Comparison of Sampling Designs for Soil Sediment Source Fingerprinting

Abstract

Sediment fingerprinting is increasingly being used to provide information that can help guide management decisions at the watershed scale. The objectives of this study were to investigate the implications of different sediment fingerprinting sampling designs on characterizing sediment dynamics in the Beheshtabad Watershed in Chaharmahal va Bakhtiari Province, western Iran. First, nitrogen, organic carbon, phosphorus, potassium, calcium, sodium, zinc, manganese, iron, and lime fingerprints were used to discriminate among four potential sediment sources including agricultural topsoil, rangeland, as well as rainfed and urban lands. Then, the suspended sediment was collected from drainage areas at five sites. Nested and local-location fingerprinting sampling designs were employed to evaluate the influence of geomorphic connectivity and land use on apportionment results by using the same source and sediment data set. By averaging all locations using the nested method, agricultural land with an average of 69% had the highest contribution to sedimentation followed by rainfed land with an average of 19.9%, rangeland with an average of 6.8%, and urban lands with an average of 5.99%. Compared to the mean of the total method samples, the local method showed greater soil loss from agricultural lands and lower soil loss from rangeland and rainfed lands. Generally, surface soil in sediments came from agricultural land use. According to the results, total nitrogen, phosphorus, organic carbon, and calcium were the optimum tracers that correctly distinguished source samples. Overall, each of the two fingerprinting sampling designs provided the same information. Thus, the fingerprinting method can determine the sources of sediments. Given the importance of the fingerprinting method, future studies can focus on determining the appropriate combination of tracers and the effect of sediment sampling time.