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The AAPG/Datapages Combined Publications Database
GCAGS Transactions
Abstract
EXTENDED ABSTRACT: An Experimental Approach to Understanding the
Response of
Benthic
Foraminifera to Cd, Hg, Pb, and Zn
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Ellen R. Brouillette and Susan T. Goldstein
Department of Geology, University of Georgia, 210 Field St., Athens, Georgia 30602
EXTENDED ABSTRACT
Benthic
foraminifera respond quickly to changes in environmental parameters
such
as salinity, temperature, water depth, grain size, and increased environmental
stress
caused by pollution (Murray, 1991; Scott et al., 2001). To understand better
how foraminifera
respond to individual pollutants, a laboratory-based experimental study was
conducted to examine the abundance, diversity, and test deformation response
of common
coastal
benthic
foraminifera to the presence of heavy metal pollutants. Four
heavy
metals were chosen (Pb, Zn, Cd, and Hg) based on observations from previous
field
studies (Magistrato alle Acque di Venezia, Thetis, 2008). Sediment was collected
in October
and June 2008 from a mudflat on the southern end of Sapelo Island, Georgia.
In the
field, sediment was sieved to separate the <63 micron fraction, which contains
abundant
juvenile foraminifera (Alve and Goldstein, 2003). In the lab, the sediment
was divided
into 20 mL individual experimental aliquots. Instant ocean (40 mL) was added
to maintain
a salinity of ~30 psu. Individual heavy metals were added based on the EPA
National
Recommended Water Quality Criteria for Saltwater (Cd, 40 mg/L; Hg, 1.8 mg/L;
Pb, 210 mg/L; and Zn 90, mg/L) and increased an order of magnitude for 6 different
concentration levels (duplicates and controls were also run). The experiments
were incubated
for 4 weeks, illuminated on a 12 hour cycle, and kept at a constant temperature
of 18°C for the duration of the experiment. The samples were individually
harvested at
the same time, preserved in ethanol and stained with Rose Bengal (Walton, 1952)
to determine
which foraminifera were alive at the end of the experiment.
Experimental assemblages were dominated by Ammonia tepida, Haynesina germanica, Psammophaga simplora, and Ovammina opaca. Additional taxa present include Miliammina fusca, Buliminella elagantissima, Textularia palustris, Textularia candeina, Triloculina sp., Quinqueloculina jugosa, Quinqueloculina polygona, Quinqueloculina seminula, and Bolivina lowmani. Aberrant test morphologies were observed in some species that grew with exposure to Zn or Cd (Fig. 1). Aberrant test morphologies were most common in assemblages grown with exposure to Zn at 90,000 mg/L where ~23% of the total assemblage was deformed. While this number may seem small it is important to note that non-polluted sites host 1-3% deformations. Individual species exhibited different responses. Populations of Haynesina germanica contained ~52% deformations, whereas those of Ammonia tepida contained ~22%. No deformations were present in the common monothalamous agglutinated species Ovamina opaca and Psammophaga simplora (Fig. 2). The differences between species may be related to their different life habits (e.g., diet, mode of test growth, and metabolism) or type of shell construction. Results indicate that at the highest concentration levels, total abundance and diversity of foraminifera decreased (Fig. 3). In some cases, these trends do not decrease uniformly, but fluctuate somewhat (Fig. 2). This may be explained by potentially different pathways taken by heavy metals in individual aliquots. Alpha diversity also decreases with an increase in Cd, Pb, and Zn; and increases in the presence of Hg (Fig. 4).
In conclusion, foraminifera respond negatively to the presence of different
heavy
metals. This is observed in the decrease in foraminiferal abundance and diversity,
and
an increase in aberrant test morphologies. While more studies are needed to
fully understand
the relationship between the presence of heavy metal pollutants and foraminifera,
this study provides exciting initial data that supports the use of benthic
foraminifera
as possible bio-indicators.
REFERENCES CITED
Alve, E., and S. Goldstein, 2003, Propagule transport as a key method of dispersal
in benthic
foraminifera (Protista):
Limnology and Oceanography, v. 48, no. 6, p. 2163-2170.
Magistrato alle Acque di Venezia, Thetis, 2008, SIOSED Project, final report of research activities developed during 2005-2007: Venice Water Authority Concessionary, Consorzio Venezia Nuova, Italy, 52 p.
Murray, J. W., 1991, Ecology and palaeoecology of benthic
foraminifera: Longman
Scientific and Technical, Harlow,
U.K., 365 p.
Scott, D. B., F. S. Medioli, and C. T. Schafer, 2001, Monitoring of coastal environments using Foraminifera and Theocamoebian indicators: Cambridge University Press, Cambridge, U.K., 176 p.
Walton,W. R., 1952, Techniques for recognition of living foraminifera: Contributions from the Cushman Foundation of Foraminiferal Research, v. 3, p. 56-60.
Figure 3. Total foraminifera observed in experimental aliquots with increasing heavy metal concentrations starting at Cd, 40 mg/L; Hg, 1.8 mg/L; Pb, 210 mg/L; and Zn, 90 mg/L.
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