Assessing water stress in Mediterranean lotic systems: insights from an artificially intermittent river in Greece

Abstract

Water stress in Mediterranean countries is the result of both variable and changing climatic conditions and widespread anthropogenic pressures. Evrotas, an intermittent river located in Southern Greece, was used as a case study to assess the impacts of water stress on Mediterranean lotic ecosystems. Based on hydrological analyses, it was revealed that during prolonged drought years, such as the summers of 2007 and 2008, the vast majority of the Evrotas riverbed was completely desiccated, primarily as a result of substantial water abstraction for irrigation. The effects of desiccation on the riverine ecosystem were evaluated using fish and macroinvertebrate assemblages according to the demands of the Water Framework Directive 2000/60/EC (WFD). Faunal responses to water stress were assessed through comparisons of assemblages attributes in perennial and intermittent reaches and pre-drought versus postdrought communities. Effects of hydrological disturbance on fish species richness, density, percentage composition and size structure were more pronounced in intermittent than in perennial sites. The most obvious and immediate impact was the elimination of populations in the intermittent reaches. However, upon flow resumption, the recolonisation from upstream perennial reaches began, thereby permitting partial re-establishment of the depleted fish communities. Nevertheless, the structural integrity of fish communities remained severely impacted and recovery was markedly slow. On the contrary, post-drought macroinvertebrate assemblages were not affected by summer droughts, and the recruitment processes were rapid after flow resumption. Our findings point to the necessity of establishing a distinction between naturally and artificially driven intermittent rivers. We, therefore, propose the introduction of an ''artificially intermittent Mediterranean river'' condition within the context of the WFD assessment applications.

Non-perennial Mediterranean rivers in Europe: Status, pressures, and challenges for research and management

“…This decrease favours the creation of disconnected pools and increases the number and extent of NPRS stretches (e.g. Benejam et al, 2010;Skoulikidis et al, 2011;Datry et al, 2014a).…”

“…Other recent studies focused on the mechanisms allowing species to cope with recurrent drying as well as to produce quantitative relationships between drying duration and frequency (Datry et al, 2014b). In most cases, taxa richness of aquatic macroinvertebrates was lower in NPRS than in PRS (Muñoz, 2003;Morais et al, 2004;Sánchez-Montoya et al, 2009, 2010Belmar et al, 2012;Datry, 2012;Datry et al, 2014b), but see Bonada et al (2007bBonada et al ( , 2008 and Skoulikidis et al (2011). The seasonal community composition differed between PRS and NPRS (Bonada et al, 2008); in NPRS, invertebrates exhibiting low dissolved oxygen requirements and pool-like strategies dominate during the contracting phase (Pires et al, 2000;Acuña et al, 2005;Bonada et al, 2007b;García-Roger et al, 2013), whereas resilient taxa and species with riffle-like strategies dominate during the expansion phase (Bonada et al, 2007b;Datry et al, 2014b).…”

“…The hydrological disturbance of NPRS affects species richness, density, biomass, composition, and size (age) structure of fish assemblages (Benejam et al, 2010;Skoulikidis et al, 2011). Several studies have indicated significantly lower fish densities in NPRS (Mas-Martí et al, 2010), while others reported higher densities due to crowding effects (Pires et al, 1999;Skoulikidis et al, 2011).…”

Recent perspectives on temporary river ecology

“…Skoulikidis et al (2011) described the effects flow cessation on a Greek river. Large sections of the river network dried during two consecutive summers, and negatively impacted fish populations, which experienced a long recovery time.…”

“…For example, there is considerable variability among regions globally in the rates of drying and rewetting along temporary rivers. Skoulikidis et al (2011) provided an extreme example of the intensity and extension of intermittency. Are there biologically relevant hydroperiod classes of temporary rivers?…”