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Robert Stelzer Ph.D.

1_Emmons Creek Bob Stelzer Dec 2005.JPG

Professor and Graduate Coordinator

Phone: (920) 424-0845

Robert Stelzer
Department of Biology
800 Algoma Blvd.
University of Wisconsin Oshkosh
Oshkosh, WI 54901



Education and Training

Postdoctoral Associate,  Institute of Ecosystem Studies, 2000-2001
Ph.D. University of Notre Dame, Ecology, 2000
M.S.  Michigan State University, Zoology, 1992


Courses Taught

Ecosystem Ecology (Bio 386/586)- spring semester

Field Ecology (Bio 325/525)- fall semester

Ecosphere in Crisis (Bio 104)- spring semester

Biology Internship (Bio 300)- all semesters



Dr. Stelzer’s research is focused on understanding the reciprocal controls between nutrients and species in aquatic ecosystems.  He primarily uses comparative approaches and experiments to address questions at the interface of aquatic ecology and biogeochemistry.  Some of Dr. Stelzer’s current research projects are described below.

Nitrogen retention in a sand plains stream
Since 2007 Dr. Stelzer and his students have been measuring nitrate retention by mass balance in Emmons Creek.  Emmons Creek is a predominantly groundwater-fed stream in Central Wisconsin that has high concentrations of nitrate in the surface water and groundwater, largely due to agricultural activity in the watershed. Nitrate retention is relatively high in Emmons Creek and shows strong seasonal variation.  Much of the variation in nitrate retention can be explained by groundwater discharge (Stelzer et al. 2011a), which suggests that the stream sediments play an important role in nitrogen processing.  This research has been primarily funded by the United States Forest Service, the National Science Foundation, the Wisconsin Department of Natural Resources, Trout Unlimited, and the University of Wisconsin Oshkosh.

Nitrogen processing in deep stream sediments
Dr. Stelzer, in collaboration with scientists from the University of Arkansas, the United States Geological Survey, University of Wisconsin La Crosse, and the University of Maine has several completed and ongoing projects focused on nitrogen uptake and transformation at the groundwater- surface water interface in streams.  This work is described in Stelzer et al. (2011b), Stelzer and Bartsch (2012), Stelzer et al. (2014, 2015) and Stelzer (2015). The group has developed a conceptual model for nitrate processing in deep sediments. The model describes nitrogen transformation as nitrate-rich oxic groundwater upwells through sediments containing particulate organic carbon (POC).  Stelzer and colleagues have shown that nitrate retention and denitrification tend to be high in deep sediments throughout a river network in Central Wisconsin, in support of the conceptual model (Stelzer and Bartsch 2012).  These results may help explain the strong relationship between reach-scale nitrate retention and groundwater discharge described above. Our more recent research has shown how both carbon quantity and quality in buried sediments can affect nitrate retention and denitrification (Stelzer et al. 2014, 2015, Stelzer 2015).  Currently, Dr. Stelzer and Dr. Thad Scott at University of Arkansas are collaborating on a project to quantify denitrification hot spots in shallow stream sediments and to determine the influence of groundwater hydrology and reaction rates on nitrate removal.

Dr. Stelzer’s current and prior research has been funded by the University of Wisconsin Water Resources Institute, the University of Wisconsin Oshkosh, the United States Forest Service, the National Science Foundation and Trout Unlimited.   Media summarizing Dr. Stelzer’s research in shallow groundwater has been produced by the University of Wisconsin Aquatic Sciences Center (,

Ecology of springs in the Emmons Creek Network Mike Louison, who is currently pursuing his PhD in Fisheries Biology at the University of Illinois investigated the use of 1st-order spring-fed streams in the Emmons Creek network by brown trout and potential controls on their use including hydrology, sediment structure, and food supply (Louison and Stelzer 2016).  Mike received in kind support from the Wisconsin Department of Natural Resources and financial support from a Graduate Student-Faculty Collaborative Grant from the University of Wisconsin Oshkosh and from the Central Wisconsin Chapter of Trout Unlimited.

Trophic dynamics and food web structure in Lake Winnebago
Dr. Stelzer and his students have collaborated with fisheries biologists at the Wisconsin Department of Natural Resources to investigate several aspects of the Lake Winnebago Food Web.  Lake Winnebago, the largest inland lake in Wisconsin (55,766 ha) is eutrophic and contains large populations of walleye, yellow perch and other sport fish and is thought to contain the largest population of lake sturgeon (Acipenser fulvescensin) in North America. The lake is the drinking water source for several cities in the Fox River Valley, supports a robust fishery and is popular for boaters.

Stelzer and his collaborators determined carbon sources for lake sturgeon through the use of natural abundance stable isotopes (carbon and nitrogen) and gut content analysis (Stelzer et al. 2008).  Gut content analysis revealed that gizzard shad (Dorosoma cepedianum) and Chironomus plumosus larvae, 56% and 33% by gut content mass, were the primary prey items for sturgeon in the winter.  Larger lake sturgeon were more piscivorous than smaller individuals.  A mixing model using delta 13C and delta 15N suggests that Chironomus contributes 49% and gizzard shad 37% to carbon assimilated by lake sturgeon. They estimated carbon half-life in lake sturgeon to be about 0.6 to 3 years based on a model incorporating metabolism and growth.  Thus, the stable isotope results integrate over a considerably longer time period than the gut content analysis.  The results provide critical baseline information about the carbon sources for lake sturgeon which can be used to assess how their role in food webs may change after future perturbations such as exotic species introduction and land-use change.

Tim Anderson, who completed his MS in 2010, measured secondary production of chironomids in Lake Winnebago for his thesis research and determined if this production was sufficient to support lake sturgeon production.  Tim’s work, published in Freshwater Science (Anderson et al. 2012) resulted in the first estimate of secondary production for this large eutrophic lake and will be useful in future investigations of energetic efficiency and trophic level interactions in Lake Winnebago and other lakes.Tim concluded that in 2008-2009 there was sufficient chironomid secondary production to support the lake sturgeon population in Lake Winnebago.  The annual production estimates for chironomids are higher than many other chironomid production rates from lakes in North America, presumably due to the eutrophic conditions of Lake Winnebago.  Tim is currently pursuing his PhD in Entomology at Purdue University.

Ryan Koenigs completed his M.S. degree in 2011 and is currently a senior fisheries biologist and the lead sturgeon biologist at the  Wisconsin Department of Natural Resources.  Ryan thesis primarily addressed age validation of walleye in the Lake Winnebago system and the implications of error in age determination for population estimates and fisheries management.  He has published three papers in leading fisheries journals from his thesis research including Koenigs et al. (2015).

Courtney Heling, a current M.S. student in the Stelzer lab, is addressing patterns and causes of spatial variation in benthic macroinvertebrates in Lake Winnebago for her thesis research.  In collaboration with biologists from the Wisconsin DNR she is sampling from offshore soft-sediment locations with a dredge, from reef locations using SCUBA, and from the littoral zone using quadrat and core samplers.  When completed, her study will be the most comprehensive surveys of benthic invertebrate diversity and abundance in a large inland lake.


Selected Publications from the Stelzer Lab (*student author)

Louison, M.J.* and R.S. Stelzer.  2016. Use of first-order tributaries by brown trout (Salmo trutta) as nursery habitat in a coldwater stream network. Ecology of Freshwater Fish 25:133-140.

Stelzer, R.S. 2015. Yearlong impact of buried organic carbon on nitrate retention in stream sediments. Journal of Environmental Quality 44: 1711-1719. doi: 10.2134/jeq2015.02.0073

Koenigs, R.*, R.M. Bruch, R.S. Stelzer.  2015. Validation of otolith ages for walleye (Sander vitreus) in the Winnebago System. Fisheries Research 167:13-21.

Stelzer, R.S., Scott, J. T., L.A. Bartsch. 2015. Buried particulate organic carbon stimulates denitrification and nitrate retention in stream sediments at the groundwater-surface water interface. Freshwater Science 34:161-171.

Stelzer, R.S., Scott, J. T., L.A. Bartsch, T.B. Parr*. 2014. Particulate organic matter quality influences nitrate retention and denitrification in stream sediments: evidence from a carbon burial experiment. Biogeochemistry 119:387-402.

Stelzer, R.S. and D.R. Kashian. 2014. The role of conservation partnerships between scientists and nonprofit agencies in freshwater science and management. Freshwater Science 33:670–673.

Stelzer, R.S., and L.A. Bartsch. 2012. Nitrate removal in deep sediments of a nitrogen-rich river network: a test of a conceptual model. Journal of  Geophysical Research- Biogeosciences, 117, G02027, doi:10.1029/2012JG001990 (12 pages).

Anderson, T.J.*, R.S. Stelzer, H.G. Drecktrah, and S.L. Eggert. 2012. Secondary production of Chironomidae in a large eutrophic lake: implications for lake sturgeon production. Freshwater Science, 31, 365-378, DOI:10.1899/11-042.1

Stelzer, R.S., L.A. Bartsch, W.B. Richardson, and E.A. Strauss. 2011b. The dark side of the hyporheic zone: depth profiles of nitrogen and its processing in stream sediments.  Freshwater Biology, 56, 2021-2033, DOI: 10.1111/j.1365-2427.2011.02632.x

Stelzer, R.S., D.R. Drover*, S.L. Eggert and M.A. Muldoon. 2011a. Nitrate retention in a sand plains stream and the importance of groundwater discharge. Biogeochemistry, 103: 91-107. DOI: 10.1007/s10533-010-9449-y Stelzer et al 2011 Biogeochemistry.pdf (The original publication is available at:

Stelzer, R.S. and B.L. Joachim*. 2010. Effects of elevated nitrate concentration on mortality, growth, and egestion rates of Gammarus pseudolimnaeus amphipods. Archives of Environmental Contamination and Toxicology 58: 694-699. DOI 10.1007/s00244-009-9384-x

Shupryt, M.P.* and R.S. Stelzer. 2009. Macrophyte beds contribute disproportionately to benthic invertebrate abundance and biomass in a sand plains stream.  Hydrobiologia 632: 329-339.  DOI 10.1007/s10750-009-9856-z

Stelzer, R.S., R.M. Bruch, H.G. Drecktrah, and M.P. Shupryt*.  2008. Carbon sources for lake sturgeon in  Lake Winnebago, WI.  Transactions of the American Fisheries Society 137:1018-1028.   Stelzer et al 2008.pdf

Kent, T.R.* and R. S. Stelzer.  2008. Effects of deposited fine sediment on life history traits of Physa snails. Hydrobiologia 596:329-340.

Stelzer, R.S. and G. E. Likens.  2006. The effects of sampling frequency on estimates of dissolved silica export by streams: the role of hydrological variability and concentration-discharge relationships. Water Resources Research 42, W07415, doi:10.1029/2005WR004615, (10 pages). Stelzer and Likens WRR 2006.pdf

Bernhardt, E.S., G. E. Likens, R. O. Hall, D. C. Buso, S. G. Fisher, T. M. Burton, J. L. Meyer, W. H. McDowell, M. S. Mayer, W. B. Bowden, S.E.G. Findlay, K. H. Macneale, R S. Stelzer, W. H. Lowe. 2005. Can’t See the Forest for the Stream? The capacity of instream processing to modify terrestrial nitrogen exports. BioScience 55: 219-230.

Stelzer, R.S., J.B. Heffernan, and G.E. Likens. 2003. The Influence of dissolved nutrients and particulate organic matter quality on microbial respiration and biomass in a forest stream. Freshwater Biology 48: 1925-1937. Stelzer et al. 2003

Stelzer, R.S. and G.A. Lamberti. 2002. Ecological stoichiometry in running waters: periphyton chemical composition and snail growth.  Ecology 83: 1039-1051.

Frost, P.C., R.S. Stelzer, G.A. Lamberti, and J.J. Elser.  2002.  Ecological stoichiometry of trophic interactions in the benthos: understanding the role of C:N:P ratios in littoral and lotic habitats.  Journal of the North American Benthological Society 21: 515-528.

Stelzer, R.S. and G.A. Lamberti. 2001. Effects of N:P ratio and total nutrient concentration on stream periphyton community structure, biomass, and elemental composition. Limnology and Oceanography 46: 356-367.

Opportunities for Student Research

There are many different ways that undergraduates and graduate students could conduct independent research and/or become involved in established research projects in Dr. Stelzer’s lab. If you think you might be interested in doing research in the Stelzer Lab feel free to stop by his office (Halsey 150) or drop him an email message.  Students work in the lab in a variety of capacities including: as students pursuing their MS thesis research, as research assistants, while pursuing independent study (Bio 446), as participants on student-faculty collaborative grants and as volunteers.

Lab Alumni

Dr. Stelzer has been fortunate to work with a great group of students in his research lab and in the classroom.  The list of lab alumni and what they are doing currently will be updated soon.

Environmental Science Links