Water Resources Research Center, University of Minnesota
Newsletter or Bulletin
Open pit mining for iron-ore and magnetic taconite in northeastern Minnesota has produced a landscape with numerous overburden deposits or man-made plateaus which are susceptible to erosion and have a physical environment hostile to natural revegetation. Many of these plateaus are in close proximity to small municipalities. This study investigated the sprinkler application of secondary treated sewage effluent to the overburden material with respect to: 1) renovation effects on wastewater, and (2) potential amelioration benefits on such nutrient-poor sites.
Two sites were evaluated, one was deposited 20 years ago and the other 2 months prior to the beginning of the study. Each site consisted of glacial tills of the Wisconsin Period and were of sandy-loam texture with 20 to 30 percent rock by volume. Compaction and poor drainage of the older site restricted irrigation rates to 0.25 centimeters per hour; treatments consisted of 0, 3.7 and 6.0 centimeters in a total of 8 applications over a 9 week period. 'rhe newer site, more representative of recently deposited material, was irrigated at rates of 0, 5, and 10 centimeters per week for 12 weeks.
Effluent and soil percolate were analyzed for total kjeldahl nitrogen, nitrate plus nitrite-nitrogen, total phosphorus, calcium, magnesium, potassium, sodium, chloride, specific conductance, and total alkalinity. Soil percolate samples were obtained at 30, 60 and 120 centimeter depths for the older site and at 50 and 100 centimeter depths at the newer site. The physical and chemical properties of soils were investigated before and after the irrigation season for both sites.
The The effects of effluent irrigation on the establishment of green ash (Fraxinus pennsylvanica Marsh.), northern white cedar (Thuja occidentalis L.) white spruce (Picea glauca (Moench) Voss), jack pine (Pinus banksiana Lamb.) eastern white pine (Pinus strobes L.) and a hybrid poplar were evaluated on the older site. On the newer site the establishment of green ash, sand cherry (Prunus pumila L. ), ,jack pine, red pine (Pinus resinosa Ait.) and Siberian larch (Larix sibirica Ledeb.) were studied in addition to a grass-legume mixture.
Irrigation of 6 cm over 9 weeks on the older, poorly drained site resulted in 98, 89 and 99 percent renovations of nitrate plus nitrite-nitrogen, total kjeldahl nitrogen, and total phosphorus, respectively. On the newly deposited material, irrigation of 60 and 120 cm over a 12-week period resulted in renovations of 99 percent for phosphorus and 80 to 90 percent for total kjeldahl nitrogen. Nitrate plus nitrite-N, calcium, magnesium and potassium concentrations in soil percolate were higher at 1 meter depth than respective concentrations in the effluent.
Effluent applications did not significantly affect the nutrient capital in the soil profiles except that Bray's phosphorus, ammonium nitrogen and sodium accumulations were detected near the soil surface.
Although irrigation of 6 cm on the old site did not increase the first year survival or growth of planted trees, green ash and the hybrid poplar exhibited a greater growth response than the other species.
Vegetation responses for the newer site were not measured at the time of publication.
Borovsky, John P., Brooks, Kenneth N., Holtschlag, David J., Mace, Arnett C.
Water Resources Research Center
Borovsky, John P.; Brooks, Kenneth N.; Holtschlag, David J.; Mace Jr., Arnett C..
Feasibility of Using Iron Ore Overburden Material as a Media for Disposal of Secondary Sewage Effluent in Northeastern Minnesota.
Water Resources Research Center, University of Minnesota.
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