Dr. Robert S. Stelzer

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

Research

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
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. Dr. Stelzer, his collaborators, and students have measured nutrient concentrations in Emmons Creek on a weekly to biweekly basis since 2005 and nitrate retention and flux since 2007.  Nitrate retention expressed per stream area 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. 2010), which suggests that the stream sediments may 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 by University of Wisconsin Oshkosh.

Nitrogen processing in deep stream sediments
Dr. Stelzer is collaborating with scientists at the United States Geological Survey (Upper Midwest Environmental Sciences Center) and UW LaCrosse to determine the extent of nitrogen processing in deep stream sediments (to 70 cm, below the hyporheic zone) in Central Wisconsin.  The group has measured high denitrification rates at depth and nitrate profiles in the porewater are consistent with nitrate processing in deep sediments.  These results may help explain the strong relationship between reach-scale nitrate retention and groundwater discharge described above.  This work is funded by a grant from the University of Wisconsin Water Resources Institute.  Robin Pagel and Ashley Winker are working as research technicians on this project during the summer.

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 is a large (55,766 ha) eutrophic lake that 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.  

In a recent project 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.  We 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.  Our 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, a M.S. candidate in the lab, is measuring Chironomus secondary production in Lake Winnebago for his thesis research.  Our past work on lake sturgeon and evidence from other studies suggest that Chironomus (locally called “lakeflies”) support considerable production at higher trophic levels.  Tim’s work will be 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.

Ryan Koenigs, a M.S. candidate in the lab and fisheries technician at the Wisconsin Department of Natural Resources, is investigating how walleye aging techniques can impact estimates of mortality and somatic growth, which are critical parameters for effective fish population management.  Ryan’s research includes the first age validation of walleye using large, known-age fish.

Robin Pagel is a M.S. student in the Stelzer Lab.  She recently completed an independent study project that assessed relationships between the phosphorus content of amphipods and that of their food resources in streams along an agricultural to urban continuum.  Robin is investigating phosphorus and nitrogen limitation in stream algae communities for her thesis research.

Selected Publications (* student author)

Stelzer, R.S., L.A. Bartsch, W.B. Richardson, and E.A. Strauss. 2011. 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. 2011. 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:       www.springerlink.com/content/m560xu8453363767/

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