Spatial distribution, eco-environmental risks, and source characterization of heavy metals using compositional data analysis in riverine sediments of a Himalayan river, Northern Pakistan

Purpose Riverine sediments are an important component of the aquatic environment as they play an essential role in influencing its eco-environmental functions. Sediments may serve as both the source and sink of heavy metals (HM). The Astore River basin is located in the Himalayas, northern Pakistan. The area is frequented by a high number of tourists and is characterized by a fragile biophysical system. This study aimed to assess the occurrence, spatial patterns, and potential sources of HM in the sediments of the Astore River network. Methods Thirty-nine samples from the Astore River and its tributaries were collected and analyzed for nine HM (Fe, Mn, Cu, Zn, Cd, Cu, Co, Pb, and Ni) using atomic absorption spectrometry. Various modified indices, i.e., modified ecological risk index (mERI) and modified sediments pollution index (mSPI), were utilized to assess the sediment ecological and pollution risks. The data were subjected to compositional data analysis (Coda) using the R program for the source characterization of HM. Results The results indicated that among the HM, Fe and Cd had the highest and lowest concentrations, respectively. Mn contributed the most to the pollution of the sediments, while Cd has the highest potential ecological impact. The mSPI indicated that the sediments were either in their natural state or showed low to moderate contamination, while only 2.5% were classified as extremely polluted. At the same time, 12.8% of the samples were categorized in the high pollution class. The ecological risk, however, showed more profound and negative bearings on the sediment quality as 33.3% and 2.5% of the samples showed considerable to high ecological risks. The spatial distribution of HM and the modified indices indicated Deosai valley as the zone of concern for management and abatement options. Conclusion Overall, this study concluded that the major contribution to HM concentration in the area was from natural sources. However, in the case of Cd and Zn, an amplification in concentration due to anthropic factors was noted. Mn and Cd stood out as the major contaminants posing profound ecological risks. A differential spatial pattern of HM contamination in valleys suggested the need for targeted and specific management plans for prevention.