Spatiotemporal Variations of Water Physicochemical Status in Pinios River Catchment, at Eastern Mediterranean Region

Knowledge on river quality variations and of exceeding quality limits is essential for the allocation of water to different uses and for applying remedial measures. Thessaly plain was extremely fertile, and up until the early 20th century the area was a breadbasket for Greece. The highly important for the national agricultural production, albeit severely degraded Pinios river, has been assessed for its Chemical-Physicochemical (C-P) status, based on the results of the National Monitoring Program for the years 2018-2020, considering 218 seasonal samples. Forty percent (40%) of the total sample number, and 70% of the 30 monitoring stations revealed a lower than good C-P status, predominately as a result of elevated phosphate, total phosphorous and nitrate concentrations. Exceptionally, the Pinios river seems to be predominately affected by point sources of organic pollution, and secondarily by agricultural return flows and land flushing processes, whereas dominant mineralization and nitrification processes control the concentration and speciation of N and P compounds. The COVID lock-down seems not to have affected aquatic quality through an increase of WWT effluents or/and diminishing of atmospheric pollution, whereas the improvement of C-P status at the river outflow via dilution by local mountain springs is threatened by an ongoing dry spell affecting the country. Within the upcoming RBMPs, urgent remediation measures in Pinios basin should both target point sources of pollution and control agrochemicals, particularly focusing on adaptation strategies on extreme weather events.