METAL ACCUMULATION AND IMPACTS ON BENTHIC ORGANISMS
IN DETENTION POND SEDIMENTS
David M. Baker
Environmental Research and Design, Inc.
3419 Trentwood Boulevard, Orlando, Florida 32812
Yousef A. Yousef
Department of Civil and Environmental Engineering
University of Central Florida, Orlando, Florida 32816-2450
ABSTRACT
Sediment cores were collected from thirteen wet detention ponds, located in
Central and South Florida and were analyzed for heavy metal content. Benthic
macroinvertibrates were collected from nine of these ponds. These organisms were
identified, enumerated and analyzed for Cu, Pb and Zn content. The Shannon-Weaver
diversity indeces were calculated for the study ponds.
The calculated diversity indeces ranged from 0.0 to 1.9 which are typical of a
stressed environment. The diversity index appeared to decline with an increase in the
metal content of the top sediment layer. Copper appears to be the most detrimental metal
to benthic organisms since it had the highest correlation with diversity index and was the
most concentrated metal in the benthic organisms.
INTRODUCTION
Numerous researchers have reported significant concentrations of nutrients, heavy
metals, pesticides, bacteria, organics and sediment in stormwater runoff (Wanielista,
1978; Harper, 1985; Yousef et al.; 1986). A comprehensive critical review for urban
stormwater quality has been recently published by Makepeace et al., (1995). The
advantage of retention/detention ponds is that they increase storage, reduce peak
discharge, and reduce pollutant loads in runoff water.
Pollutants, originating from urbanized areas are deposited in the ponds and form
a loose layer of accumulated sediments. These accumulated sediments can be
distinguished from the original parent soils by unique soil characteristics. Pond sediments
are rich in heavy metals such as lead, zinc, copper, nickel, cadmium, and chromium.
Of these, copper, lead and zinc have been reported to compromise up to 90% of all
heavy metals, excluding iron (Yousef et al., 1991).
Heavy metals are of concern as contaminants to aquatic systems because of their
toxicity at low concentrations. Metal-impacted benthic communities are generally
characterized by reduced abundance, lower species diversity, and shifts in community
composition from sensitive to tolerant taxa (Winner et al., 1980; La Point et al., 1984;
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Baker
Clements, 1991). Several investigators have noted a general decrease in tolerance to
heavy metals from chironomids to caddisflies (Trichoptera), to stoneflies (Plecoptera),
to mayflies (Ephemeroptera) (Winner et al., 1980; Clements., 1992). Some investigators
have reported that copper and mercury are the most toxic metals to benthic organisms
(Khangarot, 1991).
Analysis of the distribution and abundance of benthic organisms is routinely used
in biomonitoring studies and is expressed by the diversity index within a cormnunity
(Shannon and Weaver, 1949). In polluted environments the presence of a small number
of species with a large number of individuals per specie produces low values for the
species diversity index. Conversely, environments composed of a large number of
species with equally distributed individuals produce large diversity index values. Values
less than 1 have been reported from polluted waters (Wilhm and Dorris, 1968) and
values above 3 have been reported from oligotrophic waters (Ransom and Dorris, 1972).
Diversity index values for Florida lakes have been reported from 2 to 5 (Herbster, 1994).
STUDY SITES
The study ponds used in this report were located throughout Florida and are
shown in Figure 1. The ponds ranged in age from 1 to 25 years. The age of each pond
was considered to be from the operation start date through the actual sampling date.
Drainage basin areas ranged from 85.4 Ha to 2.99 Ha, and pond surface areas ranged
from 1.84 Ha to 0.53 Ha. Detailed data for physical characteristics, sediment metal
concentrations and benthic organism distribution for the ponds is presented in Baker
(1994).
MATERIALS AND METHODS
Core samples of pond bottom sediments were collected by driving a polycarbonate
pipe 15 to 30 cm into the pond bottom sediments and retrieving the sediment cores. The
cores were then frozen, separated into 5 or 6 layers and stored for analysis. A minimum
of 25 core samples were collected from each pond. A detailed description of the
sampling procedures used, the location of the sediment cores and the number of cores
collected from each pond are listed in a published reports by Yousef et al., (1991).
Heavy metal concentrations of each sediment layers were measured on a plasma emission
spectrophotometer following a nitric acid - sulfuric acid digestion.
Benthic macroinvertibrates were collected from May 1989 to September 1989 at
various stations for each pond with the use of an Ekman dredge. Four samples were
collected and cornposited for each station. These samples were washed through a #30
mesh screen bucket and macroinvertibrates were hand picked, preserved, identified and
enumerated as described in Standard Methods section 1005, 1985. The number of
species and total number of individuals per species were used to calculate the species
33
Baker
G
0
diversity index. The formula for the Shannon-Weaver diversity index is presented as
follows:
H’ = -Z(%) log,($)
(5-l)
RESULTS
Heavy Metal Concentrations in Bottom Sediments
Most of the particulates entering wet retention/detention ponds will settle to the
bottom and form a loose layer of accumulated sediments. The accumulated sediment
layers are very loose and uncompacted and, therefore, have a much lower wet density
than the parent soils. The accumulated sediments also have higher organic, nutrient and
metal content than the parent soils. Pollutant concentrations generally declined rapidly
from the loose top layer to the underlying parent soils.
A summary of metal
concentrations in the loose and parent layers is presented in Table 1.
Benthic Organisms
The families Plesiopora h@icidae and Diptera culicidaedae were found in seven of
the study ponds and the families Diptera cerotopogonidae and Diptera chironomidae were
found in six of the ponds. The distribution of benthic macroinvertibrates in the study
ponds is shown in Table 2. Figure 2 shows the average percent of benthic organisms
present in the study ponds. The families Diptera culicidae and Diptera chironomidae
accounted for over 60 percent of all organisms collected.
Table 3 presents the calculated diversity index and average concentrations of Cu,
Pb and Zrt in the top sediment layer. The diversity indeces ranged from 0 in the Palm
Bay pond to 1.925 in the Cleat-water Pond. The 0 value in the Palm Bay pond was
because only one family was found in the pond. As seen in figure 3 the relationship
between sediment concentrations of copper and the diversity index indicates that in
general, as the Cu content of the sediment increases the species diversity decreases.
Similar relationships were found with Pb and Zn. However Cu showed the strongest
relationship.
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Baker
TABLE 1
SUMMARY OF HEAVY METAL CONCENTRATIONS
IN BOTTOM SEDIMENT LAYERS
Sediment Metal Concentration (ug/gDry Wt.)
Metal
Layer
Number
of
Ponds
Copper
Accumulated
13
23.5
19.9
19
5
73
Parent
13
4.9
4.6
3.2
1.2
13.8
Accumulated
13
278.3
124
348.2
18
1,047
Parent
13
49.5
31.7
48.3
6
163
Accumulated
13
123.7
58.5
154.8
13
538
Parent
13
9.5
5.9
9.9
1.6
38.1
M
x
.
a
a
x
’
Mean Median Standard Min. M
Deviation
TABLE 2
SUMMARY OF BENTHIC ORGANISMS
FOUND IN NINE STUDY PONDS
Pond
Number of Samples Mean Number of
collected
~O r g a n i s m s p e r
Square foot
Mean Number-of
Families per
Square foot
Fort Myers
5
302.2
9
Tampa
4
11
2.75
Clearwater
9
10
4
4
269
3.5
MeIbourne
5
114
3.4
Palm Bay
2
5
1
Orlando
3
13.33
2
New Symma
6
963
7.33
Greenview
3
90.67
5.67
Ocala
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Baker
(3.15%)
%I
&bra udcjdae (32.88%)
Pmopom htrnbfhddae
(8.26%)
hskpom turn (10.22%)
Figure 2: Mean benthic composition of nine Central and South Florida
wet detentionl/etention ponds.
SEDlMENT
DIVERSITY INDEX AND HEAVY METAL
CON CENTRATIONS FOR SELECI’ED STUDY PONDS
Pond
Diversity Index
r-
Sediment Metal Content (JI
copper
Lead
22
237
hvmwt,)
zinc -
-Bay
0
Orlando
0.468
73
1,025
538
New smyrna
0.761
7
124
20
Melbourne
1.024
46
159
71
1.03 1
31
371
286
Tampa
1.498
13
94
56
Fort Myers
1.572
7
192
13
Greew
1.807
20
57
58.5
1.925
16
119
91
cl-er
i:
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Baker
2.5
I
0.5
Palm Bay
0
Figure 3:
10
20
30
40
50
60
Sediment Copper Conc. (ug/g dry wt.)
70
8d
Change in diversity index with top sediment layer copper concentrations
of wet detention ponds.
Metal Accumulation in Benthic Organisms
The metal content was determined for the benthic organisms collected from six
of the pond sites studied.
The metal content of the benthic organisms varied
considerably from pond to pond (Table 4). Metal concentration factors for the benthic
organisms were calculated by dividing the metal concentrations of the benthic organisms
by the metal concentrations of the of the top sediment layer (Table 4). Copper had the
highest concentration factor (mean=598), while lead had the lowest concentration factor
(mean=5).
Based on the high concentration factor, relative to the other heavy metals, and the
relatively strong relationship between copper and the species diversity index, it appears
that copper may be the most detrimental metal in bottom sediments to benthic organisms.
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Baker
TABLE 4
METAL CONTENT AND CONCENTRATION FACTORS
FOR BENTHIC ORGANISMS COLLECTED IN STUDY PONDS
Pond
T
Concentration ug/j
CR
Pb
Tampa
3 1,362
1,043
Orlando
6,750
Grdew
dry wt. T
zn
Concentration
Factor
Cll
Pb
2,975
2,412
11
53
2,400
9,750
92
2
18
1,154
189
578
58
3
10
Melbourne
1,465
415
1,100
964
13
750
Fort Myers
6,750
2,400
9,750
32
3
1.5
225
45
192
32
0
10
Mean
7,95 1
1,082
4,057
598
5
143
Median
4,108
729
2,038
75
3
17
S&L Dev.
11,823
1,076
4,512
961
5
298
New
Smyrna
Zn
SUMMARY AND CONCLUSIONS
Sediment core samples and benthic macroinvertibrates were collected from
thirteen wet detention ponds, located in Central and South Florida. The samples were
analyzed for heavy metal content and the benthic organisms were identified, enumerated
and analyzed for Cu, Pb and Zn content.
Attempts were made to evaluate the impact of sediment heavy metals on benthic
organisms for these ponds. The calculated diversity indeces varied from 0 to 1.9 which
are typical of stressed environments. Copper concentration factors for the benthic
organisms were the highest among the metals measured. The data suggests that
detention ponds retain heavy metals and may be effective in stormwater control and
protection of receiving water bodies.
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Baker
LITERATURE CITED
AAPHA, AWWA and WPCF. “Standard Methods for the Examination of Water and
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Baker, D. M. “Modeling Metal Accumulation In Wet Detention Ponds.” M.S. Env.
Thesis, University of Central Florida, 1994.
Clements, W. H. “Community Responses of Stream Organisms to Heavy Metals: A
Review of Descriptive and Experimental Approaches.” In Ecotoxicolonv of
Metals: Current Concepts and Applications, pp 363-391. Edited by M. C.
Newman and A. W. McIntosh. Boca Raton, FL: CRC Press, 1991.
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Herbster, D .
Communication, Orlando, Florida Department of Environmental Protection,
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(September 1991): 907-912.
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Reservoir by Use of Diversity Indices.” American Midland Naturalist (February
1972): 434447.
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Shannon, C. E. ; and Weaver, W. The Mathematical Theorv of Comunication. Urbana,
11: University of Illinios Press, 1949.
Wanielista, M. P. Stormwater Management Quantitv and Qualitv. Ann Arbor, MI:
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Urban Retention Basins, ” ASCE Proceedings of an Engineering. Foundation
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Technologv, pp 338-350. Henniker, NH, June 23, 1986.
Yousef, Y. A.; Lin, J; Sloat, J.; and Kaye,K. Maintenance Guidelines for Accumulated
Sediments in Retention/Detention Ponds Receiving Highway Runoff. University
of Central Florida, Florida Department of Transportation, 1991.
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