Evaluating Surface Water Nitrogen Pollution via Visual Clustering in Megacity Chengdu

Abstract

The current standards used for nitrogen pollution evaluation are lacking, and scientific classification methods are needed for nitrogen pollution to improve water quality management capabilities. This study addresses the important issue of assessing surface water nitrogen pollution by utilizing two advanced multivariate statistical techniques: self-organizing maps (SOMs) obtained using the K-means algorithm and the Hasse diagram technique (HDT). The research targets of this study are the rivers of the megacity Chengdu, China. Samples were collected on a monthly basis in 2017–2020 from different sites along the rivers, and their nitrogen pollution parameters were determined. The grouping of nitrogen pollution parameters and the clustering of sampling events using SOMs facilitate the preprocessing required for the HDT, wherein clusters are ordered according to the pre-clustered water sampling events. The results indicate that nitrogen pollution in the Chengdu River Basin, which is prominent and mainly driven by nitrate nitrogen, can be categorized into five levels. The nitrogen pollution in Tuo River is serious. Although the degree of ammonia nitrogen pollution in Jin River is higher, the pollution range is smaller. Furthermore, these results were evaluated by the SOMs and HDT to be clear and reliable. Overall, these findings can provide a basis for local environmental legislation.

Assessment of Groundwater Quality in Relation to Organic versus Mineral Fertilization

“…Nitrate (NO 3 − ) is one of the most common inorganic pollutants [6], because in the last decades, the overconsumption of both synthetic and organic nitrogen fertilizers has resulted in soil and groundwater contamination. Due to this reality, nitrogen groundwater pollution became one of the most challenging environmental concerns [12][13][14]. Infiltration from landfills, mining activities, and wastewater discharges lead to pollution with other inorganic substances, toxic substances, and compounds that can be associated with water salinity due to high concentrations of Ca 2+ , Mg 2+ , Na + , Cl − , and F − [7,15,16].…”