Human-induced changes in sediment properties and amplified endmember differences: Possible geological time markers in the future

Many rivers are facing human-induced systemregime shifts that have great environmental, ecological and social
implications, necessitating an increasing need to quantify the human influence on sediment properties and their
impacts on the source-to-sink system of marginal seas. The Huanghe and Changjiang Rivers have experienced a
dramatic reduction in sediment flux in recent decades, typifying the human influence on sediment properties of
global large rivers. Sediment samples from the two rivers were analyzed to obtain grain size, magnetic and geochemical
data. The results show a large difference in sediment properties between pre- and post-dam periods.
We applied a discrepancy factor to re-examine the magnetic and geochemical tracers that were previously
used in the two rivers. The discrepancy factors of most magnetic and geochemical tracers in the mud-sized sediments
of the tworivers increased by an average of about 109% after damconstruction. This suggests that humaninduced
changes in sediment properties have greatly improved the discriminatory ability between the sediments
from the two rivers. The results also raise the uncertainty of using previous tracers to distinguish between sediments
from the two rivers after damming. Furthermore, significant changes in sediment properties that happened
in a relatively short time may provide future geological time markers for sedimentary records with a
temporal resolution of 100–101 years. For marine environments, an approach for identifying sediment sources
based on multiple independent optimum tracers is also proposed, with composite magnetic (SIRM vs. HIRM)
and geochemical (Na2O vs. Zn) tracers being considered. The results of this work can advance our knowledge
of how human activities alter river systems, and identify a sustainable development model under systemregime
shifts for areas of high-intensity human activity.
Science of the Total Environment
Yang Yang, Jianjun Jia, Liang Zhou, Wenhua Gao, Benwei Shi, Zhanhai Li, Ya PingWang, Shu Gao⁎