title: Estimation of long-term Ca(2+) loss through outlet flow from an agricultural watershed and the influencing factors.
abstract: Soil Ca(2+) loss from agricultural lands through surface runoff can accelerate soil acidification and render soil degradation, but the characteristics of Ca(2+) 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 Ca(2+), Mg(2+), 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 Ca(2+), Mg(2+), K(+), TN, and TP were 0.43, 0.08, 0.10, 0.19, and 0.003 mmol L(-1), respectively. The average Ca(2+) loss reached 1493.79 mol ha(-1) year(-1) and was several times higher than for Mg(2+), K(+), and TN, about 140 times higher than for TP. Rainfall intensity had remarkable effects on Ca(2+) 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 Ca(2+) concentration only when rainfall intensity was less than 50 mm day(-1). In a word, much greater amounts of Ca(2+) were lost from the watershed, and this may be one important contributor to the increasing acidification of acidic soils in subtropical regions.
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Wenzhao
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Chunmei
authors.initials: C
authors.lastname: Yin
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Chunlan
authors.initials: C
authors.lastname: Chen
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Anlei
authors.initials: A
authors.lastname: Chen
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Xie
authors.affiliation: Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Xingan
authors.initials: X
authors.lastname: Fu
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China.
authors.forename: Haijun
authors.initials: H
authors.lastname: Hou
authors.affiliation: Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China. wenxuewei@ias.ac.cn.|Taoyuan Station of Agro-ecology Research, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan, 410125, China. wenxuewei@ias.ac.cn.
authors.forename: Wenxue
authors.initials: W
authors.lastname: Wei
mesh_terms: D000383:Agriculture; D002118:Calcium / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring; D009584:Nitrogen / Q000032:analysis; D010758:Phosphorus / Q000032:analysis; D011891:Rain; D012987:Soil / Q000737:chemistry*; D014872:Water Movements
chemical_list: D012987:Soil; D010758:Phosphorus; D009584:Nitrogen; D002118:Calcium
keywords: Agricultural watershed; Antecedent soil moisture; Ca2+ concentration; Ca2+ loss; Rainfall intensity; Surface runoff