Carbon accumulation within anthropogenically impacted Peruvian Coastal saltmarshes

Coastal wetlands are critical ecosystems due to the wide range of ecosystem services they provide. This study investigates the accumulation of total organic carbon (TOC) and total nitrogen (TN) in sediment cores from anthropogenically impacted saltmarsh wetlands of Puerto Viejo (PV) and Ventanilla (() from Peru. Sediment cores, each 30 cm in length, were collected by duplicate from both sites and analyzed for TOC, TN, and stable isotopes (δ¹³C and δ¹⁵N). Sediment accumulation rates (SAR) were determined using the Constant Flux Constant Supply (CFCS) model, and carbon and nitrogen accumulation rates were subsequently calculated based on SAR and elemental concentrations. The SAR were ~ 3.4 mm yr⁻¹ in PV and ~ 3.3 mm yr⁻¹ in VEN, values lower than the global average for coastal marshes (6.0 mm yr⁻¹), yet closer to those reported for non-impacted systems (4.0 mm yr⁻¹). Beginning in the early 1990´s, anthropogenic impacts such as urban expansion and increased sewage discharge coincided with elevated TOC and TN accumulation rates within both study areas. Maximum accumulation rates for TOC and TN in PV reached 235 ± 49 g m⁻² yr⁻¹ and 28 ± 3 g m⁻² yr⁻¹, while in VEN reached 459 ± 99 g m⁻² yr⁻¹ and 23 ± 9 g m⁻² yr⁻¹, respectively. Post-1990´s, markedly lighter δ¹³C values in PV and VEN ranged in − 25.2 ± 1.6 ‰ and − 19.3 ± 3.5 ‰, respectively, indicating increased inputs of non-terrestrial material in sediments. Concurrently, elevated δ¹⁵N values in PV and VEN ranged + 11.4 ± 0.65‰ and + 7.37 ± 8.16‰, respectively, suggesting that the carbon sources were derived from a mixture of terrestrial vegetation and algae, stimulated by nutrient enrichment linked to anthropogenic activity. These findings highlight the pivotal role of coastal wetlands in accumulating carbon from both natural and anthropogenic sources, reinforcing the imperative for their conservation amid escalating global human-induced pressures.