Nutrient Budget Analysis and Its Implications as an Indicator of Urban Sustainability: A Case Study on Hanoi, Vietnam

摘要

The present study was conducted to estimate the budget of nutrients, phosphorus and nitrogen, in Hanoi city in an attempt to propose an indicator of urban sustainability in terms of nutrients. Hanoi citadel area with a total area of 84.1 square kilometers was selected as the case study. Available data relating to nutrient input and output flows of the target area were collected. By using the obtained data, major nutrient input flows in the forms of water, food, and mineral fertilizer, and output flows in the forms of wastewater and solid waste were estimated and identified. The estimated results showed that, in the year of 1999, the total N input and output were around 14000 tons and 16000 tons, respectively. Major input was live stock commodities (71% of total input) and crop commodities (25%), and the major output form was as wastewater (88%). The total P input and output were around 2600 tons and 4200 tons, respectively. Major input was again livestock commodities(77%) and crop commodities(17%). The output was 71% as wastewater and the rest as solid wastes. The amount of nutrients recycled through composting was also estimated, which contributed only about 1.3% of nitrogen flow and 4% of phosphorus flow. The difference between input and output still remains uncertain, because the accuracy of the data used in the study is not reliable enough to make such a discussion. But the order of the size of flow and recycling was grasped. The small contribution of recycling by composting indicates that there is room for improvement concerning the budget of nutrients in the study area.