origin than any other porr system on the Atlantic of Pacific 

 coasts. 



The invasion biology program involves extensive collabora- 

 tion, most recently with the U.S. Coast Guard to establish the 

 National Ballast Water Information Clearinghouse at SERC. 

 As an integral part of the national effort to prevent and con- 

 trol coastal invasions, the clearinghouse will measure the 

 changing patterns of ballast water delivery and management 

 by ships arriving in all U.S. ports from overseas. SERC scien- 

 tists synthesize the national data on ballast water delivery pat- 

 terns and relate these patterns to invasions by alien species in 

 coastal ecosystems. 



Several SERC projects are exploring the ctitical role of 

 forests in the nitrogen cycle. In many pans of the world, 

 forests are becoming nitrogen-saturated, losing their ability to 

 absorb nitrogenous pollutants deposited from the atmosphere. 

 Research directed by Dr. David Correll measured atmospheric 

 nitrogen deposition and nitrogen discharges from an old- 

 growth deciduous hardwood forest for 20 years. The measure- 

 ments indicate that the forest still rerains 85 percent of its 

 atmospheric inputs of total nitrogen. Moreover, SERC's broad 

 survey of subwatersheds throughout the Chesapeake Bay 

 drainage basin showed that nitrate concentrations in streams 

 draining forested subwatersheds were very low, suggesting 

 that nitrogen saturation of forests is not yet a widespread prob- 

 lem in the Chesapeake Bay watershed. 



SERC studies were among the first to show that riparian 

 (srreamside) forests can intercept nitrogen released from adja- 

 cent croplands and thereby protect streams and estuaries from 

 nitrogen pollurion. Recenrly Dr. Donald Weller of SERC 

 developed heuristic models to predict the effects of spatial 

 arrangements of riparian forests on nutrient discharge from 

 complex landscapes. The simple mathematical relationships 

 can be used extrapolate results to broader landscapes. 



Nitrogen taken up in riparian forests can be converted to 

 gases, including nitrous oxide, which is increasing in the atmos- 

 phere and contributes to global warming and the destruction of 

 stratospheric ozone. One SERC project, directed by Dr. Thomas 

 Jordan, studied nitrous oxide releases from riparian forest soil. 

 Emitted nitrous oxide was sampled with tent-like chambers and 

 analyzed with a unique laser spectrophotometer. Less than 1 per- 

 cent of the nitrogen taken up by the forest was converted to 

 nitrous oxide. Nitrous oxide releases were limited by the supply 

 of soil moisture, nitrate, and organic carbon. 



Like riparian forests, wetlands can play a key role in reduc- 

 ing non-point nutrient runoff into Chesapeake Bay. SERC 

 scienrists, Drs. Dennis Whigham, Thomas Jordan, and 

 Donald Weller, together with collaborarors from the National 

 Resource Conservation Service and the Chesapeake Wildlife 

 Heritage, measured nurrient flow through wetlands that were 

 restored in agricultural watersheds. They found that the wet- 

 lands could trap high percentages of rhe nutrients they receive 

 from surrounding croplands while also providing important 

 wildlife habitats that enhance the species diversity in agricul- 

 tural landscapes. 



SERC continued the global expansion of its wetlands 

 research program. In collaboration with the National 

 Institute for Environmenral Srudies (Japan), and the 

 University of Utrecht (the Netherlands), SERC began 

 comparative studies of important bog and fen wetlands on 

 Honshu and Hokkaido in Japan. The five-year project will 

 focus on aspects of nutrient cycling and will be directed 

 toward helping Japan develop methods for assessing 

 wetland function. SERC scientists also completed editorial 

 work on a series of papers on nutrienr-use efficiency in 

 boreal, temperate, and tropical wetlands. SERC scientists 

 and Japanese collaborators from Kyoto University and 

 Tokyo Metropolitan University finished one of the first 

 studies in which seed transportation by water has been 

 shown to play a key role in the development of genetic 

 patterns in populations of a widespread wetland plant 

 species. 



A SERC srudy by Dr. Ilka Feller focused on mangrove 

 foresrs, the dominant coastal wetland type throughout the 

 tropics. Nutrient availability in mangrove werlands effects 

 internal nutrient cycling and nutrient conservation. Feller's 

 research showed that soil fertility can switch from nitrogen ro 

 phosphorus limitation across narrow ecotonal gradients in red 

 mangrove forests. Phosphorus limitation was found to be a 

 major factor responsible for the widespread occurrence of dwarf 

 mangrove forests in the Neotropics. Experimental increases in 

 nuttient availabiliry ro mangroves increased herbivory by 

 specialist herbivores but had no effect on generalist herbivores. 

 Feller has also discovered that herbivory by wood-boring 

 insects adds a major grazing step to the mangrove food web. 

 Previously, this food web has been assumed to be almost 

 exclusively detritus-based. Wood borers also modify canopy 

 architecture and create cavities in the wood that are used by 

 numerous other species. 



Increases in atmospheric carbon dioxide are expected to 

 cause unprecedented changes in climate and ecosystems 

 around che world. A SERC study directed by Dr. Bert Drake 

 is running two long-term field experiments to discover the 

 effects of projected increases in armospheric carbon dioxide. 

 In a Florida scrub-oak forest, increased carbon dioxide has 

 increased water-use efficiency, nitrogen fixation, and carbon 

 assimilation. In a Maryland salt marsh, a decade of exposure 

 to increased carbon dioxide has caused a persistent increase 

 carbon assimilation. A new study is now investigating the fate 

 of the extra carbon assimilated. 



Depletion of stratospheric ozone is increasing the penetra- 

 tion of harmful ultraviolet (UV-B) solar radiation ro the 

 Earth's surface. Measuring rhe intensity and ecological effects 

 of UV-B radiation is the focus of SERC's photobiology and 

 solar radiation laboratories, directed by Dr. Patrick Neale. 

 From October to December, 1997, Neale 's group traveled to 

 Palmer Station on the Antarctic peninsula for the first applica- 

 tion of methods developed at SERC to track the varying sen- 

 sitivity of phytoplankton to UV-B radiation, in particular to 

 the increase in UV-B during springtime ozone depletion. In 



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