Results and Discussion 

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Iron

        The amount of iron (Fe) increased by 1.14 g (5.13 %) in the forest floor while increasing by 74.6 (9.9 %) in the mineral soil, for a net increase of 75.7 g (9.8 %) to the system between 1990 and 1998.

Forest Floor

        In the forest floor between 1990 and 1998, iron increased approximately 5 % in amount, but, due to an increase in forest floor mass, it decreased in concentration by approximately 9 %.  The cause of these changes is unknown.

Mean Amounts and Concentrations of Iron in the Forest Floor 1990 1998 Change % Change Amount (g/cm/m2) 4.44 4.66 1.14 5.1 % Concentration (ug/g) 2332.0 2133.2 -198.9  -8.5 %

[click here for complete set of iron forest floor values]

Mineral Soil

        Between 1990 and 1998, the amount of iron in the mineral soil increased by approximately 10 %.  The largest increases in amount happened in the upper four thickness layers (0-8 cm), while concentrations increased throughout the profile.
        Iron primarily originates from chemical weathering of the parent material and is not absorbed by plants in appreciable quantities; the amount found in plants is several orders of magnitude lower than the amount in mineral soil (Heinrichs and Mayer, 1980).  Its movement in soil horizons is due mainly to chemical processes within the soil, rather than association with organic matter or uptake by biomass.  Therefore, its distribution patterns exemplify the chemical redistribution occurring as the soil restratifies into horizons.  In fact, the distinctive color of the soil horizons are caused by iron.  Its presence gives the reddish tint to the Bhs and Bs horizons, and its absence leaves the E horizon a light gray color.
        This vertical distribution of iron therefore exemplifies the podzolization that is occurring at this site.  The change between 1990 and 1998 is typical of the way many elements have increased in concentration and amount between 0-8 cm, with the largest accumulation creating a "bulge" between 6-8 cm.  At this point in time, the 6-8 centimeter segment is the primary zone where increases are accumulating, with only minimal increases below 8 cm.

Iron in the Mineral Soil

Manganese

Manganese amount increased by .18 g (14 %) in the forest floor, while the mineral soil amount increased 3.5 g (31 %) for a net increase of 3.7 g (29 %) to the system.

Forest Floor

         Manganese amount increased by .18 g (14 %)  in amount and .27 ug/g (0.21 %) in the forest floor between 1990 and 1998.  The table below shows the mean values of amount and concentration in the forest floor from the 1990 and 1998 samples.  Amount increased more than concentration due to a higher forest floor mass.

Mineral Soil

Manganese amounts and concentrations increased fairly steadily throughout the soil profile.  The net increase in amount was 3.5 g (2 %), while concentration increased .18 g (14 %).  The increase in amount was notably small between 8-10 cm, while a bulge is present at 6-8 cm, suggesting manganese is accumulating at 6-8 cm at the expense of the soil beneath.  The increases are largest in the two deepest thickness segments (13-16 cm and 16-20 cm).
        The two major sources for manganese in soil are mineral weathering and organic matter decomposition, while anthropogenic emissions account for only 11 % (Heinrichs and Mayer, 1980; Nriagu, 1989).  Manganese is chemically similar to iron and its distribution is also mostly determined by chemical soil properties, rather than biological activities.  It is not known whether the increase is due to an increase in human activities, accumulation of weathered manganese, or increased rate of weathering.

Manganese in the Mineral Soil

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Potassium

Potassium decreased .09 g (1.8 %) in the forest floor, while increasing 3.7 g (4.2 %) in the mineral soil, for a net increase of 3.62 g (3.86 %) between 1990 to 1998.

Forest Floor

        Within the forest floor, the amount of potassium decreased .09 g, or 1.25 %, while the concentration decreased 80 ug/g (14 %) in the years between 1990 and 1998.  This decrease suggests more potassium is being leached from the forest floor than is accumulating from deposition or decomposition of organic matter.  The percent decrease in concentration was larger than the percent change in amount because of an increase in forest floor mass.

Mineral Soil

        Potassium increased in the mineral soil by 3.7 g (4.2 %).  The amounts appeared not to change, except for a slight bulges at 2-4 cm and 6-8 cm.  The concentrations show a general increase between 0-8 cm.
        The distribution of amounts did not change significantly.  The increases in amounts were accumulated in "bulges" at 2–4 cm and 6-8 cm.  The concentrations of potassium did increase between 2-8 cm and "bulge out" between 6-8 cm.
        The primary source of potassium is chemical weathering from rocks, and the arkosic glacial till that forms the upper layer of the parent material is high in potassium feldspar (right?).  This mineral is cycled very rapidly through the ecosystem; plants take it up in high quantities and then release it to the soil when they decompose.  It is highly soluble and can leach easily through soil.  For these reasons, it was not expected that the patterns of potassium distribution would change much, but they change in much the same manner as the other elements, forming a bulge of accumulation between 6-8 cm depth, with very little change seem below that depth.

Potassium in the Mineral Soil

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Aluminum

         Aluminum (Al) increased 1.6 g (6.1 %) in the forest floor, while decreasing 87.9 g (7.5 %) in the mineral soil, for a net decrease of 86.3 g, or 7.2 % between 1990 and 1998.

Forest Floor

The forest floor amount increased ~ 6 % in the forest floor between 1990 and 1998, while a larger increase in forest floor mass caused the concentration to decrease by ~7 % (see table).

Mineral Soil

        In the mineral soil, the amount of aluminum decreased by 87.9 g/cm/m² (7.5 %), and the concentration increased by 1.6 ug/g (6.1 %).
        The distribution of aluminum's amount and concentration between 0-8 cm did not change greatly between 1990 and 1998.  The amounts and concentrations of aluminum also show "bulges" at 2-4 cm and 6-8 cm, as part of the general podzolization.  Below 8 cm, however, both the concentration and amount of aluminum have decreased in the 8 years.  Perhaps the decreasing concentrations in the forest floor are causing a larger percentage of non-polluted organic matter to decompose into the soil, causing the decrease in mineral soil amounts.  The primary sources of aluminum are mineral weathering and reprecipitation (dissolving in the acidic upper layers, leaching downward, and then depositing at a lower depth).  Therefore, a decrease in the aluminum inputs could affect lower layers fairly quickly.

Aluminum in the Mineral Soil

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Phosphorous

        The amount of phosphorous (P) decreased by .061 g (1.0 %) in the forest floor, while decreasing 4.7 g (7.7 %) in the mineral soil, for a net decrease of 4.76 g (7.1 %) to the system between 1990 to 1998.

Forest Floor

        The amount of phosphorous showed in the forest floor showed a slight decrease in amount and a larger decrease in concentration (see table).  An increase in forest floor mass caused the concentration to decrease by more than the amount did.

Mineral Soil

         Phosphorous in the mineral soil decreased in both amount and concentration, especially in the upper 6 cm.  The total decrease in amount was 4.7 g (7.7 %), and 35 % of this decrease occurred between 0-6 cm.  Below 6 cm, little change in amount or concentration is seen in the 8 years.  Interestingly, while aluminum is decreasing in the lower horizons, phosphorous is decreasing in the upper horizons.
        The trend for increasing amounts from 0-6 cm and then a decrease is the same trend seen in many other metals.  The formation of soil horizons is pauperizing the upper horizons, which will become an E horizon, and accumulating the metals between 4-8 cm, where a Bhs horizon will form.
        Phosphorous generally originates from the weathering of parent rock.  It is rapidly taken up by biomass and released when plants decompose.  In the soil, it is strongly associated with organic matter; organic matter and phosphorous amounts correlate almost linearly in soil.  Since phosphorous generally leaches quickly in acidic soils (Heinrichs and Mayer, 1977), and it appears that it is leaching out of this system.

Phosphorous in the Mineral Soil

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