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publications > papers > occurance and distribution of contaminents > results and discussion
Occurrence And Distribution Of Contaminants In Bottom Sediment And Water Of The Barron River Canal, Big Cypress National Preserve, Florida, October 1998
Ronald L. Miller and Benjamin F. Mcpherson
Water Resources Division, United States Geological Survey, 4710 Eisenhower Blvd., B-5, Tampa, FL 33634 USA
RESULTS AND DISCUSSION:
Variability in the analytical results is inferred from a comparison of data for the environmental and concurrent replicate samples collected at the Jerome site on the Barron River Canal. For the replicate sample, concentrations (including estimated values below the method reporting level) differed by 0 to 37 % for trace elements and by 2 to 91 % for the SVOCs. Part of this variability is due to actual differences in the composition of the samples collected (sampling error) and part is due to normal errors associated with extraction or digestion procedures and subsequent chemical analyses. Differences between the environmental and replicate concentrations at Jerome were generally small compared with the observed ranges along the canal.
Trace elements-
The range in concentrations of selected trace and major elements at the 10 Barron River Canal sites and one Turner River site is given in Table 2. Concentrations of trace elements were less than bottom-sediment probable effect levels (Environment Canada, 1999) and the aquatic-life criteria (effects-range median, ER-M) developed by Long and Morgan (1990) for the National Oceanic and Atmospheric Administration’s (NOAA) Status and Trends Program. However, concentrations of chromium, arsenic, and mercury reached 86, 82, and 60 % of the probable effect levels, respectively, in some samples.
| TABLE 2. Selected trace-element and organic carbon concentrations in bottom sediments from the Barron River Canal and Turner River and aquatic-life criteria: October 1998. |
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Element, units
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Laboratory minimum reporting level
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a Observed range in Barron River Canal and Turner River
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b Canadian probable effect levels for freshwater sediment
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c Effects- range median
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d Average crustal abundance
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| Arsenic, eµg/g |
0.1
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1 - 14
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17.0
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85
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1.8
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| Cadmium, µg/g |
0.1
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<0.1 - 0.6
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3.5
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9
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0.15
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| Chromium, µg/g |
1
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6 - 77
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90.0
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145
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102
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| Copper, µg/g |
1
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2 - 82
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197
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390
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60
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| Mercury, µg/g |
0.02
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0.02 - 0.29
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0.486
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1.3
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0.085
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| Lead, µg/g |
4
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3 - 40
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91.3
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110
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14
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| Nickel, µg/g |
2
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< 2 - 16
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f--
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50
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84
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| Selenium, µg/g |
0.1
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<0.1 - 1.4
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--
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--
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0.05
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| Zinc, µg/g |
4
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5 - 180
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315
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270
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70
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| Aluminum, % |
0.005
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0.15 - 2.4
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--
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--
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--
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| Organic carbon, % |
0.02 |
0.75 - 42 |
-- |
-- |
-- |
a Concentrations in dry weight.
b Environment Canada, 1999.
c Long and Morgan, 1990.
d Rice, 1999.
e Microgram per gram.
f Not available. |
Concentration of seven trace-elements in bottom sediment are plotted against aluminum concentration (Fig. 3). The 95 % confidence limits for clean Florida estuarine bottom sediments that were determined by Schropp and Windom (1988) are included on the figure for each trace element to help evaluate possible enrichment.
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| Figure 3. Concentrations of trace elements plotted against concentrations of aluminum in bottom sediments from the Barron River Canal and Turner River, October 1998. The 95 percent confidence intervals are for clean Florida estuarine sediments from Schropp and Windom (1988). Click on graphs for larger versions. |
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Most of the naturally occurring trace elements are incorporated in the aluminosilicate structure of clays and other weathered materials and are not readily available to aquatic biota. Trace elements from anthropogenic sources tend to be adsorbed on sediment and are usually more available to the aquatic biota. Thus, elements with element-to-aluminum ratios significantly above the upper 95 % confidence limits have the potential to produce adverse biological effects. Ratios for arsenic and nickel were within the 95 % range indicative of natural background levels for these elements. Some of the chromium and two of the cadmium ratios were near the upper 95 % confidence levels for natural bottom sediments. Lead, copper, and zinc had some ratios above the upper 95 % confidence levels and suggest that human activities may have enriched these elements above natural levels at some sites. Possible anthropogenic sources of trace element enrichment in south Florida canals include biomass burning, runoff from manure and fertilizers, release from wear of automobile parts, irrigation return flow, and municipal waste (Rice, 1999).
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| Figure 4. Ratios of concentrations of trace elements to concentrations of aluminum in bottom sediments along the Barron River Canal and from the Turner River, October 1998. Most trace ele-ment to aluminum ratios are multiplied by 10,000 except for cadmium to aluminum and arsenic to aluminum ratios that are multipled by 1,000,000 and 50,000, respectively, to show more detail. Ratios of 0 are for less-than values. [larger image] |
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The distribution of trace element-to-aluminum ratios along the Barron River canal and at the Turner River site is shown on Fig. 4. The highest ratios for arsenic, cadmium, and zinc were at the Turner River background site, possibly due to the high organic carbon concentration (42 %) and the binding effect that organic carbon can have on metals. Cadmium was strongly correlated with aluminum (p<0.0001) and organic carbon (p<0.0001). Zinc and arsenic were strongly correlated with aluminum (p<0.0009 and p<0.008, respectively) and weakly correlated to organic carbon (p<0.17 and p<0.10, respectively). Chromium was strongly correlated with aluminum (p<0.0006) but was not correlated with organic carbon (p<0.89). The high concentration of organic carbon and the correlation of cadmium, zinc, and arsenic with organic carbon concentrations partially explains the high trace element to aluminum ratios for these elements at the Turner River background site. The highest ratios for chromium and the second highest ratio for arsenic were at the Jerome site on the Barron River Canal. Arsenic and copper had small peaks in their ratios at the Barron River CR-858 site. The CR-858 and Jerome sites have a history of contamination that is the likely cause of the local peaks in some trace-element ratios.
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