第6卷‧第3期,
197803
, pp. 227-243
曾文溪下游之砷異常及板岩屑與漂砂
- 作者:
顏富士
- 作者服務機構:
國立成功大學
- 中文摘要:
臺灣西南沿海曾文溪三角洲的地下水含有0.5~2.5μg的砷,構成砷異常現象,此一砷之來源,與由濁水溪南下及下淡水河北上之板岩屑漂砂確有關係存在。本文根據91枚採自將軍溪至鹽水溪沿海之漂砂與潟湖內沉積物,及沿岸與溪流水質測得之氧化還元電位,在進行化學、礦物學,及沉積學之相關分析後,得知若干事實與砷之來源有關: 在曾文溪三角洲地區內之漂砂砷含量,由南向北漸次升高。依此升高形態,本區漂砂可略分為五區。在每一區內漂砂之含砷量與所含之板岩屑量、其表面積成正相關,此一相關由北向南漸不明顯,在溪口亦趨模糊。同時沙洲之內側(潟湖)所含砷量顯然較外側高。所有漂砂之含砷量,均較板岩本身所含者高。 漂砂平均粒徑與所含板岩屑百分比率均由南(.210 mm與20~25%)向北遞減(.189 mm與10%)。板岩屑之平均粒徑較漂砂大,但變化有限,其粒度分布形態以頂頭額汕北為界,發生顯然的變化。 根據上列事實,本文作成下列與砷來源有關之結論: 曾文三角洲地區之砷異常現象與板岩屑之存在正相關,板岩屑具有砷清潔夫(Arsenic Sca-venger)的功能,有清潔本區海面之砷污染,造成砷富集之能力。砷富集功能之顯著性可能與該板岩屑之來源區、行經水域與在本區中沉積位置有關。由下淡水河北來者較濁水溪南下者差。處溪口、沙洲外側,越往本區南者均較相對者差。 富集砷之過程可能包括有機與無機作用。富集後之砷的化學狀態與含於原板岩中者可能不同。 由於板岩屑具有富集砷之功能,同時其粒徑為本區沉積物中最粗者,足可造成良好之含水層,因之在曾文三角洲外向伸展中,此等必然漸被埋入地下深處之板岩屑,當成為良好的含水層,並將其富集之砷釋同地下水中,導至本區地下水高含砷之事實。而砷異常現象以發生於曾文溪口以北地區為主。 本區之板岩屑來自南北兩向,其南上應由下淡水河,北下則由濁水溪無疑。二者活動範圍以曾文溪口北之頂頭額汕與網仔寮汕為界。 本文並提出本區內砷之地環境地球化學循環之可能模式。
- 英文摘要:
After obtaining the relevant chemical, min-eralogical, and sedimentological data of 91sediment samples collected from the offshorebarrier islands and the lagoonal areas along theTsengwen Delta (from Chiangchungchi to Yen-shueichi) in the field and the laboratory work,this paper points out the following possibilities. The arsenic anomaly in the downstreamarea of Tsengwenchi is positively correlated withthe slate ingredient content in the sediments.Slate sand can be an arsenic scavenger that haseliminated the arsenic pollution possibly occurringin the adjacent sea, and instituted the arsenicenrichment in the sediments. The conspicuous-ness of the enrichment may be attributed tothe source of the slate sands and the siteswhere the sands deposited:Slate sands de-livered from Shiatansheichi generally showlower As values than those from Chushueichi.Sands deposited at the estuary, exterior rims ofthe barriers also contain lower As values thanthe opposite equivalents. However, the generaltrends of higher As values go north. Since the slate sand has been the depositionalloci of arsenic as well as a good material foran aquifer due to its larger particle size, on theoutgrowth of the Tsengwen Delta, the slate sandwhich certainly be subsequently covered by thefiner sediments transported from the upstreamof Tsengwenchi, will turn into the importantaquifer. In such a case the enriched arsenicmay be reliberated into the environment (groundwater) and may result in arsenic anomalyprevailing in the area.
- 中文關鍵字:
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