ASSESSING THE RELATIONSHIPS AMONG NUTRIENTS, ALGAL PRODUCTION, AND THE BIOLOGICAL INTEGRITY OF STREAMS ALONG AN URBAN GRADIENT IN THE EASTERN CORNBELT PLAINS, OHIO, USA.

J.A. Hambrook and J. Funk. U.S. Geological Survey, 6480 Doubletree Avenue, Columbus, Ohio 43229-1111

To assess relationships among nutrients, algal production, and the biological integrity of streams, quantitative periphyton and phytoplankton samples were collected from stream reaches in 30 small watersheds (drainage area 7.7 to180 km²) in southwestern Ohio, July 2001, along a gradient of urban land-use intensity (ULUI). Although neither periphyton or phytoplankton chlorophyll (Chl a) correlated significantly with ULUI, nitrogen (dissolved NO₂ plus NO₃ and ammonia plus organic nitrogen) was negatively correlated with ULUI. Phytoplankton Chl a) ranged from 0.5 ug L^-1 in an urban area to 43 ug L^-1 in an agricultural basin and correlated positively with canopy openness and daily ranges of dissolved oxygen (DO). Epilithic periphyton averaged 0-2 mm in thickness; epilithic Chl a) ranged from 2 mg m^-2 in an urban area to 142 mg m^-2 in an agricultural basin, correlating with nitrogen, daily DO maximums, the fish-community index of biotic integrity (IBI), and the number of EPT invertebrate taxa in qualitative samples. Light-extinction depths ranged from 1 to 8.4 m, correlating positively with open canopy and fish IBI but negatively with nitrogen. These relationships will be discussed in relation to the U.S. Environmental Protection Agency nutrient criteria proposed for this region as links for understanding stream invertebrate- and fish-community structure.