How Hydromorphological Pressures Co-govern Lake Water Quality in a Mediterranean Environment. A Study for Greek Natural Lakes and Reservoirs.

Hydromorphological (HyMo) conditions are increasingly recognized as key drivers of ecological quality in lakes and reservoirs, yet their role in Mediterranean systems remains poorly understood. We hypothesize that the relations between HyMo (natural or anthropogenic) metrics and quality elements (biological and physicochemical; QEs) could be quantified to benefit lake functioning and ecological quality. This attempt to quantify HyMo and QEs links, is the first for Mediterranean lakes, and aims to identify the level of QEs responsiveness to specific HyMo metrics. National monitoring data from 24 natural lakes and 26 reservoirs across Greece (2012-2021) were used. A systematic screening procedure ended with seven and eleven metrics for natural lakes and reservoirs, respectively. Redundancy Analysis and stepwise multiple linear regression were applied to identify and quantify the influence of HyMo metrics on QEs. In natural lakes, mean depth and water level were the most consistent predictors, reflecting self-purification capacity and resilience to eutrophication, while non-natural land cover and agricultural land use negatively affected phytoplankton, macrophytes, and water transparency. In reservoirs, land cover characteristics (i.e., intensive agriculture and fallow land) within the 100 m buffer zone emerged as dominant drivers of phytoplankton and Chl-a variability. Principal Component Analysis revealed four distinct typological groupings for both system types, reflecting the interplay between morphological and land use metrics. These findings confirm that HyMo functioning is a significant mediator of ecological quality in Mediterranean lakes and reservoirs, supporting the integration of system-specific HyMo metrics into Water Framework Directive assessment and ecohydrological management strategies.