Luke C Loken
Luke Loken is a Hydrologist with the Upper Midwest Water Science Center.
I am a hydrologist with the U.S. Geological Survey with a broad ecological background. My research focuses on hydrology and biogeochemistry in aquatic ecosystems at a range of ecological-scales. Some topics include: 1) The causes and consequences of spatial heterogeneity of water chemistry in lakes, rivers, and estuaries. 2) Drivers and patterns of ecosystem processes (metabolism, nutrient cycling, population dynamics). 3) The persistence of human-derived material (fertilizers, pesticides, chemicals) in river networks across landscapes.
Education and Certifications
Ph.D., Freshwater and Marine Sciences, University of Wisconsin-Madison, 2018
M.S., Freshwater and Marine Sciences, University of Wisconsin-Madison, 2014
B.S., Biology, University of Michigan, 2006
Affiliations and Memberships*
Center for Limnology (CFL) Affiliate
The Long-Term Ecological Research Network (LTER)
American Geophysical Union (AGU)
Association for the Sciences of Limnology and Oceanography (ASLO)
Society of Freshwater Sciences (SFS)
Science and Products
Below are data associated with this staff profile.
Below are publications associated with this staff profile.
Filter Total Items: 20
Spatial early warning signals in a lake manipulation
Rapid changes in state have been documented for many of Earth's ecosystems. Despite a growing toolbox of methods for detecting declining resilience or early warning indicators (EWIs) of ecosystem transitions, these methods have rarely been evaluated in whole-ecosystem trials using reference ecosystems. In this study, we experimentally tested EWIs of cyanobacteria blooms based on changes in the spa
Authors
Vince L. Butitta, Stephen R. Carpenter, Luke C. Loken, Michael L. Pace, Emily H. Stanley
Spatial heterogeneity of within-stream methane concentrations
Streams, rivers, and other freshwater features may be significant sources of CH4 to the atmosphere. However, high spatial and temporal variabilities hinder our ability to understand the underlying processes of CH4 production and delivery to streams and also challenge the use of scaling approaches across large areas. We studied a stream having high geomorphic variability to assess the underlying sc
Authors
John T. Crawford, Luke C. Loken, William E. West, Benjamin Crary, Seth A. Spawn, Nicholas Gubbins, Stuart E. Jones, Robert G. Striegl, Emily H. Stanley
Spatial variability of CO2 concentrations and biogeochemistry in the Lower Columbia River
Carbon dioxide (CO2) emissions from rivers and other inland waters are thought to be a major component of regional and global carbon cycling. In large managed rivers such as the Columbia River, contemporary ecosystem changes such as damming, nutrient enrichment, and increased water residence times may lead to reduced CO2 concentrations (and emissions) due to increased primary production, as has be
Authors
John T. Crawford, David Butman, Luke C. Loken, Philipp Stadler, Catherine Kuhn, Robert G. Striegl
The ecology of methane in streams and rivers: Patterns, controls, and global significance
Streams and rivers can substantially modify organic carbon (OC) inputs from terrestrial landscapes, and much of this processing is the result of microbial respiration. While carbon dioxide (CO2) is the major end-product of ecosystem respiration, methane (CH4) is also present in many fluvial environments even though methanogenesis typically requires anoxic conditions that may be scarce in these sys
Authors
Emily H. Stanley, Nora J. Casson, Samuel T. Christel, John T. Crawford, Luke C. Loken, Samantha K. Oliver
Regional-scale controls on dissolved nitrous oxide in the Upper Mississippi River
The U.S. Corn Belt is one of the most intensive agricultural regions of the world and is drained by the Upper Mississippi River (UMR), which forms one of the largest drainage basins in the U.S. While the effects of agricultural nitrate (NO3-) on water quality in the UMR have been well documented, its impact on the production of nitrous oxide (N2O) has not been reported. Using a novel equilibration
Authors
P.A. Turner, T.J. Griffis, J.M. Baker, X. Lee, John T. Crawford, Luke C. Loken, R.T. Venterea
Basin scale controls on CO2 and CH4 emissions from the Upper Mississippi River
The Upper Mississippi River, engineered for river navigation in the 1930s, includes a series of low-head dams and navigation pools receiving elevated sediment and nutrient loads from the mostly agricultural basin. Using high-resolution, spatially resolved water quality sensor measurements along 1385 river kilometers, we show that primary productivity and organic matter accumulation affect river ca
Authors
John T. Crawford, Luke C. Loken, Emily H. Stanley, Edward G. Stets, Mark M. Dornblaser, Robert G. Striegl
High-speed limnology: Using advanced sensors to investigate spatial variability in biogeochemistry and hydrology
Advanced sensor technology is widely used in aquatic monitoring and research. Most applications focus on temporal variability, whereas spatial variability has been challenging to document. We assess the capability of water chemistry sensors embedded in a high-speed water intake system to document spatial variability. This new sensor platform continuously samples surface water at a range of speeds
Authors
John T. Crawford, Luke C. Loken, Nora J. Casson, Colin Smith, Amanda G. Stone, Luke A. Winslow
Ebullitive methane emissions from oxygenated wetland streams
Stream and river carbon dioxide emissions are an important component of the global carbon cycle. Methane emissions from streams could also contribute to regional or global greenhouse gas cycling, but there are relatively few data regarding stream and river methane emissions. Furthermore, the available data do not typically include the ebullitive (bubble-mediated) pathway, instead focusing on emiss
Authors
John T. Crawford, Emily H. Stanley, Seth A. Spawn, Jacques C. Finlay, Robert G. Striegl
Non-USGS Publications**
Coyne, K. (2022), What You Think About How Soil and Water Health Connect May Be Wrong. CSA News, 67: 4-10. https://doi.org/10.1002/csan.20907
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Below are software associated with this staff profile.
Science and Products
Below are data associated with this staff profile.
Below are publications associated with this staff profile.
Filter Total Items: 20
Spatial early warning signals in a lake manipulation
Rapid changes in state have been documented for many of Earth's ecosystems. Despite a growing toolbox of methods for detecting declining resilience or early warning indicators (EWIs) of ecosystem transitions, these methods have rarely been evaluated in whole-ecosystem trials using reference ecosystems. In this study, we experimentally tested EWIs of cyanobacteria blooms based on changes in the spa
Authors
Vince L. Butitta, Stephen R. Carpenter, Luke C. Loken, Michael L. Pace, Emily H. Stanley
Spatial heterogeneity of within-stream methane concentrations
Streams, rivers, and other freshwater features may be significant sources of CH4 to the atmosphere. However, high spatial and temporal variabilities hinder our ability to understand the underlying processes of CH4 production and delivery to streams and also challenge the use of scaling approaches across large areas. We studied a stream having high geomorphic variability to assess the underlying sc
Authors
John T. Crawford, Luke C. Loken, William E. West, Benjamin Crary, Seth A. Spawn, Nicholas Gubbins, Stuart E. Jones, Robert G. Striegl, Emily H. Stanley
Spatial variability of CO2 concentrations and biogeochemistry in the Lower Columbia River
Carbon dioxide (CO2) emissions from rivers and other inland waters are thought to be a major component of regional and global carbon cycling. In large managed rivers such as the Columbia River, contemporary ecosystem changes such as damming, nutrient enrichment, and increased water residence times may lead to reduced CO2 concentrations (and emissions) due to increased primary production, as has be
Authors
John T. Crawford, David Butman, Luke C. Loken, Philipp Stadler, Catherine Kuhn, Robert G. Striegl
The ecology of methane in streams and rivers: Patterns, controls, and global significance
Streams and rivers can substantially modify organic carbon (OC) inputs from terrestrial landscapes, and much of this processing is the result of microbial respiration. While carbon dioxide (CO2) is the major end-product of ecosystem respiration, methane (CH4) is also present in many fluvial environments even though methanogenesis typically requires anoxic conditions that may be scarce in these sys
Authors
Emily H. Stanley, Nora J. Casson, Samuel T. Christel, John T. Crawford, Luke C. Loken, Samantha K. Oliver
Regional-scale controls on dissolved nitrous oxide in the Upper Mississippi River
The U.S. Corn Belt is one of the most intensive agricultural regions of the world and is drained by the Upper Mississippi River (UMR), which forms one of the largest drainage basins in the U.S. While the effects of agricultural nitrate (NO3-) on water quality in the UMR have been well documented, its impact on the production of nitrous oxide (N2O) has not been reported. Using a novel equilibration
Authors
P.A. Turner, T.J. Griffis, J.M. Baker, X. Lee, John T. Crawford, Luke C. Loken, R.T. Venterea
Basin scale controls on CO2 and CH4 emissions from the Upper Mississippi River
The Upper Mississippi River, engineered for river navigation in the 1930s, includes a series of low-head dams and navigation pools receiving elevated sediment and nutrient loads from the mostly agricultural basin. Using high-resolution, spatially resolved water quality sensor measurements along 1385 river kilometers, we show that primary productivity and organic matter accumulation affect river ca
Authors
John T. Crawford, Luke C. Loken, Emily H. Stanley, Edward G. Stets, Mark M. Dornblaser, Robert G. Striegl
High-speed limnology: Using advanced sensors to investigate spatial variability in biogeochemistry and hydrology
Advanced sensor technology is widely used in aquatic monitoring and research. Most applications focus on temporal variability, whereas spatial variability has been challenging to document. We assess the capability of water chemistry sensors embedded in a high-speed water intake system to document spatial variability. This new sensor platform continuously samples surface water at a range of speeds
Authors
John T. Crawford, Luke C. Loken, Nora J. Casson, Colin Smith, Amanda G. Stone, Luke A. Winslow
Ebullitive methane emissions from oxygenated wetland streams
Stream and river carbon dioxide emissions are an important component of the global carbon cycle. Methane emissions from streams could also contribute to regional or global greenhouse gas cycling, but there are relatively few data regarding stream and river methane emissions. Furthermore, the available data do not typically include the ebullitive (bubble-mediated) pathway, instead focusing on emiss
Authors
John T. Crawford, Emily H. Stanley, Seth A. Spawn, Jacques C. Finlay, Robert G. Striegl
Non-USGS Publications**
Coyne, K. (2022), What You Think About How Soil and Water Health Connect May Be Wrong. CSA News, 67: 4-10. https://doi.org/10.1002/csan.20907
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Below are software associated with this staff profile.
*Disclaimer: Listing outside positions with professional scientific organizations on this Staff Profile are for informational purposes only and do not constitute an endorsement of those professional scientific organizations or their activities by the USGS, Department of the Interior, or U.S. Government