Comparative contribution of planted and natural forest to sediment yield using biological indicators of TOC and n-alkanes

Understanding sediment sources and budgeting is crucial for effective watershed management and soil conservation. This study employs n-alkanes as biomarkers to trace sediment origins in a small watershed in Northern Iran, comparing the contribution of degraded forests, coniferous afforestation, and natural forests. Soil and vegetation samples were collected from different land use/land covers, while bed sediment samples were obtained from multiple points along the main stream. The distribution patterns of n-alkanes in sediment samples were analyzed in relation to those found in soil and vegetation samples. Additionally, several key indices including the carbon preference index (CPI), aquatic plant proxy (Paq), Hydrocarbon vegetation index (HVI), total organic carbon (TOC), total nitrogen (TN), and soil particle size distribution were measured to further refine source attribution. Using principal component analysis (PCA) and the FingerPro package in R, the contribution of different sediment sources was pinpointed. According to the PCA, the three sediment sources were well separated from each other. The results were striking: degraded forests accounted for the largest contribution at 45.10 %, followed by planted forests at 28.12 % and natural forests at 26.78 %. Considering the area of each land cover, the specific contribution of degraded forest and planted forest to sediment yield were 10.87 % and 7.14 % per hectare, nearly three times and two times that of natural forests (3.78 % per hectare), respectively. Our analysis, validated with a 70 % accuracy rate through the GOF index as well as field evidences, demonstrates that sediment fingerprinting with n-alkanes can effectively reveal erosion patterns and sediment yield rates between different types of forest land use. This insight is crucial for future soil conservation using appropriate afforestation species, ensuring that land management practices are aligned with long-term sustainability goals.