Sediment fingerprinting in northern Jordan: element-specific correction factors in a carbonatic setting

Abstract

Water reservoirs around the world suffer from accelerated sediment loads and, consequently, contamination. Notably, in water-scarce regions such as Jordan, this poses a threat to an important water source, and identifying the sediment sources is an important task. Thus, a sediment fingerprinting study in the Wadi Al-Arab catchment of northern Jordan was implemented with special attention directed to the development of suitable correction factors necessary to improve the comparability of source and sink sediments. The selection of seven conservative elements for the sediment fingerprinting was made, with specific attention directed to the chemical environment of the reservoir. Thirty-six samples from six different surface and subsurface sources and 38 sink samples from the Wadi Al-Arab reservoir were collected. In total, 27 organic and inorganic elements as well as radionuclides were analysed. Two vertical physicochemical water profiles provided information on the pH and Eh conditions and common element concentrations. The stepwise multiple regression analysis model (SMRAM) was developed to explore parameters that influence the element concentrations and their interrelations, and to calculate an element-specific correction factor. The standard selection procedure was expanded by the comparison of water and sink sediment element concentrations, a literature review concerning the pH and Eh conditions and, in selected cases, a correlation analysis. The combination of Al, Cr, Mn, Fe, 232Th, 228Th and 137Cs provided the best source discrimination, and based on Monte Carlo simulations, the mixing model revealed the existence of three major sediment source areas. These are as follows: (i) olive orchards on slopes, which delivered 59 ± 8 % of the sediments in the sink; (ii) cultivated fields on plateau and saddle positions contributed 11 ± 9 %; and (iii) slopes with natural vegetation used for grazing contributed 29 ± 15 % of the deposited sediment. With a mean residual error of 1.04 %, the sum of the source concentrations differs only slightly from sink concentrations and proves that the model is reliable. The SMRAM model revealed that the different inorganic (total inorganic carbon, TIC) and organic (total organic carbon, TOC) carbon contents and the clay/sand content influence the element concentrations of the sediment samples. Due to the carbonatic environment, it was mainly necessary to correct for TIC. Applying an expanded literature review regarding the chemical environment under investigation, in addition to the standard mass conservation and Kruskal-Wallis test, prevented possible non-conservative elements from entering the discriminant analysis.