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Blue carbon sediments as effective sinks for microplastics: A global meta-analysis
Summary
This global meta-analysis of 54 studies found that blue carbon ecosystems (mangroves, salt marshes, seagrass meadows) accumulate significantly more microplastics in their sediments than unvegetated tidal flats, with mangroves showing the strongest effect. Microplastic burial rates in these ecosystems have increased exponentially by 2.7% per year since the 1950s, roughly double the rate in bare sediments.
Blue carbon ecosystems (BCEs) typically exhibit elevated sediment accretion rates, facilitating effective sequestration of microplastics (MPs) in their sediments. However, the heterogeneity of BCEs and the complexity of environmental factors result in the accumulation and distribution patterns of MPs in BCEs remaining poorly understood. In this study, a meta-analysis was conducted with 374 observations from 54 articles to quantitatively assess the accumulation and capture effects of MPs by BCEs using Hedges' d effect sizes and enrichment index (EI). We systematically evaluated the influence of vegetation characteristics, sediment properties, and hydrodynamic conditions on the MP accumulation in BCEs. A significant accumulation and burial of MPs in BCE sediments is observed compared to unvegetated tidal flats, with an overall effect size of 1.93 (p < 0.001). Mangrove forests exhibit a more pronounced effect size of 2.46 compared to seagrass meadows (1.01) and salt marshes (1.70). The vegetated area and particulate organic carbon (POC) content are positively correlated with MP accumulation, while sediment composition displays variable relationships with MP retention. In BCEs, MP abundance and EI values in the seaward and landward fringes are significantly greater than those in the interior areas due to the fringe effect. Since the 1950s, the MP burial rate has increased exponentially by 2.7 % per year, about double the rate observed in bare tidal flats (1.4 % year). These findings provide new insights into the environmental fate and impacts of MPs in coastal wetland ecosystems.