Farming stimulated stronger chemical weathering in South China since 3.0 ka BP

Abstract

Anthropogenic impacts on weathering processes in the late Holocene have been widely demonstrated in recent studies, but the mechanism by which enhanced chemical weathering is linked to human activity remains unclear. In this study, we present a comprehensive reconstruction of sediment provenance, chemical weathering, vegetation type and evidence of human activity in core ZK20 in the estuary of the Pearl River during the last 7 ka to investigate the interactions of weathering, climate, and human activity. Evidence from major elements and clay minerals indicates an abrupt increase in chemical weathering intensity since ∼3.0 cal ka BP. This result cannot be explained by changes in provenance, climate or other natural factors but agrees well with the stronger human activity, confirming the significance of anthropogenic impacts on silicate weathering. The nearly synchronous increase in C4 plant abundance since 3.0 ka BP, as reflected by the sediment records from the upper reach and river mouth of the Pearl River, implies that the intensified weathering signal was mainly derived from contemporaneous minerals alteration (less than millennium timescale) rather than reworked old soils. We propose that the varied weathering conditions in response to agricultural activity and vegetation change intensified the alteration degree of minerals. The farming-induced biogeochemical effects, such as the releasing of acids, regulation of hydrology and uptake of cations, played a significant role in intensifying chemical weathering. This study highlights the importance of farming-related biogeochemical effects, which have been largely neglected in previous studies, in the process of chemical weathering.