Vertical characteristics of the Hani terrace paddyfield ecosystem in Yunnan, China

Abstract

The Hani terrace paddyfield in Yunnan Province, China is categorized as a ‘constructed wetland’ under the Lamsar Convention classification. The Hani terrace paddyfield ranges from an altitude of 144 to 2000 m above sea level (ASL) in the southern slopes of the Ailao Mountains, angling down at a range of 15° to 75°. In this study, we investigated the ecosystem of the terrace paddyfields in the Mengpin and Quanfuzhuang administrative villages located at the center of the cultural heritage conservation district in the Hani terrace paddyfield. The Hani terrace paddyfield ecosystem structure is “forest-village-terrace paddyfield-river” in the order of descending altitude. Soil and water samples were sequentially taken from forests, villages and the terrace paddyfields to be able to study the vertical characteristics of Hani's terrace paddyfields. PO4-P and NH3-N in water were measured to test for water contamination. Seven soil nutrient factors were tested, including organic material (OM), char and nitrogen ratio (C/N), pH, total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and available potassium (AK). Soil quality was also evaluated using the characteristics of the soil nutrient factors. Vertical changes in the landscape, wetland types, wetland plants, hydrology and soil nutrients were characterized. Results showed that: (1) Hani's terrace paddyfield can be divided into five types of wetlands; the rice varieties and cultivation patterns vary in each type of wetland. (2) Hani's terrace paddyfield has a great capacity for water conservation and a strong ability to purify contaminants. The impoundage of Hani's terrace paddyfield is about 5050 m3/hm2. Contaminants in the terrace paddyfield soils decrease exponentially with the decline in altitude. (3) Comparison of soil quality in five different land use types indicates decreasing soil quality from forest to terrace land to terrace paddyfield to water source. Except for headwater soil, single factors such as OM, TN and TP, and the comprehensive soil quality in individual sampling zones tend to increase with altitude elevation. Comprehensive soil quality in the Quanfuzhuang sampling zone is better than in the Mengpin sampling zone. Finally, a comparison of Hani's terrace paddyfield with plain paddyfields and natural wetlands highlighted the vertical characteristics of Hani's terrace paddyfield.