Rapid Increase in the Lateral Transport of Trace Elements Induced by Soil Erosion in Major Karst Regions in China

Soil
erosion, which has been recently shown to significantly perturb
carbon cycling, occurs naturally but can be either enhanced or reduced
by human activities. However, the impacts of soil erosion on terrestrial
contaminant cycles remain unclear. Here, we select eight trace elements,
i.e., arsenic, cadmium, chromium, copper, nickel, lead, zinc, and
mercury, to examine the erosional impacts of the elements’
fate and transport across China. By synthesizing the detailed distribution
of soil erosion fluxes, soil element inventories, and diverse modeling
methods, we reveal that while human activities have reduced the lateral
transport of these elements in the Loess Plateau (Central North China,
a 56% decline in the past two decades with a range of 46% to 110%)
due to soil conservation projects, they have increased these transport
fluxes in China’s major karst regions (Southwest China, a 84%
increase with a range of 55% to 150%) because of severe rocky desertification.
These fluxes have completely overwhelmed the soil conservation efforts
in the Loess Plateau. Fluxes of these elements into aquatic environments
from Southwest China reached 46% of the total input in China in 2010.
These fluxes were higher than the inputs from point sources in the
region by a factor of 50 because of impacts of excessive agricultural
cultivation and geographical and climatic factors. These findings
indicate the enormous perturbation of terrestrial contaminant cycles
caused by soil erosion in karst regions and demonstrate the need for
long-term sustainable management of soil erosion and contaminant discharge
to protect fragile terrestrial ecosystems.