Avoiding Conflicts between Future Freshwater Algae Production and Water Scarcity in the United States at the Energy-Water Nexus

Henriette I Jager,Latha M Baskaran,Rebecca A Efroymson

doi:10.3390/w11040836

Abstract

Sustainable production of algae will depend on understanding trade-offs at the energy-water nexus. Algal biofuels promise to improve the environmental sustainability profile of renewable energy along most dimensions. In this assessment of potential US freshwater production, we assumed sustainable production along the carbon dimension by simulating placement of open ponds away from high-carbon-stock lands (forest, grassland, and wetland) and near sources of waste CO 2 . Along the water dimension, we quantified trade-offs between water scarcity and production for an ‘upstream’ indicator (measuring minimum water supply) and a ‘downstream’ indicator (measuring impacts on rivers). For the upstream indicator, we developed a visualization tool to evaluate algae production for different thresholds for water surplus. We hypothesized that maintaining a minimum seasonal water surplus would also protect river habitat for aquatic biota. Our study confirmed that ensuring surplus water also reduced the duration of low-flow events, but only above a threshold. We also observed a trade-off between algal production and the duration of low-flow events in streams. These results can help to guide the choice of basin-specific sustainability targets to avoid conflicts with competing water users at this energy-water nexus. Where conflicts emerge, alternative water sources or enclosed photobioreactors may be needed for algae cultivation.

Highlights

Freshwater algal biomass production is a promising future source of energy that highlights trade-offs at the energy-water nexus
We develop and evaluate sustainability indicators to assess impacts on water that could be associated with algae production at a national scale
We illustrate the trade-off between algae production and the available water surplus (Figure 2)

Summary

Introduction

Freshwater algal biomass production is a promising future source of energy that highlights trade-offs at the energy-water nexus. Nexus research seeks to understand and minimize trade-offs [1]. The growing demand for, and interdependence among, resources such as water, energy, and food, produces hotspots of stress [2]. Renewable biofuel production systems are being designed with improved sustainability profiles. Research to understand and reduce trade-offs and build complementarities can help to improve the sustainability profiles of alternative systems. Growing microalgae in open ponds has been identified as one promising option. Microalgae can potentially produce 1–2 orders of magnitude more oil per unit land than conventional crops without compromising food production [3]. Previous studies have estimated the amount of algal biomass supply available in the US with some sustainability constraints [4,5,6,7,8]

Methods

Results

Discussion

Conclusion