Building upon previously published life cycle assessment (LCA) methodologies, we conducted an LCA of a commercial rainwater harvesting (RWH) system and compared it to a municipal water supply (MWS) system adapted to Washington, D.C. Eleven life cycle impact assessment (LCIA) indicators were assessed, with a functional unit of 1 m3 of rainwater and municipal water delivery system for toilets and urinals in a four-story commercial building with 1000 employees. Our assessment shows that the benchmark commercial RWH system outperforms the MWS system in all categories except Ozone Depletion. Sensitivity and performance analyses revealed pump and pumping energy to be key components for most categories, which further guides LCIA tradeoff analysis with respect to energy intensities. Tradeoff analysis revealed that commercial RWH performed better than MWS in Ozone Depletion if RWH’s energy intensity was less than that of MWS by at least 0.86 kWh/m3 (249% of the benchmark MWS energy usage at 0.35 kWh/m3). RWH also outperformed MWS in Metal Depletion and Freshwater Withdrawal, regardless of energy intensities, up to 5.51 kWh/m3. An auxiliary commercial RWH system with 50% MWS reduced Ozone Depletion by 19% but showed an increase in all other impacts, which were still lower than benchmark MWS system impacts. Current models are transferrable to commercial RWH installations at other locations.

Despite its widespread use, the ecological effects of shoreline armoring are poorly synthesized and difficult to generalize across soft sediment environments and structure types. We developed a conceptual model that scales predicted ecological effects of shore-parallel armoring based on two axes: engineering purpose of structure (reduce/slow velocities or prevent/ stop flow of waves and currents) and hydrodynamic energy (e.g., tides, currents, waves) of soft sediment environments. We predicted greater ecological impacts for structures intended to stop as opposed to slow water flow and with increasing hydrodynamic energy of the environment. We evaluated our predictions with a literature review of effects of shoreline armoring for six possible ecological responses (habitat distribution, species assemblages, trophic structure, nutrient cycling, productivity, and connectivity). The majority of studies were in low-energy environments (51 of 88), and a preponderance addressed changes in two ecological responses associated with armoring: habitat distribution and species assemblages. Across the 207 armoring effects studied, 71% were significantly negative, 22% were significantly positive, and 7% reported no significant difference. Ecological responses varied with engineering purpose of structures, with a higher frequency of negative responses for structures designed to stop water flow within a given hydrodynamic energy level. Comparisons across the hydrodynamic energy axis were less clear-cut, but negative responses prevailed (>78%) in high-energy environments. These results suggest that generalizations of ecological responses to armoring across a range of environmental contexts are possible and that the proposed conceptual model is useful for generating predictions of the direction and relative ecological impacts of shoreline armoring in soft sediment ecosystems.

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