 |
Thursday, June 7, 2007 - 9:00 AM
338
Light in Rivers: Hydrogeomorphic Controls and Spatial Trends
Jason P. Julian1, Martin W. Doyle1, and Emily H. Stanley2. (1) Department of Geography, University of North Carolina, 205 Saunders Hall, CB# 3220, Chapel Hill, NC 27599-3220, (2) Center for Limnology, University of Wisconsin, 680 N. Park St., Madison, WI 53706
Light is vital to the dynamics of aquatic ecosystems. It drives photosynthesis and photochemical reactions, affects thermal structure, and influences the behavior of aquatic biota. While the influence of hydrology and geomorphology on other ecosystem-limiting factors have been well studied (e.g., habitat, nutrient cycling), the more fundamental limitation of light availability has received much less attention. Here we present a benthic light availability model (BLAM) that predicts photosynthetically active radiation at the riverbed (Ebed) by quantifying light attenuation of the five hydrogeomorphic controls that dictate riverine light availability: topography, riparian vegetation, channel geometry, optical water quality, and hydrologic regime. We used BLAM to characterize longitudinal trends of Ebed in three rivers: Deep River, NC – a large turbid river; Big Spring Creek, WI – a small optically-clear stream; and along the entire 190 km of the Baraboo River, WI. We found that channel orientation alone can cause a 20% change in Ebed. Finally, we provide an example of the feedbacks between hydrogeomorphology and light availability by demonstrating how spatio-temporal changes in light-limited aquatic macrophytes influence a river’s hydrology (via a 35% increase in water depth) and geomorphology (via a 250% increase in sediment depth).