1. Fig. 1: Relief of Dane County, Wisconsin, watersheds Element Survey of Driftless Area, Wisconsin, Soils Zhuo Zhang, Philip A, Helmke, and Cynthia Stiles University of Wisconsin - Madison Major ElementsTrace Elements NAAFe*, Na*, K*As, Ba*, Ce, Cr*, Co, Cs, Eu, Hf, La, Lu, Nd, Rb, Se, Sb, Sc, Sm, Tb, Th, U, Yb, Zn* XRFFe*, Na*, K*, Si, Al, Ca, Ti, Mn, P, Mg Ba*, Zn*, Cr*, Ni, V, W ICP- MS P, S, Fe*, Na*, K*, Ca, Mg, Mn, Al B, Cu, Cd, Pb, Li, Mo, Ni, Zn*, Cr*, Co Introduction The objectives of this study are to provide a database of element concentrations in Wisconsin soils and to obtain geochemically useful information to better understand the pedogenesis of Wisconsin soils. The main analytical techniques being used are neutron activation analysis (NAA) and X-ray fluorescence (XRF). These two techniques are preferred because they do not require aqueous samples, which reduces the analytical uncertainties introduced by incomplete sample dissolution. Selected elements undetected by the first two techniques are determined by inductively coupled plasma-mass spectroscopy (ICP-MS). In addition to samples of whole soils, the clay-size fraction (<2 µm) is analyzed to determine if the results from this size fraction reduces the variability introduced by varying amounts of quartz in the whole soils.The information generated by this project is needed by scientists, regulatory agencies, consulting firms, and landowners. Fig. 2: An enlarged view of watershed with the sampling area highlighted Table 1: Elements determined in this study. (* indicates elements determined by all techniques. Bold indicates elements uniquely determined by ICP-MS). Sampling Most of the soils in Wisconsin developed from glacial deposits except those from the Southwest part of the state (the Drifltless Area) which developed over limestone and sandstone. Many of the soils have been affected by loess deposits. A preliminary set of samples is based on intensive sampling of a small watershed (about 15 km 2 ) in the Driftless Area of Dane County (Figure 1) to gain a better understanding of the compositional variability of the soils from the Driftless Area. These samples are from the A or Ap horizon (15 cm). The watershed as shown in Figure 2 contains 23 soil series developed on limestone and sandstone. Figure 5. Normalized element ranges for total soil and the clay-size fraction for sample sets one (a), (b) and two (c), (d). Box boundaries indicate 25% and 75% percentiles, a line within the box marks the median, and error bars below and above the box indicate 10% and 90% percentiles (outliers within 5% and 95% percentiles are shown). Element concentrations ( mg kg -1 ) of each group are divided by their group means, which is given in each figure. Results and Discussion The results from the watershed samples illustrate the variability of element concentrations on a small scale and portends the difficulties of executing a large scale survey. The most notable trend is that the concentrations of most elements in the surface soils from the small watershed vary with elevation. This effect is shown for Fe in Figure 3. High elevations tend to have the highest concentrations of Fe. This results from loss of the A horizon on hilltops and accumulation of sandy material (with high concentrations of quartz) in the valleys. Figure 4 shows the relationship between the concentrations of Fe and Si. Quartz has very low concentrations of almost all elements and its presence in a soil sample dilutes the concentrations of all other elements.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa Figure 4. Relationship between Fe and Si in the watershed soils. Figure 3. Illustration of Fe concentration and elevation in a single watershed. One approach to reduce the dilution effects of quartz in whole soils is to isolate and analyze the clay- size fraction of the soils (Helmke et al., 1978). The concentration of quartz is usually very low in this size fraction. Chemical methods and ultra-sonication are used to help disperse soil aggregates. However,our data (not shown) shows that there is little difference in element concentrations between these methods compared to simple dispersion in deionized water.aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa The results for the 30 samples from the 10 soil series of the statewide sample set shown in Figure 5 (a) and (b) show that the ranges of element concentrations in the clay-size fraction are much smaller than those for the total soils. Most of the ratios for the total soils are less than one. This is expected as the result of quartz and plagioclase in the sand-size fraction acting to dilute element concentrations relative to the clays. Two notable exceptions are hafnium and sodium. Hafnium is associated with zircon. Zircon is highly resistant to weathering and it becomes enriched in the sand-size fraction with weathering. Sodium is found in plagioclase, which is also found in the sand fraction of younger soils, especially those from the glaciated areas of Wisconsin. For the clay-size fraction, only Cu and Mn show a larger range. Manganese is mobile under soil redox conditions, and this is likely to cause local variations in its concentrations. The northern half of Wisconsin has numerous areas of sulfide deposits with high concentrations of Cu, which contribute to the variation of this element. aaaaaaaaaaaa Conclusions The clay-sized fraction has relatively uniform element concentrations across a wide geographic area that are independent of soil region and terrain. Analysis of the clay-size fraction is potentially the most useful for determining the background element concentrations over large geographic areas. In surface soils, divalent element concentrations are strongly associated with organic matter content (LOI and organic carbon content are indicators). Element Conc. (mg kg -1 ) / Average Conc. of Each Group (mg kg -1 ) 16 640 731578 6 64 1 48000 4 24000 38 0.4 11433600 34 130 1 13 6 0.8 15 2.4 140 (b) Clay-size Fraction (state) 5 420 37 8 42 2 23 0.6 19000 7 17000 20 0.3 620 6400 1983 0.6 63 0.4 72 54 (a) Total Soil (state) 9 500 541060 3 0.8 24000 10 17000 30 0.4 6400 311077 175 0.6 3 91 (c) Total Soil (watershed) 15 650 881796 81 57000 3 20000 43 0.4 1400 3415 170 3 16 713 250 (d) Clay-size Fraction (watershed) Email: zhuozhang@wisc.edu Table 2. Summary statistics of the major element concentrations at different areas (unit: mg kg -1 ) Trend along the transect Elements in Total SoilsElements in Clay-size Fractions Positive TrendFe, Mg, As, Co, Cr, Sc, Sm, Eu, Tb, Yb, Lu, Ti, Ca, Hf, pH Fe, Mg, As, Sc, Tb, Ca Negative TrendSi, MnMn No TrendZr, Na, Total CarbonSi, Co, Cr, Sm, Eu, Yb, Lu, Ti, Hf Spatial Element Distribution Figure 6. Kriging interpolation results and standard deviation maps of selected element concentrations Figure 7. Biplot of the principle component analysis (PCA) of the element concentrations measured by XRF Figure 8. Factor analysis (FA) of the soil properties The first two principle components account for more than 80 percent of the total variance. All the 96samples are clustered together, indicating that they have similar properties. Element Si points to theopposite direction of loss on ignition (LOI) value, which is an indicator of the organic matter content ofthe surface soils. Notice that the bivalent and trivalent elements tend to have similar properties. In total soils along the transect, Si concentrations tend to decrease with increase in elevation while those of Fe tend to increase. The Si concentrations in the clay-size fractions, however, do not show any trend (Fig. 9). In addition many trace elements in the CSF, including REE, don’t show positive trends along the hillside as they do in the total soils (Table 2). This result indicates that the element concentrations in CSF are more uniform than those in the total soils across the elevations. However, some large variations may occur at some specific locations due to the origins of the local CSF. Table 4. Variogram parameters of major element concentrations estimated before and after detrending (SS represents minimized weighted sum of squares) Figure 9. Selected element concentrations in different parts of soils along a transect with change in elevation. Watershed (n=96) Floodplain (n=9) Table 3. Changes of element concentrations in two kinds of soils with elevation ElementOriginal DataRemoved Elevation EffectRange Difference SillRangeNuggetSSSillRangeNuggetSS Fe0.767120.13170.607420.1712-31 Na1.021300410.991300390.55 K0.932400390.8622603214 Al1.124700720.76344033126 Ca0.602530570.592530570.03 Mn0.852000.64330.842000.63300 Mg0.642700450.622670442.8 Si0.746360.03110.525790.127.257 AlBaCaFeKMgMnNaPSiSrTiZr Min. 8250339112450149041523919226024400026741111 Max. 575007485000076300299002930 0 30001100014104280001775580517 Mean 42600525659024200171004890135064406103550001064400375 Median 43400529565022900173004500132067005463550001074600387 St. Dev. 815010252609680374031504441540236262002481668.6 Min. 410004044240182001110034807354470402349000583000333 Max. 562006335670247001820048501380824012203790001204400474 Mean 4830051950402130014700425010506160545362000893650381 Median 488005235110210001450043209625930477336000903640365 St. Dev. 47208463321202640436247149025897002454352