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Abstract IntroductionWe rely on coastal resources for food, water, and energy. However, over 75% of U.S. coastlines are eroding. Concurrently, the U.S. recycles less glass than other developed countries, landfilling hundreds of millions of tons every year. Recycled glass sand has many potential benefits over natural sand for combatting land loss; for example, it can be produced with controlled particle size to better resist erosion, making it an excellent—and underutilized—material for environmental restoration. ObjectivesThis research compares the physical and chemical properties of recycled glass sand to natural sands (beach and dredge) from the U.S. Gulf Coast to assess environmental safety. MethodsParticle size distribution, angularity, particle and bulk density, compaction, and permeability were evaluated using standard methods. Elemental composition and leaching were analyzed using x‐ray fluorescence and toxicity characteristic leaching procedure (TCLP), respectively. ResultsRecycled glass sand is not “sharp,” although it is less well‐rounded than natural sand. Porosity, compaction, and water permeability depend on particle size, and glass sand can be size‐separated to match or complement natural sand. Recycled glass sand is mostly silica. Additional elements used in glass processing are present at acceptable levels, and no leaching of harmful elements is detectable by TCLP. Thermally decomposable residues (e.g. label and adhesive) reliably comprised less than 1% of the material. ConclusionsThe characteristics of recycled glass sand make it a good resource for environmental restoration. 

As coastal regions experience accelerating land loss, artificial substrates may be useful in restoration efforts to replenish sediment and facilitate plant colonization. Recycled glass sand is a potential artificial substrate for marsh building due to its sustainability, availability, and similarity to natural substrates. However, differences in texture and availability of microbiota necessitate investigating how it affects plant growth. We tested the effect of three substrates (conventionally used dredged river sand, recycled glass sand, and a mix) and inoculation with natural soil microbes on the biomass and root architecture of Black mangrove (Avicennia germinans) in a greenhouse experiment. We found neither substrate nor inoculum affected biomass; however, survival was lower in mixed substrate compared to dredged and glass sand, and live inoculum increased survival from 70 to 93%. Substrate affected root architecture: mangroves grown in glass sand had 55% lower fine root length, 51% lower specific root length (length/mass), and 26% larger average root diameter than mangroves grown in dredged sand. Although an unintended fungal infection byGeotrichum candidumkilled nearly 90% of infected propagules before the experiment, surviving plants had 81% higher biomass than uninfected plants. These findings suggest that while glass sand does not affect biomass, it may affect root architecture in ways that compromise soil stability. Furthermore, inoculation with live soil may boost restoration planting success across substrates, likely by reintroducing mutualists. Overall, recycled glass sand may be a viable restoration strategy with the caveat that the developing root architecture may differ from that in more natural substrates. 

Sand made from recycled glass cullet could supplement limited dredged river sand (dredge) in coastal wetland restorations; however, its suitability for wetland plants is unknown. In two experiments, we compared the biomass of several wetland plants in recycled glass sand to growth in dredge. First, we grewSalix nigra,Zizaniopsis miliacea, andSporobolus alterniflorusin fine‐ and coarse‐glass sands, dredge, and a coarse‐glass/dredge mixture. Second, we grewTaxodium distichumandSchoenoplectus californicusin a revised coarse‐glass blend, dredge, and a mix. We characterized the substrate porosity, particle density, and bulk density for both experiments and tested how substrate nutrients, metals, and pH impactedS. californicusleaf contents. We found species‐specific responses to substrates: herbaceous species grew better in the mix and dredge than in glass alone, whereas trees grew equally well in the coarse glass, mix, and dredge. Glass sand was less dense than dredge. When saturated and compressed, finer‐grained glass sand and mixes had lower estimated porosities than coarser glass sand and dredge.S. californicusleaf chemistry resembled that of the plant's substrate. This study demonstrated that wetland plants can grow in glass sand, that mixtures of glass and dredge have species‐specific effects, and that substrate structure and chemistry could help explain these differences. Thus, it opens the door for broader field studies on how glass sand can best be used in coastal restoration efforts.