Eos,Vol. 81, No. 36, September 5,2000

Scientists Outline Recent Findings About Pollution in Chesapeake Bay

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The Chesapeake Bay on the US. mid-Atlantic coast has changed somewhat since Captain John Smith explored the region in the early 1600s, and the Powhatan Native Americans referred to the waters as Chesepiooc, the Great Shellfish Bay

For one thing, about 15 million people now live near this estuary, the largest in the United States, which measures about 320 kilometers in length and 50 kilometers across at its widest point. In addition, while the estuary is not considered to be as dirty now as it was several decades ago, a number of probl e m s including nonpoint source pollution still affect the waters and stress some populations of native species, such as blue crabs.

In its most recent State of the Bay report from 1999, the nonprofit Chesapeake Bay Foundation rated the estuarys health at 28, up one point from the previous year, but still not comparable to the 100 mark for John Smiths pristine eyeful.

Going for 100 is an admirable goal, though not one that she anticipates seeing in her lifetime, said Cathleen Hapeman, a supervisory research chemist with the U.S. Department of Agricultures (USDA) environmental chemistry laboratory

Hapeman participated in an August 23 panel discussion by government and university experts about pollution and the bay that included an examination of effects of agricul­ture runoff, animal by-products, and pesticides.

The panel, held in conjunction with the Amer­ican Chemical Society annual meeting in Wash­ington, D.C., included an examination of endocrine disruptions hot topic that hypothe­sises that chemicals present in the environ­ment can interact with endocrine systems and cause a variety of adverse health effects.

Over a dozen U.S. federal agencies are exam­ining the issue, and one of the researchers is Anthony Pait of the National Oceanic and Atmospheric Administrations (NOAA) Center for Coastal Monitoring and Assessment. Pait

provided results of his study of potential endocrine disruption in a common Chesapeake Bay fish species the killifish Fun-dulus heteroclitus. The study was conducted to assess the sensitivity of the fish to endocrine disruptors,and also to determine whether such disruptors are common in the bay and may be related to pollution runoff from agricultural fields and other land use issues.

Pait, who is completing a review of the sci­entific literature about studies of endocrine disruption in fish,said that a number of con­taminants can inhibit biological systems, including certain polycyclic aromatic hydro­carbons (PAHs),polychlorinated biphenyls (PCBs),and pesticides.

Recent work in Great Britain has indicated concerns about endocrine disruption in some fish species, he said. However, in his study, Pait was unable to find any significant problems affecting the killifish.

Conducting examinations of gonadal anom­alies in male fish, male/female ratios, and population sizes, Pait found practically no evidence of endocrine disruption. He did find somewhat increased levels of the plasma vitellogenin (an egg protein) in some male fish, and does not yet know if that is reason for concern or if there is a baseline for that protein in certain fish.

This provides an indication that endocrine disruption in the Chesapeake may not be a very severe problem, said Pait, noting that it is a problem that affects fish in some other water bodies. The result, he added, does not say the Chesapeake is clean and there are no problems. He said it would be useful to moni­tor other fish in the Chesapeake, and also to monitor fish in other coastal U.S. regions.

Wayne Robarge,a professor of soil science at North Carolina State University, has conducted studies of ammonia emissions from swine pro­duction. He said that not only are these emis­sions substantial, but that long-range transport of ammonia is likely depositing the ammonia in

water bodies up and down the eastern seaboard, including in Chesapeake Bay Robarge said the 18 million swine produced annually in his state create a $3-billion industry and possibly emit 60,000 80,000 tons of ammonia annually

Despite the significant economic significance of the industry the state legislature has placed a moratorium on new swine operations because of concerns about the generation of substantial amounts of emissions.

Robarge, however, expressed some concern about whether scientists at this point have enough information to know how to regulate the industry or how much it should be regulated.

In terms of the actual impact on the envi­ronment, Robarge said, I think the science is a long way from understanding that. Thats the dilemma. Certainly, people directly impacted financially would like us to wait. And there are other sides that would like us to proceed with regulation. My concern as a sci­entist is that we are still not at the point at which we would recommend an amount to cut, in terms of emissions. I am not confident that we know exactly what impact that is going to have on the environment.

Other scientists on the panel discussed the effects of chlorpyrifos, a common pesticide recently banned by the U.S. Environmental Pro­tection Agency; the impact to the bays marine life from runoff from copper-based pesticides; and even organic mulching techniques.

Hapeman of USDA presented research indi­cating that a mulch of hairy vetch not only is a clean way to introduce nutrients into the soil, but also minimizes the use of pesticides and the amount of pesticides and sediment that run off into the bay

Our goal here is that if we can get a good handle on how pollution arrives at the estuar­ies, we can begin to develop methodologies to ensure that pollution does not happen, she said. We want to have a clean environment, and we cannot do it unless we understand the processes that are going on.

For further information about the bay, visit the Web site of the Chesapeake Bay Foundation at http://www.cbf.org.

Randy Showstack, Staff Writer

Investigations Unveil Holocene Thrusting for Onshore Portugal

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A current paleoseismological investigation of the Lower Tagus Valley (LTV), near Lisbon, Portu­gal, brought to light unprecedented information about the seismotectonics of this area of impor­tant onshore intraplate seismicity Through a combination of geomorphic, geological, and geophysical tools, a site with evidence for recent deformation was tracked down and selected for detailed study Upon trenching, a very clear exposure of a thrust fault can be observed. Its last episode of deformation was constrained with carbon 14 to postdate A. D. 365.

Although the city of Lisbon is a regular presence in seismology textbooks (in connec­tion with its devastation by a very large offshore earthquake and tsunami in 1755),very little men­tion is made of the onshore intraplate seismicity that has affected the LTV throughout historical times.

The Vila Franca earthquake of 1531, the Setubal earthquake of 1858, and the Benavente earthquake of 1909 are the best documented examples of such destructive onshore events. They occurred within 50 km of Lisbon, with mag­nitudes ranging from M6.5 to M7.0 according to several authors [e.g.,Moreira, 1985],thus posing

in their own right a serious threat to this highly developed area.

Why then, has this seismicity remained so obscure? We believe that this is a result of the widely adopted view that intraplate earth-quakes are diffuse and difficult to associate with specific faults, making their study less appealing. Howev­er, our research shows that field investigations with the use of a paleoseismological and active tectonics approach, as applied in intraplate Europe [Meghraoui etai, 2000], can be effective for the seismic source identification in the LTV

Tectonics of Southwest Portugal

The LTV is the southeast boundary of the Lusi-tanian Basin, an aborted rift left behind in the western Iberian margin during the early attempts of inception of the North Atlantic in the Triassic.

Eos,Vol. 81, No. 36, September 5, 2000

9.0°W

QUATERNARY

TERTIARY

C R E T A C E O U S A N D J U R A S S I C

PALEOZOIC

Fig. 1. Simplified geological map of the Lower Tagus Valley and surrounding region. The locations of the trenches where Holocene thrusting was observed are marked with stars (sites VCO and VF). The intensity data refer to the 1531 Vila Fran­ca earthquake, following Justo and Salwa [1998J. Figure 2 corresponds to site VCO. The dashed polygon indicates the area currently under study

The location of this rift was probably determined by the reuse of large Late Hercynean crustal frac­tures. Following a short-lived normal passive mar­gin evolution in the Jurassic, the same inherited weaknesses were responsible for a complex tec­tonic evolution of the basin, which included important episodes of structural inversion in response to the Alpine convergence. Across the Tagus Valley the landscape changes drastically from mountain ranges of Jurassic limestone in the northwest, to the flat terrigenous fill of a Cenozoic depression the Lower Tagus Basin in the southeast.

The Lusitanian Basin aborted rift is the most active seismic region of mainland Portugal, and the large historical earthquakes can be assigned unequivocally to its southeast edge, the LTV (Figure 1). It is little surprise that classical as well as modern studies [e.g.,Fonseca and Long,

Cabral, 1995] proposed the existence of a major crustal fracture along the river valley How­ever, despite its relevance to the assessment of seismic hazard, major ambiguities have subsisted until now.The neotectonic map of Portugal [Ribeiro and Cabral, 1988] proposes an active fault of unknown dip along the Tagus River, but the conclusion is based on an interpreted linea­ment of satellite imagery and Cabral [1995] pro­vided no evidence of surface faulting during the Quaternary

Evidence for Holocene Thrusting, Lower Tagus Valley

Our study focused on the right-hand side of the LTV (Figure l),and indicated recent thrust activity the main evidence being provided by displacement of drainage, terrace uplifting, intense deformation, and the presence of a scarp for a length of at least 20 km. Guided by these observations, we selected a site where two

trenches were excavated (parallel and perpendi­cular to the main scarp), reaching a maximum depth of 3 m.The deformation observed in the trenches (Figure 2) shows thrust planes dipping toward the northwest, and affecting sediments containing pottery fragments. Carbon 14 dating of a clay colluvium cut by one of the fault planes yielded A. D. 365 655 (2-sigma calibrated age). In one of the thrust planes, a minimum dis­placement of ~3 m during the last 4000 years is needed to account for the observed deforma-tion.The thrust geometry shows a significant left-lateral component, highlighted by abundant north-south striations. The latter indicate a north-south local direction of maximum compression, instead of the northwest-southeast direction usu­ally adopted for western Portugal.

Holocene thrusting was also observed at a second site 30 km toward the south-southwest, along the strike of the LTV, where a buried paleosoil of age 5995 5825 B.C. was affected by faulting. At this site the thrust was cut by a transverse strike-slip fault, which displayed the most recent activity

The intensity data for the 1531 Vila Franca earthquake (Figure l),one of the largest to affect the L W region [Justo and Salwa, 1998], strongly suggest that the structure now discovered was the source of that event. The location of the second site described above is only 20 km north of the urban limits of Lisbon, and -15 km to the west of the largest intensities (MM IX) of the Benavente earthquake of 1909 [Moreira, 1985]. Geomorpho-logical observations even closer to Lisbon indi­cate a possible continuation of the active fault in the direction of the Portuguese capital.

We expect the current research to have great impact on the seismic hazard assessment of Lis­bon, through a better estimate of return periods and magnitudes for large intraplate earthquakes in the surrounding region, and reliable modeling of the seismic source.The current results also

indicate the validity of the approach to regions of similar tectonic setting,such as eastern North America.

Acknowledgments The paleoseismological study of the Lower

Tagus Valley is supported by Funda a o para a CiQBncia e Tecnologia (FCT), Lisbon (Programme PRAXIS XXI), and the European Center for Geodynamics and Seismology.

Authors Joao FB. D. Fonseca, Vittorio Bosi, and Susana P Vilanova, Earthquake Engineering and Seis­mology Division, ICIST, Instituto Superior Tec-nico, Lisbon, Portugal (Bosi is on leave from Servizio Sismico Nazionale, Rome, Italy); and Mustapha Meghraoui, Ecole et Observatoire des Sciences de la Terre, Institut de Physique du Globe de Strasbourg, Strasbourg, France

References

Cabral, J.,Neotect nica de Portugal Continental, Mem rias-NovaS0rie, vol. 31, Instituto Geol gico e Mineiro, Lisbon, 1995.

Fonseca, J. FB.D. and R.E.Long,Seismotectonics of SW Iberia: A distributed plate margin?, in Seismicity, Seis-motectonics and Seismic Risk of the Ibero-Maghrebian RegionJMezcua and A.Ud as (Eds.),Monografia no. 8, Instituto Geogr^Efico Nacional, Madrid, 1991.

Justo, J. L , and Salwa, C.,The 1531 Lisbon earthquake, Bulletin of the Seismological Society of America, 88,2, 1998.

Meghraoui, M.,T. Camelbeeck, K.Vanneste, M. Brondeel, and D.Jongmans, Active faulting and palaeoseismology along the Bree fault, lower Rhine graben, Belgium, J Geophys. Res. ,105,13809 13841, 2000.

Moreira,VM.,Seismotectonics of Portugal and its adja­cent area in the Atlantic, Tectonophysics, 77 7,85 96, 1985.

Ribeiro, A , and J. Cabral, Mapa neotect nico de Portu­gal, Ed. Servi os Geol gicos de Portugal, Lisbon, 1988.

Fig. 2. General view of the VCO trenches, showing the location and ages of the dated samples in relation to the fault planes. In the upper left corner, the strike-parallel trench shows Holocene buried paleosoils of different ages overthrust by Upper Pliocene-Lower Pliocene clay. In the bottom and to the right, the strike-perpendicular trench displays several thrust planes cutting Holocene deposits. Original color image appears at the back of this volume.

Eos,Vol. 81, No. 36, September 5,2000

Fig. 2. General view of the VCO trenches. showing the location and ages of the dated samples in relation to the mult planes. In the upper left corner,lhe strike-parallel trench shows Holocene buried paleosoils of different ages overthrust by Upper Pliocene-Lower Pliocene c1ay./n the bottom and to the right, the strike-perpendicular trench displays several thrust planes culling Holocene deposits.

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