;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.