Novel developing an aqueous status fingerprint to identify tempo-spatial-multivariate elements of water quality in the seven major rivers into Northwestern Pacific

Abstract

Intense human activity and climate change might deteriorate water quality of seven large-scale estuaries in Northwestern Pacific. Here, by uniting aqueous status fingerprint, the water quality pattern and underlying mechanisms were investigated in the lower reaches of the seven major rivers in China flowing into Northwestern Pacific, which was associated with the Tumen River (TUR), Liaohe River (LIR), Haihe River (HAR), Yellow River (YER), Huaihe River (HUR), Yangtze River (YAR) and Pearl River (PER). From January to December 2023, monthly overlying-water samplings were conducted at 45 sites along the lower reaches of the seven rivers, whose typical parameters were determined. The descending order of water quality indices (WQI) for the lower reaches of the seven rivers was PER (83.78 ± 2.63) > YAR (81.80 ± 1.17) > YER (78.23 ± 1.83) > TUR (75.64 ± 2.33) > HUR (69.84 ± 6.78) > HAR (66.27 ± 7.96) > LIR (62.21 ± 2.34), indicating that the LIR, HAR, and HUR presented poor water quality with low WQI values (<70.00). According to principal component absolute coefficients, an aqueous status fingerprint was firstly developed to identify tempo-spatial-multivariate elements of water quality in the lower reaches of the seven rivers. Poor water quality in rivers primarily occurred at the sites in estuaries, except for TUR and YER, whose water qualities were poor in upstream of the estuary. The poor water quality in LIR and HAR was primarily in August, while the HUR, YAR, and PER were in February and March, both of them presenting obvious seasonal distribution characteristics. Based on the aquatic status fingerprint and two-dimensional correlation analysis (2DCOS), COD_Mn and TP in TUR were the key elements, whose variations occurred in September. The key elements were F^- and BOD₅ in LIR. F^- mainly varied in November, while BOD₅ in April to June. COD_Mn and COD_Cr, as the key elements in HAR, varied from July to August and from June to September, respectively. COD_Cr was a key element in YER, whose variations were from January to April. The variation of DO, as a key element in HUR, appeared from June to August. COD_Cr was a key element in both YAR and PER, whose variations emerged from February to March and from February to June, respectively. The variance partitioning analysis revealed that the interaction of anthropogenic and natural factors had the highest contributions to water quality variations in TUR (13 %) and HUR (18 %), as were the interactive contribution of socioeconomic development (SD), pollutant discharge and land use (LU) in HAR (18 %), the independent contribution of climate fluctuations in LIR (45 %), YAR (16 %) and PER (14 %), and the interactive contribution of SD and LU (11 %) in YER. Aqueous status fingerprint combined with 2DCOS, as a simple and intuitive method, could be conducive to understanding water quality characteristics and enhancing water quality conservation in estuaries.