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The overall objective of the first area of this task is to develop biogeochemical measurement and modeling tools that contribute to quantitative relationships for assessing the consequences of land use changes on aquatic resources. The focus is on microbial indicators and related modeling development. Biogeochemical cycling mediated by soil microorganisms plays a major role in assessments of the relationship between land use changes and the movement of nutrients, organic matter and pollutants into aquatic resources. For example, microorganisms control the nature and amounts of biologically labile nitrogen that runoff from land into aquatic ecosystems. Microorganisms also control of the soil emissions of nitrogen oxides and carbon gases that affect air quality and global warming, and many other factors. Experimental research and models are required to evaluate these effects. Specific activities in this task include (1) assessing the utility of molecular tools (genetic, stable isotopic, PLFA) as indicators of the size, function, and functional capacity of microbial communities; (2) assessing the usefulness of geochemical measurements such as trace gas flux measurements, stable isotopic measurements, and laboratory incubations of potential mineralization rates as indices of ecosystem function.; (3) applying these indices in field studies (e.g. transects in ecoregion boundaries and/or ecotones in Mid-Atlantic) to determine how ecosystem function responds to climatic and land use changes; (4) developing relationships that can be used in models that describe how climate and land use changes affect ecosystem function and (5) developing a model that uses inputs from (1) - (4) and other factors for integrating and evaluating interactions of ecosystem function and biogeochemistry with climate and land use change. Our activities also will include contributions to an ORD report on potential effects of future land use on aquatic ecosystems.

The second area of this task will focus on development of approaches for assessing UV exposure and biogeochemical interactions in freshwater and coastal ecosystems. The initial phase of this project will focus on a case study in the Florida Keys, where extensive damage to coral reefs has occurred over the past few years. Current evidence indicates that a combination of global warming and UV exposure are playing a key role in the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab and at the Bodega Marine Lab, U. California-Davis (funded through a STAR agreement as part of Goal 8 research) to characterize UV exposure and effects at several coral reef sites. Our results indicate that warming and stratification of the water near the reefs results in much greater penetration of harmful UV radiation to the corals, thus enhancing UV damage. Other research will examine the interactions between UV-induced breakdown of refractory organic matter in coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-and carbon-containing substances that stimulate microbial activities. Activities also will include developing a report on UV interactions with U.S. aquatic ecosystems.

The third research area involves the development of models that can be used to assess interactions of global change with animal/plant and non-indigenous species distributions and land cover. This research includes the development of a model that can use present and future climate scenarios and projected land use changes to assess likely regional changes in plant and animal species in response to global change. This model will be used to help evaluate the influence of climate change on invasive non-indigenous species in U.S. aquatic environments.

Description:

A compelling aspect of the deterioration of coral reefs is the phenomenon of coral bleaching. Through interactions with other factors such as sedimentation, pollution, and bacterial infection, bleaching can impact large areas of a reef with limited recovery, and it might be induced by a variety of stressors including temperature and salinity extremes, and ultraviolet light. Under conditions of ocean warming, often associated with calm and stratified waters, photobleaching of UV-absorbing chromophoric dissolved organic matter (CDOM) is increased, and penetration of both UV-B. and UV-A is greatly enhanced. Indices of UV-specific effects in coral tissue are needed to test whether UV increases, associated with global climate change, are harmful to corals. To address this challenge, we have evaluated UV-specific effects in corals and have characterized factors that alter penetration of UV radiation over coral reefs. An immunoblotting assay was developed to examine UV-specific lesions (thymine dimers) in coral and zooxanthellae DNA. We observed dose-dependent increases of thymine dimers in coral (Porites porites var porites) exposed to artificial solar irradiance in a solar simulator, although effects were not strictly proportional. UV measurements were made in July 1999 at Eastern Sambo reef and nearby sites, including profiling along transects from reef to shore. Results of these analyses indicate that the coral at Eastern Sambo reef (at 34 meters) were receiving UV-B radiation that was equivalent to 25 to 30% of surface UV irradiance. However, the water just inside the reef in Hawk Channel (located closer to land) was considerably more opaque to UV. This water photobleached with loss of UV absorbance and fluorescence when it was exposed to simulated solar radiation. These results indicate that photobleaching of the DOM and transport of near-shore water out over the reefs might play a key role in controlling UV penetration to the reef surface.

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