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Soil Lysimeter Excavation for Coupled Hydrological, Geochemical, and Microbiological Investigations
Published on: September 11, 2016
Topographic drainage impedance is associated with organic matter compositions and mercury partitioning in a
Xizi Yang1, Martin Tsz-Ki Tsui2, Xiaoyu Song3
1School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong Special Administrative Region of China; State Key Laboratory of Soil Pollution Control and Safety, Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China.
Abstract:
We examined associations among topographic position, organic matter compositions, and methylmercury (MeHg) pools and partitioning in montane-alpine soils. Triplicate 60-cm soil cores were collected at 12 sites along a 1666-4503 m elevational transect on the eastern slope of Gongga Mountain, spanning an alluvial plain, an intermontane basin, and ridge-shoulder terrain. A drainage impedance index (DI), calculated from plan curvature and slope, represented potential lateral water convergence relative to downslope drainage. DI was negatively associated with the weight-averaged nominal oxidation state of carbon (NOSC) of water-extractable organic matter (adjusted R2 = 0.31, p = 0.034). NOSC was used as a formula-derived molecular descriptor of detected water-extractable organic matter. For exploratory sample-level comparisons, 21 site-depth analytical units were assigned to operational lower-NOSC (NOSC < -0.2; n = 4) or higher-NOSC (NOSC ≥ -0.2; n = 17) groups. The lower-NOSC group contained a larger median contribution of lipid-like formulas and a smaller contribution of phytochemical-like formulas. Basin surface sites contained larger bulk MeHg pools, while ridge sites had a larger operationally defined water-extractable share of MeHg. These observations identify DI as a candidate screening covariate for spatial variation in MeHg pools and partitioning. Independent transects with direct hydrologic and redox measurements can test the proposed processes in future studies.
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