Trace Element Distribution in Soils of The Pembina Escarpment, North Dakota

Abstract

Association of element concentrations for soils of northeastern North Dakota formed from different sources of parent materials were determined based on geochemical data. These soils overlie the Cretaceous Pierre Formation and parent materials consist of shale rich glacial till, residual shale, and colluvial materials. Surface and core sampling locations included a cropped field, Conservation Reserve Program land, and grassland fields in a North Dakota State Wildlife Management Area. Samples were analyzed for cadmium and other trace elements using a nitric acid digestion followed by optical emission spectroscopy. Results of a preliminary study in cropped and CRP fields showed elevated concentrations of cadmium. Later comprehensive field work in a Wildlife Management Area was carried out to examine the landscape scale variation for a suite of elements. Morphologic and laboratory analysis of soil cores indicate high clay content with mixed clay mineralogy, indicative of the influence of shale residuum on the parent materials of the escarpment soils. Chemical properties of the escarpment soils revealed high levels of organic matter (2.62-13.30 %), ultra acidic to slightly alkaline pH range, and low electrical conductivity for the soils. Average cadmium concentration of 0.28 mg/kg was reported for the samples from eight cores while 16.4 mg/kg cadmium was found in the CRP field sample. Correlations of different analytes with cadmium showed significance with shale and argillic horizons. Principal Component Analysis revealed that elevated trace element concentrations for the soils in northeastern North Dakota are linked to a variety of factors including organic matter content, clay mineralogy, pH, elevation, and electrical conductivity. Results of this study suggest that lateral as well as vertical water movement of water could be an important factor leading to transport and elevated trace metal zones in these soils.