# Salinity gradient: Impact on nature

No burning, but estuaries could feel the intakes

Source page: https://www.materialinsights.org/energy/e_salinity/nature/

What this tab covers What taking energy from this source does to land, water, air and climate, wildlife and ecosystems, with life-cycle emissions and land use where measured.

No combustion and no consumption of water or salt, but large intakes and brackish discharges can disturb estuaries; impacts are so far inferred from pilots and from desalination plants.

#### Effects on nature

| Area | Effect | Size | How it is reduced |
|---|---|---|---|
| **Air and climate** | No NOx, CO or CO2 emitted in operation.^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Salinity_Energy_v4_WEB.pdf) | Zero operational emissions | None needed |
| **Water** | Neither water nor salt is consumed, but diverting river flow changes estuary mixing; effluent is brackish and of high volume.^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Salinity_Energy_v4_WEB.pdf) | Only a limited share of river flow can pass through a plant | Cap withdrawals; discharge design to avoid recirculation |
| **Wildlife (intakes)** | Intake of both fresh and salt water can impinge and entrain organisms.^[5](https://ideas.repec.org/a/eee/rensus/v102y2019icp111-120.html) | Not yet quantified at pilot scale | Screens and low intake velocities, as for desalination plants |
| **Chemicals** | Pre-treatment against biofouling may add chemicals to discharges.^[5](https://ideas.repec.org/a/eee/rensus/v102y2019icp111-120.html) | Not quantified | Mechanical pre-treatment, fouling-resistant membranes |
| **Life cycle** | Membrane manufacturing dominates impacts; eutrophication, ecotoxicity and carcinogenic impacts can exceed those of other renewables under some assumptions.^[6](https://tethys.pnnl.gov/publications/life-cycle-assessment-salinity-gradient-energy-recovery-using-reverse-electrodialysis) | Impacts about 50% higher with natural water than with concentrated brine | Higher power density membranes; brine-based hybrids |
| **Land** | Plants can be built underground or in low buildings near the shore.^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Salinity_Energy_v4_WEB.pdf) | Small, not quantified | Use existing industrial or harbour sites |

Because no comprehensive environmental assessment of a working plant yet exists, most expected impacts are inferred from desalination plants and cooling-water intakes. The main concerns are local: entrapment of fish and larvae at intakes, chemicals used to keep membranes clean, and changes to salinity patterns where large volumes of brackish water are returned to the estuary.

A 2021 life-cycle study of reverse electrodialysis found its impacts comparable to, and often lower than, wind and solar under favourable conditions, but it did not publish a single figure in g CO2e/kWh, so none is given here.

#### Sources

1. [Salinity Gradient Energy: Technology Brief](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2014/Salinity_Energy_v4_WEB.pdf) IRENA, 2014
2. [Potential local environmental impacts of salinity gradient energy: A review (Seyfried, Palko and Dubbs, Renewable and Sustainable Energy Reviews 102)](https://ideas.repec.org/a/eee/rensus/v102y2019icp111-120.html) Elsevier, 2019
3. [Life cycle assessment of salinity gradient energy recovery using reverse electrodialysis (Mueller et al., Journal of Industrial Ecology 25)](https://tethys.pnnl.gov/publications/life-cycle-assessment-salinity-gradient-energy-recovery-using-reverse-electrodialysis) Wiley (via PNNL Tethys), 2021

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_salinity/index.md)
- [Overview](https://www.materialinsights.org/energy/e_salinity/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_salinity/correlation/index.md)
- [How energy resides](https://www.materialinsights.org/energy/e_salinity/resides/index.md)
- [Abundance](https://www.materialinsights.org/energy/e_salinity/abundance/index.md)
- [Fluctuation in time](https://www.materialinsights.org/energy/e_salinity/time/index.md)
- [Across the Earth](https://www.materialinsights.org/energy/e_salinity/geography/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_salinity/links/index.md)