• 标题：Determining rainwater chemistry to reveal alkaline rain trend in Southwest China: Evidence from a frequent-rainy karst area with extensive agricultural production
• 关键词：Atmospheric acid substances,Rainwater,Acid neutralization,Ion sources,Karst agricultural production
• 作者：Jie Zeng, Fu-Jun Yue, Si-Liang Li, Zhong-Jun Wang, Qixin Wu,Cai-Qing Qin, Ze-Long Yan

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Rainwater chemistry plays an important role in the earth-surfificial ecosystem, but studies on rainwater chemical composition of karst agro-ecosystem are rare. To explore the rainwater alkalization and the provenance of components responsible for neutralization, two-years chemical monitoring of rainwater was carried out in a karst agricultural catchment in Southwest China. The main fifindings suggest that SO42, NO3, Ca2þ, and NH4þ are the principal ions. All the ionic contents show distinctly seasonal variation (highest in winter) in response to variations in seasonal precipitation because the rain-scour process can effificiently remove atmospheric materials. Source identifification indicates that Cl and Naþ are mainly derived from marine input whereas SO42 and NO3 are controlled by anthropogenic emission, in particular, fifixed emission sources. The source of NH4þ is attributed to intense agricultural production, while Ca2þ and Mg2þ are mainly derived from calcite dissolution. The rainwater alkalization caused by the seasonal acid neutralization (via basic components, Ca2þ and NH4þ) is benefificial to crop growth but also reflflect agricultural overfertilization. Sulfur controlled the total wet acid deposition (68%e94%) and could be a potential agent of weathering.