Agricultural Non-Point Source Pollution in the Erhai Lake Basin: Unveiling Complexities and Targeted Solutions
Agricultural non-point source pollution represents a multifaceted environmental challenge stemming from dispersed emissions linked to farming activities and rural domestic wastewater. Unlike industrial point sources of pollution, these diffuse sources make monitoring, quantification, and control highly complex. The Erhai Lake Basin, a vital freshwater resource in western Yunnan Province, China, exemplifies this problem. It is increasingly pressured by escalating pollutant loads derived from intertwined agricultural production and rural settlements. Understanding the spatial and sectoral contributions of various pollutants is essential to formulating science-based, efficient management strategies that safeguard water quality in this ecologically sensitive region.
In 2007, national statistics from China illuminated that agriculture accounted for approximately 40% of the primary waterborne pollutants, a figure that has only heightened in recent years. With a population density of 256 inhabitants per square kilometer in the Erhai Lake Basin, the interdependence between agricultural activities and rural domestic sewage discharges creates overlapping pollution sources. Differentiating the relative inputs from these sources is critical for effective mitigation policies, especially considering the difficulty of centralized control over non-point sources.
Recently, a research team led by Professor Wen Xu from China Agricultural University undertook a comprehensive empirical study focused on the Haixi area of Erhai Lake Basin. By synthesizing extensive farmer survey data, comprehensive literature reviews, and meticulous statistical records, the study presents a highly localized quantification of emissions of four crucial pollutants: ammonia nitrogen (NH3-N), total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD). This approach moves beyond traditional models that conventionally emphasize nitrogen and phosphorus alone, thereby broadening the understanding of the pollutant spectrum affecting the lake’s water quality.
The findings revealed that in 2022 the Haixi area emitted 72.9 tons of NH3-N, 264.1 tons of TN, 29.2 tons of TP, and an overwhelming 1,453.3 tons of COD. Disaggregated by source, rural domestic sewage emerged as the predominant contributor to ammonia nitrogen, generating 74% of NH3-N emissions. Crop production topped the nitrogen pollutants with a 45% share of the total TN load. Meanwhile, livestock and poultry breeding dominated the emissions of phosphorus and organic pollutants, contributing 52% and 71% to TP and COD, respectively. These distinctions reflect how different agricultural activities uniquely shape the pollutant profile entering Erhai Lake.
At the crop-specific level, vegetables, corn, and beans were identified as the primary sources of pollutants within the crop production sector. Livestock emissions were largely driven by dairy cows and pigs, with dairy cattle responsible for more than half of the livestock-related pollution load. This finer resolution allows for pinpointing specific agricultural practices and livestock types that could be targeted for intervention, thus enabling more nuanced and effective policies.
Spatial analysis further highlighted key hotspots of pollution within the Haixi area. Shangguan Town, characterized by its robust livestock and poultry industry, accounted for 21% to 44% of pollutant emissions across the four pollutants. Wanqiao Town emerged as the largest contributor to crop-related pollution due to its extensive crop planting area. In the southern towns, pollution was noticeably influenced by rural domestic sewage. Although sewerage infrastructure exists, physical degradation such as damaged pipelines has led to seepage of untreated wastewater directly into the lake, exacerbating water quality problems.
This integrated, empirical approach—anchored by more than 300 farmer surveys and on-site sampling combined with localized pollution coefficients from the Manual of the Second Pollution Census Correlation Coefficients—represents a significant advancement. It enhances the precision and localization of pollution data, overcoming the limitations of generalized or national-level estimates. By resolving pollution sources down to crop and livestock types, the study provides a scientific foundation for tailored pollution control measures adapted to local circumstances.
Importantly, the study offers actionable recommendations based on spatial and sectoral insights. For instance, in northern towns where livestock production is concentrated, it advocates the adoption of comprehensive manure treatment technologies alongside the optimization of feed formulas to reduce nutrient excretion. In contrast, the central and northern crop-growing regions would benefit from restructuring planting patterns, promoting crop rotations such as rice-fava bean systems that lower pollutant runoff. Southern towns should prioritize infrastructure maintenance, especially repairing broken sewage pipelines to prevent untreated wastewater discharge.
By elucidating the complex interactions between agricultural practices, rural domestic sewage, and pollutant emissions with unprecedented granularity, this research provides critical evidence for informed environmental governance. Furthermore, the methodological framework developed for the Erhai Lake Basin can serve as a model for other lake basins facing similar non-point source pollution challenges, aiding broader efforts toward agricultural green development and freshwater ecosystem protection.
As the global community intensifies efforts to combat water pollution, localized data-driven approaches such as this work in Erhai Lake are indispensable. They enable policymakers to move beyond one-size-fits-all strategies, tailoring interventions to the specific pollution dynamics of regional landscapes. This paradigm shift is essential to protecting fragile freshwater resources while sustaining productive agricultural economies that rural communities depend on.
In sum, the research by Professor Wen Xu and colleagues marks a pivotal step forward in comprehensive agricultural pollution assessment and management. Through rigorous fieldwork and multidisciplinary data integration, it has illuminated the diverse pollutant sources afflicting the Erhai Lake Basin and charted pragmatic pathways to cleaner, more sustainable water systems. It stands as a compelling case for replicating such meticulous, farmer-informed studies worldwide to meet the escalating challenges of non-point source pollution in agricultural landscapes.
Subject of Research: Not applicable
Article Title: Farmer survey-based agricultural non-point source pollution assessment in the typical regions of the Erhai Lake Basin, China
News Publication Date: 25-Apr-2025
Web References: http://dx.doi.org/10.15302/J-FASE-2025622
Keywords: Agriculture
Tags: Agricultural non-point source pollutionecological sensitivity of freshwater resourcesErhai Lake Basin water qualityfarming activities and pollutionmanaging diffuse pollution sourcespollutant load assessmentresidential sewage and agriculturerural domestic wastewater impactscience-based management strategiesspatial pollution contributionssustainable agricultural practicesYunnan Province environmental challenges
