Background
I am currently a postdoctoral research associate in Dr. Todd Royer's laboratory at Indiana University in Bloomington. I received my PhD from the Department of Biological Sciences at University of Notre Dame in Dr. Jennifer Tank's laboratory. I received a B.S. in Biology from Virginia Tech in 2002 where I worked at the Stream Team for 2 years. I was inspired to pursue research in stream biogeochemistry because of the support from Dr's. Jack Webster, Fred Benfield, and Maury Valett. Throughout my career so far, I have had the opportunity to pursue research in variety of different places and topics with numerous collaborators, which has served to stimulate my excitement about research particularly in stream ecosystems.
Research Interests
My general research interests are in stream ecosystem ecology and biogeochemistry. I have focused much of my research to-date on the cycling of carbon and nitrogen in streams and how human activities have influenced those cycles. However, I am interested in a variety of topics from cycling of other nutrients and interactions among nutrient cycles across ecosystems (e.g. aquatic, terrestrial, wetland), to restoration and conservation of our aquatic resources. I find streams and rivers a particularly stimulating area for biogeochemical research for a number of reasons: 1) they are the intermediaries between terrestrial and downstream aquatic ecosystems, 2) they combine zones of active biogeochemical cycling with the downstream movement of water, and 3) they are particularly threatened by human activities due to the density of stream and rivers and the landscape and the societal need for freshwater resources. Here are some of my current and former research projects:
The interactions among dissolved organic matter, denitrification rates, and microbial community structure in an agricultural stream network
For my postdoctoral research, I've been working with Todd Royer at Indiana University and Laura Leff at Kent State University on this NSF-funded project examining how changes in the quality and quantity of dissolved organic matter influence denitrification rates and the community structure of denitrifiers. We've been conducting this research in Sugar Creek located in central Indiana and in Leary Weber Ditch, a tributary to Sugar Creek. We predict that agricultural streams will vary in the quality and quantity of dissolved organic matter based on seasonal hydrology, nitrogen availability, and gross primary production. To answer this question, we have been measuring denitrification, characterizing dissolved organic matter availability, and analyzing for the abundance and diversity of the nosZ gene of microbial communities approximately monthly associated with hydrologically and biologically important periods. In addition, we have conducted 2 whole-stream labile carbon additions and examined the response of denitrification and community structure after 1 week. Other associated projects that I have been involved with include a budget of the sources and sinks for dissolved organic carbon in Leary Weber Ditch by Diana Oviedo Vargas, a PhD student in the Royer lab, and how different sources of dissolved organic matter affect denitrification rates in Leary Weber Ditch by Michael Brennan, an alumni from the Royer lab.
The influence of human land use on dissolved organic carbon and nitrogen cycling in streams
As a part of my dissertation, I quantified uptake of labile dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and ammonium (NH4+) in streams from the Kalamazoo River basin in southwestern Michigan. Research on nutrient cycling of inorganic nutrients indicates that human land use can lead to saturated N and P demand from increased N and P availability, but we know much less about how biotic demand for labile DOC and DON may change with human land use. This research indicates that increased inorganic N enrichment associated with human land use promotes high biotic demand for labile DOC and that NH4+ demand can be limited by the availability of labile DOC. Thus labile DOC availability can be one mechanism for N saturation in streams. I also found labile DON and NH4+ are taken up at similar rates and that the interaction between these two solutes may lead to saturation of overall N-uptake reducing the individual demand of both solutes. Overall, anthropogenic influences can alter cycling of labile DOC and DON and that further research is needed to understand the factors driving cycling of these compounds.
Additionally, I quantified the effect of diel fluctuations in gross primary production (GPP) on uptake of labile DOC and DON in open-canopy streams in Wyoming. Previous research has found that diel fluctuations in labile DOC and DON concentrations can be found during vernal algal blooms in forested streams as well as diel changes in NO3- uptake. My results indicated that NH4+ demand increased during the day relative to night, and was primarily driven by autotrophic activity. In contrast, labile DOC demand was driven primarily by heterotrophic uptake and showed no difference between day and night. Patterns in labile DON uptake were distinct from DOC and NH4+ and were driven mainly by P availability. In contrast to above, relative demand for labile DOC and DON was similar in magnitude to NH4+ indicating that all three solutes were highly bioreactive and cycled rapidly in these autotrophic headwaters streams.
The influence of human land use on stream biofilm nutrient limitation
As a part of my dissertation, I examined how stream biofilm nutrient limitation was influenced by human land use. Research on the influence of human land use has traditionally focused on autotrophic communities because of the unsightly side-effects of eutrophication and resultant algal blooms. These results add to our understanding by showing that heterotrophic biofilms may be more sensitive than autotrophs to nutrient enrichment associated with human land use via decreased nutrient limitation. In general, nutrient saturation of stream biofilms enhances nutrient export and may stimulate hypoxia in receiving water bodies and this project suggests a major part of this saturation may be associated with heterotrophic biofilms. It is well known that autotrophic biofilms are primarily driven by light availability and we found that the confounding influence of light and nutrient availability obscured the detection of human land use impacts on autotrophic biofilms further supporting the use of heterotrophic biofilm nutrient limitation to detect anthropogenic influences. In conclusion, management of streams to optimize stream health should incorporate the ecosystem metric of community respiration because of its sensitivity to nutrient enrichment associated with human land use.
The Lotic Intersite Nitrogen eXperiment II (LINXII)
I was lucky to be involved in the LINX II project during my PhD- a project that examined the influence of human land use on the fate of nitrate in streams. For more on the overall project, check out the project's website: http://www.biol.vt.edu/faculty/webster/linx//. As part of LINX II, I have been working on 2 projects, one examining the in-stream production of DON across multiple streams and the other quantifying the mass balance of N in each of the LINX II streams.
The effect of two-stage ditch construction on stream ecosystem function
In the Midwest, agricultural land use has altered stream ecosystem function by increasing nitrogen concentrations (N) via fertilizer use and changing stream channels to increase water flow to downstream ecosystems. The combination of increased anthropogenic N and faster water velocity leads to saturated stream nutrient demand resulting in degraded downstream habitat. This nutrient saturation has even been linked to eutrophication and seasonal hypoxia in the Gulf of Mexico. Recently, two-stage ditch construction has emerged as a possible solution to this problem. The two-stage ditch is unique because it retains the function of a ditch while leading to better water quality, stabilized banks, and self-sustained sediment removal ending ditch excavation. Although these results have been found from previous research, the influence of two-stage ditches on stream ecosystem functions has been overlooked. Stream ecosystem functions, such as primary production, are typically more sensitive to ecosystem change therefore are potentially a better indicator of the influence of restoration activities in comparison to estimates of biomass or water chemistry. The goal of this project was to investigate the influence of two-stage ditch construction on stream ecosystem metabolism. After one year of pre-manipulation data, we found highest gross primary production (GPP) and community respiration (CR) in the summer compared to the winter and higher GPP and CR in the treatment reach compared to the control reach. These results indicate that whole-stream metabolism varies greatly throughout the year and should be considered when investigating the effect of the manipulation in years to come. Additionally, there is a background difference between the reaches which we will have to account for when comparing the reaches post-manipulation. Overall, whole-stream metabolism was equivalent or even higher than other agricultural streams in North America indicating that demand for N by primary producers (algae and macrophytes) and heterotrophs (microbes and fungi) is probably at a maximum. Thus, this stream is currently working at maximum capacity to reduce the N load to downstream ecosystems.
The interactions among dissolved organic matter, denitrification rates, and microbial community structure in an agricultural stream network
For my postdoctoral research, I've been working with Todd Royer at Indiana University and Laura Leff at Kent State University on this NSF-funded project examining how changes in the quality and quantity of dissolved organic matter influence denitrification rates and the community structure of denitrifiers. We've been conducting this research in Sugar Creek located in central Indiana and in Leary Weber Ditch, a tributary to Sugar Creek. We predict that agricultural streams will vary in the quality and quantity of dissolved organic matter based on seasonal hydrology, nitrogen availability, and gross primary production. To answer this question, we have been measuring denitrification, characterizing dissolved organic matter availability, and analyzing for the abundance and diversity of the nosZ gene of microbial communities approximately monthly associated with hydrologically and biologically important periods. In addition, we have conducted 2 whole-stream labile carbon additions and examined the response of denitrification and community structure after 1 week. Other associated projects that I have been involved with include a budget of the sources and sinks for dissolved organic carbon in Leary Weber Ditch by Diana Oviedo Vargas, a PhD student in the Royer lab, and how different sources of dissolved organic matter affect denitrification rates in Leary Weber Ditch by Michael Brennan, an alumni from the Royer lab.
The influence of human land use on dissolved organic carbon and nitrogen cycling in streams
As a part of my dissertation, I quantified uptake of labile dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and ammonium (NH4+) in streams from the Kalamazoo River basin in southwestern Michigan. Research on nutrient cycling of inorganic nutrients indicates that human land use can lead to saturated N and P demand from increased N and P availability, but we know much less about how biotic demand for labile DOC and DON may change with human land use. This research indicates that increased inorganic N enrichment associated with human land use promotes high biotic demand for labile DOC and that NH4+ demand can be limited by the availability of labile DOC. Thus labile DOC availability can be one mechanism for N saturation in streams. I also found labile DON and NH4+ are taken up at similar rates and that the interaction between these two solutes may lead to saturation of overall N-uptake reducing the individual demand of both solutes. Overall, anthropogenic influences can alter cycling of labile DOC and DON and that further research is needed to understand the factors driving cycling of these compounds.
Additionally, I quantified the effect of diel fluctuations in gross primary production (GPP) on uptake of labile DOC and DON in open-canopy streams in Wyoming. Previous research has found that diel fluctuations in labile DOC and DON concentrations can be found during vernal algal blooms in forested streams as well as diel changes in NO3- uptake. My results indicated that NH4+ demand increased during the day relative to night, and was primarily driven by autotrophic activity. In contrast, labile DOC demand was driven primarily by heterotrophic uptake and showed no difference between day and night. Patterns in labile DON uptake were distinct from DOC and NH4+ and were driven mainly by P availability. In contrast to above, relative demand for labile DOC and DON was similar in magnitude to NH4+ indicating that all three solutes were highly bioreactive and cycled rapidly in these autotrophic headwaters streams.
The influence of human land use on stream biofilm nutrient limitation
As a part of my dissertation, I examined how stream biofilm nutrient limitation was influenced by human land use. Research on the influence of human land use has traditionally focused on autotrophic communities because of the unsightly side-effects of eutrophication and resultant algal blooms. These results add to our understanding by showing that heterotrophic biofilms may be more sensitive than autotrophs to nutrient enrichment associated with human land use via decreased nutrient limitation. In general, nutrient saturation of stream biofilms enhances nutrient export and may stimulate hypoxia in receiving water bodies and this project suggests a major part of this saturation may be associated with heterotrophic biofilms. It is well known that autotrophic biofilms are primarily driven by light availability and we found that the confounding influence of light and nutrient availability obscured the detection of human land use impacts on autotrophic biofilms further supporting the use of heterotrophic biofilm nutrient limitation to detect anthropogenic influences. In conclusion, management of streams to optimize stream health should incorporate the ecosystem metric of community respiration because of its sensitivity to nutrient enrichment associated with human land use.
The Lotic Intersite Nitrogen eXperiment II (LINXII)
I was lucky to be involved in the LINX II project during my PhD- a project that examined the influence of human land use on the fate of nitrate in streams. For more on the overall project, check out the project's website: http://www.biol.vt.edu/faculty/webster/linx//. As part of LINX II, I have been working on 2 projects, one examining the in-stream production of DON across multiple streams and the other quantifying the mass balance of N in each of the LINX II streams.
The effect of two-stage ditch construction on stream ecosystem function
In the Midwest, agricultural land use has altered stream ecosystem function by increasing nitrogen concentrations (N) via fertilizer use and changing stream channels to increase water flow to downstream ecosystems. The combination of increased anthropogenic N and faster water velocity leads to saturated stream nutrient demand resulting in degraded downstream habitat. This nutrient saturation has even been linked to eutrophication and seasonal hypoxia in the Gulf of Mexico. Recently, two-stage ditch construction has emerged as a possible solution to this problem. The two-stage ditch is unique because it retains the function of a ditch while leading to better water quality, stabilized banks, and self-sustained sediment removal ending ditch excavation. Although these results have been found from previous research, the influence of two-stage ditches on stream ecosystem functions has been overlooked. Stream ecosystem functions, such as primary production, are typically more sensitive to ecosystem change therefore are potentially a better indicator of the influence of restoration activities in comparison to estimates of biomass or water chemistry. The goal of this project was to investigate the influence of two-stage ditch construction on stream ecosystem metabolism. After one year of pre-manipulation data, we found highest gross primary production (GPP) and community respiration (CR) in the summer compared to the winter and higher GPP and CR in the treatment reach compared to the control reach. These results indicate that whole-stream metabolism varies greatly throughout the year and should be considered when investigating the effect of the manipulation in years to come. Additionally, there is a background difference between the reaches which we will have to account for when comparing the reaches post-manipulation. Overall, whole-stream metabolism was equivalent or even higher than other agricultural streams in North America indicating that demand for N by primary producers (algae and macrophytes) and heterotrophs (microbes and fungi) is probably at a maximum. Thus, this stream is currently working at maximum capacity to reduce the N load to downstream ecosystems.
sampling in Wyoming
sampling Sugar Creek in Indiana
Leary Weber Ditch
denitrification jar and gas sample vial
setting up a nutrient release in Michigan
Ditch creek in Wyoming
biofilm growing on glass substrata exhibiting nitrogen limitation (note the N and N+P treatments are darker green)
LINX II Michigan crew 2003
LINX II Wyoming crew 2005
Post-construction two-stage ditch
flood soon after construction
