DENISE A. BRUESEWITZ 

About Me 

I am originally from Rockford, Illinois.  I graduated in 2001 with a B.S. in Biology from Winona State University in Winona, MN.  I examined competition between zebra mussels and hydropsychid caddisflies in the Upper Mississippi River with Dr. Mike Delong at the Large River Studies Center for my undergraduate thesis.  After graduation, I worked at the USGS Upper Midwest Environmental Sciences Center in LaCrosse, WI.  I was a research technician on the 'N-team' with Dr. William Richardson and Dr. Eric Strauss. We examined seasonal nitrogen cycling in Pool 8 of the Upper Mississippi River.  I came to the University of Notre Dame in the Fall of 2002 to work with Dr. Jen Tank. My full CV is available here (DBruesewitz_CV.doc).

My Doctoral Research

My current work combines my previous research interests in zebra mussels and aquatic biogeochemistry and focuses on the question:

How do zebra mussels effect nitrogen cycling in invaded ecoystems?

I am examining the effects of zebra mussels on N cycling through field sampling of the Upper Mississippi River and in Gull Lake, MI, representing both lotic and lentic systems invaded by zebra mussels. As part of my research, I have also examined the relationship between zebra mussels and N cycling on a finer scale with controlled laboratory experiments and large field mesocosms. Each focal point listed below represents a chapter of my thesis. 

1.    Seasonal effects of the zebra mussel (Dreissena polymorpha) on sediment denitrification rates in Pool 8 of the Upper Mississippi River  

-With a year-long study of several sites in Pool 8 of the UMR, we found that denitrificaiton rates are higher in the presence of zebra mussels only during winter months. It appears that they are alleviating N limitation of denitrification during times of low N avaliability to the benthos.

2.    Delineating the effects of zebra mussels (Dreissena polymorpha) on nitrogen transformation rates using laboratory mesocosms.

-In a 3-week laboratory experiment, we found that zebra mussels significantly increased sediment nitrification rates within 1 week of zebra mussel addition to mesocosms.  This increased nitrate supply along with decreased sediment dissolved oxygen concentrations allows for increased denitrification in the presence of zebra mussels.

3.    Seasonal effects of the zebra mussel (Dreissena polymorpha) on sediment nitrification and denitrification rates in Gull Lake, Michigan. 

 
-Each month for 1-year we incubated 9 shallow trays of sediment (see photos to the right) with zebra mussel rocks, and 9 sediment trays with uncolonized zebra mussel rocks. Zebra mussels are periodically increasing littoral nitrification and denitrification rates, which is consistent with results from my previous laboratory experiments.  These data suggest that zebra mussels could be altering N flux from Gull Lake.

4.   The varied effect of zebra mussels (Dreissena polymorpha) on nitrogen transformation rates across an experimental gradient of lake productivity.

- I collaborated with Steve Hamilton and Ace Sarnelle in the summers of 2005 and 2007 on the 'ZMEX' experiments in Gull Lake (see photos to the right).  These experiments are primarily being used to examine the relationship between zebra mussels and Microcystis blooms.  I examined nitrogen cycling in the mesocosms across an experimental gradient of lake productivity.

    We hypothesize that the effect of zebra mussels on N transformation rates will vary with lake nutrient status.  Denitrification in oligotrophic systems is more likely to be enhanced by zebra mussel invasion, as zebra mussels enhance deposition of N and organic material to the benthos compared to eutrophic lakes with higher organic material and nutrient delivery to the benthos. Nitrification rates were consistently higher in the presence of zebra mussels in the enclosures. Denitrification rates were higher in the presence of zebra mussels only in low nutrient enclosures. Our results suggest that invaded lakes may experience increased nitrification regardless of lake nutrient status, but oligotrophic lakes invaded by zebra mussels have more potential for elevated N loss via denitrification compared to pre-invasion rates of denitrification. 

5.  Linking shifts in littoral nitrogen transformations caused by zebra mussel invasion to whole lake nitrogen fluxes.

-Zebra mussels tend to colonize the littoral areas of a lake. I am working in Gull Lake to see if zebra mussels can indirectly increase overall N loss from the system, or if they are simply moving the hotspot of denitrification from the profundal to the littoral zone. I will be using transects across the lake to examine spatial patterns in nitrification and denitrification in Gull Lake.

Publications

D. A. Bruesewitz, J. L. Tank, S. K. Hamilton, G. Horst, and O. Sarnelle. The effects of zebra mussels on nitrogen transformation rates across an experimental gradient of lake productivity. In preparation.

S. K. Hamilton, D. A. Bruesewitz, G. Horst, and O. Sarnelle. Precipitation of phosphorus with calcite as a negative feedback to lake eutrophication. In review, Environmental Science and Technology.

D.A. Bruesewitz, J.L. Tank, and M.J. Bernot.  Delineating the effects of zebra mussels (Dreissena polymorpha) on nitrogen transformation rates using laboratory mesocosms. In press, Journal of the North American Benthological Society.

D.A. Bruesewitz, J.L. Tank, M.J. Bernot, W.B Richardson and E.A. Strauss (2006).  Seasonal effects of the zebra mussel (Dreissena polymorpha) on sediment denitrification rates in Pool 8 of the Upper Mississippi River.  Canadian Journal of Fisheries and Aquatic Sciences 63 (5): 957-969. (download PDF here.)

E.A. Strauss, W.B. Richardson, L. Bartsch, J.C. Cavanaugh, D.A. Bruesewitz, H. Imker, J.A. Heinz, D. M Soballe.  2004.  Nitrification in the Upper Mississippi River: patterns, controls and contribution to the nitrate budget. JNABS 23 (1): 1-14.

Teaching Experience

I enjoy teaching and have had the opportunity to teach many different classes during my time at Notre Dame, including:

General Biology Laboratory

General Ecology Laboratory

Biostatistics

Stream Ecology Laboratory

Microbiology Laboratory

I also participated in the Teaching Apprenticeship Program in General Ecology, University of Notre Dame Kaneb Center for Teaching and Learning (Spring 2006).

In Spring 2007, I was awarded an Outstanding Graduate Student Teacher Award for Excellence in Teaching from the Kaneb Center for Teaching and Learning. 

Future Research Interests

I am broadly interested in how human activities alter aquatic ecosystem function and biogeochemistry.  My dissertation research has focused on one aspect of this; how an invasive species, the zebra mussel, is altering nitrogen cycling in invaded lakes and rivers. 

I am seeking a postdoctoral position that will expand upon my experience not only in my research, but also in my capacity to manage research projects, advise graduate students, and if possible to continue teaching.

I would like to begin to work on a larger scale, thinking about how alterations of biogeochemical transformations and ecosystem function play out on the landscape scale.  I enjoy working in both lakes and rivers, and at the intersection of aquatic biogeochemistry and invasion biology.