Speciation and Distribution of Silver in the Danshuei River Watershed
Date Issued
2008
Date
2008
Author(s)
Lee, Cheng-Shiuan
Abstract
Spatial variations and export loading of Ag in the waters of the Danshuei Tributary were investigated. The Danshuei River is the largest estuary that flows through the city of Taipei, Taiwan. Physical filtration methods were used in this study to define Ag speciation operationally. The following forms were determined: total dissolved (≤0.45 μm), colloidal (1 kDa ~ 0.1 μm, 0.1 μm ~ 0.45 μm), truly dissolved (≤1 kDa), and particulate (≥0.45 μm) fractions. Particulate samples were further separated into different phases by sequential leaching methods. The concentrations of Ag in the total dissolved fraction (≤0.45 μm) ranged from 1.6 to 300 pM. In general, upstream concentrations fell within a fairly narrow range, 1.6 ~ 7.5 pM. Downstream Ag concentrations showed significant increases (~300 pM) as the rivers entering the urban area, indicating the strong impacts of Ag-laden discharge effluents. On average, more than 70% of the 0.45 μm filter-passing Ag was associated with colloidal matter (1 kDa ~ 0.45 μm), decreasing with increasing salinity. All fractions of dissolved Ag exhibited a non-conservative estuarine removal mixing pattern. A strong correlation was found between the colloidal Ag and colloidal Fe concentrations, implying that Fe controlled the removal behavior of Ag in the estuary. The concentrations of particulate Ag in waters ranged from 0.05 to 10 μg/g, and its spatial distribution was very similar to that of the total dissolved Ag. More than 80% of particulate Ag was associated with iron-manganese oxyhydroxide/sulfide phases. The refractory phase was elevated in hypoxic river waters, implying that reduced sulfur minerals such as pyrite were likely formed. The high affinity of Ag to suspended particulates was reflected by a high mean particle/water distribution coefficient of log Kd=5.7±0.4. The export loading flux of dissolved Ag was about 0.14 mol/day. About 86% of the Ag input from whole watershed was removed within the estuary.
Subjects
Ag
speciation
spatial distribution
Danshuei River
flux
Type
thesis
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