Studies On Water Environment Status And Water Quality Assessment Of Main Surface Water Systems In The Dezhou Irrigation District Of Lower Yellow River

With the accelerating process of industrialization and urbanization, water environmentproblem has already become the most serious ecological and environmental problem ofhuman society. Dezhou irrigation district is an important part of the lower reaches of theYellow river irrigated area, which is as the water supply for agriculture, and has also becomeimportant source of water for industrial production and the residents in Dezhou. Irrigationfrom the Yellow River played an important role in the protection of the healthy developmentof the national economy. However, with the continuous development of the Dezhou irrigationdistrict, the amount of water diversion from the Yellow River is increasing, and the irrigationdistrict also appear serious water environmental problems.The main surface water systems in Dezhou irrigation district was studied in this study.The major environmental indicators （pollutants） were analyzed for the spatial distribution andpossible sources, and water environment status of the main water systems was discussed.Moreover, water environmental quality assessment and preliminary health risk assessment ofdissolved trace metals in the main water systems were determined. The main contents andresults of this paper are as follows:1. Spatial distribution and sources of the major environmental indicators （pollutants）ofthe main water systems in Dezhou irrigation district showed that:（1） The pH was in range of7.84⁹.74, an average of8.65, and was weakly alkaline. Thehighest average pH was8.86of the Tuhai River, and average minimum was8.36of theYellow River. The variability of EC in the Weiyun-Zhangweixin River was the largest, and theaverage EC was the highest. In general, the EC of the Dehuixin River was increased along theflow direction, and the variability of other rivers were significantly which affected by pointsource pollution caused by industrial and agricultural productions extremely.（2） The concentrations of total phosphorus （TP） and dissolved total phosphorus （TDP） inthe Weiyun-Zhangweixin River were the highest, and the variability was the largest.Especially the levels of contamination in Weiyun River was more serious that in the upstream,followed by Tuhai River, and lowest in Dehuixin River as well as had a relatively stable change trend. The change trend of TP and TDP were basic consistent from the upstream to thedownstream of the each river. Moreover, the spatial distributions of phosphorus in suspendedmatter had significantly differences, which were affected by suspended matter concentrationas well as industrial and agricultural productions, and the maximum concentrations were inthe Zhangweixin River.（3） The concentrations of NO₃^--N within each river had significantly differences. Theaverage concentrations of NO₃^--N were in the ranked order Majia River＞Tuhai River＞Dehuixin River＞Weiyun-Zhangweixin River, and the variability in Majia River was thehighest. The spatial variations of NH4+-N were found insignificantly within each river, and themaximum concentration was in the Tuhai River.（4） The concentrations of dissolved trace metals of Ba, Fe, Li, Mn, Sr, Zn, and non-metalof B had significant spatial variation. The concentrations of Sr were the highest, and thelowest were Zn. And each element also had spatial differences, in particularly, spatialvariations of Fe, Mn, Zn were the most significant. The concentrations of B, Fe, Li, and Mnfrom Zhangweixin River were the highest among the rivers. The correlation analysis showedthat there was positive correlation for each of the Li-Mn, Li–B, Li–Fe, and Fe–Mn pairs,suggesting that these elements might have a similar sources, and negative correlation of theSr-Ba.（5） The sources of pollution in Dezhou irrigation district included point source pollutionand non-point source pollution. Point source pollution included wastewater from upstreamand the locality, and the pollution caused by township enterprises. Non-point source pollutionwas from the agricultural irrigation and drainage, loss of pesticide fertilizers and livestockmanure.2. According to the Surface Water Environment Quality Standard of China （GB3838-2002）, National Drinking Water Quality Standards of China （GB5749-2006） andEnvironmental Protection Agency （EPA） of the United States, the comparative evaluationmethod and comprehensive pollution index method were selected to assess water quality ofthe water environment status of Dezhou irrigation district. The results of the comparativeevaluation method were: （1） There were about82.85%of the phosphorus samples have reached Class III (0.1＜TDP≤0.2mg·L^-1) or exceeded water quality standards in the whole irrigated area. And70%samples have reached Class V (0.3﹤TDP≤0.4mg·L^-1) or exceeded class V (TDP﹥0.4mg·L^-1)in the Zhangweixin River.70%of the samples have reached the degree of heavycontamination.（2） The concentrations of NH4+-N were not exceed water quality standards, and about54.29%of the NO₃^--N samples have exceeded water quality standards. About80%NO₃^--Nsamples in Tuhai River were contaminated, the degree of contamination in Dehuixin Riverwas the minimum.（3） The concentrations of Ba、Li、Sr and Zn were not exceed water quality standards, butthe concentrations of B, Fe, and Mn have exceeded48.57%,2.86%and25.71%of drinkingwater standards, respectively.（4） On the whole, the contamination levels of Weiyun-Zhangweixin River was the mostserious among the main water systems, and the main pollutants were TDP, B, Fe, and Mn,followed by Majia River, the main pollutants of TDP, NO₃^--N, B and Mn.The results of comprehensive pollution index method were: The main water systems inDezhou irrigation district all have been contaminated. The degree of contamination were inthe ranked order Weiyun-Zhangweixin River＞Majia River＞Dehuixin River＞Tuhai River＞Yellow River Drainage. Weiyun-Zhangweixin River has reached moderate contamination.TDP, NO₃^--N, B and Mn have reached the degree of heavy contamination.3. Health risk assessment of dissolved trace metals of Ba, Fe, Li, Mn, Sr, Zn, andnon-metal of B of the main water systems in Dezhou irrigation district were assessed by EPAhealth risk assessment model via oral exposure and dermal exposure. The assessment resultswere:（1） Hazard Quotients(HQ_oraland HQdermal) associated with corresponding metals of themain water systems were assessed via two kinds of exposure methods, HQ_oraland HQ_dermalwere both less than1, and HQdermal＜HQ_oral, which indicates that the trace metals of the mainwater systems in Dezhou irrigation district may have little or no health threat to localresidents.（2） Hazard Quotients(HQ_oraland HQdermal) associated with corresponding metals of sampling sites were assessed via two kinds of exposure methods, except the HQ_oralof NO.28was greater than1(HQ_oral=1.28), the HQ_oraland HQdermalof the other sampling sites were allless than1, and HQdermal＜HQ_oral, which indicates that the trace metals of the most samplingsites in Dezhou irrigation district could pose little or no risks to local residents. However, Mnand its compounds can cause human poisoning, the contamination of Mn should be controlledactively to reduce the hazards to human health.Moreover, the paper also proposed a series of water control measures, which can providea theoretical basis for contamination control and the recovery of river ecological functions ofDezhou irrigation district.