● Erhai Lake basin faces the duel challenge of enhancing water protection and increasing farmer income.

Pollution of high-altitude lake basins by agriculture and rural activities, and the control of this pollution, have received increasing attention from academic research and government policy in China. Series of restrictions and regulations have been implemented to protect the surface water quality. These restrictions and regulations have greatly impacted and transformed the agricultural systems and rural livelihoods surrounding these lake basins. Using Erhai Lake basin in Yunnan Province as a case study, three main challenges were identified for concurrently decreasing pollution in the lake and increasing farmer income. It is contended that scientifically-sound environmental protection policies and agricultural green development practices are key to reversing the current situation. This will help to protect the lake from pollution while smallholder farmers will be able to produce healthy food in an environmentally sustainable manner, and with a fair remuneration for all the services farmers provide to the society.

● This paper examines the historical evolution of crop-livestock integration in China with a specific focus on its role in mitigating non-point source pollution.

This paper examines the historical evolution of crop-livestock integration in China with a specific focus on its role in mitigating non-point source pollution. Extensive examination of existing literature has unearthed the roots of crop-livestock integration dating back to the Western Zhou Dynasty (1046 to 771 BCE), ultimately culminating in a multifaceted and intricately interwoven system of rural development policies seen in contemporary China. This paper identifies and characterizes four distinct stages in the historical trajectory of crop-livestock integration: the era of self-sufficient subsistence production in traditional times (1046 BCE to 1948); the period where crop-livestock integration emerged as a pivotal strategy for augmenting grain and meat production under collectivist policies (1949‒1977); the phase marked by the industrialization and expansion of the livestock sector during the early years of economic reforms (1978‒2011); and the present era in which crop-livestock integration is harnessed as a mechanism for pollution control and ecological preservation in contemporary China (2012 to present). This paper illuminates the diverse contributions of crop-livestock integration in different epochs of rural development within China, which contributes to a nuanced and more theoretically grounded comprehension of circular agriculture. This understanding has the potential to be leveraged to promote sustainable rural development in broader contexts.

● Soil N mineralization (N_min) rates varied spatially among cropland fields.

Soil nitrogen mineralization (N_min) is a key process that converts organic N into mineral N that controls soil N availability to plants. However, regional assessments of soil N_min in cropland and its affecting factors are lacking, especially in relation to variation in elevation. In this study, a 4-week incubation experiment was implemented to measure net soil N_min rate, gross nitrification (Nit) rate and corresponding soil abiotic properties in five field soils (A–C, maize; D, flue-cured tobacco; and E, vegetables; with elevation decreasing from A to E) from different altitudes in a typical intensive agricultural area in Dali City, Yunnan Province, China. The results showed that soil N_min rate ranged from 0.10 to 0.17 mg·kg⁻¹·d⁻¹ N, with the highest value observed in field E, followed by fields D, C, B, and A, which indicated that soil N_min and Nit rates varied between fields, decreasing with elevation. The soil Nit rate ranged from 434.2 to 827.1 µg·kg⁻¹·h⁻¹ N, with the highest value determined in field D, followed by those in fields E, C, B, and A. The rates of soil N_min and Nit were positively correlated with several key soil parameters, including total soil N, dissolved organic carbon and dissolved inorganic N across all fields, which indicated that soil variables regulated soil N_min and Nit in cropland fields. In addition, a strong positive relationship was observed between soil N_min and Nit. These findings provide a greater understanding of the response of soil N_min among cropland fields related to spatial variation. It is suggested that the soil N_min from cropland should be considered in the evaluation of the N transformations at the regional scale.

● This study clarified the critical processes and major factors that nitrogen transport from farm fields to surface water bodies.

Agricultural non-point source pollution is increasingly an important issue affecting surface water quality. Currently, the majority of the studies on nitrogen loss have focused on the agricultural field scale, however, the response of surface water quality at the watershed scale into the nitrogen loss at the field scale is poorly understood. The present study systematically reviewed the critical processes and major factors that nitrogen transport from farm fields to surface water bodies. The critical processes of farmland nitrogen entering surface water bodies involve the processes of nitrogen transport from farmland to ditches and the transformation processes of nitrogen during migration in ditches/rivers. Nitrogen transport from farmland to ditches is one of the prerequisites and critical processes for farmland nitrogen transport to surface water bodies. The transformation of nitrogen forms in ditches/rivers is an intermediate process in the migration of nitrogen from farmland to surface water bodies. Nitrogen loss from farmland is related to soil storage and exogenous inputs. Therefore, nitrogen input management should not only consider the current input, but also the contribution of soil storage due to the historical surpluses. Ditches/rivers have a strong retention capacity for nitrogen, which will significantly affect the process of farmland nitrogen entering surface water bodies. The factors affecting nitrogen transformation in river/ditches can be placed in four categories: (1) factors affecting hydraulic retention time, (2) factors affecting contact area, (3) factors affecting biological activity, and (4) forms and amount of nitrogen loading to river/ditches. Ditch systems are more biologically (including plants and microbes) active than rivers with biological factors having a greater influence on nitrogen transformation. When developing pollution prevention and control strategies, ecological ditches can be constructed to increase biological activity and reduce the amount of surplus nitrogen entering the water body. The present research should be valuable for the evaluation of environment impacts of nitrogen loss and the non-point source pollution control.

● An improved wash-off model integrated with rainfall pollution and SCS-CN is presented.

The growing need to mitigate rainfall-runoff pollution, especially first flush, calls for accurate quantification of pollution load and the refined understanding of its spatial-temporal variation. The wash-off model has advantages in modeling rainfall-runoff pollution due to the inclusion of two key physical processes, build-up and wash-off. However, this disregards pollution load from wet precipitation and the relationship between rainfall and runoff, leading to uncertainties in model outputs. This study integrated the Soil Conservation Service curve number (SCS-CN) into the wash-off model and added pollutant load from wet precipitation to enhance the rainfall-runoff pollution modeling. The enhanced wash-off model was validated in a typical rural-residential area. The results showed that the model performed better than the established wash-off model and the commonly-used event mean concentrations method, and identified two different modes of pollution characteristics dominated by land pollution and rainfall pollution, respectively. In addition, the model simulated more accurate pollutant concentrations at high-temporal-resolution. From this, it was found that 12% of the total runoff contained 80% to 95% of the total load for chemical oxygen demand, total N, and total P, whereas it contained only 15% of the total load for NH₄⁺-N. The enhanced model can provide deeper insights into non-point pollution mitigation.

● The water environment of Erhai Lake has shown satisfactory, declining and improving.

Elucidating the spatiotemporal pattern of water quality and algal biomass is crucial for accurately tracing pollution sources and reducing the risk of algal blooms in lake systems. This study analyzed the spatiotemporal variability of water quality and algal biomass in Erhai Lake from 1994 to 2021 using water quality index (WQI), Mann-Kendall test and Sen’s slope combined methods. The potential causes of water quality deterioration and algal biomass dynamics were also elucidated. The results showed that the historical changes in the water environment of Erhai Lake mainly had three stages: satisfactory (1994‒2001), deteriorating (2002‒2010) and improving (2011‒2021). The changes in water quality and algal biomass were primarily affected by total nitrogen, total phosphorus and chemical oxygen demand in different stages. The water environment of Erhai Lake is currently improving significantly, starting in the southern area that is furthest from the sources of agricultural pollution, especially in summer and autumn. This is attributed to the implementation of control measures resulting in lower pollutant loads at particular times and places. Therefore, it is necessary to continue to promote standardized livestock farming, to strengthen rural wastewater collection and to investigate measures such as the interruption of the endogenous cycle.

● A new MARINA-Nutrients model was developed to assess air and water pollution in Europe.

Nutrient pollution of air and water is a persistent problem in Europe. However, the pollution sources are often analyzed separately, preventing the formulation of integrative solutions. This study aimed to quantify the contribution of agriculture to air, river and coastal water pollution by nutrients. A new MARINA-Nutrients model was developed for Europe to calculate inputs of nitrogen (N) and phosphorus (P) to land and rivers, N emissions to air, and nutrient export to seas by river basins. Under current practice, inputs of N and P to land were 34.4 and 1.8 Tg·yr^–1, respectively. However, only 12% of N and 3% of P reached the rivers. Agriculture was responsible for 55% of N and sewage for 67% of P in rivers. Reactive N emissions to air from agriculture were calculated at 4.0 Tg·yr^–1. Almost two-fifths of N emissions to air were from animal housing and storage. Nearly a third of the basin area was considered as pollution hotspots and generated over half of N emissions to air and nutrient pollution in rivers. Over 25% of river export of N ended up in the Atlantic Ocean and of P in the Mediterranean Sea. These results could support environmental policies to reduce both air and water pollution simultaneously, and avoid pollution swapping.

● Full time-space governance strategy for AGNPS pollution was proposed.

Ensuring food safety while reducing agricultural non-point source pollution is quite challenging, especially in developing and underdeveloped countries. Effective systematic strategies and comprehensive technologies need to be developed for agricultural non-point source pollution control at the watershed scale to improve surface water quality. In this review, a proposal is made for a full time-space governance strategy that prioritizes source management followed by endpoint water pollution control. The 4R chain technology system is specifically reviewed, including source reduction, process retention, nutrient reuse and water restoration. The 4R chain technology system with the full time-space governance strategy was applied at the scale of an administrative village and proved to be a feasible solution for reducing agricultural non-point source pollution in China. In the future, a monitoring system needs to be established to trace N and P transport. Additionally, new smart fertilizer and intelligent equipment need to be developed, and relevant governance standards and supportive policies need to be set to enhance the efficacy of agricultural non-point source pollution control.

● The source and sink status of ditches and ponds was studied in an upland area in the Jinglinxi catchment, China.

As the common features of agroecosystems, ditches and ponds benefit the irrigation and drainage, as well as intercepting non-point source pollutants. However, most ditch-pond studies have been conducted in lowland areas. To test this source-sink assumption in upland areas, this study made observations on the ecological function of the ditch and pond system in a typical catchment in China. First, the changes in ponds in the catchment were analyzed using high-resolution remote sensing data. Then, the migration of agricultural pollutants in ditches and ponds were analyzed by field sampling and laboratory detection. The results showed that over the past 15 years the length of ditches in the catchment and the number of small ponds (< 500 m²) have increased by 32% and 75%, respectively. The rate of change in nutrient concentrations in the ditches and ponds were mostly from −20% to 20%, indicating ditches and ponds can be both sources and sinks for agricultural pollutants. Lastly, the contributing factors were explored and it was found that ditches and ponds are important sinks in dry season. However, during the rainy season, ditches and ponds become sources of pollutants, with the rapid drainage of ditches and the overflow of ponds in upland areas. The results of this study revealed that the ditches and ponds could be used for ecological engineering in upland catchments to balance drainage and intercept pollutants.

● The primary pollutants of Yong’an River are total nitrogen and nitrate

The agricultural and livestock activities surrounding the rivers flowing into the lakes have caused non-point source pollution, leading to excessive amounts of nutrient salts in downstream rivers. Introducing river water into constructed wetlands along river course has proven to be an effective solution for decreasing nitrogen (N) and phosphorus (P) loads. This paper reports 9 years of monitoring the Yong’an River and its surrounding constructed wetlands in the upper reaches of Erhai Lake, located in Yunnan Province, China. This study analyzed the main types of pollutants in the river, and evaluated the removal efficiency of pollutants by the constructed wetlands. The findings indicate that total nitrogen (TN) and nitrate nitrogen (NO₃^–-N) are the primary pollutants in the Yong’an River, which exhibit variation throughout the year corresponding to the alternating wet and dry seasons. Although constructed wetlands are effective in removing NO₃^–-N and P, their efficacy in removing ammonium nitrogen (NH₄⁺-N) and organic pollutants is limited. This limitation can be attributed to the lack of timely disposal of aquatic plant residues. This research contributes to the understanding of the potential issues that may arise during the extended use of constructed wetlands and provides solutions to address them.

● Four highlights are identified for agriculture and water from the multi-pollutant perspective.

Agriculture is an important cause of multiple pollutants in water. With population growth and increasing food demand, more nutrients, plastics, pesticides, pathogens and antibiotics are expected to enter water systems in the 21st century. As a result, water science has been shifting from single-pollutant to multi-pollutant perspectives for large-scale water quality assessments. This perspective paper summarizes and discusses four main highlights related to water pollution and agriculture from the multi-pollutant perspective. These highlights reveal the spatial and temporal distribution and main sources of multiple pollutants in waters. Based on the highlights, a scientific agenda is proposed to prioritize solutions for sustainable agriculture (UN Sustainable Development Goal 2) and clean water (UN Sustainable Development Goals 6 and 14). This agenda points out that when formulating solutions for water pollution, it is essential to take into account multiple pollutants and their interactions beyond biogeochemistry.

Enhancement of farming management relies heavily on enhancing farmer knowledge. In the past, both the direct learning approach and the personnel extension system for improving fertilization practices of smallholders has proven insufficiently effective. Therefore, this article proposes an interactive knowledge learning approach using artificial intelligence as a promising alternative. The system consists of two parts. The first is a dialog interface that accepts information from farmers about their current farming practices. The second part is an intelligent decision system, which categorizes the information provided by farmers in two categories. The first consists of on-farm constraints, such as fertilizer resources, split application times and seasons. The second comprises knowledge-based practices by farmers, such as nutrient in- and output balance, ratios of different nutrients and the ratios of each split nutrient amount to the total nutrient input. The interactive knowledge learning approach aims to identify and rectify incorrect practices in the knowledge-based category while considering the farmer’s available finance, labor, and fertilizer resources. Investigations show that the interactive knowledge learning approach can make a strong contribution to prevention of the overuse of nitrogen and phosphorus fertilizers, and mitigating agricultural non-point source pollution.