Characteristics and control measures of farmland drainage pollution in Hetao Irrigation District, Inner Mongolia

Non-point source pollution from farmland drainage in the Hetao Irrigation District of Inner Mongolia is identified as the main source of pollution in Wuliangsuhai, exhibiting unique pollution characteristics and generation/discharge pathways. Through literature review and on-site investigation, this study summarized the current status of the irrigation/drainage system, analyzed the characteristics of farmland drainage pollution in the district, clarified the generation/discharge pathways of farmland drainage pollutants, and proposed specific prevention/control measures considering the influencing factors of farmland drainage pollution. The results showed that: (1) The drainage system in the district played a crucial role in transporting farmland drainage pollutants, but its drainage function was gradually weakened in recent years. (2) A significant portion of water used for irrigation during non-growing seasons accounted for 55%-60% of annual water consumption, among which the water used for washing salt in autumn every year accounted for 1/3 of the annual irrigation water with a low utilization rate of irrigation water resources. (3) Pollutants, such as chemical oxygen demand (COD), ammonia nitrogen (\mathrmNH_4^+ -N), and total nitrogen (TN), originated within the Hetao Irrigation District, with the autumn irrigation period posing the highest risk for non-point source pollution. (4) Agricultural activities were a major source of nitrogen pollution, with nitrogen seeping into the soil, migrating to shallow ground, and ultimately draining into water bodies. (5) Factors such as irrigation systems, on-farm drainage processes, and external drainage processes significantly affected farmland drainage pollution. Considering the specific characteristics of farmland drainage pollution, generation/discharge pathways, and key influencing factors in the Hetao Irrigation District, it was recommended to establish a comprehensive management model tailored to local conditions, which could be achieved through regulating source water, optimizing drainage ditches, and intercepting ecosystem process to improve the water environment in the Wuliangsuhai Basin.