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Development and Evaluation of Iron-Coated Tubes that Indicate Reduction in Soils

Dep. of Agronomy, Purdue Univ., Lilly Hall of Life Sciences, 915 W. State St., West Lafayette, IN 47907-2054

View larger version (18K): [in a new window]   Fig. 1. Map showing locations of study areas. 1. Muscatatuck Wildlife Refuge, Jennings County, IN. Lat. 38° 56' 46'', Long. 85° 47' 27''. Moore's Woods, Parke County, IN. Lat. 39° 56' 48'', Long. 87° 7' 52''. Shades State Park, Parke County, IN. Lat. 39° 55' 52'', Long. 87° 5' 39''. Jasper Pulaski Fish and Wildlife Area, Jasper County, IN. Lat. 41° 9' 12'', Long. 86° 59' 7''. 5. Eagle Creek Nature Preserve, Marion County, IN. Lat. 39° 51' 56'', Long. 86° 16' 56''. 6. Sheyenne National Grassland, Ransom County ND. Lat. 46° 26' 36'', Long. 97° 24' 20''. 7. Hamden Slough National Wildlife Refuge, Becker County, MN. Lat. 47° 0' 25'', Long. 95° 59' 14''. 8. Superior Lobe Till, St. Louis County, MN. Lat. 46° 56' 14'', Long. 92° 1' 15''.

View larger version (41K): [in a new window]   Fig. 2. Color photos of IRIS. The IRIS numbers in parentheses refer to Table 1. (A) A new IRIS never installed in a soil (not in Table 1), (B) IRIS installed in a soil for 14 d showing no removal of FH (46), (C) IRIS installed in the soil for 14 d showing partial removal of FH from part of the tube (48), (D) IRIS showing complete removal of FH from all of the tube (61), (E) IRIS showing some FH removed by organic mass attached to tube surface (7), (F) IRIS showing FH removed at a microsite above water table (9).

View larger version (74K): [in a new window]   Fig. 3. Color photos of IRIS. The IRIS numbers in parentheses refer to Table 1. (A) IRIS showing FH removal in a "white donut" pattern (42), (B and C) IRIS showing removal in a linear pattern, probably along a root (25, 32), (D) IRIS showing secondary deposition on right center of tube (66).

View larger version (78K): [in a new window]   Fig. 4. Color photos of IRIS. The IRIS numbers in parentheses refer to Table 1. The dotted black line represents the soil surface. (A) IRIS removed after 15 d in laboratory study (77), (B) IRIS removed after 24 d in laboratory study (73), (C and D) Duplicate IRIS show depletion of FH below 2 cm (53, 54); 4C shows several "white donut" patterns around 14 and 30 cm; 5D shows diagonal linear reduction pattern at 36 cm, probably caused by a root. (E) IRIS removed from natural soil during the year 2000 (19), (F) IRIS removed from filled soil pit near E the same year, (21), (G) IRIS removed from natural soil during 2001 (43), (H and I) (35 and 36) are duplicate IRIS, Fig. 5H shows depletion of FH below 2 cm, Fig. 5I represents three photos at 120° rotation and also shows depletion below 2 cm and shows "white donuts" at 14 cm and 18 cm, (J) IRIS installed in a Hamar soil shows complete removal of FH. (61), (K) IRIS installed in a Winger soil shows almost complete removal of FH from the upper part of the tube (65).

View larger version (19K): [in a new window]   Fig. 5. Changes in pH, dissolved O2 concentration, and redox potential (EH) during laboratory study. The Fe oxidation–reduction line represents the EH for Fe reduction at the measured pH (Fig. 7.6, McBride, 1994).

View larger version (31K): [in a new window]   Fig. 6. Comparison of water table (WT) depth, redox potential (EH), temperature (T) of soil at 50-cm depth or of air, and dissolution rate for four soils: (A) Clermont (5 g C kg–1 soil); (B) Avonburg (7 g kg–1); (C) Washtenaw (17 g kg–1); and (D) Brookston (26 g kg–1). The organic C values represent the weighted average for the upper 50 cm of soil. The horizontal dashed line represents the theoretical EH for Fe reduction at the pH of the soil characterization sample (Fig. 7.6, McBride, 1994).