1990－2015年三峡库区重庆段水田时空分布及演变特征

目的 水田作为三峡库区重要的耕地类型与湿地景观，对保障该区的粮食和生态安全起到了不可替代的作用。分析水田的时空分布及演变特征，为农业结构调整、水田经营政策的制定以及保障库区生态系统的安全提供一定的理论基础。方法 文章基于三峡库区重庆段1990年、2005年、2015年土地利用图像，利用ArcGIS和FRAGSTATS软件，运用土地利用转移矩阵、核密度估计以及景观指数模型等方法，分析三峡库区重庆段在不同时段水田的时空分布与演变特征。结果 2015年三峡库区重庆段水田面积为5 267.94 km²，占耕地总面积的26.70 %，平均坡度为11.87°，其中丘陵地区水田面积分最大，不同区县间水田面积差异显著。（2）近25 年草地、建设用地和水田间发生显著转移，1990—2005年水田主要转向旱地，2005—2015年水田主要转向建设用地，且转出面积大于转入面积，水田的总面积持续减少。（3）近25年来三峡库区重庆段水田面积的核密度分布呈现“西密东疏”“南密北疏”的分布格局。1990年水田分布的聚集区表现为江津和长寿2个核心分布带；2005—2015年江津的核密度值由高密度区转变为低密度区，水田分布的聚集区仅剩长寿核心分布带。（4）在7种土地利用类型中，水田的景观优势度居于中间位置，随着水田面积不断减少，水田景观的破碎化进一步扩大。结论 从粮食安全和生态保护的角度出发，未来产业结构调整和高标准农田建设中，必须稳定一定数量和质量的水田面积，充分发挥水田的生产和生态功能。

SPATIOTEMPORAL AND EVOLUTIONAL CHARACTERISTICS OF PADDY FIELD IN THE THREE GORGES RESERVOIR OF CHONGQING FROM 1990 TO 2015

Paddy field is a critical cultivated land-use type that sustains the wetland landscape and safeguards the food and ecology in the Three Gorges Reservoir (TGR). The spatiotemporal and evolutional characteristics of paddy field inform the adjustment of agricultural structure, the formulation of paddy field management, and the protection of the ecosystem in TGR. The kernel density estimation, landscape index model, and land-use transfer matrix were used to extract the spatiotemporal and evolutional characteristics of the paddy field on ArcGIS and FRAGSTATS platform using the land-use maps in the Chongqing section (1990, 2005, and 2015) of TGR. The results were showed as follows. (1) The paddy area of Chongqing was 5 267.94 km² in 2015, accounted for 26.70 % of the total arable land, and was significant unevenly distributed at different county/district. Hilly paddy fields took up the largest area proportion with an average slope of 11.87°. (2) A significant area was exchanged among grassland, construction land, and paddy field in the past 25 years. The paddy field had been decreasing since 1990. Paddy fields were primarily turned to dry land from 1990 to 2005, while construction land took up more paddy areas from 2005 to 2015. (3) The kernel density of the paddy field was higher in the southern and western parts of Chongqing. The paddy field agglomerated in Jiangjin and Changshou in 1990. From 2005 to 2015, Jiangjin became a low-density paddy zone, and Changshou remained the only district with a high-density paddy zone. (4) Among the seven land-use types, the paddy field occupied the middle position regarding the landscape dominance metric. The fragment metric increased as the area of the paddy field decreased. Therefore, economic structure adjustment and high-standard farmland construction call for high-quality paddy fields of enough quantity since paddy fields are critical to food production and ecological conservation.