The Impact of Seasonal Vegetation Changes on Retention and Yield of Sediment Across the Tajan Watershed in Sari, Northern Iran

Sediment retention (SR) and sediment yield (SY) are regulatory ecosystem services that would change due to seasonal vegetation conditions in a region. This study aimed to investigate the SR and SY in the Tajan watershed in Mazandaran Province, northern Iran, and their relationships to seasonal vegetation changes during 2022. The sediment delivery ratio model was implemented to evaluate SR and SY for four seasons using the InVEST software. Their relationship with the vegetation indices was also evaluated using geographically weighted regression (GWR) in Arc GIS 10.7. The highest level of SR and SY was observed in the central and southern parts of the watershed, respectively. The total SR and SY were estimated at 229 Mt y-1 (471 t ha-1 y-1 on average) and 5.2 Mt y-1 (11 t ha-1 y-1 on average), respectively. The maximum and minimum of SR occurred in the spring and winter, respectively, whereas the opposite was true for SY. Regional forests retained the most sediment, whereas rangelands had the highest SY. The GWR results showed a significant and positive geographic correlation between SR and vegetation indices (0.76<R2<0.84, P-value<0.01) but an inverse correlation between SY and vegetation indices (0.67<R2<0.85, P-value<0.01). Temporally, the highest geographic correlation of SR to the vegetation indices was seen in the summer, whereas the highest geographic correlation of SY to the vegetation indices was related to the winter. The results suggested that seasonal vegetation changes in the region could have a wide range of effects on the retention and yield of sediment. This study offers valuable insights for identifying areas of significant erosion throughout the watershed, during different seasons. Such information can aid managers and planners in adopting effective strategies to conserve soil and reduce erosion.