Groundwater-induced alterations in elemental concentration and interactions in semi-arid soils of the Southern High Plains, USA.

This study examined and compared arsenic (As) and other element [copper (Cu), iron (Fe), potassium (K), manganese (Mn), rubidium (Rb), and zinc (Zn)] distribution, as well as their interactions in historically irrigated and non-irrigated semi-arid agricultural soils of the Southern High Plains (SHP) in the USA, using findings from a portable X-ray fluorescence spectrometer. The portable X-ray fluorescence (PXRF) findings revealed that the concentrations of As (5.1 vs. 3.1 mg kg(-1)), Cu (7.2 vs. 6.2), Fe (7398 vs. 5677), K (8638 vs. 7061), Mn (80 vs. 68), Rb (36 vs. 27), and Zn (19.3 vs. 13.8) were higher in the historically irrigated field compared to the non-irrigated and, when examined within depths, were consistently and significantly higher (P<0.001) in the subsurface soils of the non-irrigated field, a trend not evident in the irrigated field. The strengths of the correlation among elements were higher in the non-irrigated field compared to the irrigated (average R of 0.60 vs. 0.54), suggesting a possible external input of these pollutants in the historically irrigated field which could have altered the natural background concentration and association among them. Furthermore, findings from principal component analysis (PCA) indicated that As, Mn, Rb, Fe, Zn, and K were more closely associated in the non-irrigated field and likely of lithogenic origin. The observed differences in elemental concentration and interaction between the irrigated and non-irrigated soils support the hypothesis that water from the local aquifer could be a potential source of pollutant addition to these semi-arid alkaline soils.