Yunfeng Huang

The identification and regulation of the critical source areas (CSAs) of non-point source (NPS) pollution have been proven as economical and effective ways to control such pollution in watersheds. However, the traditional models for the identification of CSAs have complex operation processes, and comprehensive systematic methods for the regulation of CSAs are still lacking. This study systematically developed a new methodological framework for the identification and regulation of CSAs in medium and small watersheds based on source-sink theory, which included the following: (1) a grid-based CSAs identification model involving the evaluation of the rationality of the source-sink landscape pattern and three geographical factors (landscape slope, relative elevation, and the distance from the river), and identifying CSAs by the calculation and division of the integrated grid pollution index (IGPI); (2) a comprehensive CSAs regulation strategy that was formulated based on three landscape levels/regulation intensities—including the optimization of the overall source-sink landscape pattern, the conversion of the landscape type or landscape combination, and local optimization for single source landscape—to meet various regulatory intensity requirements in watersheds. The Jiulong River watershed in Fujian Province of China was taken as a case study. The results indicate that: (1) the identified CSAs of the Jiulong River watershed covered 656.91 km², equivalent to 4.44% of the watershed, and through adopting multiple-intensity regulation measures for 10 key control zones that had spatially concentrated high values of the IGPI among the CSAs, the watershed IGPIs were predicted to be generally reduced and the area of CSAs was predicted to decrease by 23.84% (31.43% in Zhangzhou, the major city in the watershed); (2) the identification model can identify the CSAs with easy data access and simple operation, and the utilization of neighborhood impact analysis makes the grid-based research more scientific in the evaluation of the rationality of the source-sink landscape pattern; (3) the application of multi-scale landscape planning framework and the principle of source-sink landscape pattern regulation make the CSAs regulation strategy systematic and cost-effective, and the provision of different intensity regulation strategies makes the regulation strategy easy to implement and relatively lower cost. The proposed methodological framework can provide technical support for governments to quickly and accurately identify the CSAs of NPS pollution and effectively control such CSAs in medium and small watersheds.

The Chinese government projected 30% of total consumed potatoes as a staple food (PSF) by 2020. We comprehensively assessed the potential impacts of PSF on rice and flour consumption, rice and wheat planting, energy and nutrient supply, irrigation-water, chemical nitrogen (N), phosphorus pentoxide (P₂O₅) and potassium oxide (K₂O) fertilizer inputs and total greenhouse gases (GHG) emission for potatoes, rice and wheat, by assuming different proportions of potato substitutes for rice and flour. The results showed that per capita, 2.9 ± 0.3 and 4.7 ± 0.5 kg more potatoes per year would enter the Chinese staple-food diet, under the government’s target. PSF consumed are expected to reach 5.2 ± 0.7 Tg yr⁻¹, equivalent to substituting potatoes for 4.2 ± 0.8–8.5 ± 0.8 Tg yr⁻¹ wheat and 5.1 ± 0.9–10.1 ± 1.8 Tg yr⁻¹ rice under different scenarios. While this substitution can increase the nutrient supply index by 63% towards nutrient reference values, it may induce no significant effect on staple-food energy supply with lower chemical fertilizer (except for K₂O) and irrigation-water inputs and GHG emissions in different substitution scenarios than the business as usual scenario. The reduction in rice and wheat demands lead to wheat in the North China Plain and early rice decrease by 6.1–11.4% and 12.1–24.1%, respectively. The total GHG reduction is equal to 1.1–9.0% of CO₂ equivalent associated with CH₄ and N₂O emitted from the Chinese agroecosystem in 2005. The saved irrigation water for three crops compared to 2012 reaches the total water use of 17.9 ± 4.9–21.8 ± 5.9 million people in 2015. More N fertilizer, irrigation-water, and GHG can be reduced, if the PSF ratio is increased to 50% together with potato yield improves to the optimal level. Our results implied that the PSF policy is worth doing not only because of the healthier diets, but also to mitigate resource inputs and GHG emissions and it also supports agricultural structure adjustments in the areas of irrigated wheat on the North China Plain and early rice across China, designed to increase the adaptability to climate change.

We present a quantitative analysis of phosphorus (P) flows that characterize the food production-consumption system metabolism in a low-income, food, and phosphorus deficient country, using Comoros, a small African island state, as an example from the year 2000 to 2011. The data were interpreted in terms of the connections between crop production, livestock breeding, human consumption, and soil stock, using the substance flow analysis (SFA) model. We found that the total P input into Comoros totaled 132.37 t in 2000 and 270.60 t in 2011, whereas the total P output totaled 567.40 t in 2000 and 702.29 t in 2011. Farmers in Comoros are cropping with little or no P input, resulting in a soil P deficiency; it varied from 435.03 t in 2000 to 431.69 t in 2011. In addition, the Phosphorus Use Efficiencies (PUEs) of plant and animal production in Comoros were 131.80% and 14%, respectively, in 2011. This is the first SFA of a small island state, and the lack of a closed P loop is a major issue for the country in terms of P security and this has not changed between 2000 and 2011. This study proposes crucial solutions for improving the PUE through recycling and reusing animal manure, human excreta, and household solid organic waste.

The modern global food production system relies heavily on a considerable input of phosphorus. Sustainable food and agriculture need integrated phosphorus management, especially in phosphorus-scarce and food-deficient countries. This study aimed to investigate the phosphorus requirements to meet the future food demand for a phosphorus-scarce and food-deficient country, Comoros, as a case study. With its rapid population growth, domestic food production is far from meeting the food demand in Comoros, and the country relies on imported foods to satisfy the national needs; it is currently a net food importer, an import-dependent nation. We first calculated the virtual and embedded phosphorus flows through food trade in Comoros, from 1991 to 2013, and then estimated the phosphorus requirements for the future food demand under two scenarios. We found that the total virtual and embedded phosphorus through imported food increased from 163,313 to 493,190.97 kg and 53,190.12 to 143,009.62 kg in 1991 and 2013, respectively. Whereas, the embedded phosphorus through exported food shifted from 2548.75 to 1334.5 kg in 1991 and 2013, respectively. In addition, the Self-Sufficiency Ratio (SSR) analysis found that Comoros’s SSR is far below 100%; it varied from 46.27% in 1991 to 29.70% in 2013, indicating that the capacity of domestic production to cover domestic consumption fell by 16.57% during that period. In terms of phosphorus requirements, Comoros will require approximately 3,003,435.09 kg of phosphorus to reach 90% of the SSR or 3,337,150.10 kg to achieve 100% of the SSR, by 2030. These amounts could allow farmers to domestically produce the entire volume of food crops and livestock products that would otherwise be imported from trade.