BaseEMap: MAPPED BASELINE CONCENTRATIONS OF ELEMENTS OF ENVIRONMENTAL INTEREST IN IOWA'S STREAM SEDIMENTS

This is the second year report for BaseEMap, a long-term study to chart background concentrations of elements of environmental interest in Iowa stream sediments. This second chapter of the study describes 167 grab samples of stream sediment collected during the three semesters from Fall 2008 to Fall 2009 by students in six sections of the University of Northern Iowa Liberal Arts Core Capstone class Environment, Technology and Society. Samples consisted of sand- or silt/clay-dominant material from the stream bottom or bank within the channel.

The samples were minimally prepared and were analyzed as loose powders using low-power energy-dispersive x-ray fluorescence. Elements included As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, S, V, and Zn (as parts per million, ppm) and P (as %P₂0₅) and other elements and oxides as needed to characterize the samples or to improve spectrum deconvolution. Results for As, Cd, Co and Hg were elusive, owing to lack of calibration standards, peak interferences, or simply poor calibrations. For remaining trace elements, concentrations show log-normal distributions where either the mean or the bulk of the distribution is less than published estimates for average crustal values. Preliminary results indicate ranges (min – max ppm) as follows: Cr (10 – 62), Ni (<10 – 40), Cu (<10 – 52), Zn (9 – 150), Pb (<10 – 30), P₂O₅ (<0.13 – 0.32 %). Sand-dominant samples yielded trace element concentrations that were lower, or below limits of analysis, whereas silt/clay-rich samples had higher concentrations, especially for organic-rich samples.

Samples in this report are sparsely distributed throughout the northeast two thirds of the state with some concentration along major highways and in metropolitan areas. This project intends to produce an updateable map of element concentrations, pending more complete sample coverage statewide, while allowing a diverse population of undergraduate students to participate in environment-related research.