Between 1990 and 1998, lead (Pb) in the forest floor decreased by .18g, or 9.8 %, while lead in the mineral soil increased by 0.36 g, or 16 %, for a net increase of 0.18 g, or 4.5 % to the system between 1990-1998.  The decrease in forest floor lead amount is occurring at a rate of 213 g ha^-1 yr^-1, while the mineral soil lead content is increasing at a rate of 448 g ha^-1 yr^-1.  To compensate for this loss requires an input of 235 g ha^-1 yr^-1.

Forest Floor

        Between 1980 and 1990, a steady decrease in lead in the forest floor in amount and concentration occurred.  The amount of forest floor lead declined by .40 g (19.7 %) and the concentration declined by 52.4 ug/g (26 %).
        Between 1990 and 1998, lead amounts in the forest floor decreased  by .18g, or 9.8 %, while the mineral soil increased by twice that amount.  This indicates that, though lead is spreading to the lower horizons, atmospheric deposition is continually replacing a portion of the amount that is being removed.  No data exists for the lead inputs for this part of CT.
        The rate of decrease in lead amounts remained fairly constant across the 18 years, while the rate of decrease in the concentration varied.  Amount appears to be a better indicator variable for the rate of lead movement.  Between 1980-1990, we found a rate an annual rate of decrease in lead amounts of 210 g ha^-1 yr^-1.  Between 1990 and 1998, the annual decrease in amount was 212.5 g ha^-1 yr^-1.  The constancy of the decrease across the 18 years suggests that the transport of lead from the forest floor is determined by factors that remain relatively constant.  It is more likely to depend upon characteristics of the site, rather than on the amount of lead present or on more variable qualities.  This also suggests that atmospheric deposition is at a relatively constant level.
        This decrease compares with the decrease reported by other researchers.  Friedland et. al. (1992) measured thirty sites across the northeast and measured their decrease between 1980 and 1990.  In that time period, the average decrease in lead concentration was 25.0 ug/g, which is much larger than the 7 ug/g we measured in that time period.  However, this is affected by the fact that the North Haven forest floor mass increased relative to the average northeastern forest floor.  As amount is not affected by forest floor mass, and because it appears to be a more constant indicator, it may be better for comparisons.  They found an average annual rate of decrease in lead amounts of 130 g ha^-1 yr^-1.  Between 1980 and 1990 we measured a larger annual decrease, of .21 g m^-2, or 210 g ha^-1 yr^-1 during that time period.  More research is needed to determine the causes for this faster migration rate in North Haven.

(Note: The Groff samples were analyzed at two points in time and with different analytical methods. The closeness of the replication is some evidence for the accuracy of the analyses for comparative purposes.  The error bars around the Groff means are based on 20 sampling sites while at the later dates only 5 samples were obtained.  In the tables below, only the original Groff analysis is listed.)

Lead in the Forest Floor

Mineral Soil

        Within the mineral soil, between 1990 and 1998, lead has increased by .36 g (16 %), or 450 g ha^-1 yr^-1.  Although the distribution of lead does not appear to have "changed" in the mineral soil over the 8 year period, the changes are subtle, reasonable and expected.
         In the upper several thickness zones -- down to 4 cm -- the lead migrating into the mineral soil from the thick forest floor (high in lead) has kept pace with the rate at which lead in this soil has migrated downward.
         Below about 5 cm there is a clear increase in the amount of lead which has moved down to this depth over the time period.  Based on the patterns shown, there has been about 0.13 g m^-2 of lead which has moved into the lower horizons (6-16 cm) in 8 years.  In the lowermost thickness zone no change in lead amount has occurred, indicating that the migrating lead has not yet reached 16-20 cm.
         To move downward this far over a period of eight years, assuming that each thickness segment is adequately represented by its median, the rate of movement is roughly 12 mm/yr.  This directional migration and its rate is a measure of the time required for lead to migrate through the mineral soil.  This rate falls within the 3-19 mm/yr range found by Miller and Friedland (1994) for sites in Vermont at high elevations.

Note: In the following figures in which the elements vs depth are shown, the amounts of the element are expressed as a square meter that is 1 cm thick.  For concentration thickness of the sample size is not a relevant consideration, and the concentrations are given for the entire sample.  All points are plotted at the average depth of a sample (for example, the point for 0-2 cm depth is shown at 1 cm).

Lead in the Mineral Soil

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Zinc

Since 1990, the amount of zinc decreased .04 g (8.2 %) in the forest floor and increased .20 g (8.7 %) in the mineral soil, for a net increase of 0.16 g., or ~ 6 %, to the system.  This slight decrease in the forest floor compared to a much larger increase in the mineral soil suggests that inputs to the system are remaining at a fairly high level.

Forest Floor

The forest floor shows a decline of ~ 30 % in both concentration and amount of zinc between 1980 and 1998 (Please see table below).  Zinc amounts decreased at a rate of 144 g ha^-1 yr^-1 between 1980 and 1990, and 101 g ha^-1 yr^-1 for the entire 18 years.  Craig (1991) found that between 1980-1990, the 30 northeastern sites he studied decreased in lead amounts by an a rate of 130 g ha^-1 yr^-1.  However, for zinc, the concentration, rather than the amount, seems to reduce at a more constant rate and may be a better indicator.  The concentration in New Haven decreased by a rate of .99 ug g^-1 yr^-1 between 1980 and 1990 and by a rate of 1.05 ug g^-1 yr^-1 over the 18 year period.  Between 1980-1990, Craig (1991) reported an average rate of decrease of 1.38 ug g^-1 yr^-1, which is higher than the rate of decrease we found.

(Note: The Groff samples were analyzed at two points in time and with different analytical methods. The closeness of the replication is some evidence for the accuracy of the analyses for comparative purposes.  The error bars around the Groff means are based on 20 sampling sites while at the later dates only 5 samples were obtained.  In the tables below, only the original Groff analysis is listed.)

Zinc in the Forest Floor

Mineral Soil

        Within the mineral soil, a front seems to have moved downward by about 6 cm. While the amounts in the 0-2 cm range are very similar, zinc amounts increased by .10 g, or 36 %, between 2-8 cm.  Zinc concentrations increased by a significant amount between 2-10 cm.  Below these depths the amounts and concentrations show no significant differences.
        This data suggests a pulse had already entered the 0-2 cm of soil and that in the following eight years, it moved downward by about 8 cm.  However, the fact that the zinc concentration and amount did not change in the uppermost thickness segment seemed unusual, considering that it changed in the underlying thicknesses.  The 1990 data has been verified by repeated testing.  Further investigation is underway to determine if the source of difference is simply a processing error in 1998, or whether a more complicated explanation is necessary to explain this anomaly.  It is likely that more research is needed, because this pattern occurred in several other elements, including manganese and iron.
         In 1990, a slight bulge in zinc amounts in the 4-6 cm range indicated incipient pedogenesis (general soil forming processes) (Marsh and Siccama, 1997).  In 1998, no bulge occurs between 4-6 cm, but a much more pronounced bulge occurs between 6-8 cm.  This thickness layer shows higher concentrations of many elements studied.  Even as the amounts change, zinc and other minerals show a trend of movement from the upper horizons to the 6-8 cm, demonstrating the continued formation of soil horizons.  The upper layers are slowly forming an E horizon, while the 6-8 cm area is slowly becoming a Bhs layer.  Perhaps this leaching from upper soil horizons is the reason no increase occurred in the 0-2 cm depth between 1990 and 1998.

Note: In the following figures in which the elements vs depth are shown, the amounts of the element are expressed as a square meter that is 1 cm thick.  For concentration thickness of the sample size is not a relevant consideration, and the concentrations are given for the entire sample.  All points are plotted at the average depth of a sample (for example, the point for 0-2 cm depth is shown at 1 cm).

Zinc in the Mineral Soil

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Copper

        Between 1990 and 1998, the amount of copper (Cu) decreased by .009 g (5.2 %) in the forest floor, and increased by .23 g, or 40 % in the mineral soil, for a net increase of 0.22 g, or 30 %.  The amounts and concentrations of copper in the forest floor and mineral soil are much higher than the average values for the New England area (Marsh and Siccama, 1997; Friedland et. al., 1986).  In 1978, forest floor copper amounts were approximately three times the amount of the average of other pine-oak forests, and the second highest in the New England area, second only to a forest directly downwind of a smelter (Andresen et. al. 1980).

Forest Floor

        In the 18 years between 1980 and 1998, the amount and concentration of copper in the forest floor both decreased by approximately 45 % (see table below).  The major decrease occurred in the first ten years, between 1980 and 1990, and only declined ~5 %  between 1990 and 1998.
        For copper, neither concentration nor amount reduces at a steady rate over the 18 years.  The amount of copper in North Haven decreased at a rate that is an order of magnitude faster than the rate of the 30 northeastern sites studied by Craig (1991).  While the rate in North Haven was 118 g ha^-1 yr^-1 between 1980 and 1990, and 70.6 g ha^-1 yr^-1 over the entire 18 years, the average rate in the northeast was 10 g ha^-1 yr^-1.  The cause of this discrepancy is unknown.  The discrepancy is even larger between rates of decrease in concentrations.  For the entire northeast, the average rate of decrease between 1980 and 1990 was .06 ug g^-1 yr^-1, while the decrease for the North Haven forest was 1.09 ug g^-1 yr^-1 between 1980-1990, and .76 ug g^-1 yr^-1 between 1980-1998.  The reason that New Haven's rate of decrease would be this much larger is unknown, but it may relate to the generally high levels of copper present.

(Note: The Groff samples were analyzed at two points in time and with different analytical methods. The closeness of the replication is some evidence for the accuracy of the analyses for comparative purposes.  The error bars around the Groff means are based on 20 sampling sites while at the later dates only 5 samples were obtained.  In the tables below, only the original Groff analysis is listed.)

Copper in the Forest Floor

Mineral Soil

        Within the soil, the amount and concentration increased throughout the 20 cm, with the greatest increases occurring in the top four cm, and smaller increases occurring with depth.  The net increase in Cu amount in the soil horizons is 0.23 g, or almost 50 %.  These patterns suggest that copper is leaching from the forest floor in relatively large amounts and is pervading the lower horizons in a diffuse manner.

Note: In the following figures in which the elements vs depth are shown, the amounts of the element are expressed as a square meter that is 1 cm thick.  For concentration thickness of the sample size is not a relevant consideration, and the concentrations are given for the entire sample.  All points are plotted at the average depth of a sample (for example, the point for 0-2 cm depth is shown at 1 cm).

Copper in the Mineral Soil

          In their study of five northeastern forest sites, Siccama and Marsh (1997) found North Haven to have the highest local copper levels of all five sites sampled, which they attributed to a local source of pollution.  Since the increase in the mineral soil copper amounts are much larger than the decrease in forest floor amounts, it is likely that the site is near a source of copper pollution.  The reasons that the forest floor has decreased in copper while the mineral soil continues to accumulate it may indicate slightly decreasing deposition of copper.
        The movement downward does not seem to be as a front, because the amount of increase itself decreases with depth.  This may be because lower horizons are less able to bind copper.  It may indicate that a specific percentage of all lead at a particular depth is moved downward in a time period.  It may also provide a snapshot view of a continual flow of copper through the mineral soil.  This last hypothesis could be tested by an examination of the soil in a number of years to see if the decreasing deposition of copper has resulted in relatively lower amounts of copper in the upper horizons.
           In the different locales they sampled, Siccama and Marsh (1997) found very few consistent patterns with depth for copper, suggesting a strong dependence on biogeochemical properties of the site.  Heinrichs and Mayer (1977) found that Cu does not accumulate in soil found in a beech forest ecosystem, but that in a spruce forest it accumulates in the mineral soil.  With only these two data points from 1990 and 1998, it is impossible to tell if Cu is accumulating or whether changing inputs have created higher levels of Cu leaching from the system, but further study should give more insight in this matter.

Magnesium

Between 1990 and 1998, the amount of magnesium increased by .95 g (23 %) in the forest floor while the amount increased by 11.0 g (9.7 %) in the mineral soil, for a net increase of 12 g, or 10 %, to the system.

Forest Floor

        The amount of magnesium (Mg) in the forest floor increased by > 20 % in amount and concentration between 1980 and 1998 (please see table).  Greater increases occurred after 1990.  The rate of increase in magnesium amounts was much lower (110 g ha^-1 yr^-1) between 1980-1990 than between 1980-1998 (589 g ha^-1 yr^-1).  However, the rates of change in concentrations were more consistent, 5.23 ug g^-1 yr^-1 between 1980-1990 and 4.68 ug g^-1 yr^-1 for the entire period of 1980-1998.  The source of the increase in magnesium amounts is not known.

 

 Magnesium in the Forest Floor

[For the entire data set, please click on either graph]

Mineral Soil

         In the mineral soil, little change was seen in magnesium concentration or amount in the uppermost horizon.  Magnesium increased in both concentration and amount between 2-8 cm.  The total increase in amount between 2-8 cm was 3.4 g (16 %).  Below this depth, the amounts are fairly approximate.  The increasing presence of magnesium in the forest floor is likely to be responsible for this increase in the magnesium between 2-8 cm.  This distribution may suggest that a front of magnesium had already infiltrated the soil to a depth of 2 cm by 1990, which then progressed approximately 6 cm in the next 8 years.  It may also suggest that soil organizational processes are moving incoming magnesium to the lower horizons, as E and Bhs horizons begin to form.  The absence of change in the uppermost horizon, and the pattern of distribution below, is similar to that seen in zinc and several other elements.  The peak between 6-8 cm depth is the zone where many elements are accumulating as part of the pedogenesis process.

Note: In the following figures in which the elements vs depth are shown, the amounts of the element are expressed as a square meter that is 1 cm thick.  For concentration thickness of the sample size is not a relevant consideration, and the concentrations are given for the entire sample.  All points are plotted at the average depth of a sample (for example, the point for 0-2 cm depth is shown at 1 cm).
 

Magnesium in the Mineral Soil

[For the entire data set, please click on either graph]

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Calcium

       Between 1990 and 1998, the amount of calcium increased by 1.67 g (23 %) in the forest floor while increasing by 1.31 g (10.7 %)  in the mineral soil, for a net increase of 2.97 g (12.4 %) to the system.

Forest Floor

The amount of calcium (Ca) in the forest floor increased fairly steadily between 1980 and 1998, by approximately 20 % in amount and concentration (see table below).  Despite large error bars due to variability in the measurements, this trend does appear to be important.  The rate of increase in amount was more constant than the rate of change in concentration.  Amounts of calcium increased faster over the entire eighteen year period (1667 g ha^-1 yr^-1) than over the years 1980-1990 (1300 g ha^-1 yr^-1).  Concentration increased more quickly in the first 10 years (22.7 ug g^-1 yr^-1) than over the eighteen years as a whole (13.8 ug g^-1 yr^-1).

 

 Calcium in the Forest Floor

[For the entire data set, please click on either graph]

Mean Amounts and Concentrations of Calcium in the Forest Floor 1980 1990 1998 Change % Change Amount (g/m2) 10.4 11.7 13.4 2.97 29 % Concentration (ug/g) 1003.7 1230.9 1252.3 248.6 24.8 %

Mineral Soil

        In the mineral soil, calcium increased between 1990 and 1998 in both amount and concentration.  The most clear increase between 1990 and 1998 in both amount and concentration occurred between 6-10 cm and 13-20 cm, but the increase appears to be of approximately the same magnitude throughout the soil profile.  Increasing inputs may cause this steady increase, since calcium generally leaches very quickly through acidic soils (Heinrichs and Mayer 1977).

        In both sample years, the distribution of calcium seems to generally increase in amount with depth, while decreasing in concentration.  (The soil increases in density with depth.)  A slight bulge appears between 6-8 cm that suggests accumulation as the soil forms new horizons, although much less pronounced than that of other minerals at the same depth.

Note: In the following figures in which the elements vs depth are shown, the amounts of the element are expressed as a square meter that is 1 cm thick.  For concentration thickness of the sample size is not a relevant consideration, and the concentrations are given for the entire sample.  All points are plotted at the average depth of a sample (for example, the point for 0-2 cm depth is shown at 1 cm).
 

Calcium in the Mineral Soil

[For the entire data set, please click on either graph]

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