Olivine-based marine carbon dioxide removal field trial shows no adverse effects on the benthic community

Marine enhanced rock weathering (mERW) with olivine is a promising carbon dioxide removal (CDR) strategy, but its ecological impacts remain uncertain. In 2022, a first-of-its-kind mERW field trial was conducted on a sandy beach in Southampton, New York (USA), assessing macrobenthic community responses and trace metal accumulation using a before–after control–impact (BACI) design. Abundance and species richness at olivine-treated sites returned to control levels within ~2 months, while diversity and evenness remained unchanged. Although community composition shifted after placement, these changes were consistent across all treatments, indicating high natural variability or cumulative nourishment effect rather than an olivine-specific effect. Multivariate analyses revealed community reassembly not captured by standard metrics. Concentrations of olivine-associated metals (Ni, Cr, Co, Mn) were comparable across treatments over ~1 year, with no evidence of accumulation. Despite environmental heterogeneity, our results provide the first field evidence that mERW deployment does not cause detectable adverse effects on benthic communities over seasonal timescales.