Chemical Property Variation Trend Analysis and Quality Evaluation of Water in Wei River

Xiaoxiang QIU,Aigang LU

1.College of Chemistry and Life Science,Weinan Normal University,Weinan 714099,China;2.Shaanxi Key Laboratory of Riverine Wetland Ecology and Environment,Weinan 714099,China

Wei River is one of the rivers flowing through Weinan.It feeds into the Yellow River from west to east in the territory with a main stream overall length of 818 km,and divided into upper,middle and lower reaches[1].The drainage area of Wei River is of 134 800 km2.The total water resource volume of Wei River is of 11 056 000 000 m3,in which the surface water resource volume is of 100.40 m3.The climate of Weinan city is semihumid and semiarid,and the obvious characteristics of such climate are less rainfall,big wind throughout the year and low temperature.The annual average amount of precipitation can reach 450-700 mm,and the monthly amount of precipitation changes greatly,especially for the precipitation from July to October,accounting for more than 60% of the total amount of precipitation in one year.In recent years,the demand for water has grown due to the quality of people’s lives,the conversion of modern agricultural production mode and industrialization with the flourishing development of economy,such that the water resource of Wei River becomes deficient;and meanwhile,the produced sanitary sewage,water containing agricultural fertilizer and industrial sewage are discharged into Wei River without treatment mostly,which results in continuously aggravated pollution of Wei River,seriously threatening the orderliness of production and living in Weinan.

Therefore,this study conducted stationing and sampling along Wei River at three different sites from Jan-uary to December of 2014,further andlyzed water quality variation trend of Wei River and performed quality evaluation.By monitoring water in Wei River,pollutant type and distribution could be made clear,revealing pollution way,such that pollution variation trend and possible problems could be predicted and prompted.Monitoring water in Wei River is of significance in correctly understanding water quality,solving existing problems,discovering potential problems,improving people’s quality of life and ecological environment in Weinan,rationally utilizing water resource and finally realizing permanent development.

Research Methods

Monitoring sites and items

The monitoring sites covered Shawangdu,Shuyuan and Tongguan Diaoqiao in Weinan,3 state-controlled sections in total.The monitoring period was from January to December of 2014 with a monitoring frequency of 12 times yearly.

The monitoring items were the test items of surface water(quoted from “Technical Specifications Requirements for Monitoring of Surface Water and Waste Water”),and 12 pollution indexes had to be measured for Wei River,such as water temperature,pH,dissolved oxygen(DO),chemical oxygen consumption (Mn method)CODMn,five-day BOD(BOD5),ammonia nitrogen(NH3-N),chemical oxygen consumption (Crmethod)CODCr,volatile phenol VP,oils,total phosphorus(TP),total nitrogen (TN)and fluoride F.Sample collection was conducted according to related technique standards and specifications[2].

Analysis methods for monitoring

The analysis methods for water monitoring was selected according to The Method for Testing Water and Waste Water(the fourth edition)by the State Environmental Protection Administration:the editorial board for“The Method for Testing Water and Waste Water”[3].

Analysis of Water Quality Variation in Wei River

Analysis method for water quality variation trend

With the three sections of Wei River as the study object,the periodic time series method was used for managing monitoring data including twelve pollution indexes and organic pollution index according to time series.To analyze the variation trend of Wei River and to understand the significant difference of the variation trend in statistics,in “Technical Specifications of Environmental Quality Report Compilation”the Spearman rank correlation coefficient method,the requirements of which were as follows:

The time period serial numbers Y1,Y2,···,YNof data were listed,corresponding data was then endowed with serials numbers X1,X2,···,XNand arranged from small to large,and rank correlation coefficientYsfor testing was calculated according to following formula:

Wherein:direpresents the difference of variableXiand variableYi;Xirepresents the serial number according to concentration values of periods 1-N from small to large;andYirepresents the serial number according to time.

According to actualconditions(one-or two-sided test),significance level of 0.05 or 0.01 and data size n,the absolute value of Spearman rank correlation coefficientYsand the critical valueWpthereof are compared,ifYs＞Wp,the variation trend is of significance,but otherwise it is not;and ifYsis a negative value,the variation is on the decrease,and ifYsis a positive value,the variation is on the increase.

Variation trend analysis and discussion of Wei River water quality

With Shawangdu,Shuyuan and Tongguan Diaoqiao sections as study objects,the variation trends of water temperature,pH,DO,CODMn,BOD5,NH3-N,CODCr,VP,oils,TP,TN and F were analyzed from January to December of 2014 using national standard method.The analysis result was shown in 1-12.

Changes in water temperatureThe Shawangdu,Shuyuan and Tongguan Diaoqiao sections were selected and determined forinter-monthly water temperature changes in 2014.It was found by water temperature monitoring that,among the water temperatures of the three sections from January to December,the water temperatures of August were the highest.Shawangdu section had a higher water temperature among the three sections.The results were shown in Fig.1.

Changes in pHpH can reflect the acidity or alkalinity of a water sample,if pH＜7,the water sample is acidic,and if pH＞7,it is alkaline.From Fig.2,the pH values of all the three sections were greater than 7,i.e.,they were alkaline.Seen from the overall trend,the alkalinity from April to May and that from November to December were the largest.For Shawangdu section,the alkalinity of December was the largest;in the case of Shuyuan section,the alkalinity from April to May was the largest;and for Tongguan Diaoqiao,the alkalinity of November was the largest.

Changes in oilsAs shown in Fig.9,the oils of Shawangdu section were on the decrease which was not significant;Shuyuan section showed a downtrend which was not obvious;and Tongguan Diaoqiao section had a nonsignificant uptrend.The reason was that the coverage by oil slick could influence the self cleaning capacity of water.Therefore,the water quality of Tongguan Diaoqiao section was worse.

Changes in organic matterShawangdu section:DO showed a significant uptrend (Fig.3);CODMn presented a non-significant downtrend(Fig.4);BOD5was on the decrease which was not significant(Fig.5);NH3-N showed a significant downtrend(Fig.6);CODCrexhibited a non-significant downtrend(Fig.7);volatile phenol exhibited a non-significantdowntrend(Fig.8);and all the monitoring values of DO,CODMn,BOD5and oils could satisfy the Class IV water standard,NH3-N exceeded the standard,and the volatile phenol belonged to the Class III water standard.

Shuyuan section:DO showed a significant uptrend(Fig.3);CODMnpresented a non-significantdowntrend(Fig.4);BOD5 was on the decrease which was not significant(Fig.5);NH3-N showed a significant downtrend(Fig.6);CODCr exhibited a non-significant uptrend (Fig.7);volatile phenol exhibited a significant uptrend(Fig.8);and all the monitoring values of DO,CODMn,BOD5and oils could satisfy the Class IV water standard,NH3-N exceeded the standard,and the volatile phenol belonged to the Class III water standard.

Tongguan Diaoqiao section:DO showed a significant uptrend(Fig.3);CODMnpresented a non-significant downtrend (Fig.4);BOD5was on the decrease which was not significant(Fig.5);NH3-N showed a significant downtrend (Fig.6);CODCrexhibited a non-significant downtrend (Fig.7);volatile phenol exhibited a significant uptrend(Fig.8);and all the monitoring values of DO,CODMn,BOD5and oils could satisfy the Class IV water standard,NH3-N exceeded the standard,and the volatile phenol belonged to the Class III water standard.

Changes in inorganic matterThe F of Shawangdu section was very low,showing a non-significantuptrend(Fig.12);for Shuyuan section,its F was very low,showing a non-signifi-cant downtrend(Fig.12);and The F of Tongguan Diaoqiao section was very low as well,showing a non-significant downtrend(Fig.12).

Water eutrophicationThe content of nutrient element N or P in plant was investigated.For Shawangdu section,TP showed a non-significant downtrend(Fig.10);TN showed a significant downtrend (Fig.11);and all TP monitoring values could satisfy the Class IV water standard while TN exceeded the standard.In the case of Shuyuan section,TP exhibited a non-significant downtrend (Fig.10);TN exhibited a significant downtrend (Fig.11);and all TP monitoring values could satisfy the Class IV water standard while TN exceeded the standard.For Tongguan Diaoqiao section,TP showed a nonsignificant downtrend (Fig.10);TN showed a significant downtrend(Fig.11);and all TP monitoring values could satisfy the Class IV water standard while TN exceeded the standard.

Water Quality Evaluation of Wei River

Evaluation index and method

In order to reflect water quality truly and accurately,the“integrated index”methodreflecting the combined impact of various pollutants was applied.Since the pollution of Wei River was mainly organic pollution,this study investigated the pollution indexes including DO,CODMn,BOD5and NH3-N,and calculated the organic pollution index.Based on the organic pollution index,water quality variation of Wei River was analyzed and evaluated[5].

wherein:A is the integrated index of organic pollution;L is the monitoring value of each water quality index,mg/L;and C is the evaluation standard of each water quality index,mg/L.

Water quality evaluation of WeiRiver

Based on the water quality monitoring data from January to December of 2014,the integrated indexes of organic pollution of the three sections were calculated.The results showed that:in the period from January to April and the period from July to September,the pollution level of Shawangdu section was the highest,the second was Shuyuan section,and the pollution of Tongguan Diaoqiao section was lightest.From May to June,Shuyuan suffered heaviest pollution,Shawangdu was next to it,and the pollution was the lightest for Tongguan Diaoqiao section(Fig.13).Comprehensively,the integrated indexes of organic pollution of Shawangdu,Shuyuan and Tongguan Diaoqiao sections showed significantdowntrends,indicating that the water quality was getting better.In October,the three sections presented lowest pollution levels throughout the whole year.

The above analysis result showed that:the three sections had obviously-improved water quality,indicating the pollution control measures were significantly effective in this year and thus had to be consolidated continuously and improved.It was worth noting that it was necessary to take effective measures from January to June to prevent water quality from deteriorating,to thereby ensure the water quality was stable and reached the standard throughout the whole year.

Discussion

From the analysis of Wei River’water quality variation trend,the twelve pollution indexes can be classified into 6 types,in which the organic pollution index and the eutrophication index were worth noting.The main organic pollution factor NH3-N influencing the water quality of Wei River showed a significant downtrend at each of Shawangdu,Shuyuan and Tongguan Diaoqiao sections,and CODMnand BOD5exhibited a non-significant downtrend at each of Shawangdu,Shuyuan and Tongguan Diaoqiao sections,indicating that it was necessary to pay attention to the variation trends of CODMnand BOD5at the three sections and that powerful measures were needed to control organic pollution.Furthermore,we could knew that in water of Wei River,NH3-N and TN were relatively higher than other factors,resulting in the characteristic of high organic matter;and NH3-N exceeded the standard in the case of present data though it presented a significant downtrend,so it was necessary to take more-effective measures to control pollution.

The monitoring data of Shawangdu,Shuyuan and Tongguan Diaoqiao sections throughout 2004 satisfied the Class IV water standard substantially.The organic pollution index indicated that the pollution at Tongguan Diaoqiao section was the lightest.In overall,the water quality of Wei River became better obviously,and it was necessary to consolidate and strengthen the control and management of Wei River while improving existing control measures.In addition,it was indicated by the monitoring data from January to June of 2014 that it was necessary to take measures in time to better control pollution.

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