Heavy Metals in the Environment: Using Wetlands for Their Removal - Chapter 5 pot

CONTENTS Toxicity Assessment with Planted Tree Seedlings ...72 Basal Area of Tree Trunks ...72 Green Leaf Area ...72 Productivity of Emergent Plants ...75 Metabolism of the Underwater Ec

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PART II

Lead in a Cypress-Gum Swamp,

Jackson County, Florida

Part II has four chapters summarizing the studies of a lead-ﬁlled swamp in Florida Chapter 5 contains the ecological studies by Lowell Pritchard, Jr Chapter 6 contains the chemical studies by Shanshin Ton and Joseph J Delﬁno Chapter 7 has the studies of leaded wetland microcosms by Shanshin Ton Finally, Chapter 8 reports the computer simulation of a model of lead in the wetland

by Shanshin Ton and Howard T Odum

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Ecological Assessment of the Steele

City Swamps* Lowell Pritchard, Jr.

CONTENTS

Toxicity Assessment with Planted Tree Seedlings 72

Basal Area of Tree Trunks 72

Green Leaf Area 72

Productivity of Emergent Plants 75

Metabolism of the Underwater Ecosystem 75

Invertebrate Animals 77

Indices of Biodiversity 79

Overview Conclusion 79

At the time of this study the Steele City Swamps showed varying degrees of impact, caused less by the large quantities of lead that was ﬁltered than by the high acidity of the battery plant water Figure 5.1 shows the distribution of lead in sediments, with larger values upstream and along the pathway of water ﬂow At Station A (Figure 5.2) there were a few dead trees, and the wood (in cross section) was strangely red colored Much of the pond at B was devoid of trees but covered

in part with ﬂoating plants (Nymphaea) The waters were turbid with underwater objects visible only a few inches below the surface Gum trees were scattered at Stations C and F, but these had just a few leaves each In backwater areas (Stations D and H) more trees were found including cypress In other words, trees were absent in the areas where the most lead had been absorbed (Figure 5.2) Station RF (reference forest) was in a pond which had not received lead wastes and had a normal concentration of cypress and swamp black gum trees

A limited ecological assessment was made by testing seedling survival and growth in the ﬁeld,

by measuring the area of green leaves, by estimating plant productivity with two methods, and by sampling enough underwater invertebrates to calculate indices of biodiversity Details on the methods are given in Appendix A5A

* Condensed by the Editor.

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72 HEAVY METALS IN THE ENVIRONMENT: USING WETLANDS FOR THEIR REMOVAL

TOXICITY ASSESSMENT WITH PLANTED TREE SEEDLINGS

Tree seedlings (pond cypress, bald cypress, and swamp black gum) were planted where bare bottoms had become exposed, measured September 24, 1990 and monitored again June 6, 1991

In the interim there were very high water levels because of heavy rains Since wetland tree seedlings die if covered with water, mortality was large (Table 5.1) Surviving seedlings showed growths 10

to 30 cm Growth and survival at station F may indicate that the sediments, although still containing lead (Chapter 6), were not toxic to new seedlings

BASAL AREA OF TREE TRUNKS

By measuring the diameter of live trees, the area of the trunk cross sections may be calculated, which is called the forest basal area Table 5.2 shows zero values in the upper stations without trees, increasing downstream to 57 cm2/m2 of land, a bit less than that in the reference forest

GREEN LEAF AREA

In a normal wetland forest there are several layers of leaves on top of each other The area of leaves per area of ground below is called the leaf area index Leaf area of the sparse tree areas was

weight Isoconcentration lines were calculated with data from Mundrink (1989).

5

100 50 10

15

100 meters

2 5

10 1

1 5

1 1

1

+

+ +

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ECOLOGICAL ASSESSMENT OF THE STEELE CITY SWAMPS 73

and measurements are shown Overall drainage pattern in this area is from northwest to southeast.

Number Planted

Number Surviving

Average Growth of Survivors (cm)

SAPP BATTERY SITE

West Swamp

US 231

A

B

C

D

E

F

G

Steele City Bay

N

(Feet)

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measured by the annual litterfall into baskets set above the water (Table 5.2) In a fully developed forest there may be 4 to 7 m2 of leaves per square meter of ground, but much less (0 to 2.9) in the impacted wetland with few healthy trees remaining (Table 5.2) The index was about 3 in the reference wetland without lead (Figure 5.3, Table 5.3)

Floating lilies (Nymphaea odorata) were present at Stations B, C, D, F, and G and the index

on July 7, 1991 ranged from 0.70 to 1.25 (Table 5.2) A statistical analysis of variance comparing values from the different stations did not ﬁnd any difference between stations that was greater than the general variation among data samples

Location

Water Lilies LAI (mean ± S.D.)

Trees Basal Area (cm 2 /m 2 )

Trees LAI (mean ± S.D.)

Trees Leaf Area/Basal Area (m 2 /m 2 )

S.D = standard deviation.

Location

Mean ± S.E

Litterfall (g/m 2 )

Fraction Canopied

Corrected Litterfall (g/m 2 )

Leaf Area/Mass

Corrected LAI (m 2 /m 2 )

0 1 2 3

Location

Method:

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PRODUCTIVITY OF EMERGENT PLANTS

Since cypress and black gum drop their leaves in winter, and water lilies in this area die back

in winter, the leaf area at the end of summer is a measure of a year’s leaf production However, the total organic matter made by plant photosynthesis (gross production) is much greater than this estimate of net storage in the leaves, since much of the organic matter that was made during the year went to support necessary respiration of leaves, limbs, trunks, roots, and insects The ratio of gross plant production to net production from studies of similar wetlands was used to estimate gross production (Table 5.4)

METABOLISM OF THE UNDERWATER ECOSYSTEM

The oxygen generated by the photosynthesis of underwater plants (algae and macrophytes) goes into the water as dissolved oxygen, increasing during hours of sunlight At night plants, animals, and microbes use this oxygen to operate their normal metabolism, and the dissolved oxygen goes down (community respiration) Oxygen also diffuses into waters from the atmosphere until the molecules going into water equal those diffusing out (equilibrium) If the dissolved oxygen in the water gets higher than the atmosphere’s equilibrium level, it diffuses out If the dissolved oxygen

is less than the equilibrium level, then oxygen diffuses in Summarizing these processes, the dissolved oxygen is the balance between gross photosynthesis and diffusion in, minus community respiration and diffusion out

By measuring the dissolved oxygen every few hours for 24 h or more and plotting a graph, a curve of dissolved oxygen is usually observed going from a minimum at sunrise after a night of respiration to a maximum near sunset after a day of photosynthesis With methods given in Appendix A5A, one may subtract out the diffusion so that respiration can be calculated from the oxygen

Table 5.4 Ecosystem Productivity in Sampled Locations

Location

Herbaceous

LAI = leaf area index.

wetland forests in Brown et al (1984: p 317) GPP for trees in other locations is a fraction

of reference forest GPP based on the ratios of their LAI.

Gosselink 1986: p 274) and assigning productivities based on the ratios of LAI.

365.25 d/year.

Appendix F), a transformity for gross primary productivity (GPP) of the reference forest was calculated (1317 sej/J) Empower of run-in and rain was divided by the energy flow This transformity was used to convert the GPP at other locations to emergy.

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decrease at night The oxygen increase in daytime is the gross photosynthesis minus the concurrent respiration You can add the night respiration to the daytime oxygen increase to get an estimate of gross photosynthesis

It helps to plot the hourly changes in dissolved oxygen on a “rate of change” graph after corrections for the diffusion (Figure 5.4) Points above the horizontal line are increases (positive), and points below the line are decreases (negative) The shaded area above the line is net photosyn-thesis, and the shaded area below the line is night respiration To get the gross photosynphotosyn-thesis, an estimate is made of the daytime respiration using some assumption about the way it varies In Figure 5.4 the daytime respiration (darkly shaded) is made to increase during the day, based on the idea that the more sugar made by the plant the more respiration there is See Appendix A5A

for more details

In Figure 5.4 the respiration (below the line) is greater than the daytime net photosynthesis (above the line) In other words, in the course of a day and night, more oxygen is used than is produced This means that the swamp water remains below equilibrium with the atmosphere most

of the time, a condition resulting from the quantities of decomposing organic matter from litterfall stream transport, tree roots, and animals

The results of diurnal curve measurements of oxygen and the resulting calculations of metab-olism are summarized for several stations in Table 5.5 and Figure 5.5 As expected, respiration was consistently higher than underwater photosynthesis; rates were higher in summer, and slightly higher downstream

The gross primary production of the below-water ecosystem and the above-water canopy estimates were combined in Figure 5.6 Because so many trees were missing, the upper stations had lower totals

parts per million per hour.

Time, Hours

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

Observed

Corrected for Diffusion

Net Photosynthesis

24 hour Respiration

Gross Photosynthesis

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INVERTEBRATE ANIMALS

With procedures detailed in Appendix A5A, small animals, mostly aquatic insects, were sampled with a cylindrical collector from underwater and the taxonomic family identiﬁed (Lists

of types, dates, and stations are in Appendix A5B, Tables A5B.2 and A5B.3.) The numbers of animals per square meter (density) increased a little downstream away from the lead source (Figure 5.7, Table 5.6)

Location

Distance

to Site (m)

Depth (m)

P g (g O 2 /m 3 /d)

R 24 (g O 2 /m 3 /d)

P g (g O 2 /m 2 /d)

R 24 (g O 2 /m 2 /d)

21, 1990; W = winter measurement, February 1, 1991; AVG = average; g = grams; m = meters; d =

0.0 1.0 2.0 3.0 4.0 5.0 6.0

0.0 1.0 2.0 3.0 4.0 5.0

Distance from discharge, meters

SUMMER

WINTER

R

P

A B

B

C

D

F

G

g 24

Pg

R24

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and/or leaf area indices.

0.0 5.0 10.0 15.0 20.0

Location

(a)

(b)

(c)

Families

RP

12.0 10.0 8.0 6.0 4.0 2.0 0.0

15.0 10.0 5.0 0.0 3.0 2.0 1.0 0.0

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INDICES OF BIODIVERSITY

Often pollution causes the biodiversity of ecosystems to diminish There may be large numbers

of one species (example: Station A1 in Table 5.6) In this study four indices of diversity were calculated from a series of winter and summer data on invertebrates (Table 5.6) Details on these indices are included in Appendix A5A:

S is the number of kinds (families) represented (richness)

H is the “information theory content in bits per individual (Shannon)”

D is the Simpson index

M the number of species in a set of individuals counted (Margalef)

In Figure 5.8 three indices were adjusted to a common scale showing similarity among indices The lowest diversity values were in areas formerly most stressed with lead-acid (Stations

A and F), but for most of the stations the results were highly variable, not consistent indicators

of lead content

OVERVIEW CONCLUSION

The measurements in this chapter show that, in the absence of a tree canopy, the processes of the aquatic ecosystem are dominant and returning to normal, with restoration little affected by residual lead A much longer time may be required for restoration of the wetland forest, a delay inherent in the slower turnover time and reseeding of trees

Distance (m)

Density (N/m 2 )

August 21, 1990

February 3, 1991

were added for the winter sampling event.

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(RF), and reference pond (RP) (a) 08/21/1990, and (b) 02/03/1991.

0

0.5

1

1.5

Location

0

0.5

1

1.5

2

(a)

(b)

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