The Center's three main buildings (77,000 square feet) house wet and dry laboratories, an aquaculture facility for rearing test organisms, and a library. Forty-five ponds ranging 0.01 to 0.5 acres, 13 outdoor raceways, a mesocosm facility, and indoor environmental chambers facilitate a variety of experimental studies with simulated field environments. The outdoor mesocosm facility, used for manipulative experiments in aquatic ecology, features controlled water retention, effluent sterilization and filtration, automated systems for water delivery (river water), temperature control, and remote communication linkage for data storage. A fleet of vessels is equipped for research on large rivers, wetlands, and inland lakes. A system of deionizers, tanks, and pumps provides large quantities of reconstituted water for aquatic studies in the laboratory.
Study sites have included Lake Pepin, a natural riverine lake on the Upper Mississippi River that extends about 75 to 110 km downstream from the Twin Cities (Minneapolis and St. Paul, Minnesota) metropolitan area. Analyses of cores from the downstream section of Lake Pepin showed that the historic accumulation of mercury, cadmium, and lead in these sediments has paralleled human population growth in the Twin Cities metropolitan area. Concentrations of these metals in deposited sediments have declined since the mid-1970s; however, sediment-accumulation rates have concomitantly increased, and the accumulation rates of these metals in the sediments have not diminished. Lake Pepin traps sediment, associated contaminants, and nutrients (McHenry et al. 1980; Rada et al. 1990; Maurer et al. 1995), reducing the transport of potentially harmful pollutants from the Twin Cities metropolitan area, the Minnesota River basin, and other upstream sources to the reach of river downstream from the lake. Concentrations of PCBs and certain metals in fish, burrowing mayflies, and fine-grained, bed sediments are generally greater in the reach from the Twin Cities through Lake Pepin than in the reach downstream from the lake (Bailey and Rada 1984; Steingraeber et al. 1994; Beauvais et al. 1995, Meade 1995). The lake lost 21% of its volume to sedimentation between 1897 and 1986 (Maurer et al. 1995), and it's sediment-trapping ability will diminish as it fills with sediment and loses volume.
During the past 3 years, we have also examined the stratigraphy and historic deposition of mercury in the Sudbury River (eastern Massachusetts), a system contaminated by wastes from a former industrial site. The most contaminated strata now lie buried under more recent deposits. In the reservoir nearest the industrial source, for example, the most contaminated sediments (41 to 44 ug Hg/g) were 6 to 12 cm deep. Surficial sediments (0-1 cm) were substantially contaminated at all downstream areas, with mercury concentrations about one-fourth to one-half those in the most-contaminated strata in most cores. 210Pb dating of the cores showed that the annual rates of mercury accumulation diminished in the most recently deposited strata (deposited in the 1990s) with increasing distance downstream from the industrial site; recent accumulation rates were 1.1, 0.57, and 0.18 ug Hg/cm2 per yr, respectively, at coring sites 3 km, 5 km, and about 30 km downstream from the industrial site. In reservoirs just downstream from the industrial site, mercury-accumulation rates have declined notably since industrial operations ceased in the 1970s and have diminished further since remediation at the site.
Nymphs of burrowing mayflies (Hexagenia) were exposed in 21-day bioaccumulation tests to surficial sediments (upper 4 to 6 cm) from contaminated and reference areas (treatments) in the basin. Tests included fine-grained sediments from reservoirs, flowing reaches, riparian wetlands, and a riverine lake. Mean concentrations of total mercury in test sediments ranged from 880 to 22,059 ng/g dry weight for contaminated areas and from 90 to 272 ng/g for reference areas. The accumulation in mayflies of methylmercury--the highly toxic form accumulated in fish and biomagnified in aquatic food chains--was unrelated to total mercury concentrations in sediments. Little methylmercury was produced from the large sedimentary inventories of inorganic mercury in the contaminated reservoirs, which had the most contaminated sediments. In contrast, methylmercury was actively produced in the lesser contaminated, wetland sediments. The mean final concentrations of methylmercury in test water and mayfly nymphs were greater in treatments with contaminated-wetland sediments than in treatments with contaminated sediments from reservoirs, flowing reaches, and a riverine lake. The survival of mayflies exceeded 90% and did not vary among treatments, whereas the growth of mayflies varied among treatments, but was unrelated to mercury exposure.
Toxic conditions in the sediment may have contributed to the recent, widespread declines of fingernail clams (Musculium transversum) in the Upper Mississippi River, which occurred largely during low-flow periods associated with drought (Wilson et al. 1995). Fingernail clams are very sensitive to un-ionized ammonia. The production of ammonia by microbial decomposition in the sediments is enhanced by high temperature and an abundant supply of biogenic matter, conditions associated with low flow and drought. Concentrations of un-ionized ammonia in sediment pore water may become high enough during such periods to adversely affect fingernail clams (Frazier et al. 1996).
The decline in submersed vegetation in the Upper Mississippi River in the late 1980s remains unexplained, but may involve sediments and nutrients. In addition, sediments in backwater areas where submersed vegetation has been lost are now more readily subjected to resuspension by wind-generated turbulence, which reduces light penetration and decreases the stability of bottom substrates for colonization by rooted plants. It is evident that the re-establishment and recovery of aquatic vegetation has been hindered by limited light availability in the river (Kimber et al. 1995; Owens and Crumpton 1995). Moreover, sedimentation is the primary long-term threat to many aquatic habitats in the impounded Upper Mississippi River.
The USGS has the multidisciplinary scientific capability and geographically distributed work force needed to address many complex questions concerning possible linkages of sedimentary, biogeochemical, and ecological processes to habitat degradation, declining flora and fauna, and human impacts in the Mississippi and other large river systems. In addition, the transport and biogeochemistry of nitrogen in the Mississippi River, including nitrogen transformations and their relation to toxic conditions in the sediment, are areas of much-needed research.
Beauvais, S. L., J. G. Wiener, and G. J. Atchison. 1995. Cadmium and mercury in sediment and burrowing mayfly nymphs (Hexagenia) in the Upper Mississippi River, USA. Arch. Environ. Contam. Toxicol. 28:178-183.
Frazier, B. E., T. J. Naimo, and M. B. Sandheinrich. 1996. Temporal and vertical distribution of total ammonia nitrogen and un-ionized ammonia nitrogen in sediment pore water from the Upper Mississippi River. Environ. Toxicol. Chem. 15:92-99.
Kimber, A., J. L. Owens, and W. G. Crumpton. 1995. Light availability and growth of wildcelery (Vallisneria americana) in Upper Mississippi River backwaters. Regulated Rivers--Res. Manage. 11:167-174.
Maurer, W. R., T. O. Claflin, R. G. Rada, and J. T. Rogala. 1995. Volume loss and mass balance for selected physicochemical constituents in Lake Pepin, Upper Mississippi River, USA. Regulated Rivers--Res. Manage. 11:175-184.
McHenry, J. R., J. C. Ritchie, and C. M. Cooper. 1980. Rates of recent sedimentation in Lake Pepin. Water Resour. Bull. 16:1049-1056.
Meade, R. H. (Editor) 1995. Contaminants in the Mississippi River, 1987-92. U.S. Geological Survey Circular 1133, Denver, Colorado. 140 pp.
Owens, J. L., and W. G. Crumpton. 1995. Primary production and light dynamics in an Upper Mississippi River backwater. Regulated Rivers--Res. Manage. 11:185-192.
Rada, R. G., J. G. Wiener, P. A. Bailey, and D. E. Powell. 1990. Recent influxes of metals into Lake Pepin, a natural lake on the Upper Mississippi River. Arch. Environ. Contam. Toxicol. 19:712-716.
Steingraeber, M. T., T. R. Schwartz, J. G. Wiener, and J. A. Lebo. 1994. Polychlorinated biphenyl congeners in emergent mayflies from the Upper Mississippi River. Environ. Sci. Technol. 28:707-714.
Wiener, J. G., C. R. Fremling, C. E. Korschgen, K. P. Kenow, E. M. Kirsch, S. J. Rogers, Y. Yin, and J. S. Sauer. In press. Mississippi River. In M. J. Mac, P. A. Opler, and P. D. Doran, eds. National Status and Trends Report. U.S. Geological Survey, Biological Resources Division, Washington, DC.
Wiener, J., T. Naimo, C. Korschgen, R. Dahlgren, J. Sauer, K. Lubinski, S. Rogers, and S. Brewer. 1995. Biota of the Upper Mississippi River ecosystem. Pages 236-239 in E. T. LaRoe, G. S. Farris, C. E. Puckett, P. D. Doran, and M. J. Mac, eds. Our Living Resources. U.S. Department of the Interior, National Biological Service Report, Washington, DC.
Wilson, D. M., T. J. Naimo, J. G. Wiener, R. V. Anderson, M. B. Sandheinrich, and R. E. Sparks. 1995. Declining populations of the fingernail clam Musculium transversum in the Upper Mississippi River. Hydrobiologia 304:209-220.
Autobiography:James G. Wiener (BRD, Upper Mississippi Science Center, P.O. Box 818, La Crosse, Wisconsin 54602) has worked as a scientist in the U.S. Department of Interior since 1979, mostly studying the fate, bioavailability, and effects of contaminants in freshwater ecosystems, with emphasis on mercury and cadmium. During 1979-1990, he was a fishery research biologist with the Midwest Science Center. In 1990, he became Leader of the Section of Aquatic Ecology at the Upper Mississippi Science Center, overseeing the section's research on riverine and aquatic ecology, ecotoxicology, and habitat restoration. Jim became Scientific Director at the Upper Mississippi Science Center in December 1996. Phone 608-783-6451, Fax 608-783-6066, E-mail firstname.lastname@example.org
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