Phytoremediation of soil contaminated with low concentrations of radionuclides

Primary sludge, secondary sludge, and wood ash from a pulp and paper mill were combined with sand to create a synthetic topsoil (C:N ratio of 18:1) to restore an abandoned gravel pit. Synthetic topsoil was applied to field microcosms at rates equivalent to 0, 2170, 4341, or 6511 kg N/ha; each was seeded with grass. Fifteen chemical constituents in leachate were measured during two field seasons. Cadmium, Ni and Zn were mobilized rapidly by soil disturbance. Chloride and SO₄-S eluted rapidly from the sludge along with Na. Nitrate leached with Ca late in each field season when sludge N-mineralization and nitrification exceeded plant uptake and microbial immobilization. Ammonium elution was negligible. Dissolved organic carbon (DOC) was mobilized by decomposition of organic matter in the sludge, as were Mg and K. Copper eluted with DOC, probably as an organic ligand. Lead and ortho-P were below our detection limits. We concluded that a synthetic topsoil with a 30:1 C:N ratio applied at a rate of 2100-4300 kg N/ha should provide adequate plant nutrition while minimizing water quality hazards.     

Mining Impacts on Trace Metal Content of Water,Soil, and Stream Sediments in the Hei River Basin,China

The impacts of mining to watersheds are highly variabledepending on the type of mining, processing of ores, andenvironmental factors. This study examined the Hei River incentral China, for impacts of gold and iron mining onconcentrations of metals in river water, river sediments andstream-channel soils. No production processing of ores occurson-site at either mine. Total metal content and extractablemetals using DTPA were determined. Total concentrations of Cd,Cu, Pb and Zn were high in some stream sediments and soils nearthe mine sites; metal concentrations ranged from 4–24, 11–100,11–380, and 33–1600 μg g^-1 for Cd, Cu, Pb, and Zn,respectively, in soil. Total cadmium was high in all soilsand sediments. Extractable metals were low, with the exceptionof Pb and Cu. At the gold mine, extractable Pb ranged from 8 to33%; extractable Cu ranged from 3 to 21% of total metalconcentration. Chromium and Ni were not above typicalconcentrations in either soils or river sediments. An abundance of carbonates, high river water pH, and high water flow rates all appear to contribute to limiting quantities of metals in the river water. If mining activities are not changed, impacts of mining on downstream metal concentrations in river water should be nominal.     

Soil organic matter in a ponderosa pine forest with varying seasons and intervals of prescribed burn

Prescribed burning is used to reduce fuel loads and return ponderosa pine forests of the Western U.S. to their historical structure and function. The impact of prescribed burning on soil is dependent on fire severity which is largely managed by burning in the fall or the spring; frequency of fire will also regulate long-term fire impacts. The objective of this study was to determine if soils and soil organic matter (SOM) were affected by prescribed burning in the fall or the spring using singular or multiple prescribed burns. Prescribed burning was initiated in the spring of 1997 and fall of 1997 at 5-year intervals and once during a 15-year period on a study site located within the Malheur National Forest of the southern Blue Mountains of eastern Oregon. Soils were sampled by major genetic horizon in 2004. The 5-year interval plots had burned twice with 1–2 years of recovery while the 15-year interval plots had burned only once with 6–7 years of recovery. Samples were analyzed for pH, carbon (C), nitrogen (N), C/N ratio, cation exchange capacity, base saturation, water repellency, and humic substance composition by alkali extraction. Fall burning decreased C and N capital of the soil (O horizon +30 cm depth mineral soil) by 22–25%. Prescribed burning did not have an effect on fulvic or humic acid C concentration (FA and HA, respectively) of the mineral soil and only a minor effect on FA and HA concentration of the O horizon. One or two fall burns decreased humin and the alkali non-soluble C (NS) content of O horizon by 15 and 30%, respectively. Initiating fall burning in fire-suppressed stands may not preserve soil C, N, humin, and NS content, but may replicate the natural fire regime. Spring burning using a return interval of 5 or more years reduces the fuel load while having little impact on soil C, N, and SOM composition and may be used to prepare a site for subsequent fall burns.     

A comparison of soil properties after contemporary wildfire and fire suppression

Forests that were subject to frequent wildfires, such as ponderosa pine/Douglas-fir forests, had fire-return intervals of approximately 6–24 years. However, fire suppression over the last century has increased the fire-return interval by a factor of 5 in these forests, possibly resulting in changes to the soil. The objective of this study was to determine if soils of recently burned areas (representative of the natural fire-return interval) have different properties relative to soils in areas without recent fire. To assess this, recent low-intensity, lightning-caused, spot wildfire areas were located within fire-suppressed stands of ponderosa pine/Douglas-fir of the central, eastern Cascade Mountains of Washington State. Soil horizon depths were measured, and samples collected by major genetic horizons. Samples were analyzed for pH, C, N, C/N ratio, cation exchange capacity (CEC), base saturation (%BS), hydrophobicity and extractable P. Results show very little difference in soil properties between sites burned by low-severity fires and those areas left unburned. Such minimal changes, from these low-severity fires, in soil properties from fire suppression suggest there has also been little change in soil processes.     

Cadmium,copper, and zinc adsorption by a forest soil in the presence of sludge leachate

Samples from three genetic horizons of an acidic forest soil were equilibrated with solutions containing Cd, Cu, and Zn in the presence and absence of a municipal sewage sludge leachate. Copper adsorption was greater than Cd and Zn in all three horizons, while Cd and Zn adsorption was quite similar. Relative to a NaN0₃ background solution, sludge leachate reduced Cu adsorption in all horizons; however, in the presence of leachate Zn adsorption increased in the B2 and C horizons, while Cd adsorption decreased in the Al and was unaffected in the B2 and C horizons. Distribution coefficients generally increased as solution concentration and adsorption increased. In all horizons additions of Cd and Zn were able to reduce apparent surface charge. Copper not only reduced surface charge in the Al horizon, but caused a charge reversal in the 132 and C horizons. Adsorption data were best fit by linear or Freundlich equations. Differences in adsorption between sludge leachate and NaN0₃ solutions could not be explained simply by differences in metal activities as calculated using the GEOCHEM program. Competition from cations and organics present m the sludge leachate appears to contribute to lower metal adsorption.