| 摘要: | 埔心溪流域為桃園縣境內灌溉引用水源之一，然因早期環保意識缺乏，以及國內常見灌排不分之故，使得流域上游流經工業區的黃墘溪水質惡化，不論是渠道溪水或底泥常有重金屬濃度偏高的現象，影響整個流域的灌溉用水安全，長久下來衝擊引用此灌溉水源的承受農地土壤之品質。本研究為瞭解埔心溪流域補助灌溉用水水質與渠道底泥現階段受重金屬污染的程度與分佈狀況，於民國一0二年十月至一0三年三月枯水期間，針對埔心溪流域設置六個採樣點(中工公園、24-1號河水、24-6號河水、25-3號河水、24號河水、圳頭新堰)，進行灌溉用水採樣與分析；另於民國一0三年二月九日一期稻作整田前，進行一次渠道底泥採樣作業，分析底泥所含重金屬濃度。水質及底泥之採樣方式參照環保署公告之程序，樣品於桃園農田水利會水質暨土壤實驗室(具TAF認證資格)檢驗分析，分析方法依據行政院環境保護署公佈之檢驗方法實施，並確實依照品保品管規定執行相關作業流程。
研究結果顯示灌溉水質指標項目在各次採樣中，以電導度、硫酸鹽、氯鹽、氨氮及重金屬銅等超出灌溉用水水質標準次數最為頻繁，且在所有採點中，新莊二號溪25-3號河水的灌溉水質不合格率為各採樣點最高。若以灌溉用水品質分級來看，僅中工公園與24-6號河水二處灌溉水質尚可(接近C2-S1等級)，其餘各點灌溉水質不佳，不適合做為農田灌溉使用。如比較採樣的時間點，則發現於夜間採樣所得的灌溉水水質較差，雨天則因雨量稀釋作用而降低灌溉水污染程度。進一步將水質檢測的結果利用相關係數分析後，可推測新莊二號溪上游之印刷電路板製造產業為該區可能的污染源。底泥的檢測結果則顯示，各採樣點以銅超出底泥品質指標上限值情況最為嚴重，但鎘在本次調查檢測中未被驗出。而從底泥重金屬之富集程度可看出，銅、鉛、鋅的含量明顯受到人為污染影響，25-3號河水渠道的底泥甚至已達「非常嚴重」之程度。最後，將所有水質與底泥的測值經模擬推估後可知，灌溉水所含的重金屬濃度於短時間內不致使土壤污染達食用作物農地管制標準，但若加上沖刷底泥所含的重金屬濃度來計算，則將大幅度縮短所需年限。
綜上結果，埔心溪流域各支流已受到不同程度的污染，建議水利會於高污染區段採取較密集的監測採樣頻率，並進行渠道底泥清除工作，以確保農地土壤及農作物產品的安全。
;While the Pu-Hsin Creek has been serving as an important source of irrigation water in Taoyuan County, due to the poorly-planned policy of water resources management in Taiwan its catchment basin is oddly also the receiving water body from effluents of industrial zones situated in the upstream area. Given that illegal discharges of untreated wastewater from industrial plants along the waterway have occurred repeatedly over the past few decades, water and sediment quality in irrigation channels of the entire Pu-Hsin Creek basin have been impacted, resulting in several incidents of agricultural land contamination with heavy metals. To understand the current state of irrigation water quality and heavy metal concentrations in the sediment of the irrigation channels, as well as the spatial variations of these parameters within the entire Pu-Hsin Creek basin during the dry season when the solutes in the irrigation water were experiencing low dilution rates, water and sediment sampling campaigns were conducted from October 2013 to March 2014 at six sites, namely (i) the Chung-Kung Park, (ii) the Weir #24-1 on the Huang-Chien Creek, (iii) the Weir #24-6 on the Chung-Fu branch, (iv) the Weir #24 on the Pu-Hsin Creek, (v) the Weir #25-3 on the Hsin-Chuang Creek, and (vi) the Zuntou diversion dams. The campaigns included day-time and night-time, as well as clear-day and raining-day samplings. All the aqueous and sediment samples were processed and analyzed in a TAF certificated laboratory affiliated with the Taoyuan Irrigation Association using the NIEA methods.
Results of aqueous sample analysis from 10 campaigns show that among all the examined parameters associated with irrigation water quality, electrical conductivity, sulfate, chloride, ammonium-nitrogen and copper concentrations were the ones frequently exceeded the irrigation standards; of all the 6 sampling sites, samples taken from the Weir #25-3 (representative of the Hsin-Chuang Creek quality) had the highest exceeding rates (defined as the ratio of the sample number that exceeded irrigation standards to the total sample number), and only Chung-Kung Park and the Weir #24-6 had adequate irrigation water quality. It was also observed that day-time samples had better water quality than night-time samples, and compared to raining days, the pollution level in samples from clear days was relatively alleviated. Further analysis of these water quality data using Pearson Product-Moment Correlation suggested that PCB plants located in the upstream area of the Hsin-Chuang Creek might have been the probable pollution source in this watershed. Results of sediment analysis indicated that although cadmium was not detected, sediments in the irrigation channels of this basin have been markedly polluted by copper. Enrichment Factor analysis suggested that copper, lead and zinc accumulated in sediments were most likely resulted from anthropogenic activities, and the sediment quality in the channel of the Weir #25-3 have reached the “very severe” level. Lastly, based on all the analytical data resulted from this investigation, it was estimated that the level of heavy metals in the receiving farm land would not immediately (i.e., on a timescale of decades) exceed the control standards of the SGPR Act if only heavy metals in irrigation water were taken into account; however, this estimation was drastically shortened to be less than a year when the sediment was considered.
Taken together, these results point out that the branches of the Pu-Hsin Creek basin have experienced different severity of pollution. As a result, it is suggested that for highly polluted area, the Irrigation Association may need to increase the sampling frequency and implement dredging activities for contaminated sediments to ensure food safety and public health. |
