Research on rural domestic sewage discharge, influencing factors and pollution loads in the Yangtze river basin – Nature

Executive Summary

This report presents an analysis of rural domestic wastewater discharge characteristics within China’s Yangtze River Basin, evaluated through the lens of the United Nations Sustainable Development Goals (SDGs). The study utilizes geographic information visualization, pollutant load assessment, and correlation analysis to provide a comprehensive overview. Findings indicate that average per capita discharge levels are relatively low at 39.24 L/day. Correspondingly, pollutant levels are also low, with Chemical Oxygen Demand (COD) at 27.50 mg/day, ammonia nitrogen (NH₃-N) at 1.53 mg/day, total nitrogen (TN) at 2.74 mg/day, and total phosphorus (TP) at 0.22 mg/day. At a basin-wide scale, the current discharge has a negligible impact on maintaining target water quality standards, a key component of SDG 6 (Clean Water and Sanitation). However, significant regional disparities exist, posing challenges to localized water quality. The analysis reveals that discharge levels are strongly correlated with social factors such as education and income, linking directly to SDG 8 (Decent Work and Economic Growth) and SDG 12 (Responsible Consumption and Production), as well as natural factors like temperature and rainfall. This research provides critical data for managing rural wastewater and advancing sustainable development in similar regions globally.

Introduction: Aligning Rural Wastewater Management with Sustainable Development Goals

The management of rural domestic wastewater is a critical challenge that intersects with multiple Sustainable Development Goals. Historically, rural environmental infrastructure has been underdeveloped, hindering progress towards SDG 6 (Clean Water and Sanitation). Untreated rural sewage, a major source of nonpoint source pollution, releases significant amounts of nitrogen and phosphorus into water bodies. This exacerbates eutrophication and threatens aquatic ecosystems, directly impacting SDG 14 (Life Below Water) and SDG 15 (Life on Land). Furthermore, contaminated water sources pose severe risks to public health, food safety, and the well-being of rural communities, undermining SDG 3 (Good Health and Well-being) and SDG 11 (Sustainable Cities and Communities).

In China, the rural population of 477 million generates substantial wastewater, yet the treatment rate is only 45%. The Yangtze River Basin, home to approximately 70% of China’s population and vital freshwater resources, faces mounting pressure from this discharge. The conflict between rural wastewater pollution and the preservation of ecosystem services constrains coordinated regional development and jeopardizes the drinking water safety for 400 million people. Addressing this issue is paramount for achieving sustainable development and ensuring the long-term ecological security of the region.

Methodology for SDG-Aligned Assessment

Study Area and Scope

The study focuses on the Yangtze River Basin, China’s largest river basin. It encompasses areas across 18 provinces, municipalities, and autonomous regions. The research investigates the characteristics of rural domestic wastewater, its pressure on water quality objectives in line with SDG 6.3 (improving water quality by reducing pollution), and the socio-economic and natural factors influencing discharge levels.

Data Sources and Processing

• Wastewater Discharge Levels: Data were sourced from the Ministry of Ecology and Environment of China’s “Handbook of Statistical Methods and Coefficients for Emission Sources.”
• Socio-Economic Data: Information on population, education, disposable income, and consumption expenditures was obtained from the China Statistical Yearbook (2022) and provincial statistical yearbooks.
• Natural Environment Data: Average annual temperature and precipitation data were sourced from the NOAA National Centers for Environmental Information (NCEI). Average annual humidity data were generated from China’s ground climate dataset.
• Water Quality Targets: Data for tributaries were sourced from the “Handbook on the Functional Zoning of Important Rivers and Lakes in the Country.”

Analytical Framework

1. Geographic Information Visualization: Kriging interpolation was used in ArcGIS to visualize the spatial distribution of wastewater discharge, identifying hotspots and areas requiring targeted interventions to meet SDG 6.
2. Correlation Analysis: Spearman’s correlation analysis was conducted using SPSS to identify the relationships between wastewater discharge and various social and natural factors, providing insights relevant to SDG 8, SDG 11, and SDG 12.
3. Pollutant Load Assessment: A standardized pollution load method was employed to quantify the environmental impact of pollutants relative to water quality standards, directly assessing pressures on aquatic ecosystems as outlined in SDG 14 and SDG 15.

Analysis of Findings in the Context of SDGs

SDG 6: Status of Rural Water and Sanitation

The overall state of rural wastewater discharge in the Yangtze River Basin reflects significant gaps in achieving Target 6.2 (adequate and equitable sanitation for all). While the average discharge level of 39.24 L/(capita·day) is low compared to urban and developed nation standards, it points to underdeveloped water infrastructure and services.

• Overall Discharge Characteristics: The average per capita emission levels for key pollutants were found to be:
  • Chemical Oxygen Demand (COD): 27.50 mg/day
  • Ammonia Nitrogen (NH₃-N): 1.53 mg/day
  • Total Nitrogen (TN): 2.74 mg/day
  • Total Phosphorus (TP): 0.22 mg/day
• Regional Disparities: Significant regional differences highlight inequities in development. Discharge levels progressively increase from upstream to downstream regions. The average discharge in the downstream Taihu Lake Basin (57.72 L/day) is more than double that of the upstream Yalong River Basin (26.32 L/day). This trend indicates that as regions develop economically, their environmental footprint grows, posing a future challenge to sustainable water management.

SDG 14 & 15: Ecological Impact on the Yangtze River Basin

The standardized pollution load analysis indicates that, on a macro scale, the discharge of rural domestic sewage has a limited effect on maintaining the Class II water quality objectives for the main tributaries. This suggests that current pollution levels do not pose a systemic threat to the basin’s aquatic life (SDG 14) or freshwater ecosystems (SDG 15). The median equivalent pollution load ratios were negligible:

• COD: 0.13%
• NH₃-N: 0.22%
• TN: 0.41%
• TP: 0.17%

However, certain regions face acute pressure. The Han River Basin, for instance, exhibits equivalent pollution load ratios between 57.22% and 58.39%, indicating a significant localized threat to water quality and ecosystem health. This underscores the need for targeted interventions to prevent ecological degradation in vulnerable sub-basins.

SDG 8, 11, & 12: Socio-Economic and Natural Drivers of Pollution

The analysis identified key drivers of wastewater discharge, linking environmental outcomes to patterns of economic growth, community development, and consumption.

• Social Factors (SDG 8, 11, 12):
  • Education and Income: Years of education, per capita disposable income, and consumption expenditures are all significantly and positively correlated with wastewater discharge levels. This suggests that as economic conditions improve (SDG 8), consumption patterns change (SDG 12), leading to increased water use and pollution. This trend highlights the urgent need to decouple economic growth from environmental degradation to build sustainable communities (SDG 11).
• Natural Factors:
  • Climate: Average annual temperature and humidity are positively correlated with discharge, while average annual rainfall shows a significant negative correlation. These factors influence water usage habits for hygiene and daily activities.

Conclusion and Recommendations for Sustainable Development

This study provides a crucial baseline for understanding the challenges of rural wastewater management in the Yangtze River Basin and its implications for achieving the Sustainable Development Goals. The findings lead to the following recommendations:

1. Strengthen Sustainable Infrastructure: The low discharge levels reflect a need for improved rural water and sanitation infrastructure. As China implements rural revitalization strategies, it is critical to integrate sustainable wastewater treatment solutions that support SDG 6 and ensure the long-term effectiveness of these initiatives.
2. Implement Targeted Monitoring and Management: The notable pollution pressure in specific upstream regions, coupled with rapid socio-economic changes from poverty alleviation actions, necessitates continuous monitoring. This will help manage emerging pollution threats and ensure that progress towards SDG 1 (No Poverty) does not compromise water quality targets under SDG 6.3.
3. Promote Further Research for Tailored Solutions: This macro-scale research should be supplemented with micro-level studies that account for local topographical and climatic variations. Such research is essential for developing context-specific, effective management strategies that can be applied to complex river systems globally, advancing the broader 2030 Agenda for Sustainable Development.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on rural domestic wastewater discharge in the Yangtze River Basin connects to several Sustainable Development Goals (SDGs) due to its focus on water quality, environmental health, rural development, and public well-being. The following SDGs are addressed:

• SDG 6: Clean Water and Sanitation: This is the most central SDG. The entire study revolves around analyzing wastewater discharge, pollutant loads (COD, nitrogen, phosphorus), and the impact on water quality in the Yangtze River, directly addressing the core themes of water and sanitation management.
• SDG 3: Good Health and Well-being: The article explicitly links rural domestic sewage to public health risks. The introduction states that indiscriminate discharge can pose a “threat to the safety of drinking water” and “adversely affects… public health,” and is “directly related to… maternal and child health.”
• SDG 11: Sustainable Cities and Communities: The research focuses on rural areas, a key component of sustainable communities. It highlights the “lack of suitable governance models and regulatory strategies” for rural environmental management and the need for investment in “rural environmental infrastructure,” which are crucial for creating sustainable human settlements.
• SDG 14: Life Below Water: The article discusses the pollution of the Yangtze River Basin, a major freshwater ecosystem that ultimately affects marine environments. It mentions problems like “water quality eutrophication” caused by nutrients such as nitrogen (N) and phosphorus (P) from domestic sewage, which aligns with the goal of reducing pollution from land-based activities.
• SDG 2: Zero Hunger: The introduction connects water pollution to food security by stating that the issue “adversely affects rural food production, food safety, and public health” and is related to “food supply security.”
• SDG 8: Decent Work and Economic Growth: The study identifies a significant correlation between socio-economic factors and pollution levels. It analyzes how “per capita disposable income” and “consumption expenditures” influence wastewater discharge, linking economic conditions directly to environmental outcomes.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the issues discussed, several specific SDG targets can be identified:

1. Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.
   • The article directly addresses this target by analyzing the pollutant load (COD, NH3-N, TN, TP) from untreated rural sewage. It notes that in China, the “rural domestic sewage treatment rate reaching only 45%,” highlighting the significant proportion of untreated wastewater.
2. Target 6.5: By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate.
   • The study’s comprehensive analysis of the entire Yangtze River Basin, covering multiple provinces and tributaries, serves as a basis for integrated water resource management. It provides “reference data for the analysis and management of rural domestic wastewater discharge” at a large basin scale.
3. Target 3.9: By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.
   • The article’s concern with pollutants in drinking water sources directly relates to this target. It mentions that the issue influences “drinking water safety for approximately 400 million people in the middle and lower reaches of the Yangtze River.”
4. Target 11.1: By 2030, ensure access for all to adequate, safe and affordable housing and basic services and upgrade slums.
   • Wastewater management is a basic service. The article’s finding that “investment in rural environmental infrastructure have consistently lacked effective attention” points to the gap in providing this essential service in rural communities.
5. Target 14.1: By 2030, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution.
   • The study quantifies nutrient pollution (nitrogen and phosphorus) from a land-based source (rural domestic sewage) that flows into a major river system, which is a primary pathway for pollutants to reach marine environments.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article mentions and uses several quantitative and qualitative indicators that align with official SDG indicators for measuring progress.

1. Proportion of wastewater safely treated (Indicator 6.3.1):
   • The article explicitly states that “the rural domestic sewage treatment rate reaching only 45%” in China. This percentage is a direct measure for this indicator.
2. Ambient water quality (related to Indicator 6.3.2):
   • The study provides detailed measurements of water quality parameters, including “a chemical oxygen demand (COD) of 27.50 mg/(capita·day), an ammonia nitrogen (NH3-N) content of 1.53 mg/(capita·day), a total nitrogen (TN) amount of 2.74 mg/(capita·day), and a total phosphorus (TP) content of 0.22 mg/(capita·day).”
   • It also assesses the impact on “maintaining the target water quality standards” (e.g., Class II and Class III), which serves as a benchmark for ambient water quality.
3. Pollution Load and Intensity:
   • The article calculates the “Equivalent Pollution Load” to quantify the pressure of pollutants on the river system. This method provides a standardized indicator of pollution impact.
   • It also measures the average water discharge level, “39.24 L/(capita·day),” which is an indicator of water use intensity and wastewater generation in rural areas.
4. Socio-economic Drivers:
   • The analysis uses “educational level,” “per capita disposable income,” and “consumption expenditures” as indicators to understand the social and economic factors driving pollution, which is relevant for developing targeted policies.

4. Summary Table of SDGs, Targets, and Indicators

Source: nature.com