Rainwater chemistry plays an important role in the earth-surfificial ecosystem, but studies on rainwater chemical compo
sition of karst agro-ecosystem are rare. To explore the rainwater alkalization and the provenance of components respon
sible 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 emis
sion, in particular, fifixed emis
sion 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 ba
sic components, Ca2þ and NH4þ) is benefificial to crop growth but also reflflect agricultural overfertilization. Sulfur controlled the total wet acid depo
sition (68%e94%) and could be a potential agent of weathering.
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