Historical Record of Trace Metals offshore Southwestern Taiwan
| Autor: | Chun-Yu Lee, 李純瑜 |
|---|---|
| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 Rapid economic and industrial development over the past five decades in Taiwan has caused the expense of environment. Heavy metals pollution issue has gradually emerged after the 1980s and the contaminated area has extended to the coastal environment. With the tectonic setting and climatic condition in Taiwan, a considerable amount of pollutants could be carried into the marine environment. The aim of this study is to investigate the distribution and transportation of heavy metals through sedimentary records offshore southwestern Taiwan. Gaoping River (GPR) is the largest river in southern Taiwan and stands out of other major world rivers for its high concentrations of dissolved and particulate metals. Gaoping Submarine Canyon (GPSC) has been proven to be the major pathway for the transportation of terrestrial materials discharged from GPR into the deep sea. In this study, 210Pb dating, grain size and geochemical analyses (Zn, Cr, Pb, Co, Ni, Cu, Cd, Fe, Mn, Al, Ti, Mg, K) were applied to the sediment cores sampled in three different sedimentary environments around the GPSC: (I) Gaoping Slope sites, (II) Deep sea sites at lower reach of GPSC, and (III) Penghu Submarine Canyon site. Since trace metals could be derived from natural or anthropogenic sources, reference background materials (UCC, ACST, UC-YC and Average Shale) are compared to distinguish the source of the trace metals. Compared to previous studies conducted in the nearshore regions, pollution signals are hardly to be found in our further seaward sites (Gaoping Slope & deep sea), most of the measured trace metals display a stable temporal distribution with a level near or under the natural background. However, slight enrichment of Pb and its sharp increase were still recorded within the surface sediments at the Gaoping Slope sites while the records are absent in the deep sea. Moreover, the Gaoping Slope cores which have conformably recorded the pollution of Pb can even clearly illustrate the onset of the industrial development in Taiwan despite their subtle difference from the natural background. Other than the anthropogenic input of the trace metals, natural hazards (earthquakes, typhoons, etc.) are also found to accelerate the accumulation of trace metals in the marine environment. The comparable amount of cumulative mass of the trace metals between Gaoping slope and the deep sea sites and the relatively consistent Ti/Al molar ratio between these two sedimentological regimes, all suggesting that the sediments discharged from GPR could cross the narrow shelf and made a considerable amount to transport and accumulate in the deep sea. Though deep sea can act as an important sink for the terrestrial materials due to the cross-shelf transport, pollution record was not found in the deep sea sites as the pollution signals can be largely diluted during the further seaward transport, implying the pollution in the deep sea is insignificant in the study area. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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