Megan Fork, PhD student in the lab, is one of the student bloggers for the Nicholas School. She just put up her first post - you can follow her at In PhDeep.
Not really lab news, but how cool is this? Curiousity finds evidence of ancient stream beds on Mars.
This past week, Ewan Isherwood passed his qualifying exams and defended his research proposal, entitled 'Effects of hydrologic modification on Everglades vegetation communities.' Ewan is a Master's student at FIU, and is planning to complete his thesis this coming spring. Congratulations Ewan!
Megan Fork successfully defended her MS thesis on June 12, 2012. Megan's thesis, 'Direct and indirect effects of organic matter sources on denitrification in Florida Rivers,' uses natural variation in dissolved organic matter (DOM) to assess the roles of terrestrial and aquatic sources of organic matter as fuels for denitrification. Her research shows that, as terrestrial organic matter becomes more abundant, organic matter actually becomes more limiting to denitrification. This counter-intuitive result reflects two features of terrestrial OM: first, the complex organic molecules that make it up are not very bioavailable. Second, the tea color of complex OM reduces light and therefore primary production within the river. Our previous work in Florida springs has shown that this aquatic productivity fuels a lot of denitrification, so by reducing aquatic productivity, terrestrial OM reduces the amount of bioavailable OM that can drive denitrification.
Megan will officially graduate from FIU's Department of Biological Sciences at the end of the summer, but she is already in Durham looking for another exciting questions to serve as a dissertation topic. Congratulations Megan! Our paper on denitrification in the Floridan Aquifer was just published in the open access journal Biogeosciences. Co-authors include Andrea Albertin and Matt Cohen at the University of Florida, Brian Katz at the US Geological Survey, and Megan Fork, currently finishing her MS at Florida International University and soon to begin her PhD in the lab.
This paper is the first to provide direct measurements of denitrification over the scale of an entire regional aquifer. To achieve this, we added a large amount of existing data (mostly from co-author Brian Katz) to our own sampling of the Floridan Aquifer springs, and developed new ways to use noble gases to develop null predictions of N2 gas concentrations. Basically, we use argon and neon to estimate how much N2 should be in the water, then calculate denitrification (which produces N2 gas) by difference. This paper also demonstrates the large effect of denitrification on groundwater N isotopes. One reason we care about this is that we use isotopes to identify sources of N: synthetic fertilizers have low or 'light' isotope signatures, while organic waste (from urban and animal husbandry sources) are 'heavy'. , we have to account for these effects or we will get the source wrong. You can read the Duke press release here, and get the paper here. You can learn more about our other springs research here. Tim Covino, PhD student of soon-to-be colleague Brian McGlynn, has been awarded an NSF post-doctoral fellowship to work with Emily Bernhardt and I at Duke. Tim's dissertation developed the use of pulsed solute additions to streams to assess nutrient uptake kinetics, and his post-doctoral work will expand the application of these approaches to new systems and new ecological questions. Congratulations Tim and welcome aboard!
The Bernhardt and Heffernan labs were fortunate to have our friend and mentor Nancy Grimm as our guest this past week. Nancy is a world-renowned expert in biogeochemistry, stream and riparian ecology, and urban ecosystems. She is currently on leave from Arizona State Unviersity, where she was a collaborator and unofficial committee member, while she serves as program director for the National Science Foundation's Ecosystem Science Program.
Nancy's first talk addressed her work in desert streams and their past and future response to climate variability. Some of her lab's current work builds on my dissertation research on desert wetlands, which was very exciting to see! Nancy's second talk focused on funding opportunities at NSF, covering programs as small as supplemental support for high school students to programs as large as the new foundation-wide sustainability initiatives. There are lots of new programs at NSF as well as changes to how proposals and panels are working, so this was really helpful and interesting. We also got a chance to take Nancy out to the Eno River, which runs through north Durham and eventually in to Falls Lake. The land surrounding the Eno is largely undeveloped, thanks to the Eno River Land Trust, and the Eno River State Park is just beautiful. We spent lots of time talking about floods, vegetation, and nitrogen in rivers; turning over rocks to see mayfly, stonefly and caddisfly larvae; and spooking turtles sunning on boulders and logs. Good times. Megan Fork, currently my MS student at FIU, and Anna Braswell, who received her MS from the University of Alabama, have both accepted positions in my lab through the Environment Ph.D. program.
Our paper describing diel and longitudinal patterns of nitrogen isotopes in the Ichetucknee River was just published in the Journal of Geophysical Research - Biogeosciences. You can get it here.
Building on our previous studies of diel variation in nutrient chemistry, we found large variation in N isotopes in the Ichetucknee River, FL. Unfortunately, it appears that uptake by plants (autotrophic assimilation) and denitrifying microbes have similar effects in this system, so we were not able to discriminate between these pathways. On the plus side, we observed some novel behaviors such as diel hysteresis, and found evidence that denitrification varies over the course of the day. Check it out! This is the home page of the Heffernan Lab at Duke University. We are part of the Ecohydrology and Hydroecology Research Group in the Nicholas School of the Environment at Duke University. Here you can find all sorts of information about our research, teaching, and outreach. If you have any questions, contact Dr. Heffernan. Feel free to look around!
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Welcome!This is the homepage of the Heffernan Lab at Duke University. Here you can find all sorts of information about our research, teaching, and outreach. If you have any questions, contact Dr. Heffernan. Dr. Jim HeffernanI am an Assistant Professor in the Nicholas School of the Environment at Duke University. My research is focused on the causes and consequences of major changes in ecosystem structure, mostly in streams and wetlands. Archives
May 2018
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The Heffernan Lab at Duke University |
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