Analysis of Rural Water Pollution Sources of Lushui Reservoir in Hubei Province

Lanjing LI, Mo CHEN

1. Department of Botany, Bonn University, Bonn 53173, Germany; 2. School of Resources and Environmental Science, Hubei University, Wuhan 430072, China

Abstract Pollution resulting from increased human activities is threatening the drinking water quality in China. Lushui Reservoir was selected as a typical example to represent polluted drinking water sources with rapid social economic development. This study analyzed the pollution load of Lushui Reservoir from rural areas by estimating the chemical oxygen demand (COD), ammonia nitrogen, total nitrogen and total phosphorus contributed by domestic sewage, agricultural activity, livestock breeding and aquaculture activity. Results show that the annual chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus loads in Lushui Reservoir were 180.44, 22.99, 33.15, and 3.99 t, respectively. The highest contribution to pollution load in all four aspects is domestic sewage, which was 89%, 96%, 82%, and 79%, respectively. Therefore, policies for sustainable development in the region should be directed primarily towards a reduction of domestic pollution.

Key words Water pollution, Environmental assessment, Rural areas, Lushui Reservoir

1 Introduction

Drinking water safety is a basic guarantee for human health and life safety. One of the global goals of the 21century is to ensure safe water supply and guarantee drinking water security for all countries. Lack of safe drinking water and proper sanitation are the biggest causes of disease in the world. By 2025, it is estimated that 2.4 billion people will live in water-stressed countries, and 3.4 billion people will live in water-scarce countries. Water scarcity forces people to drink contaminated water and thus increase the risk of water-borne diseases. Every year, 2 million people die from water-borne diseases such as diarrhea.

The problem of China’s water resources is a question of supply and demand, and water shortage is the biggest issue. While drinking water is lacking, industrial and agricultural water consumption is increasing day by day. Water shortage and water pollution have become more and more serious. According to the statistical data of Information Offce of the State Council of China, 400 of China’s 600 cities lack water. The total amount of freshwater in China is 6.200 billion m, which takes less than 0.018% of the global in total. The total water consumption has reached 5.3 trillion m, which is close to saturation. Among all the problems, excessive industrial water use and serious pollution are the most prominent. However, industrial water consumption continues to increase and the situation is very serious. Besides, water shortages have a major impact on food safety. Agriculture water consumes 68% of China’s water resources. Even more serious is that almost half of the water sources are polluted, the water quality in many areas is threatened, and the water quality of the original clean water sources has declined.

To understand the water quality threat from land pollutants, Lushui Reservoir, a reservoir located in Hubei Province of Central China, was selected for analyzing its source of pollution. The sources of pollution in Lushui Reservoir mainly include pollution from the upstream river and pollution from the reservoir area. This study presents an assessment of pollution sources in Lushui Reservoir. The assessment makes use of currently available data, applying a set of methodologies to the data for drawing conclusions to help design the pollution control approaches. Data was gathered through literature survey and field surveys in 2018.

2 Method and data collection

2.1 Current status of the reservoir

Lushui Reservoir is a direct-controlled reservoir managed by Changjiang Water Resources Commission. It is a large (II) type water conservancy hub with flood control, irrigation, power generation, tourism and water supply functions. It consists of the main dam, 15 auxiliary dams, a power station, a ship lift, and North-South irrigation canal. The controlled watershed area of Lushui Reservoir is 3 400 km, accounting for 86% of the total Lushui drainage basin (Fig.1). The total storage capacity of the reservoir is 7.42×10mwith an average water depth of 10.6 m. The reservoir bank is 132 km, and the average annual water inflow volume is 2.71×10 m. The annual average irrigation water is 1×10m.

Fig.1 Watery system of Lushui Reservoir

Before 1990, the water quality in Lushui Reservoir was better than the Class II standard of

National

Surface

Water

Environmental

Quality

Standard

and the transparency of the water body could reach about 4 m. With the rapid development of the social economy, the water quality has deteriorated year by year. In 2001, the entire water supply of Chibi City in Hubei Province had been stopped for 10 d due to the reservoir water pollution, which had a severe impact on the livelihood of residents and the economic development of this region. According to the long-term monitoring results, before 2000, the water quality in front of the main dam of the Lushui Reservoir was Class III throughout the year; from 2001 to 2005, the water quality in March was mainly Class IV, and in the rest of the time was Class III; from 2006 to 2010, the water quality was Class IV or V for half of the time.

2.2 Upstream contamination

According to the environmental monitoring station of Chibi City, among three times on-site monitoring in Tongcheng and Chongyang urban sewage outfalls in 2018, only the water quality on sewage outlet of Tongcheng Sewage Treatment Plant on July 3 and sewage outlet of Chongyang Sewage Treatment Plant on July 6 reached the grade 1B of

Discharge

Standard

of

Pollutants

for

Municipal

Wastewater

Treatment

Plant

(GB 18918-2002). The monitoring results of all the remaining sites exceeded the corresponding emission standards.In the rainy season, the muddy water is discharged from the upper reaches of the Lushui River into the Lushui Reservoir due to large precipitation in the whole river basin. The total phosphorus concentration in the river far exceeds Class III river standard of

Environmental

Quality

Standard

for

Surface

Water

(0.2 mg/L), which is the major factor that influences the total phosphorus in Lushui reservoir.

2.3 Reservoir contamination

The pollution sources in the reservoir area can be divided into domestic sewage, agricultural activity, livestock breeding and aquaculture activity. Domestic sewage can be divided into rural domestic sewage and urban domestic sewage.

2.4 Rural domestic sewage

Currently, there are 17 428 rural residents in Lushui Reservoir area. According to

National

Environmental

Protection

Plan

for

Drinking

Water

Sources

compiled by Chinese Research Academy of Environmental Sciences, the coefficient of daily domestic sewage of the rural population is 80 L/person. The villages along the Lushui Reservoir have rural domestic sewage treatment facilities, and the effluent is accounted for in accordance with grade 1B of

Discharge

Standard

of

Pollutants

for

Municipal

Wastewater

Treatment

Plant

(GB18918-2002), which is the COD: 60 mg/L, ammonia nitrogen: 15 mg/L, total nitrogen: 20 mg/L, total phosphorus: 1 mg/L.

2.5 Urban domestic sewage

At present, there are currently 27 498 urban residents in Lushui Reservoir area. The daily domestic water quota for urban residents is 150 L/person. The prediction of the amount of domestic sewage can be calculated as follows:

Domestic sewage=Daily average domestic water×Conversion factor×Collection rate

Conversion rate is taken as 0.8. The collection rate is taken as 1. Since the sewage pipe network is not yet fully constructed, all the wastewater produced is directly or indirectly discharged into the Lushui Reservoir. The effluent is accounted for in accordance with the standard of COD: 200 mg/L, ammonia nitrogen: 25 mg/L, total nitrogen: 30 mg/L, total phosphorus: 4 mg/L. Although the sewage discharge facilities are not in normal operation, considering the interception and absorption of pollutants by aquatic plants in the process of sewage entering the reservoir, the entering-lake coefficient is calculated as 60%.

2.6 Agricultural non-point source pollution

Agricultural non-point source pollution refers to the chemical fertilizer applied in agricultural production that enters the farmland. The nutrients cannot be completely absorbed by the crops, and the residuals are discharged into the water body with the surface runoff. According to statistical data, the total cultivated area of Lushui Reservoir is 296.87 ha and the total amount of annual fertilizer application in Lushui Reservoir is 120 t.

2.7 Livestock pollution

According to the data provided by the Agricultural Bureau of Chibi City, there are 1 520 pigs in individual households and family farms in Lushui Reservoir. The livestock emissions can be estimated with reference to empirical coefficients. The daily pollutant discharge coefficients of pig farms in central and southern regions: COD: 50 g/pig, ammonia nitrogen: 10 g/pig, the total nitrogen is 21.6 g/pig, the total phosphorus is 6.8 g/pig, and the inflow coefficient is calculated as 12%.

2.8 Aquaculture pollution

The total area of fish ponds around Lushui Reservoir is about 83.13 ha, and the total amount of aquatic products is about 2 600 t. According to the on-site survey, the aquaculture output in this area varies according to the water depth. Based on the

Manual

of

the

First

National

Pollutant

Source

Survey

of

Aquaculture

Industry

Pollution

Source

Discharge

Coefficient

and the actual situation of Lushui Reservoir, the pollutant discharge coefficient of freshwater fish farming aquaculture is used. According to the actual situation of aquaculture, the loss of pollutants is calculated as 35% of the input.

3 Results

According to Table 1, among the main pollutants of the Lushui Reservoir, annually, the COD emissions were 344.9 t, the ammonia nitrogen emissions were 40.23 t, the total nitrogen emissions were 71.41 t, and the total phosphorus emissions were 10.26 t. Statistical analysis shows that the chemical oxygen demand from domestic sewage accounts for 75% of the total emissions, and plays a decisive role in COD contribution.

Table1 Discharge quantity of water pollutant in the reservoir area (t/year)

Domestic sewage also contributes most to the ammonia nitrogen, which accounts for 85% of the ammonia nitrogen emissions. Besides, Domestic sewage accounts for 58% of the total nitrogen emissions, occupying a dominant position; followed by agricultural pollution, 23% and livestock pollution, 17%.

As indicated in Table 2, the discharge of pollutants is closely related to the sewage treatment capacity, and only when pollutants enter rivers and lakes can they constitute water pollution. Statistical analysis shows that the annual pollutants in the Lushui Reservoir area are mainly 180.44 t of chemical oxygen demand, 22.99 t of ammonia nitrogen, 33.15 t of total nitrogen, and 3.99 t of total phosphorus.

Table 2 Lake inflow quantity of water pollutant in the reservoir area (t/year)

Domestic sewage accounts for the largest proportion of COD, ammonia nitrogen total nitrogen and total phosphorus in the Lushui reservoir area, which are 89%, 96%, 82% and 79%, respectively. The reason is that domestic sewage with high organic concentration is directly discharged into the reservoir without treatment.

Agricultural pollution mainly contributes to total nitrogen and total phosphorus, which separately accounts for 13% and 7%. A large number of phosphate fertilizers are applied in agricultural activities, and most of the unabsorbed phosphate fertilizers flow into rivers and lakes with the erosion of water.

Livestock pollution plays 11% contribution to the total phosphorus. The high phosphorus content in livestock manure results in a high proportion of livestock pollution in total phosphorus pollution.

4 Discussion

Due to the low discharge standard of the sewage treatment plants in upstream cities such as Tongcheng and Chongyang, upstream water pollution is the main factor affecting the water quality of Lushui Reservoir. According to the environmental status of Lushui Reservoir and the inflow of pollutants in the reservoir area, domestic sewage is the main source of pollution affecting the water quality. Domestic sewage treatment construction is seriously lagging behind, and the established sewage treatment facilities have not effectively treated domestic sewage. Fertilizers used in agriculture are directly discharged into the water body along with surface runoff; a large volume of untreated livestock and poultry manure also directly enters the river; fish baits used in aquaculture is directly discharged into the waterbody, resulting in serious pollution in the local water body. For a long time, affected by traditional concepts and planned economic factors, Lushui Reservoir has formed a system of sectoral division, regional division, and multi-head management in ecological management, which is not conducive to the sustainable use of water resources. To solve these problems, the following actions are recommended.

(i) Minimizing the pollution from upstream water. It is recommended that the municipal government immediately report to the Xianning municipal government, requesting it to urge Tongcheng and Chongyang counties to strengthen the construction of urban sewage pipe networks and sewage collection and improve the discharge standards of sewage treatment plants. In addition, we recommend that the Lushui Reservoir have garbage interception and filtering facilities at the river entrance to prevent floating garbage from entering the reservoir and filter out suspended pollutants in the water.

(ii) Reinforcing strict management. Buildings unrelated to water source protection should be closed. In the first-level protection areas, mainly includes the land administration bureau family area, the swimming pool in Xinwangjiao, and the ship repair yard, totaling about 3 300 m. In the second-level protection area, mainly includes Resident concentration area and farmhouse, totaling about 10 400 m.

(iii) Improving sewage pipe network construction. The domestic sewage of the rural residents within the drainage area should be included in the sewage pipeline network, and after being treated by the sewage treatment plant, it can be discharged into the water body. It is recommended to build a main coastal sewage collection pipeline in the core protection area, and send the sewage to the downstream sewage treatment plant, to avoid sewage or sewage treatment plant tailwater from entering the lake.

(iv) Improving the garbage collection mechanism. It is recommended to promote the treatment and utilization of rural organic wastes and the collection and transfer of inorganic wastes. The methods of village collection, town transfer, and county treatment are recommended to use to collect and treat all the garbage in the villages along the lake. For example, provide 2-3 garbage collectors for each village, and each town should have at least one garbage transfer truck that meets the standards.

(v) Carrying out farmland runoff pollution prevention. It is recommended to actively guide and encourage farmers to use agriculture technologies such as soil testing fertilization, irrigation, and drainage separation to control the loss of nitrogen and phosphorus in farmland. Besides, it is recommended to promote the use of biological pesticides or high-efficiency, low-toxicity and low-residue pesticides.

(vi) Strengthening the centralized of the livestock industry. It is recommended to implement the separation of humans and animals, separation of farms from villages to reduce pollutant emissions. In addition, qualified livestock farms must incorporate sewage into the sewage pipe network. Livestock breeding should be prohibited in Class A protected area and new livestock farms should be prohibited in Class B protected area.

(vii) Reinforcing the management of aquaculture. In the case of local water quality exceeding the standard, some fish ponds should be ecologically closed and returned to the lake to ensure that the water bodies in the reservoir area meet the water quality standards.