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

Analyzing water quality variations 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. The research was based on the results of the national monitoring program for the years 2018–2020, considering 218 seasonal samples. A total of 39% of the total samples and 70% of the 30 monitoring stations revealed a lower-than-good C-P status based on Water Framework Directive (2000/60/EC) boundaries. The exceedances are attributed predominately to elevated phosphate, total phosphorous, and nitrate concentrations. Exceptionally, the Pinios River seems to be mainly affected by point sources of organic pollution and secondarily by agricultural return flows and drainage processes, whereas dominant mineralization and nitrification processes control the concentration and type of nitrogen and phosphorus compounds. The coronavirus lockdown seems not to have affected aquatic quality significantly, 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 river basin management plans, prompt remediation measures in the Pinios basin should target point sources of pollution and control agrochemicals, particularly focusing on adaptation strategies for extreme weather events.