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Environmental Applications and Research Group — Publications

Zebra Mussel Monitoring Research Program at the Bureau of Reclamation: Summary of 1996 Monitoring Activities

Technical Memorandum No. 8220-97-11
Tracie Greene

Materials and Methods
Results and Discussion
Future Plans


The Bureau of Reclamation (Reclamation) manages water related resources in 17 western states, west of the Mississippi River. These states rely in part on Reclamation to deliver water for agricultural, industrial, and recreational needs. Besides being the largest wholesale supplier of water in the United States, the agency is the nation's sixth largest hydroelectric power generator. Reclamation projects include 343 storage dams and reservoirs (308 of these sites offer a variety of recreation activities), 58 hydroelectric power plants, and 54,550 miles of canals and other conveyance and distribution facilities. Infestation by zebra mussels would very likely have a dramatic effect on Reclamation's ability to provide these services and manage facilities.

The zebra mussel (Dreissena polymorpha) is a mollusk native to the Caspian Sea region of east- central Asia. It has spread rapidly throughout North America's eastern waters since 1988. Despite its spread in eastern waters, this mollusk has only reached as far west as Oklahoma (Figure 1). It potentially could move swiftly and explosively throughout western waters and facilities. It is presently known only to occur in the navigable portion of the Arkansas River as far west as Tulsa, Oklahoma. This is within 90 miles of the nearest Reclamation facility, and there are six Reclamation facilities within 250 miles of the site. Although the mollusk is not known to exist in Reclamation facilities, we are monitoring several at-risk facilities in Oklahoma and developing plans to deal with the mussels should they arrive. If the veligers (free-swimming larvae of zebra mussels) are allowed to enter pipes, attach and grow, they may clog intakes and distribution pipelines in industrial and domestic facilities, increase corrosion potential of steel and iron pipes and structures, taint and contaminate potable water supplies, encrust hulls of boats, decrease recreational uses of water, displace native species and destroy or alter food chains.

Details on 1995 activities can be found in the Summary of 1995 Activities, Bureau of Reclamation Technical Memorandum No. 8220-96-15. In order to provide early detection of zebra mussels in at-risk facilities, monitoring activities continued in 1996. Also, the sensitivity testing of the bridal veil method was continued. In cooperation with Dr. James Schooley of northeastern State University (NSU), other monitoring techniques including pumped and towed methods were tested (Monitoring the abundance and growth of zebra mussels in waters of the western United States - Fall 1996; Dr. James K. Schooley).

Materials and Methods

Reclamation is providing a monitoring program to at-risk Oklahoma water districts so that early detection of zebra mussel infestations will be possible. Five water districts and one navigation system are currently involved in the Reclamation's monitoring program. The participants are: Arbuckle Master Conservancy District (Davis, OK), Central Oklahoma Master Conservancy District (Norman, OK), Foss Reservoir Master Conservancy District (Foss, OK), Kerr-McCellan Navigation System (Tulsa, OK), Lugert-Altus Irrigation District (Altus, OK), and McGee Creek Authority (Atoka, OK). Two other Reclamation-affiliated water districts have not participated to date, but they will again be invited to participate in the 1997 monitoring program. These are Fort Cobb Reservoir Master Conservancy (Anadarko, OK) and Mountain Park Master Conservancy District (Mountain Park, OK).

Participants were sent sampling kits containing the following items:

The samplers (R1, R2, Folded and Unfolded) were placed by cooperating field staff in locations that were easily accessible for making monthly collections. Samples R1, R2 and unfolded are replicates. The only difference is the folded sample. They were hung (6-12 feet deep) from concrete or metal works around outlet structures, or from boat docks. The samplers or "traps" consist of a plastic mesh cage and a bridal veil substrate which is believed to be a desirable attachment site for the free swimming veligers. Every month, fresh bridal veil substrates were exchanged with those that have been in place and they are then returned to Reclamation's Denver Office for analysis. After receipt, all samples were stored at 5 C until analysis.

During sample analysis, the bridal veil was rinsed with water to dislodge any attached veligers (free swimming larvae of zebra mussels). The sample wash was then poured through a screen cup (Figure 2) with a Spectra Mesh Woven Polymer Filter (60 micron mesh opening). This filter size was chosen due to the approximate size of the veliger (70-300 microns in diameter). Most veligers will not be able to pass through the filter, and will become concentrated on its surface. The filter was rinsed into a petri dish and this rinse was then analyzed for the presence of veligers under a microscope with a double polarizing light source. While veligers are detectable under a traditional microscope without polarized light, this method makes them easier to distinguish from silt residues (attached to the bridal veil) which often contaminate the samples (Figure 3). The bridal veil and water samples were disposed of properly to prevent the possible contamination of local water facilities. Following analysis of the samples, letters were sent to the respective participants indicating the results of their sampling.

In cooperation with Dr. James Schooley, students at Northeastern State University in Tahlequah, Oklahoma, pumped and towed samples were taken every two weeks at McGee Creek Authority and Kerr-McCellan Navigation System. Plankton nets with 64 Micron mesh (Wildlife Supply Company) and 30 cm or 50 cm diameter openings (1:3 diameter:length bias) were used (Figure 5). Sampling equipment was sterilized before use at uninfested sites. Four samples were taken from each site. The first three were five meter vertical tows using the 50 cm net at the upper pool edge of the dam or lock, the fourth was a pumped sample of known volume (365 liters) using the existing service water systems at the dam or lock which passed through the 30 cm net. At the McGee Creek fishing pier, the water column was sampled with a Van Dom Horizontal Alpha Bottle (Figure 4). Samples were preserved in 5% buffered formalin and sent to Reclamation's Denver Office for analysis.

During sample analysis, sample volumes were measured in a graduated cylinder and recorded. Each sample was poured through a screen cup with a 60 micron Spectra Mesh Woven Polymer filter attached. This concentrated sample was observed and results were recorded.

Results and Discussion

Appendix A shows the sites where bridal veil monitoring kits were placed and the results of their analysis. No veligers were found in the Reclamation affiliated water districts, but veligers (free swimming larvae) and small (1 - 10 mm), medium (11-2 1 mm) and large (22-32 mm) zebra mussels were found in the Keff Lock Navigational System samples. Keff Lock, operated by the U.S. Army Corps of Engineers (Corps), was used as a control site again in 1996 to test detection methods at a site known to be infested by zebra mussels. The same processing method was used for all six participants. Positive veliger samples were found in the August and September samples from Keff Lock. Small and medium zebra mussels were also found in August, September and October. In the August samples, 7 small and 2 medium-sized dead zebra mussels were found as well as approximately 40 veligers. In the September samples, 2 medium-sized dead zebra mussels as well as approximately 170 veligers were found. In the October samples, 1 medium-sized dead zebra mussel was found. No veligers were found in the October samples.

In the 1995 results, the memorandum reports no veligers were found, as opposed to the 1996 results. In the 1996 monitoring program, more bridal veil samples were added to improve the ability to detect veligers (the free-swimming larvae of zebra mussels). Two extra bridal veil nettings were added to each kit. One netting was folded and the other was unfolded. The purpose of the folding was to determine if more veligers would attach to a substrate that was folded. The purpose of the unfolded netting was to determine if the quantity of clay and silt contaminants would decrease. The results did not show an appreciable difference in either the numbers of veligers detected or particle contaminants using folded and unfolded nettings.

Appendix B shows sites where plankton net tows and pumped samples were taken and the results of their analysis. These samples were taken to measure a large volume of water for veligers. No veligers were found in either towed or pumped samples. But, there were veligers found in the bridal veil samples from Kerr Lock Navigation System (infested). These results suggest that the bridal veil sampling method is sensitive enough to detect veligers at the levels seen in nearby infested waters. The results do not necessarily imply that the pumped and towed sampling methods were not sensitive enough for detection: it may suggest that reproduction of zebra mussels did not occur at the time of the year that the pumped and towed samples were taken. Claudi and Macki, (I 994) suggest that spawning may last from 3 -5 months depending on the temperate latitudes. They also report that reproduction usually begins when water reaches 12 C (55 F). It is also possible that the volume of the sample could have been too small for detection, as well as the possibility that low density levels may have been a factor in the negative findings.

Future Plans

Sample Collection
Monthly monitoring for veligers will continue using the bridal veil substrates at all sites. Additionally, veliger monitoring will be continued including the use of plankton net tows (mesh size of 63 microns) to predict peak time of reproduction. Raw (untreated) water from selected sites will continue to be pumped through a garden hose and filtered by plankton nets for quantities of veligers. Larger volumes of samples will be taken to detect veliger densities. Samples throughout the reproduction season will be taken. Monitoring for settlement of adult mussels will be conducted annually by Dr. James Schooley.

Environmental Parameters
The most critical parameters affecting the degree of zebra mussel establishment in Oklahoma are likely to be water salinity, temperature, pH level, calcium concentration, dissolved oxygen, and turbidity. Depending on the values, these factors can either increase or decrease growth and reproduction of zebra mussels. Measurements of water quality parameters (such as dissolved oxygen, turbidity, temperature, pH, etc.) are needed to complete necessary risk assessments. A temperature data logger will be installed to determine the temperature of the sites during the monitoring period. A cooperative study with a regional academic institution has been initiated to determine other water quality parameters, the growth rates, reproduction rates, and the time of the year that the mussel veligers are found as well as other biological factors.

Risk Assessment
Future work includes site visits for risk assessment. Also, the results of a survey conducted to determine the probability of infestation of zebra mussels will be used in the risk assessment of the sites. The survey will include environmental parameters, the distance to the nearest known infestation, habitat suitability, public use, and operations and maintenance.



Funding for these activities was provided by Great Plains Region, Reclamation Water Research Project (EE025) "Biological Control of Mollusks" and Reclamation's Program Analysis Office. Assistance from Dr. James Schooley and the cooperators with the Arbuckle Master Conservancy District (Davis, OK), Central Oklahoma Master Conservancy District (Norman, OK), Foss Reservoir Master Conservancy District (Foss, OK), Lugert-Altus Irrigation District (Altus, OK), McGee Creek Authority (Atoka, OK) is greatly appreciated.

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