Environmental impacts of thermal emissions to freshwater: spatially explicit fate and effect modeling for life cycle assessment and water footprinting

Abstract

Thermal emissions from electric power generation plants can lead to environmental impacts. However, such emissions have neither been comprehensively integrated in life cycle assessment (LCA), a method to quantify environmental impacts throughout the life cycle of a product, nor in water footprinting. This study presents a spatially explicit (0.5 arc degree resolution) fate and effect model for assessing the impact of thermal emissions from power production in the USA on freshwater ecosystems. We developed a two-step regionalized fate model to capture short-range and long-range thermal effects. Effect factors were derived as a function of ambient temperature and used in conjunction with the fate factor to calculate the impacts. The impacts are measured as the potentially disappeared fraction (PDF) of species in the affected freshwater ecosystem volume over time. The long-range freshwater ecosystem impacts are dependent on the distance to sea as well as the ambient temperature, while the short-range effects are mainly influenced by the induced temperature change at the point of mixing. Our analysis showed that 95 % of the modeled grid cells in the USA have an impact of 2.5 × 10−6 to 2.5 × 10−4 PDF m3 years per MJ emitted heat. For natural gas power production, thermal pollution can have a significant contribution to total freshwater ecosystem quality. This study shows that thermal effects can be calculated on a spatially explicit level based on background data. It reveals the variability within a large region of the world, covering various geographic regions, and therefore helps generalizing the results for other regions.