Relationships among biotic, abiotic parameters and ecological status in Shahid Rajaee reservoir (Iran)

Human activities in riverine water bodies can cause loading of nutrients and other pollutants in receiving systems, affecting species interactions and population dynamics. The present study aimed to investigate the influence of anthropogenic alteration on an artificial water body, i.e., the Shahid Rajaee reservoir, in Iran that is experiencing a serious water crisis. The reservoir is subject to high anthropogenic nutrient loads from the Shirinroud and Sefidroud rivers, the effect of which needs to be evaluated considering the strategic importance of the reservoir as a source of drinking water. A field sampling campaign was carried out at seven stations (one in each of the two river mouths and five in the reservoir itself) each month from April to July 2016. The study entailed sampling of benthic macroinvertebrate fauna at the river mouths and plankton communities at the reservoir stations. In addition to macroinvertebrate and plankton, abiotic and nutrient variables were measured at all stations. Substantial loading of organic matter, mainly from the Shirinroud River, was detected throughout the sampling period, with a detrimental effect on both benthic and plankton communities. The decline in plankton diversity was particularly noticeable at stations close to the river mouths during June and July, with a bloom of Dinoflagellata and Cyanobacteria and strong dominance of larger zooplankton taxa, e.g., Copepoda. Our results suggest that river water quality, affected by human activities, alters the planktonic communities in Rajaee reservoir. Our assessment indicates that measures on both the Shirinroud River and the reservoir are required to mitigate and prevent even stronger eutrophication of the reservoir ecosystem.