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.