In 2005, the monitoring of water quality of the 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 Standards for the Quality of Surface Water Environment (GB3838－2002), whereas the assessment of nutrition status of water body was carried out according to Technical Regulations on the Assessment Method and Classification for Eutrophication of Lakes (Reservoirs), which is formulated by China National Environmental Monitoring Center.

5.1 Monitoring of Water Quality of the Reservoir

In 2005, a total of 13 monitoring sections were set up in the Reservor areas, 6 were along the  mainstream of the Yangtze River, and 7 were established along the primary tributaries of the Yangtze River. The location of the mainstream sections were at Zhutuo, Tongguanyi and Cuntan of Chongqing, Qingxichang in Fuling, Tuokou in Wanzhou and Guandukou in Badong. The locations of the tributary monitoring sections included Beibei at the Jiangling River, Linjiangmen, Wujiangwulong, Yulinhekou, Pengxihekou, Daninghekou and Xiangxihekou. Water quality assessment included 13 items such as pH value, disolved oxygen, permanganate index, BOD₅, ammonia nitrogen, petroleum, total phosphorus, mercury, cadmium, arsenic, copper, lead and hexavalent chromium.

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

5.1.1 Monitoring of the water quality of the mainstreams of the Yangtze River in the Reservoir Area 

In 2005, water of river sections in the mainstream of the Yangtze River of the Reservoir area enjoyed relatively good quality with all 6 sections meeting Grade III national surface water quality standard. No case of inferior to Grade V standard were observed during each month.

From May to September, some pollutants of 5 monitoring sections went beyond water quality standard but Guandukou Section, which still met Grade III standard. The pollution was striking during July and September.Total phosphorus, lead and permanganate index were the major pollutants failing to meet the standards. The water quality of these sections could meet or superior to Grade III quality standards in other months.

Table 5-1 Water quality of the mainstreams of the Yangtze River in Three Gorges Reservoir Area in 2005`

Section

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sept.

Oct.

Nov.

Dec.

Whole

year

Zhutuo

III

III

III

III

III

III

V

IV

IV

III

III

III

III

Tongguanyi

III

III

III

III

III

III

V

IV

IV

III

III

III

III

Cuntan

III

III

III

III

IV

IV

V

V

IV

III

III

III

III

Qingxichang

III

III

III

III

IV

IV

V

V

IV

III

III

III

III

Tuokou

III

III

III

III

III

III

V

IV

IV

III

III

III

III

Guandukou

III

II

III

III

III

III

III

III

III

III

III

III

III

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

In 2005, tributaries of the Yangtze River in the Reservoir area had relatively poor water quality, no monitoring sections met Grade I and II standard, 3 sections meeting Grade III water quality standard and 4 meeting Grade IV standard, accounting for 42.9% and 57.1% respectively. Among them, the water of Beibei, Wulong and Linjiangmen sections met Grade III standard. While the sections of Yulin River Mouth (RM), Pengxi River Mouth, Daning River Mouth and Xiangxi River Mouth, only met Grade IV water quality standard due to the concentration of total phosphorus.

Table 5-2 Water quality of the primary tributaries of the Yangtze River
in Three Gorges Reservoir Area in 2005

Section

River name

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.

Aug.

Sept.

Oct.

Nov.

Dec.

Whole

year

Beibei

Jialing

III

III

III

III

III

III

V

III

III

IV

III

III

III

Linjiangmen

Jialing

III

III

IV

III

III

III

V

III

III

III

III

III

III

Wulong

Wujiang

II

III

III

III

III

III

III

III

III

III

III

III

III

Yulin RM

Yulin

III

III

III

III

IV

V

IV

V

IV

IV

IV

III

IV

Pengxi RM

Pengxi

IV

IV

IV

III

IV

IV

IV

III

III

IV

III

IV

IV

Daning RM

Daning

IV

IV

IV

IV

IV

III

III

IV

IV

IV

IV

IV

IV

Xiangxi RM

Xiangxi

IV

IV

IV

IV

IV

IV

IV

IV

V

IV

IV

IV

IV

5.2 Early Warning Monitoring of Water Blooms in the Reservoir Area and Emergency Monitoring

5.2.1 Early warning monitoring of water blooms

In 2005, early warning monitoring on water blooms at the back water areas of 13 primary (or Class I) tributaries of the Yangtze River in the Chongqing area of the Three Gorges Reservoir was carried out. 26 monitoring sections were established in the 13 Class I tributaries with one section in the middle and one section at the end of each tributary. The assessment of comprehensive nutrition status of the water body included 5 items such as chlorophyll a, total phosphorus (TP), total nitrogen, transparency and permanganate index.

The monitoring results indicated that during March-May and September-October of 2005, 12.5% (March), 23.1% (April), 19.2% (May), 19.2% (Sept.) and 7.7% (Oct.) of the sections of the back water areas of the Class I tributaries of Chongqing Reservoir area was under eutrophication. Among the eutrophicated sections, the water of Nanmenkou Section at the Zhuxi River of Wanzhou District and Daocheba Section of Shennuxi Brook of Wushan County were under very serious eutrophication.

Table 5-3 Synthetical nutrition status of the water bodiesof the backwater area in the Yanze River

Nutrition	Mar.		Apr.		May		Sept.		Oct.
staus	Section	Proportion	Section	Proportion	Section	Proportion	Section	Proportion	Section	Proportion
	amount	(%)	amount	(%)	amount	(%)	amount	(%)	amount	(%)
Oligotrophic	6	25	6	23.08	4	15.38	5	19.23	5	19.23
Mesotropher	15	62.5	14	53.85	17	65.38	16	61.54	19	73.08
Light eutropher	1	4.17	3	11.54	3	11.54	4	15.38	2	7.69
Middle eutropher	1	4.17	1	3.85	1	3.85	1	3.85
Hyper eutropher	1	4.17	2	7.69	1	3.85
Total	24	100	26	100	26	100	26	100	26	100

5.2.2 Emergency monitoring of water bloom

In 2005, many water blooms at different degree occurred in the backwater areas of some Class I tributaries of the Yangtze River of the Reservoir areas. The environmental monitoring stations of the Reservoir areas at different levels carried out emergency site monitoring activities in time. The monitoring outcomes of Chongqing Environment Monitoring Center and the Water Environmental Monitoring Center of the Yangtze River Basin showed that the occurrences of water blooms were relatively concentrated during March and July.

In early March of 2005, water blooms happened in the Baolong River and Daxi River in Wushan County with about 3 km section of the former and 5 km of the latter under moderate eutrophication. During the mid 10-day of March, water blooms occurred at the Baolong River, Daxi River and Daning River of Wushan County and the Tongzhuang River, Chixi River of Zigui County and waters near Muyu Island near the Dam. Among them, the infected length was about 5 km for the Baolong River under moderate eutrophication, 7 km for the Daning River under light eutrophication and 5 km for the Daxi River under moderate-to-severe eutrophication. The water of the Tongzhuang River, Chixi River and waters near Muyu Island of Zigui County became brown. During the late 10 days of March, water blooms occurred in the Baolong River and Shennu Brook of Wushan County, Modao Brook, Tangxi River, Pengxi River, Changtan River and the Bajiao of the Yangtze River in Yunyang County with the infected length of about 4.0 km, 2.5 km, 3.0 km, 2.5 km, 3.0 km, 1.5 km and 1.0 km respectively, the water of such sections was under moderate to severe eutrophication.

In April, dinophyceae water bloom occurred at the Meixi River, its water showing the color of soy sauce with Peridiniopsis sp. in dominance 3.0×107 /L. During late April and the first 10 days of May, the Rangdu River in Wanzhou District experienced a water bloom with moderate eutrophication. In the first 10 days of May, water blooms also occurred in the Meixi River, Zhuyi River and Caotang River of Fengjie County with the water under light to moderate eutrophication. In the last 10 days of May, the water of the Meixi River was under moderate eutrophication again.  

In July, blue algae water blooms occurred at Xiangxi River. The water of the river showed blue-green color with strong stinky smell. The dominant algae species was Oscillatoria sp. with the density of 1.1×108 /L of such algae cells.