Identifying groundwater ammonium hotspots in riverside aquifer of Central Yangtze River Basin

• Published in: The Science of the total environment 2024-11, Vol.953, p.176094, Article 176094
• Main Authors: Shen, Shuai, Zhang, Jingwei, Du, Yao, Ma, Teng, Deng, Yamin, Han, Zhihui
• Format: Article
• Language: English
• Subjects: Ammonium hotspots; Central Yangtze River Basin; Geostatistical analysis; Hydrochemistry; Riverside aquifer
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.176094

Elevated ammonium (NH4-N) contents in groundwater are a global concern, yet the mobilization and enrichment mechanisms controlling NH4-N within riverside aquifers (RAS) remain poorly understood. RAS are important zones for nitrogen cycling and play a vital role in regulating groundwater NH4-N contents. This study conducted an integrated assessment of a hydrochemistry dataset using a combination of hydrochemical analyses and multivariate geostatistical methods to identify hydrochemical compositions and NH4-N distribution in the riverside aquifer within Central Yangtze River Basin, ultimately elucidating potential NH4-N sources and factors controlling NH4-N enrichment in groundwater ammonium hotspots. Compared to rivers, these hotspots exhibited extremely high levels of NH4-N (5.26 mg/L on average), which were mainly geogenic in origin. The results indicated that N-containing organic matter (OM) mineralization, strong reducing condition in groundwater and release of exchangeable NH4-N in sediment are main factors controlling these high concentrations of NH4-N. The Eh representing redox state was the dominant variable affecting NH4-N contents (50.17 % feature importance), with Fe2+ and dissolved organic carbon (DOC) representing OM mineralization as secondary but important variables (26 % and 5.11 % feature importance, respectively). This study proposes a possible causative mechanism for the formation of these groundwater ammonium hotspots in RAS. Larger NH4-N sources through OM mineralization and greater NH4-N storage under strong reducing condition collectively drive NH4-N enrichment in the riverside aquifer. The evolution of depositional environment driven by palaeoclimate and the unique local environment within the RAS likely play vital roles in this process. [Display omitted] •Extremely high levels of geogenic NH4-N are investigated in riverside aquifer (RAS).•Control factors of NH4-N enrichment in groundwater ammonium hotspots are identified.•Strong reducing condition is dominant factor affecting NH4-N contents in RAS.•Organic matter mineralization provides continuous source for NH4-N enrichment in RAS.