Water quality and nitrogen loading in KS streams
Walter Dodds, David Graham, Mark Schneegurt.
Fertilizer production has doubled global N2-fixation (Vitousek 1994, Vitousek et al. 1997b) and use has contaminated many aquatic ecosystems. NO3- can be toxic to humans, and N pollution harms water quality (Carpenter et al. 1998, Dodds 2002). Nitrifying bacteria, N2-fixing bacteria, and heterotrophic bacteria that process NO3- are key to N cycling (Kemp and Dodds, in press). N retention in small streams is central to mitigating anthropogenic N deposition (Alexander et al. 2000, Peterson et al. 2001). This research aims to contrast gene expression and metabolic responses of nitrifying, N2-fixing, and NO3- assimilating bacteria to pulses and chronic N loading. We hypothesize that short-term pulses of NH4+ common in streams will cause expression of nitrifying genes of inactive nitrifiers, whereas chronic loading will stimulate cell growth and reproduction, and that N2 fixing organisms will be more abundant in pristine, low N systems and will not respond to N pulses. Samples from high and low N streams will be evaluated for nitrifier numbers and diversity using fluorescent in-situ hybridization, small sub-unit rRNA hybridization methods (Knapp et al., submitted) and denaturing gradient gel electrophoresis before and after N amendments. The genes for N2 fixation (nifH) will be used to assess activity in pristine and chronically N-loaded streams. A reduction in nifH gene activity may indicate chronic N loading and compromised biotic integrity. Community structure of the N2-fixing guild will be examined using PCR-based techniques and sequencing after RFLP segregation (Zehr and McReynolds, 1989, Ueda et al. 1995). FISH will be used to measure the overall abundance of microbes harboring nifH genes.
Alexander, R. B., R. A. Smith, and G. E. Schwarz. 2000. Effect of stream channel size on the delivery of nitrogen to the Gulf of Mexico. Nature 40: 58-761.
Carpenter, S.R., Caraco, N., Correll D.L., Howarth RW, Sharpley AN, and Smith VH. 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecol. Applic. 8:559-568.
Dodds, W. K. 2002. Freshwater Ecology: Concepts and Environmental Applications. Academic Press. 569 pp
Kemp, M. J. and W. K. Dodds (in press). Comparisons of nitrification and denitrification in pristine and agriculturally influenced streams. Ecological Applications
Peterson, B. J. W. M., Wollheim, P. J. Mulholland, J. R. Webster, J. L. Meyer, J. L. Tank, E. Marti, W. B. Bowden, H. Maurice Valett, A. E. Hershey, W. B. McDowell, W. K. Dodds, S. K. Hamilton, S. Gregory, and D. J. Morrall. 2001. Control of nitrogen export from watersheds by headwater streams. Science 292:86-90
Vitousek, P. M. 1994. Beyond global warming: Ecology and global change. Ecology 75:1861-1876.
Vitousek, P.M., et al. 1997b. Human alteration of the global nitrogen cycle: Causes and consequences. Ecological Applic. 7:737-750.
Ueda et al. 1995 Remarkable N2-fixing bacterial diversity detected in rice roots by molecular evolutionary analysis of nifH gene sequences. J Bacteriol 177:1414-1417.
Zehr, J.P, M.T. Mellon and S. Zani. 1998. New nitrogen-fixing microorganisms detected in oligotrophic oceans by amplification of nitrogenase (NifH) genes. Applied and Env. Microbiol. 64(9): 3444-50.
Knapp, A., Linacre, Dodds, Head, and Graham. Quantification of nirS and nirK genes using real-time PCR in prairie streams. Applied and Environmental Microbiology. Submitted, under review.