for the degradation of Beitang over the past 30 years from the perspectives of institutions, management, concepts and technology, and proposes corresponding countermeasures to protect and restore Beitang.