**5. Conclusions**

At present, policy design for natural resources, especially in the energy sector, only rudimentarily accounts for cross-sectoral effects among the different resources, despite the clearly visible interdependencies among the resource systems. Given the discussed sustainability objectives, adequate policy design, however, must encompass and account for the full spectrum of social, ecological, and economic preconditions. Traditionally, policy design has been framed and analyzed per sector. Only more recently, cross-sectoral e ffects among the nexus resources have been accounted for, and mostly rudimentarily. Against the background of the advanced EPI literature, the approach used in this paper allowed the assessment of the state of policy integration across the sectors energy, water, and land. The review of EU resource governance indicates that the adaptation or consolidation of singular measures under the paradigm of EPI does not su ffice to meet the needs of cross-sectoral and transnational challenges, such as the integrated managemen<sup>t</sup> of natural resources. Instead, it will require the institutionalization of a comprehensive system perspective as conceptualized by the WEL Nexus in order to overcome the current particular interests. Thus, further research is required on the implementation of a nexus policy perspective in the EU, specifically, whether fundamentally new institutional settings are required, or integrating a coherent, cross-sectoral perspective into the existing structures provides a more e fficient approach to policy coherence. Specifically, the question of what role the member states play needs to always be taken into account.

Furthermore, comprehensive scientific research is needed to systematically analyze the systemic interrelations between natural resources (i.e., the true feedbacks and interactions among the resources and their drivers) for deriving scenarios that can serve as a foundation for the development of e ffective nexus governance options.

In order to analyze progress towards the objective of more integrated policy making, research into the operationalization of relevant concepts is necessary. As this review has demonstrated, synthesizing EPI and WEL Nexus provides a useful analytical framework for estimating the state of policy integration. At the same time, the already existing policy approaches should be further refined as to successively obviate the currently remaining policy ine fficiencies. As the above analysis shows, a policy framework in line with a comprehensive WEL Nexus approach will likely confront a number of challenges very similar to those encountered in previous measures of policy integration, so that the handling of these challenges may provide significant insights for the e ffective implementation of a WEL Nexus approach. Answering these questions will require careful analysis, given the current debates around the 'right' degree of EU integration and the balance between fully integrated and intergovernmental politics.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1073/12/23/4446/s1, Table S1: List of policy documents investigated, according to document type and year of publication.

**Author Contributions:** Conceptualization, S.V.; Methodology, S.V. and C.M.; Investigation, all; Formal Analysis, all; Writing—Original Draft Preparation, S.V. and C.M.; Writing—Review and Editing, S.D. and F.S.; Supervision, S.V.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
