Impact of Dietary and Self-sufficiency Changes on Nitrogen Load in the Kasumigaura Watershed

Abstract

Recently, dietary change has been increasingly recognized as a viable strategy to reduce nitrogen pollution. This is because raising animal-based proteins results in significantly higher nitrogen loads compared to raising (cultivating) their plant-based alternatives. In Japan, there has been a rise in animal-based food consumption in recent decades, which could have detrimental effects on water quality. However, dietary changes are rarely considered in watershed environmental conservation. Given Japan’s low food self- sufficiency of 38%, shifting diets could improve both domestic and international water quality. Therefore, the aim of this study was to evaluate whether dietary changes among the Japanese population could result in nitrogen load reduction and water quality improvement in the Kasumigaura watershed. Firstly, nitrogen load from each point source and non-point source was quantified by examining various nitrogen flows, using land-use data to capture the contributions from different sources. This analysis also incorporated food production- related anthropogenic nitrogen from crops and livestock. The estimated nitrogen load in 2020 was around 4,403 tons/year, and it was a reasonable value compared with previous research. Then, the impact of dietary and self-sufficiency changes on the nitrogen load was estimated. The results suggest that the reduction of animal proteins has significantly lowered the nitrogen load in the watershed, therefore offering a promising approach to improving water quality.