Introduction
Wetlands are among the most ecologically significant ecosystems on Earth, serving as biodiversity hotspots, hydrological regulators, and carbon storage reservoirs. In arid and semi-arid regions such as southwestern Iran, wetlands also play vital socioeconomic and cultural roles. The Hoor-al-Azim wetland, located on the Iran–Iraq border in Khuzestan province, is one of the largest and most important wetlands in the Middle East. It provides critical habitats for migratory birds, fish species, and local communities, while also acting as a buffer against desertification. Despite its ecological importance, Hoor-al-Azim has faced increasing environmental pressures in recent decades, including reduced inflow from the Karkheh River, prolonged droughts, dam construction, oil extraction, and agricultural exploitation. These stressors have significantly altered the hydrology and biodiversity of the wetland. Reconstructing past climatic and environmental changes is crucial for understanding the long-term dynamics of wetlands and for developing strategies for sustainable management. Sediment cores serve as natural archives, preserving pollen grains, spores, and geochemical signatures that reflect past vegetation, climate, and hydrological conditions. Radiocarbon dating, combined with palynological analysis, provides a reliable framework for reconstructing Holocene environmental history. This study aims to determine the sedimentation rate of Hoor-al-Azim over the past 1,500 years using radiocarbon (¹⁴C) dating and to interpret past climatic changes based on pollen analysis.

Materials and Methods
Three sediment cores were collected from different stations within the Hoor-al-Azim wetland using PVC coring tubes with an internal diameter of 4.5 cm. Each core was sectioned into intervals of 5 cm, carefully sealed, and transported to the laboratory for analysis. Visual inspection of sediment color, texture, and organic content was conducted prior to laboratory treatments. Radiocarbon dating was performed on selected organic-rich samples using Accelerator Mass Spectrometry (AMS). Age calibration was carried out with OxCal software version 4.2 and the IntCal13 calibration curve, providing chronological control with a 95.4% confidence interval. Sedimentation rates were estimated by interpolating calibrated ages against core depth. For palynological analysis, subsamples were treated with hydrochloric, hydrofluoric, and bromic acids to remove carbonates, silicates, and organic matter, respectively. Residues were mounted on microscope slides and examined under light and scanning electron microscopes. Pollen and spore taxa were identified using standard atlases and reference materials, and their relative abundances were calculated.

Results and Discussion
Radiocarbon dating results indicate that the studied sediment cores span approximately the last 1,500 years, placing the record within the late Holocene. The average sedimentation rate was estimated at ~0.3 mm/year, which is relatively low compared to humid regions but consistent with arid and semi-arid wetland systems. Variability in sedimentation rates reflects hydrological fluctuations and anthropogenic impacts. Periods of increased sediment deposition correspond to wetter climatic intervals and higher fluvial input from the Karkheh River, whereas reduced sedimentation rates coincide with drought episodes and reduced inflow due to dam construction and water diversion. Palynological analysis revealed a diverse assemblage of pollen and spores, including taxa from Cycadaceae, Dipteridaceae, Characeae, and other aquatic and terrestrial plants. The presence and abundance of certain taxa suggest alternating phases of humid and dry conditions.
For example, increases in aquatic pollen types (e.g., Chara sp.) correspond to wetter intervals, while higher frequencies of xerophytic taxa reflect drier episodes. These findings are consistent with regional paleoclimate studies, which highlight the occurrence of multi-centennial oscillations in precipitation and temperature across the Middle East during the late Holocene. The results also emphasize the strong influence of anthropogenic activities on the wetland system. In particular, recent decades have witnessed intensified water regulation through dams, extensive oil extraction, and land-use changes that have reduced water inflow and altered the natural sediment balance. Such interventions have contributed to habitat degradation, loss of biodiversity, and reduced resilience of the wetland to climatic variability.


Conclusion
This study demonstrates that sediment cores from Hoor-al-Azim wetland provide valuable insights into long-term environmental dynamics. The combination of radiocarbon dating and palynological analysis allowed the reconstruction of 1,500 years of sedimentation history and climatic variability. Findings show that the wetland has experienced alternating wet and dry phases, with sedimentation rates averaging 0.3 mm/year. Climatic oscillations, compounded by human interventions such as dam construction and oil exploitation, have significantly influenced the ecological trajectory of the wetland. Understanding these past changes is essential for designing effective conservation and management strategies. Protecting Hoor-al-Azim requires an integrated approach that considers both natural variability and anthropogenic pressures. Long-term monitoring of sedimentation, hydrology, and vegetation, coupled with regional climate models, will enhance our capacity to predict future changes and safeguard the ecological and socioeconomic values of this unique transboundary wetland.