Land-Water People  People involved in Land-Water research at Toolik Field Station and Graduate Student Research Projects
George mixing rhodamine dye for an experiment in Toolik Lake (photo by Sally MacIntyre)	Mandy Barr taking dissolved inorganic carbon sample at stream site
Mary Anne Evans enjoying view from top of Slope Mountain (photo by fellow hiker)	Karen Jo Riseng driving across Toolik Lake (photo by Kristi Judd)
	Erica Gwynn (blue shirt) and Kristi Judd (red shirt) extracting soil water samples at the LTER experimental plots (acidic) (photo by Alan Striegle).

People involved in Land-Water research at Toolik Field Station

Heather Adams  - Graduate student at University of Michigan. Heather studies the interactions of controls on aquatic bacterial activity at different spatial and temporal scales, and has been conducting her Ph.D. research at Toolik since the summer of 2003, her second season at the site.  See Graduate Student Research Projects below.

Sarah Barbrow - New graduate Student at the University of Michigan. Sarah received her Bachelor's degree at Princeton, and will start in the Ph.D. program at Michigan in Fall of 2007.  Sarah is working as a research assistant at Toolik Lake during summer 2007.

Natalie Day - Natalie is an NSF-REU student from Lewis and Clark University who will work at Toolik during summer 2007.

Mary Anne Evans - Recent Ph.D. student from the University of Michigan, now a postdoctoral researcher at Michigan State University. Mary Anne studied the controls on phytoplankton and primary productivity in lakes around Toolik. See Graduate Student Research Projects below.

Amanda Field -- LTER Senior Land-Water Research Associate.  Amanda received her Masters degree studying the use of stable isotope measures to determine primary productivity in the Laurentian Great Lakes.  She has been working on the project since 2004.

George Kling - Principle Investigator on Arctic LTER project and project coordinator for Land-Water group. George started work at Toolik Field Station in 1988. For more information about George see http://biology.lsa.umich.edu/~gwk/ 

Ashley Larsen - Ashley is an NSF-REU student from the University of Michigan that will work at Toolik during summer 2007.

Anne Roberts - Anne just graduated with a Bachelor's degree from Hartwick College, and is working at Toolik as the LTER Land-Water research assistant for the summer of 2007.

Christopher Wallace - Recent LTER Senior Land-Water Research Associate. Chris received his Masters degree studying the ecology of diatoms in vernal ponds. He has been working on the project since 1999.

Graduate Student Research Projects 

Heather Adams:  As the major mediators of nutrient mineralization, bacteria play a central role in ecosystem function, and so it is important to understand what limits bacterial activity.  Carbon substrate quality and quantity, in addition to temperature and inorganic nutrient availability, control bacterial activity, and different bacterial communities may vary in their response to these controls. 

The main question of my research is:  how do the controls on bacterial production interact, and how do those interactions play out at different spatial and temporal scales?  More specifically, my first hypothesis is that the importance of different controls will correspond to the environmental situation.  For example, streams receive carbon inputs with a distinctive terrestrial composition, while lakes receive more labile carbon inputs from in-lake algal production.  In addition, temperature or nutrient chemistry will vary with elevation and landscape position.  My second hypothesis is that bacterial community dynamics will alter the strength of different controls on activity.  Bacterial communities may be transported from terrestrial to aquatic systems, resulting in a mixture of communities and carbon substrates that may favor certain bacteria or alter overall community growth.  Dormant bacterial cells can become active when their preferred carbon resource appears, or active cells may then be at a metabolic disadvantage given the new mix of substrates.  The goal of my research in graduate school is to help to answer the questions posed by these hypotheses. 

Mary Anne Evans: The ultimate factors that determine phytoplankton primary production (PP) in a water column have long been understood to be light, nutrients, temperature, and the physiological state of the phytoplankton cells.  The effects of these factors on PP have been well-characterized at the level of the individual cell and of the community.  However, these factors are proximally controlled by environmental conditions.  The critical environmental conditions that set the levels of light and nutrients available to phytoplankton are the diel variation in surface irradiance, the vertical movement of water, and the storm-induced flushing or mixing of nutrients into the euphotic zone.  These physical conditions are integrated at the ecosystem level, and function in linear and non-linear combinations to determine the resources available to phytoplankton cells.  It is these combinations that must be understood to predict PP within an ecosystem.  The problem is that these combinations of physical controls are dynamic in space and time.  For example, mixing varies strongly on time scales of minutes (MacIntyre et al. 2000) to seasonally-forced upwelling (Thebault et al. 1999), and is influenced by heterogeneous spatial structure (Gobler and Sanudo-Wilhelmy 2001).  Despite this recognition of dynamics, determining the relative strengths and influences of rapid and sporadic events, such as storm-induced runoff of nutrients into a lake or a wind-induced redistribution of phytoplankton into different light environments, is a subject of much interest (e.g., Gervais et al. 1997, Robarts et al. 1998, Thebault et al. 1999, Barber et al. 2001, Brookes et al. 2003).

For my dissertation I am studying how primary production is affected by these.  I am using arctic tundra lakes as a study system because of the following desirable characteristics: (1) The lakes are oligotrophic and nutrient limited (Levine and Whalen 2001), and thus are sensitive to the effects of in-flowing or redistributed nutrients; (2) The lakes experience severe summer storm events at a sufficiently high frequency to study reliably -- for example, events with stream discharge 10 times greater than base flow are common; (3) From an internal mixing standpoint, substantial internal wave activity has been documented within the metalimnion of these lakes; and (4) these lakes are instrumented each summer by S. MacIntyre with multiple strings of data loggers to measure temperature and conductivity; this extremely rare level of instrumentation provides a unique opportunity to integrate physical and biological studies.  This dissertation will contribute to scientific theory regarding sporadic events, which occur in many systems, and will improve predictions of the biological response to a changing climate which is expected to alter patterns of storm events in the future. 

In my dissertation research so far I have observed storm-induced peaks in PP in response to both wind-mixing and in-flow events.  I am currently conducting additional work which will determine the effect of such events on annual rates of PP and on within and between year variability in PP.