挠力河流域耕地变化及其对流域植被及蒸散发特征的影响

Changes in Cultivated Land and Its Effects on Vegetation and Evapotranspiration Characteristics in the Naoli River Basin

挠力河流域地处三江平原腹地,是中国重要的粮食主产区。近年来,随着中国粮食安全和区域农业结构调整,在耕地扩张及种植结构等方面发生了重要的土地利用变化。因此,识别耕地变化及其生态效应对地区生态保护具有重要意义。研究分析了1980—2020年的土地利用变化,然后基于归一化植被指数(NDVI)和实际蒸散发数据,利用耕地变化生态影响指数估算其生态影响,利用蒸散发变化估算其耗水影响。研究发现:①40 a间流域耕地面积从7273.22 km^(2)显著增加至15313.62 km^(2),增加了110.55%,主要来自于林地和湿地的开垦;②流域内近20 a发生了较为显著的水田和旱地的互转,在面积上旱改水大于水改旱;③2000—2020年流域的NDVI和蒸散发均呈现增加趋势,增幅分别为8.15%和18.58%,耕地区域NDVI的增加主要集中在作物生长季节,相反在非生长季对NDVI变化贡献低;④各类耕地变化对流域NDVI和年蒸散发的贡献率不尽相同,退耕还林对保护生态和减少耗水有贡献,湿地开垦虽然增加了生长季NDVI但也增加了流域耗水,水改旱有利于流域保水,而旱改水工程增加蒸发耗水,可能带来水资源安全风险。

The Naoli River Basin is located in the hinterland of the Sanjiang Plain and is an important grain production area in China.In recent years,with the guarantee of food security and the adjustment of regional agricultural structure in China,there have been significant changes in land use,such as cultivated land expansion and planting structure adjustment.Therefore,identifying changes in cultivated land and their ecological effects is of great significance for regional ecological protection.This study analyzed changes in land use from 1980 to 2020 and then estimated their ecological impact using the ecological impact index of cultivated land change based on normalized difference vegetation index(NDVI)and actual evapotranspiration data.In addition,changes in evapotranspiration were estimated to determine the degree of water consumption.The results show that:①the area of cultivated land in the basin has increased significantly from 7273.22 km^(2)to 15313.62 km^(2)over the past 40 years,an increase of 110.55%,mainly due to the reclamation of forests and wetlands;②in the past 20 years,there has been a significant conversion between paddy fields and dry land,with a greater increase in conversion from dry land to paddy fields;③From 2000 to 2020,both NDVI and evapotranspiration in the basin showed an increasing trend,with an increased amplitude of 8.15%and 18.58%,respectively.The increase in NDVI in cultivated areas mainly occurs during the crop growing season,while the contribution of non-growing seasons to NDVI change is low;④different types of changes in cultivated land have varying contributions to the NDVI and annual evapotranspiration in the basin.Returning cultivated land to forest has contributed to ecological protection and reduced water consumption.Although the reclamation of wetlands has increased NDVI during the growing season,it has also increased water consumption in the basin.The conversion from paddy fields to dry land is beneficial for water conservation in the basin,while the conversion from dry land to paddy fields increases evaporation and water consumption,potentially posing a risk to water resource security.