Temporal-spatial variability of soil salinity in greenspace of Tianjin Binhai Economic-Technological Development Area

Abstract: Both salinization and alkalinization of soil threaten the livability and urban green space in the coastal regions of the Tianjin Economic-Technological Development Area (TEDA). Salt content and pH value are two important parameters to indicate soil salinity. The objective of this study was to quantify the spatial distribution patterns of salt content and pH value and provide a theoretical basis for improving local soil, management and protection of green spaces, and soil quality evaluation as well. Focusing on the spatial complexity and regular pattern of soil salinization in TEDA, the soils at both 0-20 cm (top-soil) and 60-80 cm (sub-soil) depths were collected in 2006, 2008 and 2011 from 73 sampling sites distributed in the green spaces of the TEDA, in which the soil was nearly completely replaced with fresh soil at around twenty years ago. Salt content and pH value were measured using an electrical conductivity meter and a pH meter, respectively, and thereafter analyzed with both geostatistical and traditional statistical methods. The results showed that there was no salinization in all the top-soils collected in 2006, 2008 and 2011. Variation coefficients of the salt content in the top-soils were 32.4%, 82.9% and 49.3% in 2006, 2008 and 2011, respectively, showing moderate variability. The sub-soils collected in 2006, 2008 and 2011 had salt contents of 2.82g/kg, 1.91 and 1.65g/kg respectively, with decreasing salinity from moderate (top sub-soil) to mild (bottom sub-soil) level. Variation coefficients of sub-soil salinity were 123.9%, 100.2% and 103.5% for 2006, 2008 and 2011, respectively, which exhibited strong variability. Soil pH values were higher in both north and southeastern sides and had minor variability. The means of soil pH value increased slightly with soil depth, but decreased slightly over time in both top and sub-soils. Variation function analysis results showed the independence of spatial distribution for top-soil salinity, but a strong spatial dependence for the sub-soil salinity, which were largely affected by structural factors. On the other side, the pH values of both levels had strong spatial correlations. The characteristics of temporal and spatial distributions that reflected total salt content and pH value were expressed in Kriging spatial interpolation maps. The spatial distribution of the top-soil salinity exhibited planar structure, while a symmetrical ring shape pattern for the sub-soil. Meanwhile, heterogeneous distributions of pH value were found in both top-soil and sub-soil. In addition, sectional profiles of total salt content in the soils sampled during the three years more intuitively reflected the trend of salt content in the green space soil. Total salt content and pH value of the soil in this region was lower than 3 g/kg and pH value 8.5 respectively. In conclusion, the soil quality in the green space was generally stable, and within the range of the foreign standard for green space soil. The study can provide valuable information for remediating salinization and improving soil quality in the coastal saline soils.