Impact Analysis of Population Growth and Fertilizer Use on Nitrogen Runoff in Nam Ngum Basin, Laos
2022 年 13 巻 1 号 p. 176-183
詳細
2022 年 13 巻 1 号 p. 176-183
Human population growth has led to increased energy and food production, fertilizer usage and wastewater flows. Increased nitrogen availability is a worldwide cause of eutrophication of rivers, lakes and estuaries, however, quantitative evaluation the impacts of nitrogen loads has been insufficient in developing countries because of poor data availability. The Nam Ngum River basin, Laos, which supplies quality water for domestic use in the Vientiane Metropolis, was selected as the target area for this study. The Nam Ngum River basin is 415 km long with a 17,000 km2 catchment area, and the main land uses in 2000 were paddy (15.6%), forest (32.3%), shrub (40.3%) and urban (0.2%). By UN estimation, population in Laos is expected to increase 2.1 times from 2000 to 2050, and fertilizer use also will increase to produce sufficient food. Therefore, future water quality is a main concern in this river basin. Meteorological and hydrological data from 1995 to 2004, and spatial data such as topography, land use, and soil properties were collected for model simulation. A conceptual nitrogen balance model with three nitrogen pools was developed and combined with a rainfall runoff model. Simulated river discharge and nitrogen loads agreed with the observed data. Then, we investigated future nitrogen load variations in the basin under different population growth and agricultural modernization scenarios. As a result, even when population in the basin increased 2.1 times, nitrogen load did not change significantly (11,676 tons/year in 2000 and 11,822 tons/year in 2050). However, the fertilizer increase scenario, from 25 kg/ha/season to 50 kg/ha/season, showed significant increase in nitrogen loading, from 11,676 ton/year to 17,010 ton/year. Our results provide initial insight into the magnitude and spatial distribution of nitrogen loading in Nam Ngum River Basin, showing that this type of model may be useful for future impact assessments.
