9220886 Paerl The ability to fix atmospheric N2 in oxygenated N-limited surfaces waters should cyanobacteria (HC). Despite their periodic dominance in small freshwater impoundments however. HC are often conspicuously absent in chronic N-limited large lakes, estuaries and coastal waters; yet these waters generally exhibit N:P loading and concentration ratios favorable for HC N2 fixers. Excessive turbulence may prevent the establishment and dominance of heterocystous bloom forming taxi in wind and tide-exposed largewater bodies. The project will examine this ecological paradox by experimentally evaluating the relative roles large-scale vertical mixing and small-scale shear play in conrolling structural and consortial integrity, growth and bloom formation in natural and cultured HC populations. N-limited estuarine (Neuse River, NC), large lake (Tahoe, CA-NV) and coastal (Boque Sound, NC), support benthic but not planktonic N2 will serve as experimental field sites. We will utilize concentric cylndrical Couette vessels for evaluating the structural and growth impacts of small-scale shear regimes (representative of turbulent surface waters) on common HC species. %%% This work will elucidate environmental factors controlling N2 fixation and N-limitation on regional and global scales. Planktonic cyanobacteria contribute to primary production, entrophication, nitrogen availability and flux. This work facilities predictive modeling of HC blooms and resultant regional and global C and N budgets and fluxes.
