CDOM in the Kolyma River, June 30, 2013

For a PDF of my CV, click here. 

Inland waters are integral to the transportation and transformation nutrients and organic matter, as materials move from land to sea. Most of my work focuses on a landscape scale, linking watershed characteristics to the quantity and quality of organic matter and nutrients.  I am also interested in the fate of these materials - how much does terrestrial organic matter contribute to food webs, or incorporated into microbial processes? I  primarily use remote sensing, organic matter spectroscopy, stable isotopes, and bulk measurements in my research. Below are the main projects I've been involved in.

Remote Sensing of Organic Matter in Large Arctic Rivers

The Arctic Ocean watershed

The Arctic Ocean watershed

How has carbon cycling shifted in response to climate change in the Arctic?  A complex question, but my dissertation research aims to answer part of it.  I use remote sensing tools to estimate the amount of colored dissolved organic matter and dissolved organic carbon in the six largest Arctic rivers.  I've traveled to the Mackenzie (Canada), Yukon (Alaska), and Kolyma (Russia) rivers for this project, and we have additional data from three other Russian rivers (the Ob, Yenisey, and Lena rivers).  Unfortunately, there is very little available chemistry data available for these river, particularly in Russia, prior to about 2003.  By utilizing the available Landsat imagery, dating back to 1984, I  constructed records of DOM concentrations and fluxes may have changed over the past thirty years.  

In the Ob' and Yenisey rivers, changes in permafrost and peatland extent may have led to shifts in discharge-normalized DOM concentrations.  In addition, DOM concentrations in the Mackenzie have increased over a 30 year period.  Not only climate change, but broad-scale atmospheric patterns such as the Arctic Oscillation may play a role in DOM fluxes from these rivers.  The remote sensing imagery also gives us greater data density in recent years than is generally available from on-the-ground sampling, and can reveal spatial patterns.  A preliminary case study of this is available here, based on previous research that I conducted as part of The Polaris Project.  This project is part of the larger Arctic Great Rivers Observatory.  Papers detailing these results are in review.

 

 

Terrestrial Organic Matter in Midwestern Lakes from Remote Sensing

Water sample from a colored lake in northern Wisconsin

Water sample from a colored lake in northern Wisconsin

With over 10,000 lakes in Minnesota alone, aquatic systems in the Upper Midwest are an important part of the landscape. Monitoring these many small lakes remains difficult, however. With satellite remote sensing, we can estimate the amount of colored dissolved organic matter (CDOM) in lakes across Minnesota, Wisconsin, and Michigan based on field-collected measurements from hundreds of lakes.  CDOM is a reliable proxy for terrestrial organic matter, as most is formed as water leaches out complex molecules from leaves and other plant material, much like tea leaves steeping in a mug. My work ties watershed characteristics - such as forest and wetland extent, or slope - to organic matter within lakes, to find out how lake water quality is controlled by the terrestrial ecosystem.  Additionally, these remote sensing tools can be used to trace CDOM through time, going back to the 1980s, to examine whether climate, land use change, or atmospheric chemistry (e.g., sulfur deposition) have long-term influence on regional aquatic carbon cycling.

 

 

 

Nitrogen Export from Texas Rivers Driven by Storm Events

Colorado River in flood

Colorado River in flood

Texas watersheds vary greatly in terms of land use, climate, and size.  However, most are inherently "flashy" systems, with freshwater discharge punctuated by large peaks after storm events.  These pulses have long been known to be important in maintaining the health of Gulf Coast estuaries;  Texas has even passed legislation to study and maintain standards of these pulses on a statewide basis.  There has been little study of the associated nutrient delivery from storm events, however.  I am part of a project to quantifying nitrogen delivery from Texas rivers, by targeted sampling of floods and base flow from 2011 - 2013, on four different river systems - the Colorado, Guadalupe, San Antonio, and Nueces rivers.  Land use plays a large role in the nitrogen export from all of these rivers during base flow, as Colorado and San Antonio rivers have high inorganic nitrogen inputs from agriculture and municipal sources.  However, regardless of land use, the large floods that occur periodically dominate export of all nitrogen species.  My work links to larger efforts modeling climate and land use influences on nitrogen fluxes in the past, present, and future.  Ultimately, this data is being used to drive estuarine productivity models.