In 2004, the monitoring of water quality of mainstream and tributaries of the Yangtze River, early-warning monitoring for water blooms during sensitive period as well as monitoring of pollution belts in riverbanks constituted all components of water environmental quality monitoring work in the Three Gorges Reservoir area. The assessment and testing method of water quality were conducted in accordance with the "Environment Quality Standards for Surface Water (GB3838-2002)", whereas the assessment of nutrition status of water body was carried out according to the "Technical Regulations on the Assessment Method and Classification for Eutrophication of Lakes (Reservoirs)", which is formulated by China National Environmental Monitoring Center.

Sketch map for location of water quality monitoring sections in Three Gorges Reservoir area of the Yangtze River

5.1 Monitoring of Water Quality of the Mainstreams of the Yangtze River in the Reservoir Area

16 monitoring sections were set up in the mainstream of the Yangtze River in the reservoir area, and six water quality monitoring activities were conducted during the three water periods, ie, dry period (Februrary), level water period (May) and high water period (August). Three vertical lines in the left, middle and right side of each monitoring section were set to collect water samples at the depth of 0.5m under the water surface for analysis. Water quality assessment included 15 items such as pH value, disolved oxygen, permanganate index, BOD₅, ammonia nitrogen, petroleum, volatile phenol, total phosphorus, COD, cyanide, mercury, lead, cadmium, arsenic and hexavalent chromium.

5.1.1 Annual water quality monitoring in the reservoir area 

In 2004, water quality of the sections in mainstream of the Yangtze River of the reservoir area met or was superior to Grade III water quality standard. No sections meeting Grade I water quality standard were observed, and sections of water quality meeting Grades II and III standards accounted for 6.3% and 93.7% of the total samples respectively.

During dry period: no section meeting GradeⅠwater quality standard was observed in the mainstream of the reservoir, and the number of sections of water quality meeting the Grade II and III standards took up 50.0% respectively.

During level water period: no sections with Grade I water quality were observed, and the number of sections meeting Grade II and III water quality standards took up 37.5% and 62.5% respectively.

During high water period: there were no sections meeting Grade I and II water quality standards and the water quality of each section monitored met Grade III standard.

Table 5-1 Assessment result of water quality of the mainstreams of the Yangtze River in Three Gorges Reservoir Area in 2004

Section	Location	Dry period	Level water period	High water period	Whole year
Zhutuo	Yongchuan City	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Tongguanyi	Jiangjin City	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Wanglongmen	Yuzhong District	Ⅱ	Ⅲ	Ⅲ	Ⅲ
Cuntan	Jiangbei District	Ⅱ	Ⅲ	Ⅲ	Ⅲ
Huangcaoxia	Changshou District	Ⅱ	Ⅲ	Ⅲ	Ⅱ
Yazuishi	Fuling District	Ⅱ	Ⅱ	Ⅲ	Ⅲ
Qingxichang	Fuling District	Ⅲ	Ⅱ	Ⅲ	Ⅲ
Mishiquan	Fengdu County	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Jiutiaohe	Zhongxian County	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Lian'erqi	Zhongxian County	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Tongziyuan	Wanzhou District	Ⅱ	Ⅱ	Ⅲ	Ⅲ
Shaiwangba	Wanzhou District	Ⅱ	Ⅱ	Ⅲ	Ⅲ
Xiayansi	Yunyang County	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Yanmatou	Yunyang County	Ⅲ	Ⅲ	Ⅲ	Ⅲ
Baidicheng	Fengjie County	Ⅱ	Ⅱ	Ⅲ	Ⅲ
Peishi	Wushan County	Ⅱ	Ⅱ	Ⅲ	Ⅲ

5.1.2 Year-on-year water quality variations

There was no obvious change in water quality of the mainstreams of the Yangtze River in the reservoir area compared with the previous year. The water quality of most sections of the river still met Grade III water quality standard, and the number of sections meeting Grade II water quality standard declined by 13.7 percentage points.

Table 5-2 Year-on-year comparison of the water quality of the mainstreams of the Yangtze River in the Three Gorges Reservoir Area

Water periods	Dry period		Level water period		High water period		Whole year
Year	2003	2004	2003	2004	2003	2004	2003	2004
Number of total sections monitored	15	16	15	16	15	16	15	16
Percentage of sections meeting Grades I~ II water quality standards (%)	33.3	50	33.3	37.5	20	0	20	6.3
Percentage of sections meeting Grade III water quality standard (%)	53.3	50	66.7	62.5	80	100	80	93.7
Percentage of sections meeting or being better than Grade III water quality standard (%)	86.7	100	100	100	100	100	100	100

5.2 Monitoring of Water Quality of Tributaries of the Yangtze River in the Reservoir Area

A total of 9 monitoring sections were set up in 6 tributaries of the Yangtze River in the reservoir area, including 2 sections under national water quality monitoring program (Daxigou section in Jialing River and Maliuzui section in Wujiang River) and 7 others (Beibei and Linjiangmen section in Jialing River, Wulong section of Wujiang River, Yulin River mouth, Xiaojiang River mouth, Daning River mouth and Xiangxi River mouth). Three vertical lines and three monitoring spots were set up in each of the three sections of Daxigou, Maliuzui and Linjiangmen, while three vertical lines and six monitoring spots were set up in each of the two sections Beibei and Wulong.

For the setions of Yulin River mouth, Xiaojiang River mouth, Daning River mouth and Xiangxi River mouth, two vertical lines and two monitoring spots on each line were set up. One monitoring work of water quality was carried out in each month to all the river sections, totaling 12 times throughout the whole year of 2004.

5.2.1 Water quality of sections under national monitoring program

The water quality monitoring work of river sections under national monitoring program included 23 basic items (excluding total nitrogen) in accordance with the "Environmental Quality Standards for Surface Water (GB3838-2002)".

The assessment results indicated that in 2004, the water quality of Maliuzui section of Wujiang River fell into Grade V standard, while water quality of Daxigou section of Jialing River was inferior to Grade V standard. Fecal coliform bacteria were the only pollutant and generally exceeded the standard. Comparing the water quality in twelve months of the year, we could see that in the Maliuzui section of Wujiang River, water quality was Grade IV in January and February, Grade V from May to October, worse than Grade V in March, April, November and December. The annual average water quality of this section was of Grade V The Daxigou section of Jialing River met Grade V water quality standard in each month of the whole year. Generally speaking, the water quality of Wujiang River was better than that of Jialing River.

Table 5-3 Water quality of the national river monitoring sections in the Yangtze River tributaries of the Three Gorges Reservoir areas in each month of 2004

Month

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec.

Whole year

Section

Daxigou section

Water quality1

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than Grade Ⅴ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Worse than GradeⅤ

Water quality2

Ⅲ

Ⅱ

Ⅲ

Ⅲ

Ⅲ

Ⅱ

Ⅲ

Ⅲ

Ⅱ

Ⅲ

Ⅲ

Ⅱ

Ⅲ

Maliuzui section

Water quality1

Ⅳ

Ⅳ

Worse than GradeⅤ

Worse than GradeⅤ

Ⅴ

Ⅴ

Ⅴ

Ⅴ

Ⅴ

Ⅴ

Worse than GradeⅤ

Worse than GradeⅤ

Ⅴ

Water quality2

Ⅲ

Ⅲ

Ⅲ

Ⅲ

Ⅱ

Ⅱ

Ⅱ

Ⅱ

Ⅲ

Ⅲ

Ⅱ

Ⅱ

Ⅱ

Note: Water quality1: Each of the 23 basic items was included in the assessment.
Water quality2: 22 items were included in the assessment, excluding fecal coliform    bacteria.

5.2.2 Water quality of ordinary sections

For ordinary sections, water quality assessment included 11 items such as pH value, dissolved oxygen, BOD₅, ammonia nitrogen, permanganate index, arsenic, hexavalent chromium, copper, cadmium, lead and petroleum.

The assessment results showed that the water quality of the sections of the Yangtze River tributaries in the Three Gorges Reservoir area was good. One section met Grade II water quality standard; 5 sections met Grade III water quality standard and one met Grade IV water quality standard, taking up 14.3%, 71.4% and 14.3% of the total respectively. Among all these sections, the Xiangxi River mouth section met Grade II water quality standard, and the water quality of five sections at Linjiangmen, Yulin River mouth, Wulong, Xiaojiang River mouth and Daning River mouth met Grade III standard. Beibei section of Jialing River only met Grade IV water standard due to the concentration of petroleum exceeding the standard.

5.3 Early Warning Monitoring of Water Blooms in Sensitive Period in the Reservoir Area

5.3.1 Nutrition status of the water bodies

In the first ten days of June 2004, early warning monitoring was conducted to some Class I tributaries of the Yangtze River in the reservoir area upon the coming of sensitive period of water bloom. 24 monitoring sections were established in 12 Class I tributaries with one section in the middle and one section at the end of each tributary. The assessment of nutrition status of the water body included 5 items including chlorophyll a, total phosphorus , total nitrogen, transparency and permanganate index. The results indicated the followings.

During the first ten days of June 2004, over 50% of Class I tributaries of the reservoir area were in a state of eutrophication. Among the 24 sections, 14 were under eutrophication, accounting for 58.3% of the total, the rest 10 were under intermediate eutrophication, taking up 41.7% of the total. Among the eutrophicated sections, 12 were under light eutrophication and were distributed mainly in Longhe River of Fengdu County, Ruxi River and Huangjin River of Zhongxian County, Baolong River in Wushan County, Modao Brook, Changtan River and Daxi River in Yunyang County. Two sections in Zhuxi River of Wanzhou County were under moderate eutrophication. The sections under intermediate nutrition were mainly distributed in Quxi River of Fengdu County, Daning River and Shennü Brook in Wushan County and Tangxi River, Modao Brook and Changtan River in Yunyang County.

5.3.2 Occurrence of water bloom

In the spring and summer of 2004, many water blooms at different degree occurred in some Class I tributaries (including reservoir bends) of the Yangtze River in the reservoir area. The occurrences were relatively concentrated in a certain period of time with rather fixed covering area.

Water blooms happened in Xiangxi River in the late February, the mid March, early April and early June, which lasted for 5 days, one month and ten days respectively, and the river sections affected mainly ranging from over 2 km upstream of the Gorge to the inflow river mouth with a length of about 20 km. The water was turbid and resembled the color of soy sauce or with a tint of chartreuse. The dominant algae were Cyclotella sp. and Asterionellopsis sp..

Water blooms occurred at Daning River in late March to early April, late May, early June and late June, which lasted for about ten days. The range of water bloom in Shennü Brook were concentrated in the river section from Bawu Gorge to Daning River mouth, Shuanglong-Yinwotan-longmen river section and the section from Maduhe river to river mouth with a length of nearly 25 km. The water body appeared the color of light chartreuse, chartreuse or light soy sauce color and smelled quite fishy. Cyclotella sp, Asterionellopsis sp, Peridinium, Pandorina and Microcystis were the dominant algae.

The water blooms in both Shennü Brook and Baolong River occurred from the late May to early June and late June, each lasting for about ten days. The occurrence in Shennü Brook ranged from Daoche Dam to No. 6 navigation mark, about 1.5 km long. There were red threadlike things in water body with dominating algae being Pyrrophyta, Cyclotella sp. and Pandorina. The water bloom in Baolong River involved the river section between Hongyan River and Putao Dam with a length of about 2.5 km. The water body appeared chartreuse in color with fishy smell. The dominated alga was Microcystis.

In early March, Fenghuangshan Reservoir bend in the front of the Dam had water blooms lasting for one week or so. The water body looked like soy sauce and the dominant algae were Asterionellopsis sp. and Peridinium.

5.4 Monitoring of Pollution Belts in Riverbanks

In 2004, one monitoring activity was conducted to the pollution belt near the sewage outlet of Yunyang Sewage Treatment Plant during level water period (the last ten days of October) and dry period (the last ten days of December) respectively. One section was set up 150m upstream from the sewage outlet as the inflow control section. Another five sections with varied intervals were identified 500 m downstream of the waters near the riverbank. Six vertical lines with varied intervals were set up in each section for sample collection in line with the diffusing pattern of the pollutants, and three vertical sampling points in each vertical line were identified for collecting water samples from the depth of 0.5m, 5m and 10m beneath the water surface for analysis. During the monitoring process, such items as water depth, flow speed, flow and the distance to the bank were also measured. The water quality monitoring items included permanganate index (COD_Mn), ammonia nitrogen (NH₃-N) and total phosphorus (TP).

5.4.1 Hydrological conditions

After impoundment of the Three Gorges Reservoir, the water surface gradient of the Yangtze River had mitigated, leading to very low velocity of water flow. During the level water period, the maximum velocity of surface water flow was 20cm/s with the average of only 6cm/s. In the dry period, the velocity near the bank was generally less than 2cm/s. The sharp decrease of flow velocity was not conducive to the dilution and diffusion of pollutants and made it easy to form high-concentration pollution belts near the sewage outlets.

5.4.2 Range of the pollution belts

The range of the polluted areas of the river varied due to different loads of COD, NH₃-N and TP as well as different velocity of water flow. The monitoring results indicated that there were both pollution belts of which the monitoring items were in excess of that of the background level and pollution belts of which the water quality could not meet Grade II standard in the sections downstream of the sewage outlets of Yunyang County.

● Level water period

The pollution belt with COD_Mn exceeding the level of the control section was over 320m long and 60 ~100m wide. The TP pollution belt with the concentration of TP more than the level of the control section was over 320m in length and 60~150m in width. The TP pollution belt failing to meet the Grade II water quality standard was nearly 250m in length and 20~80m in width. The NH₃-N pollution belt with its concentration exceeding that of the background level was approximately 300m long and 30~80m wide. And The NH₃-N pollution belt with its concentration failing to meet Grade II water quality standard was around 160m in length and 20~80m in width.

● Dry period

The permanganate index pollution belt with the COD_Mn in excess to the control section was around 50m long and 10~40m wide. The TP and ammonia nitrogen pollution belts with the TP and NH₃-N level exceeding that of the control section were more than 320m in length and 40~150m in width. The TP pollution belt with TP level failing to meet Grade Ⅱ water quality standard was nearly 150m long and 40~60m wide. Both the length and width of the pollution belt with the concentration of ammonia nitrogen failing to meet national standard were about 10 m.

Table 5-4 Range of pollution area of each water quality monitoring item in level water period

Section	Distance to the sewage outlets	Width of pollution belts over the control level (m)			Width of pollution belts whose level failing to meet Grade Ⅱ water quality standard (m)
	(m)	CODMn	TP	NH3-N	CODMn	TP	NH3-N
1	10	60	60	60	－	66	60
2	50	80	80	80	－	80	80
3	150	100	100	30	－	20	20
4	240	70	120	80	－	20	－
5	320	70	150	－	－	－	－

Table 5-5 Range of pollution area of each water quality monitoring item in dry period

Section	Distance to the sewage outlets	Width of pollution belts over the control level (m)			Width of pollution belts whose level failing to meet Grade Ⅱ water quality standard (m)
	(m)	CODMn	TP	NH3-N	CODMn	TP	NH3-N
1	5	10	40	40	－	40	10
2	50	40	50	50	－	50	－
3	150	－	110	110	－	60	－
4	240	－	150	150	－	－	－
5	320	－	150	150	－	－	－