Identifying environmental risk associated with anthropogenic activities in Zanjanrud River, Iran, using an integrated approach

The deterioration of river quality has already become a growing threat to the health of aquatic environments around the world. Hence, a sound temporal and spatial monitoring of water and sediment pollution in rivers is required for effective watershed management. The variability of water parameters (e.g., discharge, velocity, temperature, DO, pH, turbidity, phosphorus, nitrogen, etc.) and suspended sediment-associated metals (e.g., Ag, Al, Cu, Na, Pb, Mn, Mg, Fe, etc.) has been analyzed in the Zanjanrud River. The study period covered from October 2015 to March 2017 including dry and wet seasons at five sampling sites along the main stretch of the river with a bi-weekly frequency of sampling. Principal component (PCA) and cluster analysis (CA) were performed to reveal links between variables. The Geochemical Abundance Index (GAI), Accumulation Factor (AF) and Modified River Recovery Capacity (MRRC) were also calculated. The results revealed that the river is highly influenced by effluents from residential, industrial and agricultural activities. The GAI index indicated contamination by Cd, Cu, P and Zn immediately after the discharge from Zanjan city during the monitoring period. The AF showed only slight differences in metal levels In suspended sediments between the head and tail sites of the study river. The PCA results indicated linkages among several metals and sites and also pointed out to the influence of nitrogen and phosphorus inputs from residential and industrial areas on the water quality of the river. A considerable improvement of several environmental parameters along the river flow from the first discharge point to the tail site was observed. Our results suggest that efficient sewage treatment systems and a control over agricultural diffuse pollution near the polluting sites will considerably improve the water and sediment quality of the Zanjanrud.