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

Abstract

Mangrove forests are critical ecosystems that sequester carbon and nitrogen in their sediments and regulate coastal biogeochemical cycles. However, rapid degradation due to urban expansion, deforestation, and industrial development may impact their carbon and nitrogen burial capacity. Here, we reconstruct ~70 years of carbon and nitrogen sediment burial from nearby pristine and anthropogenically impacted mangroves in Brazil. Impacted site had finer sediment textures and higher 210Pb-derived sedimentation rates than pristine locations. Carbon and nitrogen accumulation rates were elevated in recent sediments in both pristine and impacted sites, storing catchment 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 pristine mangrove sediments, and from 36.1 to 422 g m−2 yr−1 (218 ± 121 g m−2 yr−1) in impacted mangroves, exceeding global averages (194 g m−2 yr−1). Pristine mangroves exhibited a greater capacity to accommodate variability in carbon sequestration. In contrast, impacted mangroves appear less capable of retaining elevated carbon loads discharged into the estuary. This study underscores the vital role of mangrove ecosystems in buffering anthropogenic nutrient inputs through carbon and nitrogen burial in sediments, and reveals long-term impacts of mangrove degradation in rapidly urbanizing coastal regions.