*3.3. Decommissioning Phase*

In this phase, few impacts are expected. A RED plant built on palafittes should not require large-scale activity using heavy machinery. In the case of the pipes that have been colonised by algae and sessile organisms, their removal will eliminate this artificial habitat and also the organisms that installed themselves there. The soil is not expected to be severely impacted by the type of foundations used. On the other hand, the noise associated with demolition may temporarily affect the behaviour of birds and fish. Finally, the infrastructure of the proposed ecotourism centre should not be demolished since these facilities offer attractive spaces for tourism and assist in the conservation of species in the area.

### **4. Conclusions**

A preliminary environmental assessment of the potential impacts of a 50 kW net output RED power plant using SGE on the coastal lagoon of La Carbonera was carried out. Many impacts depend on the size and location of the SGE plant and the water intake or on the technology to be implemented. In this case, a small-scale SGE power plant, using the RED technology, combined with an ecotourism centre, would provide renewable energy and protection of resources for the lagoon system and the nearby area around it, as well as providing well-paid jobs for local people that may eventually encourage an improvement in the care of coastal ecosystems.

Although several water schemes can be used in this ecosystem (FW/MW, FW/HW, and MW/HW), everything will depend on the availability of saline water. In both cases, there are alternatives; for instance, to use the dilute solution (FW) through wells on the coast, and the concentrated solution (HW) directly from the lagoon (according to hydrological studies) or through marine water evaporation ponds.

In terms of the potential impacts, the most concerning are the change in the volume of water in the lagoon and the disposal of the final effluent. While many negative potential responses could be expected, if the EIA covers information on the biotic and abiotic characteristics of the ecosystem at a given point in time, in addition to the site characteristics, many of these impacts could be minimised or avoided.

While the study in [22] suggested that most of the impacts due to the implementation of SGE occur in the construction phase, this study shows that although the impacts then may be very evident, even with mitigation measures, the ecosystems in La Carbonera could recover from these temporary effects. More damaging to the ecosystems would be the permanent and constant changes in characteristics which an SGE plant would induce, such as in the hydrodynamics (changes in water flows or volume) and salinity gradients. Therefore, it must be taken into account that since they are highly variable ecosystems that have close hydrological connectivity with the surrounding systems, any modification can have implications for neighbouring systems.

From the results of the Receptors and Responses analysis, the importance of monitoring these features during and after the construction phase must be underlined [79]. Many of the Receptors analysed are also present in other systems with potential for SGE. Even though methodologies for their characterisation already exist for most of them, it is still difficult to find quantitative criteria which demonstrate how positive or negative these Receptors are when SGE technology is applied.

Even so, this work offers the first attempt to evaluate the potential changes induced by SGE plants. This analysis for La Carbonera is important at the present time even though the technology discussed is as yet untested at a large scale, and there are no plants using it in Mexico. Small pilot plants, such as that suggested here, could offer insights for successful larger developments in the future.

Finally, although this system is healthy at present, an EIA would serve to minimise negative impacts. In this way, the benefits of SGE, zero greenhouse gas emissions, and the use of renewable sources could be successfully harnessed at La Carbonera.

**Author Contributions:** Conceptualisation, E.M.-C. and R.S.; methodology, E.M.-C. and M.L.M.; software, E.M.-C.; validation, R.S., C.E., M.L.M., and E.M.; formal analysis, E.M.-C. and R.S.; investigation, E.M.-C.; writing—original draft preparation, E.M.-C. and R.S.; writing—review and editing, E.M.-C., R.S., C.E., M.L.M., and E.M.; visualisation, E.M.-C. and R.S.; supervision, C.E., M.L.M., and E.M.; project administration, R.S.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the CONACYT-SENER-Sustentabilidad Energética project: FSE-2014-06-249795 Centro Mexicano de Innovación en Energía del Océano (CEMIE-Océano).

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing not applicable. No new data were created or analysed in this study. Data sharing is not applicable to this article.

**Acknowledgments:** We are grateful to Jill Taylor for the English revision, and to Roberto Rivera for support in managing Autocad. The authors thank the Centro Mexicano de Innovación en Energía del Océano (CEMIEOcéano) for providing support in the research in the CONACYT-SENER-Sustentabilidad Energética project: FSE-2014-06-249795 Centro Mexicano de Innovación en Energía del Océano (CEMIE-Océano). Finally, thanks to the Civil Engineering Postgraduate of the UNAM and CONACYT for the grant awarded for the development of this project.

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