Research Projects

Understanding hotspots and hot moments of greenhouse gas fluxes using soil oxygen.

Soil oxygen effects many ecosystem processes, including greenhouse gas (nitrous oxide, methane and carbon dioxide) production. However, soil oxygen is rarely directly measured, but is instead frequently modeled from easier-to-measure soil properties (e.g., soil moisture).  Previous soil oxygen measurements indicate measured soil oxygen fundamentally differs from modeled soil oxygen. Specifically, the models fail to predict rapid changes in soil oxygen observed in wetlands, ecosystems known to produce greenhouse gases.  These model-data mismatches may correspond to significant emission events of greenhouse gases.  Addressing this objective may transform scientific understanding of the soil processes leading to greenhouse gas emissions and the ability of an ecosystem to remove greenhouse gases from the atmosphere. Due to the low cost of measuring soil oxygen, the results of this project may ultimately lower the financial burden of mitigating greenhouse gas emissions.  The objective of this project is to understand if improving predictions of soil oxygen dynamics increases scientific knowledge of when and where greenhouse are emitted.

Collaborators: Five Rivers Metroparks, Terry Loecke, Trenton Franz, Kristy Hopfensperger, Ashely Smyth

Students Trained: Karla Jarecke (UNL M.S. 2015, SBB paper)

Undergraduates and Technicians: Cain Silvey, David Mosckiki

Funding: USDA-NIFA Carbon Cycle Science, NSF-Ecosystems


Water Quality, Climate Change and Agriculture


Terry Loecke, Marty St. Clair and Diego Riveros-Iregui installing stream nitrate sensors.

As a graduate student, I gained valuable insight into studying stream N cycling while training with leading stream ecologists on the Lotic Intersite Nitrogen eXperiment 2.  In that project, we established that agriculture and associated high nitrogen loads can impair a stream’s ability to remove N.  Future riverine N loading will be determined by the interaction between agriculture and climate change. I led a grant to NSF-Ecosystems (via the RAPID mechanism) to ask how drought-flood cycles, termed “weather whiplash,” would affect N loading to streams.  We’ve shown that weather whiplash, which is predicted to increase with climate change, increases riverine N loading.   The 2012 US drought created N-enriched soil; heavy spring (2013) rains mobilized soil N to streams, resulting in record-high N concentrations. Climate change is predicted to simultaneously increase drought and extreme rainfall frequency.  Our observations may be a harbinger of a future in which increased climatic variation amplifies negative trends in water quality in a region already grappling with impairments. We are continuing to explore the intersection of climate change, agriculture and water quality using an extensive nitrate monitoring network in Iowa.



Collaborators: Terry Loecke, Adam Ward, Steve Thomas, Diego Riveros-Irequi, Carrie Davis, Marty St. Clair

Students Trained: Kaycee Reynolds (UNL M.S., 2015, ES&T paper)

Undergraduates and Technicians: Craig Adams


Technological Advances for Understanding Water Quality


UNL’s Water Sampling UAV flying near a saline wetland/lake complex in Lincoln, NE.

If you’re an aquatic ecologist, you spend a lot of time collecting water samples. Some places are difficult to access and field crews and equipment (e.g., boats) are expensive to maintain. We are exploring how a water sampling Unmannned Aerial Vehicle (UAV) fits into the limnology tool box.  Working with computer scientists and robotics engineers, we’ve assisted with designing a UAV that can fly (in windy Midwestern conditions) and collect water samples, as well as do basic limnological profiling.  We are completing the field testing for this in 2016 to compare the UAV method to traditional hand-collected data or sensor data.

Collaborators: Carrick Detweiler, Sebastian Elbaum, Keunyea Song

Undergraduates and Technicians: Austin Brewer, Shawyan Ahmadian

Funding: USDA National Robotics Initiative


Biogeochemical Implications of Aquatic Ecosystem Restoration

Five of my former and current projects all contribute towards understanding the biogeochemical implications of aquatic ecosystem restoration techniques aimed at mediating wetland loss or eutrophication.

Wetland coverage in the CONUS has decreased dramatically over the last century, largely due to agricultural activities.  Increasingly, we recognized the important ecosystem services wetlands uniquely provide like carbon storage and water purification.  Thus, many programs are aimed at increasing wetland coverage by restoration.  I started working in restored wetlands in coastal North Carolina, at the Timberlake wetland, a long-term field site run by Emily Bernhardt and Marcelo Ardon.  We were interested in understanding how this coastal wetland would change as salt water intrusion, an analog of sea level rise, occurred under periods of drought. We found the response largely depends on the soil iron pool size and reactivity.  We continued work on this topic closer to home by studying naturally occurring saline wetlands near Lincoln.  Rather than understanding how salinization affected freshwater wetlands, as had been the case at Timberlake (and the study of a large review I co-authored), in this case, we were concerned that naturally saline sites were “freshening.” Post-doc Keunyea Song and students devised a clever saline addition experiment aimed at understanding if salt water additions to surface soils would aid in creating crusts for obligate plants to grow.

Midwestern (U.S.) lakes are highly eutrophic, thus, great management effort goes into mitigating the effects of eutrophication.  Alum is a popular tool to improve water clarity, albeit temporarily.  I started studying alum additions to lakes with the largest of them (known): Grand Lake St. Mary’s (OH), received two alum additions that totaled over $10M in costs.  We found that alum interacts with other biogeochemical cycling in unpredicted ways. We also studied the effectiveness of alum additions compared to control (no treatment) and rough fish removal methods in the Fremont Lakes of Nebraska.  We found that rough fish removal together with alum addition was best for improving water quality. We know that managing phosphorus (P) is critical for reducing eutrophication; most lake restoration strategies are aimed at altering P, including alum additions and dredging.  We measuring internal P loading in lakes restored at different times to understand how time since restoration affects P cycling.  We’ve found that hypereutrophic lakes (TP = ~200 ug/L; Chl a >100 ug/L) can create a perpetual phosphorus cycle, wherein biotic and abiotic mechanisms begin to support one another making it difficult to shut off internal loading.



Timberlake & Saline Restoration: Emily Bernhardt, Ashely Helton, Marcelo Ardon, Geoff Poole, Rob Payn, Keunyea Song

Grand Lake St. Mary’s & Fremont Lakes Alum Additions: Steve Thomas, Mike Archer, Mark Pegg, Kevin Pope, Chad Hammerschmidt, Geraldine Nogaro

Phosphorus Lags in Reservoir Restoration: Mike Archer, Keunyea Song

Students & Technicians: Valerie Schoepfer (Timberlake; UNL M.S., 2013), Christa Webber (Fremont, UNL M.S., 2014).

Funding: National Science Foundation (Timberlake), OH Water Institute (Grand Lake St. Mary’s), Nebraska Dept. of Environmental Quality (Fremont), Nebraska Saline Wetland Partnership (Saline Restoration)