Nengwang Chen, Yinqi Wu, Jiezhong Wu, Xiuli

Yan, and Huasheng Hong.Biogeoscience, 2014. 119: 95-109.

Natural and human factors controlling

dissolved silica (DSi) export from the watershed were investigated for the

Jiulong River watershed in Southeast China, which is a subtropical region where

tectonic activity and high runoff combine to create a global hot spot for DSi

flux. Results showed that river DSi was fairly high (246 ± 76 µmol

L−1) due to granite lithology and increased human perturbation. The

percentage of granite, paddy soil, arable land, and forest land each explain

47–69% of the spatial variation in DSi level at the subwatershed scale. Land

use change (deforestation for agriculture) and soil erosion increased DSi transfer

from terrestrial systems towards the river. Discharge explains over 95% of the

variation in DSi fluxes, and a discrepancy of up to 16% of watershed DSi export

was observed between low and high flow conditions. DSi retention is more

significant in the dry season, likely due to biological uptake by diatoms in

reservoirs under low flow conditions and higher residence time. However, this

may be offset by high runoff flush in the wet season, which might cause

unfavorable conditions for diatom growth and DSi depletion. There has been

little overall change in DSi in estuarine water in recent decades. However,

seasonal variation and occasionally fluctuation of DSi during extreme

hydrological events (rainstorms) does exist, with important implications for

the coastal ecosystem. This research confirmed that human activities and land

use change have substantially altered Si delivery, cycling and riverine export

to the coast in this region.

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