The Arctic (or subarctic) is characterized by a harsh climate and nutrient-poor soil; what makes it even harsher in Monchegorsk (67851 0 N and 32848 0 E) is that metal pollution originating from the Ni-Cu smelting industry has severely damaged the soil and ground vegetation, resulting in formation of an industrial desert (barren ground). A pilot-scale (4 ha) field test was carried out under such conditions to study how to apply municipal sewage sludge for rehabilitation of degraded land. After sewage sludge had been composted, an artificial substratum made from the compost was introduced to the remediation test field, and then willow, birch and grasses were planted on the substratum. The transformation of the artificial substratum was observed in the test field during 3 years. The portion of Cu in residual form was greater than that in other forms, it is hence considered that Cu has low bioavailability in the artificial substratum. Furthermore, the metal distributions statistically increased in fractions of humic acid (insoluble in water under acidic conditions), so the mobile amounts of Ni and Cu became small.The conclusion drawn from the field survey and analysis of extractable metals indicates that the lost vegetation is being restored even while pollution continues to be discharged from the smelter operation.
A complex stress-strain state (SSS), which varies in space and time, develops when a stratum of clayey soil freezes owning to phase transformation of pore water to ice, and its volume increases. Quantitative evaluation of this SSS is another of the problems of applied frozen-soil mechanics. The temperature interval Δθ = θ e − θ b and the time interval corresponding to it Δt = t e − t b from the beginning to end of the active phase transition for a single layer z(t) in the soil are factors most critical to its solution. In first approximation, this interval can be determined on the assumption that z(t) β√t (where β is a proportionality factor). It follows henceforth that at depths z 1 < z 2 , the time required for attainment of the freezing front t 1 < t 2 (Fig. 1); here, t 2 − t 1 = (z 2 2 − z 1 2 )/β 2 . The time period Δt increases with increasing Δθ. In clayey soils, the interval Δθ = θ e − θ b may be more than 4°C (θ e = −1.5 -−2.0°C for sandy loams, −2 -−3°C for clayey loams, and −4°C and more for clays [1]). The period Δt will also increase with increasing z(t), varying within broad limits, and may require several tens of days and more.The heat-conduction equation for freezing finely disperse soils [2]
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