渭-库绿洲多尺度景观格局与盐度关系

中国盐渍化土壤面积大,分布广,对区域农业发展构成了严重的威胁。探索土壤景观格局与盐度的关系将有助于盐渍化监测和评估。该研究选择渭-库绿洲GF-1影像为数据源,结合研究区同期38个样点不同剖面土壤盐度数据,对样点缓冲区景观格局与土壤盐度做Pearson相关分析和逐步回归分析,揭示土壤盐度空间分布格局,探讨景观格局与盐度的定量关系。结果表明:1)水平方向上,土壤盐分高值区主要集中分布在绿洲东部荒漠地带和绿洲西部农牧交错区;垂直方向上,渭-库绿洲表层土壤盐渍化现象最为严重,其他各层土壤盐渍化情况相对较轻,盐渍化程度随着深度下降呈降低趋势;2)绿洲区域易受人类活动影响,景观破碎化程度高,而同一区域不同梯度下,随着缓冲距离的增加,区域景观类型增多、均质性降低、多样性增强;3)耕地利用数量指标能较好指示土壤盐度状况,而水体面积、盐渍地面积、其他用地面积、最大斑块指数(largest patch index,LPI)、蔓延度(contagion index,CONTAG)和分维数(perimeter-area fractal dimension,PAFRAC)对盐度影响相对较弱;4)除0~10 cm层外,自10~20 cm至80~100 cm层逐步回归方程的自变量中,耕地面积、水体面积和最大斑块指数LPI为负效应,而盐渍地面积、其他用地面积、CONTAG和PAFRAC为正效应,最优回归方程决定系数为0.537。该研究确定了渭-库绿洲土壤盐度的分异规律,以及不同盐度对绿洲景观格局的影响程度。研究结果可为西北干旱区绿洲土壤盐度预警提供理论依据,同时为干旱区景观格局研究提供一定的参考价值。

Relationship between multi-scale landscape pattern and salinity in Weigan and Kuqa rivers delta oasis

Abstract: Saline soil occupies a large area and is widely distributed in China. Soil salinization poses a great threat to regional agriculture development. Exploring the relationship between landscape pattern and soil salinity will facilitate the monitoring and assessment of soil salinization. In this study, Weigan and Kuqa rivers delta oasis taken as a study area, the effects of soil salinity on regional landscape pattern was investigated through the analysis of multi-scale landscape pattern and soil salinity in different sections with the combination of regional soil salinity variation regularity. GF-1 satellite imagery (taken on July 19, 2014) was used as the main data source, land use/land cover types of the study area were divided into 5 categories using the maximum likelihood supervised classification: arable land, forest and grassland (including the garden, natural forests and grasslands), water, saline land (heavily) and others (including slightly and moderately saline land, desert, mountains, etc.). 11 landscape indices were selected including class area (CA), number of patches, largest patch index(LPI), percentage of landscape(PLAND), patch density(PD), landscape shape index(LSI), fractal dimension (perimeter-area fractal dimension, PAFRAC), aggregation index(AI), interspersion and juxtaposition index(IJI), shannon's diversity index(SHDI), contagion index(CONTAG). Combined with soil salinity data at different depths of 38 samples collected in 22-28 July 2014, to the center of a circle of sampling points, a total of 5 circular buffer gradients with 0.5, 1, 2, 3 and 5 km radius buffer was chosen as the unit of analysis. Pearson correlation analysis and stepwise regression analysis were applied to analyze the relationships between landscape pattern and soil salinity and reveal the spatial distribution pattern of soil salinity. In the end, the typical pattern of oasis, oasis-desert ecotone pattern, desert landscape pattern and Weigan and Kuqa rivers delta oasis overall landscape pattern were analyzed. The results showed that: 1) On the horizontal direction, highly salinized soil was mainly distributed in the eastern desert and western farming-pastoral zone of the oasis; On the vertical direction, soil salinization problem was most serious on soil surface and was less serious in the other soil layers. The degree of soil salinization decreased as the increase of depth; 2) The fragmentation index of oasis was higher than other landscape because of the oasis area easily affected by human activities. Under different gradient, the region landscape types increased, heterogeneity decreased, diversity increased, when buffer distance increased; 3) The amount of cultivated land could indicate soil salinity, but the other indexes including land area, saline land area, water area, LPI, CONTAG and PAFRAC exhibited limited influence on salinity; 4) For the independent variables from soil depth 10-20 to 80-100 cm, the arable land, water area and LPI had negative relationship with soil salinity while it became positive for indexes including salinized land area, CONTAG and other PAFRAC. The best regression model was obtained with R2= 0.537. The study confirmed that the character of soil salinity distribution and the degree of influence of different level of salinity on oasis landscape pattern. Our results can provide some basic information for soil salinity warning/alarming in arid area in northwest China. Meanwhile, it can serve as a reference to the research on landscape pattern in arid areas.