Contrasting carbon and nitrogen burial in pristine vs. impacted mangrove sediments.

Mangrove forests are critical ecosystems that sequester carbon and nitrogen in their sediments and regulate coastal biogeochemical cycles. However, rapid degradation may impact their carbon and nitrogen burial capacity. Here, we reconstruct ~70 years of carbon and nitrogen sediment burial from pristine and anthropogenically impacted mangroves in Brazil. A total of two cores were collected at the relatively pristine site, and three cores were collected at the impacted site. Impacted site had finer sediment textures and higher 210Pb-derived sedimentation rates than pristine location. Carbon and nitrogen accumulation rates were elevated in recent sediments in both relatively pristine and impacted sites, storing nutrient inputs. Enriched δ15N and δ13C signatures at impacted site indicate anthropogenic nutrient inputs and organic matter source shifts towards a marine origin. Organic carbon burial rates ranged from 23 to 747 g m-2 yr-1 (229 ± 214 g m-2 yr-1) in relatively pristine mangrove sediments, and from 36.1 to 422 g m-2 yr-1 (218 ± 121 g m-2 yr-1) in impacted mangroves, within global averages (194 g m-2 yr-1). Relatively pristine mangroves exhibited a greater capacity to accommodate variability in carbon sequestration. In contrast, impacted mangroves exhibit a more constrained range of variability in accumulation rates. This study underscores the critical role of mangrove ecosystems in buffering nutrient inputs through carbon and nitrogen burial in sediments, and emphasizes distinct carbon and nitrogen accumulation patterns between diverse estuarine settings with varying degrees of urbanization.