Detailed Research Information

Detailed project information for
Study Plan Number 02098

Branch : Aquatic Ecology Branch

Study Plan Number : 02098

Study Title : Impact of aluminum-laden sediment discharge on viability of native freshwater mussels in the Potomac River

Starting Date : 06/01/2004

Completion Date : 07/30/2007

Principal Investigator(s) : Villella, Rita

Primary PI : Villella, Rita

Telephone Number : (304) 724-4472

Email Address : rita_villella@usgs.gov

SIS Number :

Primary Program Element :

Second Program Element :

Status : Completed

Abstract : BACKGROUND
Dalecarlia and Georgetown reservoirs are operated by the Washington Aqueduct Division of the US Army Corps of Engineers (COE) to provide drinking water to the greater Washington, DC area. Water is drawn from the Potomac River upstream of Washington and treated in open reservoirs with aluminum sulfate and ferric chloride to flocculate suspended sediments and contaminants. The accumulated sludge is then flushed back into the Potomac within an area where the National Park Service manages river bottom resources. Historically, many water treatment plants discharged sludge directly into streams and lakes because there appeared to be little environmental significance to the practice. Sediment loads from Dalecarlia and Georgetown reservoirs have been estimated in the range of 17,800 to 153,600 kg per event, which are small, compared to the total estimated daily sediment loads of 300,000 to 20 million kg per day in the mainstem Potomac (EA Engineering 2001). The added components to the sludge, aluminum and iron, were generally thought to be non-toxic to aquatic life because these elements are largely insoluble in the neutral pH range of river water and they eventually settle into the sediments.

The belief that aluminum discharge from water treatment plants is of little environmental significance does not account for the possible effects on freshwater mussels. Mussels are long-lived benthic filter feeders that largely consume flocculated detritus. Because the majority of aluminum added by water treatment plants is believed to associate with fine organic matter, mussels may actually concentrate much of the flocculated aluminum during feeding and respiration. Freshwater mussels have been shown to accumulate aluminum primarily in the gills followed by concentrations in the visceral mass and foot (Malley et al. 1988). The impact of filter feeding solid aluminum particles on mussel gill integrity is unknown, but if nothing else, will increase the energy and protein costs associated with separating and packaging the particles in mucus for expulsion.

Flocculated aluminum may also impact mussel reproduction. Freshwater mussels produce parasitic larvae known as glochidia, which are brooded in specialized gill pouches for as long as one year, then are released to attach to the gills of a host fish to complete metamorphosis to the adult mussel form. Solid aluminum may have direct caustic effects on adult mussel gills, and the irritation may cause premature emptying of brood pouches (Howells et al. 1996). In addition, when acidic waters containing dissolved aluminum pass into the alkaline gill environment, AL(OH)3 forms as a gelatinous precipitate that can either directly suffocate a fish or adult mussel, or interfere with the ability of glochidia to attach to the gills of the host (Huebner and Pynnonen 1992). Although the pH of the lower Potomac is generally in the range of 7 to 8, pulses of more acidic water are known to pass through the area during high water events.

An even greater concern is the impact of aluminum sedimentation on juvenile mussels. After dropping from their host fish, freshwater mussels spend several years buried within sediments, acting primarily as pedal-foot feeders. The most contaminated sediments in many temperate lakes and rivers are often in the top 30 cm (Rada et al. 1990). Adult freshwater mussels typically burrow from 1 to 25 cm in sediment and feed by filtering phytoplankton and detritus (McMahon 1991). Conversely, juvenile mussels typically burrow less than 8 cm (Neves and Widlak 1987) and feed on bacteria, detritus and colloidal particles in the pore water (Yeager and Cherry 1994). Though adult mussels are exposed to metal concentrations dissolved in water and deposited in sediments, juvenile mussels are most likely exposed to elevated metal concentrations found in association with sediment or pore water. It is unknown as to how much total aluminum the Washington, DC water treatment plants have discharged since their inception, or where the flocculated aluminum has settled or transported.

Testing by the COE indicates that discharged along with aluminum are high concentrations of ammonia, nitrogen, phosphate, and total organic carbon, which suggests a strong potential for development of anoxic conditions in deposition areas. Testing done by EA Engineering showed high concentrations of ammonia (2.2 to 16.4 mg/L), nitrogen (3 to 52 mg/L), total phosphate (1.93 to 44.7 mg/L) and total organic carbon (80 to 259 mg/L) (EA Engineering 2001). These measurements indicate a strong potential for the development of anoxic conditions in both sediments and the overlying water column in the deposition areas, with ammonia, in particular, having the greater potential for creating toxic effects in the benthic environment. Anoxic conditions would not only directly suffocate embedded juvenile mussels, but would mobilize solid aluminum within the restricted water space occupied by the juvenile mussels, greatly increasing direct toxicity. Ammonia has been shown to be toxic to freshwater mussels with an ammonia concentration of 5 mg/L found to be lethal to 40% of Amblema plicata and Pyganadon grandis in 7 days (Horne and McIntosh 1979). The authors also found that ammonia is sometimes lethal to mussels in water even though oxygen levels are not low enough to indicate pollution. Increasing concentrations of un-ionized ammonia has also been linked to a decreased ciliary response in Elliptio complanata with reductions of 50% at concentrations of 0.06 mg/L (Anderson et al. 1978).

Though uptake and storage of contaminants has been studied in freshwater mollusks there is less available information on toxicity. But there is little doubt that contaminants have played a role in the decline in population density, range and species diversity (Havlik and Marking 1987). The Potomac River historically supported 14 species of freshwater mussels (Johnson 1970). At least seven species of freshwater mussels are known to presently inhabit the Potomac River in the Washington, DC area, two of which, Lampsilis cariosa and Leptodea ochracea, are listed by the surrounding states. In addition, there are historic records of a federally endangered mussel, Alasmidonta heterodon, from the Potomac River within Washington, DC (Strayer et al. 1996), and remnant populations may still exist. In addition to providing biodiversity, robust populations of freshwater mussels can significantly impact river ecology through filtration of suspended particles, repackaging of nutrients, and mixing of the upper sediment layer (Nedeau et al. 2000). Aluminum discharge may not only decrease biodiversity of faunal communities, but alter riverine function as well. The purpose of this study is to determine the distribution of mussels within the lower Potomac River and determine the impact of aluminum sedimentation from DC water treatment plants on downstream mussel communities in the Potomac River by mapping mussel populations above and below the discharge point and correlating mussel presence with aluminum concentrations in sediment. This information will assist the National Park Service in making recommendations to the COE for future water treatment plant operation that protects and restores benthic animals to the lower Potomac River.
OBJECTIVES
The objectives of this study are:
1) Determine freshwater mussel presence, diversity, and relative abundance above and below discharge points of the Dalecarlia and Georgetown water treatment plants in Washington, DC
2) Determine correlation of sediment aluminum with mussel presence, diversity, abundance and population age structure in the Potomac River, Washington, DC
HYPOTHESIS
Species richness and abundance of freshwater mussels is lower below the water treatment outfalls than above the treatment outfalls.
Mussel population age structure below the treatment outfalls is dominated by older individuals than populations above the outfall.

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Branch :	Aquatic Ecology Branch
Study Plan Number :	02098
Study Title :	Impact of aluminum-laden sediment discharge on viability of native freshwater mussels in the Potomac River
Starting Date :	06/01/2004
Completion Date :	07/30/2007
Principal Investigator(s) :	Villella, Rita
Primary PI :	Villella, Rita
Telephone Number :	(304) 724-4472
Email Address :	rita_villella@usgs.gov
SIS Number :
Primary Program Element :
Second Program Element :
Status :	Completed
Abstract :	BACKGROUND Dalecarlia and Georgetown reservoirs are operated by the Washington Aqueduct Division of the US Army Corps of Engineers (COE) to provide drinking water to the greater Washington, DC area. Water is drawn from the Potomac River upstream of Washington and treated in open reservoirs with aluminum sulfate and ferric chloride to flocculate suspended sediments and contaminants. The accumulated sludge is then flushed back into the Potomac within an area where the National Park Service manages river bottom resources. Historically, many water treatment plants discharged sludge directly into streams and lakes because there appeared to be little environmental significance to the practice. Sediment loads from Dalecarlia and Georgetown reservoirs have been estimated in the range of 17,800 to 153,600 kg per event, which are small, compared to the total estimated daily sediment loads of 300,000 to 20 million kg per day in the mainstem Potomac (EA Engineering 2001). The added components to the sludge, aluminum and iron, were generally thought to be non-toxic to aquatic life because these elements are largely insoluble in the neutral pH range of river water and they eventually settle into the sediments. The belief that aluminum discharge from water treatment plants is of little environmental significance does not account for the possible effects on freshwater mussels. Mussels are long-lived benthic filter feeders that largely consume flocculated detritus. Because the majority of aluminum added by water treatment plants is believed to associate with fine organic matter, mussels may actually concentrate much of the flocculated aluminum during feeding and respiration. Freshwater mussels have been shown to accumulate aluminum primarily in the gills followed by concentrations in the visceral mass and foot (Malley et al. 1988). The impact of filter feeding solid aluminum particles on mussel gill integrity is unknown, but if nothing else, will increase the energy and protein costs associated with separating and packaging the particles in mucus for expulsion. Flocculated aluminum may also impact mussel reproduction. Freshwater mussels produce parasitic larvae known as glochidia, which are brooded in specialized gill pouches for as long as one year, then are released to attach to the gills of a host fish to complete metamorphosis to the adult mussel form. Solid aluminum may have direct caustic effects on adult mussel gills, and the irritation may cause premature emptying of brood pouches (Howells et al. 1996). In addition, when acidic waters containing dissolved aluminum pass into the alkaline gill environment, AL(OH)3 forms as a gelatinous precipitate that can either directly suffocate a fish or adult mussel, or interfere with the ability of glochidia to attach to the gills of the host (Huebner and Pynnonen 1992). Although the pH of the lower Potomac is generally in the range of 7 to 8, pulses of more acidic water are known to pass through the area during high water events. An even greater concern is the impact of aluminum sedimentation on juvenile mussels. After dropping from their host fish, freshwater mussels spend several years buried within sediments, acting primarily as pedal-foot feeders. The most contaminated sediments in many temperate lakes and rivers are often in the top 30 cm (Rada et al. 1990). Adult freshwater mussels typically burrow from 1 to 25 cm in sediment and feed by filtering phytoplankton and detritus (McMahon 1991). Conversely, juvenile mussels typically burrow less than 8 cm (Neves and Widlak 1987) and feed on bacteria, detritus and colloidal particles in the pore water (Yeager and Cherry 1994). Though adult mussels are exposed to metal concentrations dissolved in water and deposited in sediments, juvenile mussels are most likely exposed to elevated metal concentrations found in association with sediment or pore water. It is unknown as to how much total aluminum the Washington, DC water treatment plants have discharged since their inception, or where the flocculated aluminum has settled or transported. Testing by the COE indicates that discharged along with aluminum are high concentrations of ammonia, nitrogen, phosphate, and total organic carbon, which suggests a strong potential for development of anoxic conditions in deposition areas. Testing done by EA Engineering showed high concentrations of ammonia (2.2 to 16.4 mg/L), nitrogen (3 to 52 mg/L), total phosphate (1.93 to 44.7 mg/L) and total organic carbon (80 to 259 mg/L) (EA Engineering 2001). These measurements indicate a strong potential for the development of anoxic conditions in both sediments and the overlying water column in the deposition areas, with ammonia, in particular, having the greater potential for creating toxic effects in the benthic environment. Anoxic conditions would not only directly suffocate embedded juvenile mussels, but would mobilize solid aluminum within the restricted water space occupied by the juvenile mussels, greatly increasing direct toxicity. Ammonia has been shown to be toxic to freshwater mussels with an ammonia concentration of 5 mg/L found to be lethal to 40% of Amblema plicata and Pyganadon grandis in 7 days (Horne and McIntosh 1979). The authors also found that ammonia is sometimes lethal to mussels in water even though oxygen levels are not low enough to indicate pollution. Increasing concentrations of un-ionized ammonia has also been linked to a decreased ciliary response in Elliptio complanata with reductions of 50% at concentrations of 0.06 mg/L (Anderson et al. 1978). Though uptake and storage of contaminants has been studied in freshwater mollusks there is less available information on toxicity. But there is little doubt that contaminants have played a role in the decline in population density, range and species diversity (Havlik and Marking 1987). The Potomac River historically supported 14 species of freshwater mussels (Johnson 1970). At least seven species of freshwater mussels are known to presently inhabit the Potomac River in the Washington, DC area, two of which, Lampsilis cariosa and Leptodea ochracea, are listed by the surrounding states. In addition, there are historic records of a federally endangered mussel, Alasmidonta heterodon, from the Potomac River within Washington, DC (Strayer et al. 1996), and remnant populations may still exist. In addition to providing biodiversity, robust populations of freshwater mussels can significantly impact river ecology through filtration of suspended particles, repackaging of nutrients, and mixing of the upper sediment layer (Nedeau et al. 2000). Aluminum discharge may not only decrease biodiversity of faunal communities, but alter riverine function as well. The purpose of this study is to determine the distribution of mussels within the lower Potomac River and determine the impact of aluminum sedimentation from DC water treatment plants on downstream mussel communities in the Potomac River by mapping mussel populations above and below the discharge point and correlating mussel presence with aluminum concentrations in sediment. This information will assist the National Park Service in making recommendations to the COE for future water treatment plant operation that protects and restores benthic animals to the lower Potomac River. OBJECTIVES The objectives of this study are: 1) Determine freshwater mussel presence, diversity, and relative abundance above and below discharge points of the Dalecarlia and Georgetown water treatment plants in Washington, DC 2) Determine correlation of sediment aluminum with mussel presence, diversity, abundance and population age structure in the Potomac River, Washington, DC HYPOTHESIS Species richness and abundance of freshwater mussels is lower below the water treatment outfalls than above the treatment outfalls. Mussel population age structure below the treatment outfalls is dominated by older individuals than populations above the outfall.
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U.S. Department of the Interior \|\| U.S. Geological Survey 11700 Leetown Road, Kearneysville, WV 25430, USA URL: http://www.lsc.usgs.gov Maintainer: lsc_webmaster@usgs.gov Last Modified: October 21, 2002 dwn Privacy Policy and Disclaimers \|\| FOIA \|\| Accessibility