Implementation of the EU ecological flow policy in Italy with a focus on Sardinia

Abstract

River ecosystems are characterised by a naturally high level of hydrodynamic perturbations which create aquatic-terrestrial habitats indispensable for many species, as well as for the human beings’ welfare. Environmental degradation and habitat loss caused by increasing anthropogenic pressures and global change affect freshwater aquatic ecosystems worldwide and have caused changes in water flow regimes and channels morphologies. These, in turn, decreased the natural flow capacity and reduced habitat availability, thus causing severe degradation of rivers’ ecological integrity. The ecological flow (e-flow) is commonly intended as the quantity, timing, duration, frequency and quality of water flows required to sustain freshwater, estuarine and near shore ecosystems and the human livelihoods and well being. Maintaining the e-flow represents a potential tool for restoring and managing river ecosystems, to preserve the autochthonous living communities, along with environmental services and cultural/societal values. In the last decade, methods for the determination of the e-flow in European rivers moved from a simply hydrological approach towards establishing a linkage between the hydrological regime and the good ecological status (GES) of the water bodies, as identified by the European Water Framework Directive (WFD; 2000/60/EC). Each Member State is required to implement and integrate into the River Basin Management Plans (RBMP) a methodology for the determination of the e-flow, ensuring that rivers can achieve and maintain the GES. The competent river basin authorities have thus to ascertain whether national methodologies can be applied to different river typologies and basin environment characteristics. In this context, we narratively review the e-flow assessments in the heterogeneous Italian territory, in particular on a water scant region such as Sardinia, by analysing laws, guidelines and focusing on study cases conducted with micro and meso-scale hydraulic-habitat approaches. In the sight of a more ecological-based application of national e-flow policy, we suggest that meso-habitat methods provide a valuable tool to overcome several limitations of current e-flow implementation in the Italian territory. However, to face future challenges, such as climate change adaptation, we stress the need for further experimental studies to update water management plans with greater attention for nature conservation. N n-c om me rci al us e o nly Implementation of the EU ecological flow policy in Italy with a focus on Sardinia 23 release from dams and other types of derivation (Acreman et al., 2016). The environmental flow (e-flow) is commonly intended as the quantity, timing, duration, frequency and quality of water flows required to sustain freshwater, estuarine and near shore ecosystems and the human livelihoods and well being (Tharme, 2000). The concept of e-flow has been discussed for more than 40 years (Tharme, 2003; Acreman and Dunbar, 2004; King and Brown, 2006; Poff and Matthews, 2013; Acreman, 2016) and it is now worldwide recognized by several national and regional water protection policies, e.g. the European Water Framework Directive (European Commission, 2015), the South African National Water Act (Forslund et al., 2009) and the Brisbane Declaration (Arthington et al., 2018). Many countries have incorporated e-flow provisions as they have updated water policy and laws (Le Quesne et al., 2010). Over the last few years, there has been a growing consensus about the need of science-based approaches and requirements for the assessment of e-flows in order to achieve successful management of freshwater ecosystems, conciliating natural habitats conservation with the supply of freshwater for human usage (Acreman and Dunbar, 2004). The achievement of such a trade-off can become more critical in the sights of modified hydrological conditions that will result as a consequence of current climate change (Tonkin et al., 2019). Tharme (2003) identified >200 methods to assess the water requirements of aquatic species and habitats, and support e-flows management practices to achieve both ecological and social targets (see also Acreman and Dunbar 2004). However, to date, there are still several limiting factors for the implementation of successful eflow policy, due, mainly, to limitations in institutional capacity, scientific knowledge and monitoring resources. These have been summarized by Le Quesne et al., (2010) in four crucial issues: i) the scarcity of knowledge about sites and speciesspecific e-flows requirements; ii) the lack of political decision and effort to recognizing a need to maintain sufficient water in rivers and wetland systems; iii) imperfect understanding of the practical issues and costs of implementation to achieve the e-flow regime; iv) the lack of a design and maintenance of robust monitoring systems to assess the ecological and other outcomes of environmental watering in an adaptive management framework. In order to overcome these general issues, research and monitoring of e-flows’ adjustments is often required (Richter, 2009; Zang et al., 2012), as well as, the synthesizing of knowledge and experience gained from individual case studies (Arthington et al., 2004; Poff et al., 2010). In fact, regional and local approaches have a fundamental role in the understanding e-flow methods limitations. They will be crucial for the implementation of an applicable methodology to define e-flows by River Basin Authorities. This is particularly needed in a context where heterogeneous climatic regions (e.g. Alpine, Mediterranean) occur and a homogeneous and more ecological-based methodology for the definition of the eflow is requested. In this context, we review the status of e-flow implementation in Italy, with a focus on a region with high water scarcity such as Sardinia, by analyzing laws, guidelines and study cases conducted with hydraulic-habitat approaches, both at micro and mesoscale. The final aim of this review is to highlight current challenges and limitation that make difficult the application and adaptation of a common e-flows methodology and give cues for the selection of a suitable habitat simulation models that could be integrated to overcome these limits. THE EUROPEAN GUIDANCE ON E-FLOWS Nowadays, in Europe, the most significant pressures causing failure to achieve the Good Ecological Status (GES) are the hydro-morphological ones (affecting ca. 40 % of surface water bodies, with the highest proportion reported for rivers and transitional waters) (E.E.A. Report n. 7/2018). The largest proportion (26%) of water bodies is affected by physical alterations in the channel, bed, riparian zone, whereas up to 24% of the investigated water bodies are affected by the presence of structures, such as dams/barriers and locks, that alter the rivers’ longitudinal continuity (E.E.A. Report n. 7/2018). Since 2012, to implement e-flows management in the River Basin Management Plans the European Commission (EC) has asked the Member States (MSs) to focus on pressures affecting the hydrological status of water bodies (Schmidt and Benítez Sanz, 2012). However, the lack of harmonized methodologies and, consequently, of sufficient or sufficiently consistent data for the definition of e-flows’ assessment by each MS has raised several operational and interpretation difficulties (Acreman and Ferguson, 2010). For this reason, in 2015, the EC released the e-flow Guidance Document (Ecological flows in the implementation of the Water Framework Directive; WFD CIS Guidance Document No. 31). In this document, the definition of e-flow is provided within the context of the Water Framework Directive (WFD) as “a hydrological regime consistent with the achievement of the environmental objectives of the WFD in natural surface water bodies as mentioned in Article 4(1)” and is interpreted as the “amount of water required for the aquatic ecosystem to continue to thrive and provide the services we rely upon”. Once terminology has been clarified, concern has then arisen on how to No n-c om me rci al us e o nly