Concentrations and spatial distribution of chlorine in the pedosphere in China: Based on the China Geochemical Baselines Project

Abstract

The China Geochemical Baselines (CGB) project obtained harmonious geochemical baseline data covering all of China and provided reliable data for 76 elements, including chlorine, from 3382 top (0–25 cm) and 3380 deep (>100 cm) sediment or alluvial soil samples. Chlorine concentrations were determined by X-ray fluorescence spectrometry under strict quality control. The median chlorine concentration values, which were considered geochemical baseline values, in the top and deep samples were 78 μg/g and 72 μg/g, with mean values of 1609 μg/g and 1176 μg/g, respectively. Chlorine concentrations ranged as 8–372,643 μg/g and 9–210,374 μg/g in the top and deep samples, respectively. Generally, salt-forming parent material provides a reliable source of chlorine in the pedosphere, and the geochemical behavior of chlorine determines its ability to migrate in different media. Soils with low chlorine concentrations are distributed in southwest and southern China. This is mainly due to the subtropical, temperate monsoon climate with precipitation of >800 mm throughout the year, a dense network of rivers, and abundant surface runoff. Soils with high chlorine concentrations are distributed in northwestern and northern China and coastal areas. The chlorine concentrations are affected by various factors, including the sedimentary region, landscape, arid climate, low precipitation, high evaporation, surface runoff, groundwater, and salt lake distribution. Previous studies on chlorine have primarily focused on saline areas. Thus, this is the first study to estimate the concentration and spatial distribution of chlorine in the Chinese Mainland. This study provides basic geochemical data for salt mineral development, regional climate, environmental monitoring, and efficient land use in both saline and non-saline areas.