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Patrick (Pat) J. Mulholland

Karl SimpsonPatrick (Pat) Mulholland was on the leading edge of stream biogeochemical and watershed research for over 30 years, and he was instrumental in shaping the careers and research of countless individuals through his keen insights, openness to sharing ideas, and compassion for mentoring. His work as a scholar and intellectual contributor to the field was complimented by his leadership skills to bring researchers together to address complex ecological questions. Pat was an international leader and distinguished scientist. He was a Fellow of the American Association for the Advancement of Science, and a Fellow of the American Geophysical Union. In addition, Pat was named the Distinguished Scientist of the Year by Oak Ridge National Laboratory (ORNL) in 2011, was cited as a contributing scientist to the Nobel Peace Prize in 2007, and received the Award of Excellence from the North American Benthological Society in 2011.

Pat's background was not typical of a stream ecologist. The quantitative rigor that was the hallmark of his work reflected his training as an engineer. Pat received Bachelors and Masters Degrees in Civil and Environmental Engineering from Cornell University, and a Ph.D. in Environmental Biology from the University of North Carolina at Chapel Hill. His dissertation work was a major ecological contribution on carbon dynamics in a wetland-stream ecosystem (Mulholland and Kuenzler 1979, Mulholland 1981). After receiving his doctoral degree, Pat moved to ORNL, where he spent his entire 31-year career. At ORNL, Pat quickly became involved in the "spiralling" project studying phosphorus dynamics in Walker Branch, and he was lead-author and co-author on a series of seminal publications that shaped our understanding of nutrient cycling in streams (e.g., Mulholland et al. 1983, Mulholland et al. 1985). Following from the pioneering work on nutrient spiralling, Pat’s research focused on questions of ecosystem structure and stability with a series of studies using laboratory as well as natural streams to address research questions encompassing aspects of ecosystem stability and food web structure and function (Mulholland et al. 1991a, Mulholland et al. 1991b, Mulholland et al. 1994). Pat also made major contributions to our understanding of watershed hydrology, particularly in understanding the influence of watershed flow paths on stream nutrient and dissolved organic carbon concentrations and the importance of storm flows on stream chemistry(Mulholland 1993, 2004). Pat’s work on stream ecosystem metabolism revolutionized our understanding with innovations allowing accurately measuring whole ecosystem metabolism rates in streams (Marzolf et al. 1994), leading to more detailed understandings of stream metabolism dynamics (Roberts et al. 2007), the importance of the hyporheic zone in metabolism (Mulholland et al. 1997), and a synthesis of continental-scale patterns to examine the factors controlling metabolism rates (Mulholland et al. 2001). Pat also played a leading role in our understanding of how nitrogen dynamics in streams varies across biomes (Mulholland et al. 2008, Mulholland et al. 2009).

In addition to his research contributions to freshwater science, Pat was an active member and leader of the Society for Freshwater Science. He was a member of the Executive Committee, chair of the Awards Committee, member of the Endowment Committee, and Associate Editor of J-NABS. In addition to his service to NABS, he served on countless advisory boards, committees, and review panels for the National Science Foundation, Department of Energy, Environmental Protection Agency, CALFED, and Everglades National Park.

Pat was a wonderful collaborator, and a quiet and humble leader. He possessed a strong work ethic, great focus, broad vision, and wonderful creativity. Pat was a natural mentor having formally advised 10 graduate students and seven postdoctoral scholars, and he worked with countless additional students and scientists at all stages of their careers with an openness to sharing ideas and insights that was second nature to him. He was encouraging to everyone.

Selected Publications

  • Marzolf, E. R., P. J. Mulholland, and A. D. Steinman. 1994. Improvements to the diurnal upstream-downstream dissolved-oxygen change technique for determing whole-stream metabolism in small stream. Canadian Journal of Fisheries and Aquatic Sciences 51:1591-1599.
  • Mulholland, P. J. 1981. Organic carbon flow in a swamp-stream ecosystem. Ecological Monographs 51:307-322.
  • Mulholland, P. J. 1993. Hydrometric and stream chemistry evidence of three storm flowpaths in Walker Branch Watershed. Journal of Hydrology 151:291-316.
  • Mulholland, P. J. 2004. The importance of in-stream uptake for regulating stream concentrations and outputs of N and P from a forested watershed: evidence from long-term chemistry records for Walker Branch Watershed. Biogeochemistry 70:403-426.
  • Mulholland, P. J., C. S. Fellows, J. L. Tank, N. B. Grimm, J. R. Webster, S. K. Hamilton, E. Marti, L. Ashkenas, W. B. Bowden, W. K. Dodds, W. H. McDowell, M. J. Paul, and B. J. Peterson. 2001. Inter-biome comparison of factors controlling stream metabolism. Freshwater Biology 46:1503-1517.
  • Mulholland, P. J., R. O. Hall, D. J. Sobota, W. K. Dodds, S. E. G. Findlay, N. B. Grimm, S. K. Hamilton, W. H. McDowell, J. M. O'Brien, J. L. Tank, L. R. Ashkenas, L. W. Cooper, C. N. Dahm, S. V. Gregory, S. L. Johnson, J. L. Meyer, B. J. Peterson, G. C. Poole, H. M. Valett, J. R. Webster, C. P. Arango, J. J. Beaulieu, M. J. Bernot, A. J. Burgin, C. L. Crenshaw, A. M. Helton, L. T. Johnson, B. R. Niederlehner, J. D. Potter, R. W. Sheibley, and S. M. Thomas. 2009. Nitrate removal in stream ecosystems measured by 15N addition experiments: Denitrification. Limnology and Oceanography 54:666-680.
  • Mulholland, P. J., A. M. Helton, G. C. Poole, R. O. Hall, S. K. Hamilton, B. J. Peterson, J. L. Tank, L. R. Ashkenas, L. W. Cooper, C. N. Dahm, W. K. Dodds, S. E. G. Findlay, S. V. Gregory, N. B. Grimm, S. L. Johnson, W. H. McDowell, J. L. Meyer, H. M. Valett, J. R. Webster, C. P. Arango, J. J. Beaulieu, M. J. Bernot, A. J. Burgin, C. L. Crenshaw, L. T. Johnson, B. R. Niederlehner, J. M. O'Brien, J. D. Potter, R. W. Sheibley, D. J. Sobota, and S. M. Thomas. 2008. Stream denitrification across biomes and its response to anthropogenic nitrate loading. Nature 452:202-205.
  • Mulholland, P. J. and E. J. Kuenzler. 1979. Organic carbon export from upland and forested wetland watersheds. Limnology and Oceanography 24:960-966.
  • Mulholland, P. J., E. R. Marzolf, J. R. Webster, D. R. Hart, and S. P. Hendricks. 1997. Evidence that hyporheic zones increase heterotrophic metabolism and phosphorus uptake in forest streams. Limnology and Oceanography 42:443-451.
  • Mulholland, P. J., J. D. Newbold, J. W. Elwood, L. A. Ferren, and J. R. Webster. 1985. Phosphorus spiralling in a woodland stream: seasonal variations. Ecology 66:1012-1023.
  • Mulholland, P. J., J. D. Newbold, J. W. Elwood, and C. L. Hom. 1983. The effect of grazing intensity on phosphorus spiralling in autotropic streams. Oecologia 58:358-366.
  • Mulholland, P. J., A. D. Steinman, E. R. Marzolf, D. R. Hart, and D. L. DeAngelis. 1994. Effect of periphyton biomass on hydraulic characteristics and nutrient cycling in streams. Oecologia 98:40-47.
  • Mulholland, P. J., A. D. Steinman, A. V. Palumbo, D. L. DeAngelis, and T. E. Flum. 1991a. Influence of nutrients and grazing on the response of stream periphyton communities to a scour disturbance. Journal of the North American Benthological Society 10:127-142.
  • Mulholland, P. J., A. D. Steinman, A. V. Palumbo, J. W. Elwood, and D. B. Kirschtel. 1991b. Role of nutrient cycling and herbivory in regulating periphyton communities in laboratory streams. Ecology 72:966-982.
  • Roberts, B. J., P. J. Mulholland, and W. R. Hill. 2007. Multiple scales of temporal variability in ecosystem metabolism rates: Results from 2 years of continuous monitoring in a forested headwater stream. Ecosystems 10:588-606.
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