Hydrochemical Characteristics, Controlling Factors, and High Nitrate Hazards of Shallow Groundwater in an Urban Area of Southwestern China
Groundwater nitrate (NO<sub>3</sub><sup>−</sup>) contamination has emerged as a critical global environmental issue, posing serious human health risks. This study systematically investigated the hydrochemical processes, sources of NO<sub>3</sub><sup>−</su...
Saved in:
| Main Authors: | , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-06-01
|
| Series: | Toxics |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2305-6304/13/6/516 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | Groundwater nitrate (NO<sub>3</sub><sup>−</sup>) contamination has emerged as a critical global environmental issue, posing serious human health risks. This study systematically investigated the hydrochemical processes, sources of NO<sub>3</sub><sup>−</sup> pollution, the impact of land use on NO<sub>3</sub><sup>−</sup> pollution, and drinking water safety in an urban area of southwestern China. Thirty-one groundwater samples were collected and analyzed for major hydrochemical parameters and dual isotopic composition of NO<sub>3</sub><sup>−</sup> (δ<sup>15</sup>N-NO<sub>3</sub><sup>−</sup> and δ<sup>18</sup>O-NO<sub>3</sub><sup>−</sup>). The groundwater samples were characterized by neutral to slightly alkaline nature, and were dominated by the Ca-HCO<sub>3</sub> type. Hydrochemical analysis revealed that water–rock interactions, including carbonate dissolution, silicate weathering, and cation exchange, were the primary natural processes controlling hydrochemistry. Additionally, anthropogenic influences have significantly altered NO<sub>3</sub><sup>−</sup> concentration. A total of 19.35% of the samples exceeded the Chinese guideline limit of 20 mg/L for NO<sub>3</sub><sup>−</sup>. Isotopic evidence suggested that primary sources of NO<sub>3</sub><sup>−</sup> in groundwater include NH<sub>4</sub><sup>+</sup>-based fertilizer, soil organic nitrogen, sewage, and manure. Spatial distribution maps indicated that the spatial distribution of NO<sub>3</sub><sup>−</sup> concentration correlated strongly with land use types. Elevated NO<sub>3</sub><sup>−</sup> levels were observed in areas dominated by agriculture and artificial surfaces, while lower concentrations were associated with grass-covered ridge areas. The unabsorbed NH<sub>4</sub><sup>+</sup> from nitrogen fertilizer entered groundwater along with precipitation and irrigation water infiltration. The direct discharge of domestic sewage and improper disposal of livestock manure contributed substantially to NO<sub>3</sub><sup>−</sup> pollution. The nitrogen fixation capacity of the grassland ecosystem led to a relatively low NO<sub>3</sub><sup>−</sup> concentration in the ridge region. Despite elevated NO<sub>3</sub><sup>−</sup> and F<sup>−</sup> concentrations, the entropy weighted water quality index (EWQI) indicated that all groundwater samples were suitable for drinking. This study provides valuable insights into NO<sub>3</sub><sup>−</sup> source identification and hydrochemical processes across varying land-use types. |
|---|---|
| ISSN: | 2305-6304 |