Seasonal constraint of dynamic water temperature on riverine dissolved inorganic nitrogen transport in land surface modeling

Abstract

Riverine dissolved inorganic nitrogen (DIN) transport plays an important role in the link between terrestrial and marine ecosystems, while the seasonal changes of water temperature exert a strong control on DIN dynamics. However, the response of the flow of DIN to dynamic water temperature in large rivers is not well known at the global scale. In this study, based on a recently developed land surface model coupled with riverine water temperature and DIN transport schemes, two numerical simulations, with and without dynamic water temperature, were implemented to investigate the seasonal constraint of dynamic water temperature on the change in riverine DIN flow. Results show that the water temperature could be a key controlling factor for the spatial distribution of global DIN flows. After integrating dynamic water temperature estimation into land surface modeling, the annual amplitudes of DIN flow were 5%–25% smaller than before between 30°N and 30°S, while approximately 10% larger in other latitudinal zones. Less denitrification was out of the scope of 40°N–20°S in summer. In eastern China, the dynamic water temperature made the DIN flow reduce by 1%–3% in summer, while it made it increase by 1%–5% in winter. A seasonal constraint of dynamic water temperature, making the amplitude of monthly fluctuation reduce by about 60%, was found in global large rivers. This study shows the importance of dynamic water temperature in the seasonal modeling of riverine DIN flow, and provides a scientific reference for land surface model development and water environment management.摘要水体温度变化对河流可溶性无机氮(DIN)输送有着强烈控制作用. 然而, 在全球尺度上河流DIN输送量对水温度变化的响应尚不清楚. 因此, 本文基于陆面过程模式, 耦合河流水温估算和DIN传输方案, 设定有, 无动态水温情景, 对比研究陆面模拟中水温变化对河流DIN通量变化的影响. 结果表明: 在考虑水温动态变化后, 在30°N和30°S之间, DIN通量年振幅减小5%–25%. 在中国东部地区, 水温动态变化使河流DIN通量在夏季减少1%–3%, 在冬季增加1%–5%, 对DIN通量具有明显的季节性约束作用, 表明动态水温的表达在河流DIN输送模拟中的重要性.