Identification of rainy season nitrogen export controls in a semi-arid mountainous watershed, North China

H K M Mihiranga; Yan Jiang; M G S Sathsarani; Xuyong Li; Tharindu Ritigala; Hailu Demissie; Wei Wang

doi:10.1016/j.scitotenv.2022.156293

Identification of rainy season nitrogen export controls in a semi-arid mountainous watershed, North China

Sci Total Environ. 2022 Sep 15:839:156293. doi: 10.1016/j.scitotenv.2022.156293. Epub 2022 May 27.

Authors

H K M Mihiranga¹, Yan Jiang², M G S Sathsarani³, Xuyong Li¹, Tharindu Ritigala⁴, Hailu Demissie⁵, Wei Wang¹

Affiliations

¹ State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: yanjiang@rcees.ac.cn.
³ Agronomy Division, Tea Research Institute, Talawakelle, Sri Lanka.
⁴ University of Chinese Academy of Sciences, Beijing 100049, China.
⁵ University of Chinese Academy of Sciences, Beijing 100049, China; Department of Chemistry, Arba Minch University 1000, Ethiopia.

PMID: 35644383
DOI: 10.1016/j.scitotenv.2022.156293

Abstract

A comprehensive understanding of the nutrient export process and export controls is demanded effective pollution mitigation in fragile riverine ecosystems. In this study, behaviors of the full range of nitrogen (N) under stormflow (5-events) and baseflow (2-events; before and after the rainy season, multiple sites) were assessed to explore N export controlling mechanisms according to the identified main components causing the changes in N exports, N transport pathways, seasonal trends, and nutrient supply watershed regions through the 2020 rainy season in a semi-arid mountainous watershed, northern China. Results showed increments in riverine dissolved organic-N (DON) and particulate-N (PN) loadings as the leading cause of N flux and composition changes through the rainy season, although nitrate-N (NO₃-N) contributed 69.6% of total-N (TN). Storm runoff generated 3-fold and 4-fold average increments in DON and PN fluxes. DON and PN shared 1-66% (18.1%) and 1-44% (9.7%) of TN through storms, registered consistency in behavior, mainly originated from near-stream soil, and were primarily transported by shallower subsurface flow. Our results broaden the understanding of PN delivery in catchment wetting-up periods by highlighting the decoupling of primary origins/transport pathways of PN from sediments. Results suggested hydrological functioning parallel to the catchment wetting-up as the principal governor of storm N evolution; soil moisture levels build up in the early rainy season, soil water runoff dominance during peak discharge fluctuations, groundwater runoff dominance at the end of the rainy season. Cumulative rainfall and antecedent soil moisture exerted more significant control over storm N exports than individual rainfall features. The assessment of N behaviors through river network disclosed watershed regions responsible for excessive N delivery and influences of unsustainable agriculture, sewage treatment work, and damming on natural riverine N fluxes. These findings could be useful references for the formulation of water pollution control strategies in the future.

Keywords: Dissolved organic-N; N export control; N export process; Particulate-N; Rainy season; Semi-arid mountainous watershed.

MeSH terms

China
Ecosystem
Environmental Monitoring
Nitrogen* / analysis
Rivers
Seasons
Soil
Water Movements
Water Pollutants, Chemical* / analysis

Substances

Soil
Water Pollutants, Chemical
Nitrogen