impacts of human activities and the changing face of 

 landscapes. 



Recent depletion of stratospheric ozone has increased the 

 penetration of ultraviolet (UV) solar radiation to the Earth's 

 surface. Measuring the intensity and ecological effects of UV 

 radiation is the focus of SERC's photobiology laboratory, 

 directed by Dr. Patrick Neale. Working in the Rhode River 

 and in Antarctica (where the world's largest increases in UV 

 were found), SERC made a number of new discoveries this 

 year. Year-round studies at the Rhode River were the first to 

 measure the seasonal variation of UV sensitivity in marine 

 phytoplankton. Related research showed that species of 

 planktonic dinoflagellates produce UV-absorbing compounds 

 that protect their photosynthetic systems from UV damage 

 and that UV inhibition of photosynthesis is continuously com- 

 pensated by repair processes. Studies in Antarctica revealed 

 that UV has greater effects on enzymes of carbon assimilation 

 than on photosynthetic photochemistry for McMurdo Sound 

 diatoms. Observations from the Weddell-Scotia Sea (An- 

 tarctica) showed that UV sensitivity is correlated with 

 hydrographic characteristics (deeper mixed diatoms are more 

 sensitive to UV). Models of the effects of ozone depletion on 

 the productivity of Weddell-Scotia Sea under varying mixing 

 conditions showed that the greatest loss of productivity (on an 

 areal basis) is when there is a moderate amount of mixing 

 (mixing depth is comparable to light penetration depth). 

 During 1997 SERC also initiated the first study of UV effects 

 on photosynthesis in Arctic kelp species. SERC continued to 

 advance the development of instruments to monitor changes 

 in UV radiation throughout the world. SERC completed con- 

 struction of II 18-channel (SR-18) UV-B spectroradiometers 

 and, jointly with the National Institute of Standards and 

 Testing, set up a three-site UV-monitoring network to sup- 

 port studies of solar UV degradation of materials. SERC also 

 measured UV spectral transmission in Chesapeake Bay and 

 Indian River Lagoon, Florida. 



Increases in atmospheric carbon dioxide are expected to 

 cause unprecedented changes in climate and ecosystems 

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

 established a site at the Kennedy Space Center for the study of 

 the effects of elevated CO : on a scrub-oak ecosystem. Sixteen 

 large open-top chambers enclose sections of forest allowing 

 experimental enrichment of CO : concentrations. Preliminary 

 results indicate that elevated CCK increases photosynthesis, 

 root and shoot growth, and soil water content. In addition, 

 vegetation grown under elevated CO : is less nutritious for 

 herbivorous insects. SERC has also obtained continued fund- 

 ing to determine the fate of carbon accumulating in a salt 

 marsh as a result of long-term experimental exposure to 

 elevated CO*. 



Nonindigenous species are invading the world's coastal 

 waters at accelerating rates due to transport of marine or- 

 ganisms in ballast water of cargo ships. Such invasions may 

 have devastating ecological consequences. SERC's Invasions 

 Biology Program, headed by Drs. Gregory Ruiz and Anson 



"Tuck" Hines, is comparing the patterns and impacts of 

 species introductions in coastal ecosystems in the Chesapeake 

 Bay, Florida, central California, and Alaska. SERC samples 

 marine organisms in the ballast water of ships arriving to the 

 Chesapeake Bay and Prince William Sound (Alaska) and 

 studies patterns of species invasions in both sites. In addition, 

 SERC has implemented a national program with the U.S. 

 Coast Guard that will survey every vessel arriving to each U.S. 

 port from a foreign port to determine the amount of ballast 

 water they deliver and whether they have undergone oceanic 

 exchange to reduce the density of alien coastal organisms. 

 This will continue for two to five years and will provide a 

 direct measure of ballast water supply and changes over time 

 to every pore system in the country — upon this background, 

 SERC plans to test for changes in the rates of invasion at mul- 

 tiple sites. Another collaborative project measures the effects 

 of the recent European green crab invasion on native biota in 

 Australia. This will be compared directly to similar ongoing 

 SERC studies of invasions by this crab in California and 

 Massachusetts. 



Mainly through agriculture, humans have drastically in- 

 creased the availability of the plant nutrients nitrogen and 

 phosphorus. This has led to increased discharge of nutrients 

 into coastal waters causing excessive growth of phytoplankton 

 with deleterious effects on coastal ecosystems. In the 

 Chesapeake Bay, excessive phytoplankton production con- 

 tributed to the death of submersed aquatic vegetation and the 

 depletion of dissolved oxygen. In addition, recent outbreaks of 

 toxic plankton such as Pftesreria in Chesapeake Bay may have 

 been fostered by elevated nutrient levels. SERC scientists 

 Drs. Thomas Jordan, Donald Weller, and David Correll are 

 investigating the factors that control discharge of nutrients 

 from watersheds in different physiographic provinces through- 

 out the Chesapeake Bay drainage basin. Nitrogen discharge 

 increases with the proportion of cropland in the watershed. 

 However, the study also revealed the importance of the charac- 

 teristics of water flow from the watershed. Watersheds with 

 steady flowing streams, indicating a dominance of 

 groundwater flow, tend to release more nitrate and less or- 

 ganic nitrogen and organic carbon than do watersheds where 

 stream flow is more uneven. This finding provides a basis for 

 predicting the nutrient releases by watersheds and suggests 

 the importance of soil permeability. Nutrient releases may be 

 intercepted by riparian (streamside) forests or wetlands. 

 Another study by Jordan, Weller, and Correll is investigating 

 whether uptake of nitrogen in riparian forests is due to the ac- 

 tion of soil bacteria that convert nitrogen to gaseous forms 

 that are released to the atmosphere. Yet another study by 

 Drs. Dennis Whigham and Thomas Jordan measures uptake 

 of nitrogen and phosphorus by restored wetlands that capture 

 runoff from crop fields. These studies are very relevant to land 

 use planning aimed at reducing nutrient pollution. 



SERC's home research site on the Rhode River is being 

 used as a model system for investigating the responses of 

 phytoplankton to nutrient releases from the watershed. 



7° 



