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SOLAR ULTRAVIOLET RADIATION AND AQUATIC CARBON, NITROGEN, SULFUR AND METALS CYCLES
Citation:
Zepp, R G. SOLAR ULTRAVIOLET RADIATION AND AQUATIC CARBON, NITROGEN, SULFUR AND METALS CYCLES. Chapter 5, E.W. Helbling and H. Zagarese (ed.), UV Effects in Aquatic Organisms and Ecosystems. Royal Society of Chemistry, Cambridge, Uk, , 137-183, (2003).
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
Solar ultraviolet radiation (290-400 nm) has a wide-ranging impact on biological and chemical processes that affect the cycling of elements in aquatic environments. This chapter uses recent field and laboratory observations along with models to assess these impacts on carbon, nitrogen, sulfur and metals cycles. Much emphasis is placed on the interactions of LJV radiation with carbon capture and storage, decomposition, and trace gas exchange. UV exposure generally inhibits phytoplankton photosynthesis and also affects microbial processes both through direct inhibition of bacterial activity as well as through effects on the biological availability of carbon and nitrogen substrates. One important aspect of LJV interactions with carbon cycling involves the formation and decomposition of UV-absorbing organic matter, principally chromophoric dissolved organic matter (CDOM). CDOM controls UV exposure in the sea in many freshwater environments and it can be directly photodecomposed to dissolved inorganic carbon, carbon monoxide, and various carbonyl-containing compounds. UV can potentially affect nitrogen and sulfur cycling in a variety of ways including alterations in nitrogen fixation, effects on the biological availability of dissolved organic nitrogen, UV photoinhibition of organisms such as bacterioplankton and zooplankton that affect sources and sinks of dimethylsulfide (DMS) and UV-initiated photoreactions that oxidize DMS and produce carbonyl sulfide. Metal cycling also interacts in many ways with UV radiation via photoinhibition of microbial redox cycling, direct photoreactions of dissolved metal complexes and of metal oxides and indirect reactions that are mediated by photochemically-produced reactive oxygen species (ROS). Photoreactions can affect the biological availability of essential trace nutrients such as iron and manganese, transforming the metals from complexes that are not readily assimilated to free metal ions or metal hydroxides that are available.