SS4.10 Interdisciplinary Contributions to the Maintenance of the Integrity of Aquatic Ecosystems
Date: Tuesday, June 11, 2002
Time: 4:00:00 PM
Location: Colwood
 
LelandHV, Water Resources Div., U.S. Geological Survey, Boulder, Colorado, USA, hvleland@usgs.gov
Frey, J, W, Water Resources Div.,U.S. Geological Survey, Indianapolis, Indiana, USA, jwfrey@usgs.gov
Mueller, D, K, Water Resources Div., U.S. Geological Survey, Denver, Colorado, USA, mueller@usgs.gov
 
PHYTOPLANKTON GROWTH AND ASSEMBLY IN RELATION TO NUTRIENT SUPPLY AND OTHER ENVIRONMENTAL FACTORS IN THE WHITE RIVER, INDIANA
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The White River drains two equivalent-sized major subbasins (totaling 29,400 km2) that differ substantially in geology, land use and degree of flow regulation. The West Fork is highly regulated and its soils are primarily of glacial origin, whereas the East Fork is largely unregulated and more of the subbasin is defined by its bedrock geology. Net gains and losses in algal biomass in relation to nutrient loadings (N, P, SiO2) were determined for major segments of both forks during periods of low flow (winter and summer) in order to determine origins and amounts of major nutrients that contribute to increased algal production. Reactive P and inorganic N varied seasonally in the West Fork as constraints on growth and assembly of species, while silica concentrations declined in late-summer to levels (<0.3 mg/L SiO2) indicative of growth limitation. The spring phytoplankton in downstream segments of both forks was dominated (in biomass) by pennate diatoms (Naviculales). In contrast, summer and autumn assemblages were dominated by chlorophytes (Chlorococcales). Centric diatoms (Thalassiosirales) were generally abundant only in nutrient-enriched segments of the West Fork. Patterns in community structure indicated that assembly of the phytoplankton was constrained by nutrient supply as well as by light and flow regime.