Reinforced Soil Salinization with Distance Along the River: A Case Study on the Yellow River
Clarifying the relationship between salt-affected soils and their adjacent river systems is critical to alleviate the challenges posed by soil salinization on agricultural production. Among the various biophysical and land management factors linked to soil salinization, very few studies have addressed what is intuitively a fundamental parameter: the distance along the river. Using the Hetao Irrigation District on the Yellow River as a case study, we collected and analyzed over 5300 soil samples and 17 soil parameters to provide more in-depth insight into the relationship between salt-affected soils and their distance along the river. Soil salinization was reinforced by the distance along the river, as a trade-off between ion accumulation and soil nutrient regulation. With every kilometer along the river, soil exchangeable sodium and cation exchange capacity increased by 8.89×10 -4 and 1.26×10 -2 cmol kg -1 , respectively, which led to an increase in exchangeable sodium percentage by 9.59×10 -5 . The increase in exchangeable sodium along the river was mainly due to Na + accumulation from upstream to downstream. Soil pH increased by 1.21×10 -3 , while soil total water-soluble salt content increased by 16.4 mg kg -1 every kilometer. This increase in salt content is likely due to ions leaching from the soils upstream and partially accumulating in the soils downstream, especially for Cl - , SO 4 2- , and Na + . Greater organic inputs on the less salt-affected soils upstream may explain the slight decline in soil organic matter with distance along the river. Future saline soil amelioration for reutilization initiatives at regional scales will benefit from accounting for the changes in soil physicochemical properties resulting from the distance along the river.