Increases in the seaward river flux of nutrients driven by human migration and land-use changes in the tide-influenced delta

Jing Zhang; Ya Nan Du; Guo Sen Zhang; Yan Chang; Ying Chun Zhou; Zai Feng Zhang; Ying Wu; Jia Wei Chen; An Yu Zhang; Zhuo Yi Zhu; Su Mei Liu

doi:10.1016/j.scitotenv.2020.144501

Increases in the seaward river flux of nutrients driven by human migration and land-use changes in the tide-influenced delta

Sci Total Environ. 2021 Mar 20:761:144501. doi: 10.1016/j.scitotenv.2020.144501. Epub 2020 Dec 14.

Authors

Jing Zhang¹, Ya Nan Du², Guo Sen Zhang³, Yan Chang³, Ying Chun Zhou⁴, Zai Feng Zhang⁵, Ying Wu³, Jia Wei Chen⁴, An Yu Zhang³, Zhuo Yi Zhu³, Su Mei Liu⁶

Affiliations

¹ State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 3663 Zhongshan Road North, Shanghai 200062, China. Electronic address: jzhang@sklec.ecnu.edu.cn.
² Yangtze River Estuary Survey Bureau of Hydrology and Water Resource, Changjiang Water Resources Commission, 2412 Pudong Avenue, Shanghai 200136, China.
³ State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 3663 Zhongshan Road North, Shanghai 200062, China.
⁴ KLATASDS-MOE, School of Statistics, East China Normal University, 500 Dongchuan Road, Shanghai 200241, China.
⁵ Nantong Environmental Monitoring Center, Ministry of Ecology and Environment, 18 Qingnian Middle Road, Nantong 226006, China.
⁶ Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, 238 Songling Road, Qingdao 266100, China.

PMID: 33360130
DOI: 10.1016/j.scitotenv.2020.144501

Abstract

Most large megacities are located on areas adjacent to tide-influenced deltas. However, contribution of megacities to seaward nutrient fluxes in tide-influenced deltas are poorly quantified in regional and global levels. We analyzed nutrient concentrations and water current data for a large and tide-influenced delta, the Changjiang (Yangtze River) since 1980. Concentrations, species ratios and fluxes of nutrients in tide-influenced delta has been found to differ dramatically from those at upstream. Over the period 2004 to 2015, the seaward nutrient fluxes of dissolved inorganic nitrogen and dissolved silica increased by 5%-10%, but dissolved inorganic phosphorus increased by 15%-20%, in the tide-influenced delta of the Changjiang. Consequently, the DIP/DIN decreases by 11% and DIP/DSi increases by 14% at the river mouth relative to those farther upstream the tidal limit. The legacy and/or recycled contribution accounts for 10%-30% of this increased nutrient flux, hence additional sources are predominantly those involving anthropogenic land-use changes. These findings have implications not only for the Changjiang but also for other riverine systems with respect to management strategy. Nutrient dynamics in tide-influenced deltas near urban areas should receive increased research and policy attention. By not considering nutrient sources in tide-influenced deltas, knowledge of the seaward fluxes and species ratios of nutrients from land sources is incomplete and can be biased, to the point that assessments of their impacts on adjacent marine environments may be inaccurate and mitigation policies therefore ineffective.

Keywords: Changjiang; Human dimensions; Land-use changes; Megacities in the tide-influenced delta; Nutrient species ratio; Nutrients; Seaward nutrient fluxes.