Grantee Research Project Results
2002 Progress Report: Assessing the Interactive Effects of Landscape, Climate, and UV Radiation on River Ecosystems: Modeling Transparency to UVR and the Response of Biota
EPA Grant Number: R829642Title: Assessing the Interactive Effects of Landscape, Climate, and UV Radiation on River Ecosystems: Modeling Transparency to UVR and the Response of Biota
Investigators: Morris, Donald P. , Williamson, Craig E. , Pazzaglia, Frank J. , Weisman, Richard N. , Hargreaves, Bruce R.
Institution: Lehigh University
EPA Project Officer: Packard, Benjamin H
Project Period: July 30, 2002 through July 29, 2006
Project Period Covered by this Report: July 30, 2002 through July 29, 2003
Project Amount: $825,850
RFA: Assessing the Consequences of Global Change for Aquatic Ecosystems: Climate, Land Use, and UV Radiation (2001) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration , Water , Climate Change
Objective:
Climate influences the transparency of lotic ecosystems through rain-mediated transfer of ultraviolet (UV)-attenuating substances from watershed to water, and solar radiation-mediated photochemical reactions of some of these substances. Land cover also affects the transfer of water, along with UV-attenuating substances, into streams and rivers. Forests control erosion of sediments; wetlands release dissolved organic matter; and human development of land for agriculture, roads, and buildings tends to increase storm runoff at the expense of groundwater recharge. Two factors control the biotic effects of UV radiation (UVR) in aquatic ecosystems: exposure to UVR, and physiological resistance mechanisms.
The objective of this research project is to determine how current watershed and river properties (including land use and land cover) interact with climate and solar radiation to determine current UV exposure, and how living organisms have adapted to survive this UV exposure. An additional goal is to establish the tolerance or susceptibility of macroinvertebrates to UVR exposure and how this may be modified by temperature and oxygen. Only by understanding present interactions under a range of conditions can we hope to predict the response of aquatic ecosystems to future change, including anticipated increases in extreme weather conditions and increases in UV-B associated with ozone destruction in the stratosphere.
Progress Summary:
Research in Year 1 of the project focused on three main areas: (1) environmental regulation of the UV environment of streams and rivers in the Lehigh River Watershed; (2) in-stream processes that may regulate water column transparency; and (3) response of macroinvertebrates to UVR.
The UV environment of streams and rivers is principally determined by water column transparency, channel depth, and the presence of riparian canopy. Each of these factors can be influenced by climate change and anthropogenic factors that operate on a watershed scale. Transparency is directly regulated by concentrations of chromophoric DOM (CDOM) and suspended sediments that absorb UVR. During Year 1 of the project, we have initiated a watershed-wide sampling program designed to document seasonal and storm event-mediated changes in UVR transparency in the main stem and major tributaries of the Lehigh River. We also have initiated a similar study of small watersheds (mostly first order streams) encompassing largely homogeneous land uses and landscapes. Both the large- and small-scale approaches will provide effective means of modeling transparency based on landscape/land use characteristics of individual watersheds.
The presence of a riparian forest canopy can significantly reduce the exposure of streams to solar UVR. During Year 1, we began investigating how canopy architecture influences UV exposure. We have found that canopy gap measurements can be related to incident UVR, and we have begun to develop a relationship between stream order and canopy gap. Investigations are continuing into the role of reach orientation (relative to the solar track) in modeling incident radiation through a riparian canopy. We also have made progress in our attempts to develop an overall model to relate incident UVR to topographic and riparian features of the watershed. Our approach has been based on a modification of the SHADE model originally designed to model temperature from solar radiation.
Because the UV environment of streams is influenced by channel depth, suspended sediment, and CDOM concentration, an important component of our research has been related to the fluvial geomorphology of our watersheds. This work has focused on understanding how channel form and process impacts the UV environment of organisms and how the amount and timing of discharges influences the amount and optical nature of CDOM and suspended sediments. Each of these factors can be influenced by climate change (e.g., precipitation) and anthropogenic influences (e.g., land use) that operate on a watershed scale.
Processes occurring within the channel, such as photobleaching or microbial processing of CDOM, can influence water column transparency in lotic environments. We have developed a method of assessing photobleaching potential of CDOM (photobleaching rate constant, k) and we are documenting its seasonal variability and environmental regulation. We also have utilized a plug flow bioreactor system to study how microbial processing and photobleaching interact to influence optical properties of CDOM.
Assessing the potential influence of UVR on macroinvertebrate communities is an important component of our study. Laboratory exposures have been conducted on a number of common macroinvertebrate groups using our phototron system. The lethal dose of UVR was found to vary by a factor of two across these taxonomic groups and little evidence has been found for photoenzymatic repair.
Future Activities:
Future activities will investigate susceptibility to UVR across more taxonomic groups. We also will investigate the possibility that macroinvertebrate populations are variability-adapted to different UV environments.
Journal Articles:
No journal articles submitted with this report: View all 37 publications for this projectSupplemental Keywords:
climate influences, ultraviolet, UV, ultraviolet radiation, UVR, land use, land cover, climate, solar radiation, ozone, photobleaching, chromophoric dissolved organic matter, CDOM., RFA, Air, Scientific Discipline, Geographic Area, Water, Ecological Risk Assessment, EPA Region, State, Watersheds, Wet Weather Flows, climate change, Water & Watershed, Environmental Monitoring, urban runoff, hydrologic models, vulnerability assessment, Global Climate Change, solar radiation, water quality, global change, aquatic ecology, aquatic food web, climate models, climate variability, land and water resources, regional hydrologic vulnerability, vegetation models, hydrology, Region 5, UV radiation, wetlands, land use, ecological research, Lake Superior, storm water, dissolved organic matter, aquatic ecosystems, Michigan (MI), land management, hydrologic dynamics, stormwater runoff, water resourcesProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.