This year SERC scientists published 35 research papers as a 

 result of a series of ongoing atmospheric, terrestrial, and 

 aquatic studies. Measurements were made of incident and 

 undersea spectral irradiance, especially of ultraviolet B wave- 

 lengths, over the Weddell-Scotia confluence in Antarctica dur- 

 ing the austral spring in October, 1993, during the transit of a 

 low ozone "hole". The intensity of the shortest wavelengths, 

 such as 304 nm, increased significantly. Such increased doses 

 of ultraviolet radiation were simulated on an oceanographic 

 research ship and natural phytoplankton, especially diatoms, 

 were exposed to test whether they were able to synthesize 

 ultraviolet-absorbing compounds as a defense mechanism. 

 Pigments such as mycosporine-like amino acids increased 

 and could help protect the diatoms from increased ultraviolet 

 radiation. 



SERC scientists have been conducting a long-term study of 

 the effects on plant communities ot elevated carbon dioxide con- 

 centrations, such as are anticipated to occur on Earth 50 years 

 from now. Respiration of C3 plants is strongly inhibited by ele- 

 vated carbon dioxide. This, in combination with increased photo- 

 synthesis, results in large increases in plant biomass. Studies of 

 these C3 plants have now shown that the mechanism of inhibi- 

 tion of respiration is a reduction in the concentration of cyto- 

 chrome c oxidase. Plants grown in elevared carbon dioxide also 

 had more non-structural carbohydrates and less nbulose bis- 

 phosphate carboxylase, a key enzyme for photosynthesis. Thus, 

 they had less photosynthetic capacity per weight of tissue, but 

 the whole plants still out-produced normal plants in ambient car- 

 bon dioxide concentrations. 



With concerns over the possible thinning of the strato- 

 spheric ozone layer and the resultant increase in ultraviolet-B 

 (UVB) radiation at the Earth's surface, SERC scientists con- 

 ducted studies of the relative penetration of UVB and white 

 light into hardwood deciduous forests. Under closed canopies, 

 mean UVB transmittance through the canopy was only I to 

 2% of incident radiation. This transmittance increased to 30% 

 during the leafless season. Vertically, the UVB radiation was 

 extinguished rapidly, with 40-70% absorbed by the top 25% 

 of the canopy. When compared with white light penetration, 

 UVB had a higher transmittance. 



Nitrogen is a key nutrient in receiving waters, such as Ches- 

 apeake Bay. When these waters receive to much nitrogen, 

 algae become to productive resulting in reduced levels of dis- 

 solved oxygen at night or in deep stratified layers of water. In 

 the case of Chesapeake Bay, much of the nitrogen inputs ar- 

 rive as nitrate, ammonium, and organic nitrogen dissolved in 

 rain water. SERC scientists have measured the volume and 

 nitrogen contents of each rainfall event for 20 years. Nitrate is 

 the most abundant nitrogen nutrient in the rain and its 

 delivery via the rain has more than doubled over this period. 

 Ammonium is the second most abundant and its delivery has 

 also more than doubled. Organic nitrogen delivery fluctuated 

 but declined, if anything, over this time period. 



SERC scientists also have conducted long-term studies of 

 how the rates of discharge of nutrients from subwatersheds of 



Chesapeake Bay vary with geology, land use, and variations in 

 weather. Nutrient concentrations were measured for 153 

 streams in various parts of the Coastal Plain, Piedmont, and 

 Appalachian physiographic regions. Concentrations of nitrate 

 were strongly related to land use within any one geologic re- 

 gion, with low concentrations in streams draining forested 

 lands and high concentrations in streams draining agricul- 

 tural lands. However, under conditions of similar land use, 

 concentrations of nitrate were much higher in Piedmont and 

 Appalachian streams than in Coastal Plain streams. This was 

 primarily due to the fact that groundwater draining Coastal 

 Plain streams has a relatively shallow trajectory, which allows 

 the vegetation in the stream riparian zone to intercept more 

 nitrate than in the other regions, where groundwater path- 

 ways are often to deep for plant roots to have an effect. 



Another study by SERC scientists found that agricultural 

 livestock populations in the Chesapeake Bay region release sig- 

 nificant concentrations of hormones into streams and the Bay. 

 An important source of estrogen in streams is chicken manure 

 that is spread on farm fields as fertilizer. Another source of es- 

 trogen and testosterone was sewage treatment plant effluent. 

 Testosterone was found in the streams during the growing sea- 

 son, but not during the rest of the year. Estrogen reaches the 

 streams by surface runoff during storms, while testosterone 

 reaches the streams in both groundwater and surface runoff. 



The blue crab is presently the most important fishery in 

 Chesapeake Bay. A better understanding of its biology and 

 ecology is fundamental to maintaining this species in the Bay. 

 SERC scientists use ultrasonic telemetry to study the behavior 

 of blue crabs in the turbid waters of the Bay. Although adults, 

 on average, move faster and stay in deeper water, both alter- 

 nate between periods of slow meandering movement with 

 faster, directionally-onented movement. Fertilized females mi- 

 grate long distances into high salinity areas near the mouth of 

 the Bay to incubate their eggs. They complete this migration 

 cycle only once per rwo to five year generation. Adult abun- 

 dance is determined by both recruitment and survival of juve- 

 nile crabs. Cannibalism by large blue crabs was the source of 

 75 to 97% of the mortality of juvenile crabs. By seeking ref- 

 uge in the shallows juveniles avoid some of this cannibalism. 



The European green crab has been introduced to the west 

 coast of North America with an initial population developing 

 in San Francisco Bay. SERC scientists have been monitoring 

 the expansion of the green crab range and the mechanisms of 

 expansion. These studies also show that this exotic crab is im- 

 pacting the populations of clams and amphipods in estuanne 

 habitats. 



The education program at SERC also had a successful year. 

 Many visiting groups took part in such activities as the Java 

 History Trail, the Discovery Trail, canoeing on the tidal creek, 

 and estuanne activities in the shoreline area. These groups in- 

 cluded handicapped, elderly, children, and minorities. SERC 

 also hosted a large number of workshops and educational out- 

 ings for teachers, administrators, and scientists. At SERC 

 these groups can combine meetings and lectures with seeing 



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