Estimation of long-term Ca2+ loss through outlet flow from an agricultural watershed and the influencing factors

Zhang, Wenzhao; Yin, Chunmei; Chen, Chunlan; Chen, Anlei; Xie, Xiaoli; Fu, Xingan; Hou, Haijun; Wei, Wenxue

Estimation of long-term Ca2+ loss through outlet flow from an agricultural watershed and the influencing factors

2016

Soil Ca²⁺ loss from agricultural lands through surface runoff can accelerate soil acidification and render soil degradation, but the characteristics of Ca²⁺ loss and influencing factors in watershed scale are unclear. This study was carried out in a watershed with various land uses in a subtropical region of China. The outlet flow was automatically monitored every 5 min all year round, and the water samples were collected twice a year from 2001 to 2011. The concentrations of Ca²⁺, Mg²⁺, K⁺, total nitrogen (TN), and total phosphorus (TP) of water samples were measured. The dynamic losses of the nutrients through the outlet flow were estimated, and the relationships between the nutrient losses and rainfall intensity as well as antecedent soil moisture were investigated. The results showed that great variations of nutrient concentrations and losses appeared during the investigation period. The average concentrations of Ca²⁺, Mg²⁺, K⁺, TN, and TP were 0.43, 0.08, 0.10, 0.19, and 0.003 mmol L⁻¹, respectively. The average Ca²⁺ loss reached 1493.79 mol ha⁻¹ year⁻¹ and was several times higher than for Mg²⁺, K⁺, and TN, about 140 times higher than for TP. Rainfall intensity had remarkable effects on Ca²⁺ concentration (P < 0.01) and loss (P < 0.05) when it reached rainstorm level (50 mm day⁻¹), while a quadratic relationship was observed between antecedent soil moisture and Ca²⁺ concentration only when rainfall intensity was less than 50 mm day⁻¹. In a word, much greater amounts of Ca²⁺ were lost from the watershed, and this may be one important contributor to the increasing acidification of acidic soils in subtropical regions.

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