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Ohio Sea Grant College Program
and Stone Laboratory

Ohio Sea Grant and Stone Laboratory

The Impact of Zebra Mussels on the Dynamics of Heavy Metals

Project Number: R/ZM-002, Completion Report

Start Date: 9/1/1992

Completion Date: 8/31/1993

Revision Date: 10/23/1998

Principal Investigator(s)1.Peter C. Fraleigh, Biology University of Toledo*
Co-Principal Investigator(s)2.Paul L. Klerks, Biology University of Toledo*
This shows the current affiliation and may not match affiliation at time of participation. *

Funding Record

Source: Ohio Sea Grant College Program
Source FundState MatchPass Through
Total$ 108,354.00$ 67,066.00$ 0.00

Objectives

To determine if the presence of zebra mussels leads to a reduction in metals present in the water column, an increase in metals accumulated in biota, and an increase in the deposition of metals on the lake bottom (as feces or pseudofeces). It is hypothesized that the presence of zebra mussels will lead to increased flux from the water column to the lake bottom.

Rationale

Zebra mussels have become very abundant in parts of North America, especially Western Lake Erie. Consequently, much more water is being processed by filter-feeding organisms. The increased filter-feeding is likely to have changed the fluxes of metals (uptake from solution, uptake with suspended matter, deposition on lake bottom as pseudo feces), especially since the fate of metals is intimately connected to the behavior of such particles as algae, detritus, and suspended matter.

Methodology

Laboratory experiments: rates of uptake, accumulation and excretion as feces and pseudofeces will be determined for zinc and chromium (radioisotopes) in solution and on suspended material of various compositions and in various concentrations. Field experiments: mussels from a single source and age-class will be suspended above sediment traps (and traps without mussels) along a pollution gradient. Together with subsequent ICP analyses (Cu, Zn, Cr, Hg, Pb, Se, As, Cd) on mussels, feces (from depuration) and sediment from traps, this will quantify Dreissena's effects on sedimentation rates and on metal flux to the lake bottom.

Benefits & Accomplishments

Benefits:
The research conducted in this project has demonstrated that the establishment of high densities of zebra mussels (as has occurred in western Lake Erie) has had a strong impact on the cycling of metals. This research showed that several environmental fluxes of metals are changed by the mussels: a large increase in metal biodeposition, an increase in metal bioaccumulation, and a decrease in watercolumn metal levels. Thus sediment contamination is increased while watercolumn contamination is decreased by the presence of zebra mussels. The research also confirmed that it is very likely that the filtering activity of zebra mussels is responsible for the decreased turbidity observed in Lake Erie following the establishment of the zebra mussel. The information obtained in this research is important to agencies and groups involved with planning and use of these aquatic resources.

Results:
This research has shown that the presence of large numbers of zebra mussels (such as observed for western Lake Erie) has significantly affected the environmental cycling of copper, nickel and zinc.

  1. The presence of mussels resulted in an increase of the rate of metal deposition on the lake bottom. At densities representative of western Lake Erie, the mussels roughly doubled the rate at which metals were being deposited on the lake bottom; mussel biodeposition rates equalled (for copper and nickel) or exceeded (for zinc) baseline deposition rates. In the field experiment conducted in western Lake Erie, metal biodeposition rates declined strongly with increasing distance from the Maumee River mouth.
  2. The increase in metal deposition as a function of mussel density was mostly due to an increased sedimentation rate. This effect was observed in all experimental protocols (laboratory experiments, semi-field conditions, as well as full field conditions). Zebra mussels strongly affected the rate by which sediment is deposited on the lake bottom. Sediment biodeposition averaged 140% of normal sedimentation rates. This biodeposition was shown to increase with increasing seston levels in the watercolumn. In addition, research showed an increase in sediment organic content, which may also influence metal binding by the sediment as well as affect transfer of the metal to other organisms.
  3. The increase in metal deposition as a function of mussel density was also (but to a much lesser extent) due to an increase in the concentration of copper, nickel and zinc in deposited sediment. This effect was observed under field conditions as well as in laboratory experiments with flow-through Lake Erie water. This will result in increasing sediment contamination when zebra mussels are present. The exact reason for this increase was not evident, but may be a consequence of metal uptake patterns (see below). For the field experiment in western Lake Erie, metal concentrations in the deposited sediment declined with increasing distance from the Maumee River mouth.
  4. Zebra mussels also affect the environmental cycling of metals through metal bioaccumulation. Metal bioaccumulation was changed both via changes in tissue metal levels (increases for copper and nickel, decreases for zinc) as well as changes in tissue mass. The latter were shown to be dependent on mussel density (increases in tissue weight being less at higher mussel densities). However, in long-term experiments metal bioaccumulation was of minor importance compared to the magnituted of metal biodeposition.
  5. Short-term experiments with nickel and zinc radioisotopes showed that mussels accumulate metals from both the particulate anddissolved fractions of water. This uptake differed between experiments and between high- and low-turbidity water used within the same experiment, indicating that the relative magnitude of uptake from water and particulates is dependent on the composition of the seston. Short-term metal bioaccumulation reflected the changes in metal levels in the watercolumn, and showed a rapid loss of zinc contrasting with the total retention (within 24h) of nickel. Similar experiment were not conducted with copper, due to problems with availability and use of the very short-lived 64Cu isotope (half-life 12.7 hours). However, results from our other experiments indicate that copper tends to behave similar to nickel with respect to processing by zebra mussels.
  6. The increased fluxes of metals from the watercolumn to the sediment (through biodeposition) and to the biota (through bioaccumulation) means that watercolumn metal levels will be reduced. The exact magnitude of this change can not be fully assessed with the available data, but based on changes in seston levels it is at least ...
  7. The results from this research project have, in part, been dissiminated by a presentation at the Fifth International Zebra Mussel Conference. More widespread dissimination will result from the publication of articles in the peer-reviewed literature (1 manuscript has been submitted while 2 additional ones are in preparation).

Publications & Media

Peer-reviewed reprints
Peer-reviewed reprintsKlerks, P. L., P. C. Fraleigh and J. E. Lawniczak. Effects of zebra mussels (Dreissena polymorpha) on metal cyling
In preparation.
Peer-reviewed reprintsKlerks, P. L., P. C. Fraleigh and J. E. Lawniczak. Effects of zebra mussels (Dreissena polymorpha) on seston levels and sediment deposition in western Lake Erie
Submitted to Can. J. Fish. Aquat. Sci.
Peer-reviewed reprintsKlerks, P. L. and P. C. Fraleigh. Uptake of nickel and zinc by the zebra mussel Dreissena polymorpha
In preparation.
Conference, symposia, or workshop proceedings, and summaries
Conference, symposia, or workshop proceedings, and summariesKlerks, Paul L. 1995, The Impacts of Zebra Mussels (Dreissena polymorpha) on the Environmental Cycling of Metals
Presented at the Fifth International Zebra Mussel & other Aquatic Nuisance Organisms Conference 1995. Toronto, Ontario, February 21-24.
Conference, symposia, or workshop proceedings, and summariesKlerks, P., P. Fraleigh, J. Lawniczak, J. Jerry and J. Savino. 1995, Impact of zebra mussels (Dreissena polymorpha) on the environmental cycling of metals.
Presented at the Fifth International Zebra Mussel & other Aquatic Nuisance Organisms Conference 1995. Toronto, Ontario, February 21-24. (Abstract published in program).

Supported Students

StudentLawniczak, J.E. (Graduate, M.S.)
The University of Toledo
Title: The impact of zebra mussels (Dreissena polymorpha) on the dynamics of sediments and heavy metals in western Lake Erie