John T Crawford (Former Employee)
Science and Products
Network controls on mean and variance of nitrate loads from the Mississippi River to the Gulf of Mexico
Excessive nitrate loading to the Gulf of Mexico (GoM) has caused widespread hypoxia over many decades. Despite recent reductions in nitrate loads observed at local scales, decreases in nitrate loading from the MRB to the GoM have been small (1.58 % during 2002-2012) with a low level of analytical confidence in this trend. This work seeks to...
Crawford, John T.; Stets, Edward G.; Sprague, Lori A. Limited nitrate retention capacity in the Upper Mississippi River
The Mississippi River and other large rivers have the potential to regulate nitrogen export from terrestrial landscapes, and thus mitigate eutrophication in downstream aquatic ecosystems. In large rivers, human-constructed impoundments and connected backwaters may facilitate nitrogen removal; however, the capacity of these features is poorly...
Loken, Luke; Crawford, John T.; Dornblaser, Mark M.; Striegl, Robert G.; Houser, Jeffrey N.; Turner, Peter A; Stanley, Emily H. Methane in groundwater from a leaking gas well, Piceance Basin, Colorado, USA
Site-specific and regional analysis of time-series hydrologic and geochemical data collected from 15 monitoring wells in the Piceance Basin indicated that a leaking gas well contaminated shallow groundwater with thermogenic methane. The gas well was drilled in 1956 and plugged and abandoned in 1990. Chemical and isotopic data showed the...
McMahon, Peter B.; Thomas, Judith C.; Crawford, John T.; Dornblaser, Mark M.; Hunt, Andrew G. 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...
Crawford, John T.; Loken, Luke C.; West, William E.; Crary, Benjamin; Spawn, Seth A.; Gubbins, Nicholas; Jones, Stuart E.; Striegl, Robert G.; Stanley, Emily H. CO2 time series patterns in contrasting headwater streams of North America
We explored the underlying patterns of temporal stream CO2 partial pressure (pCO2) variability using highfrequency sensors in seven disparate headwater streams distributed across the northern hemisphere. We also compared this dataset of [40,000 pCO2 records with other published records from lotic systems. Individual stream sites exhibited...
Crawford, John T.; Stanley, Emily H.; Dornblaser, Mark M.; Striegl, Robert G. 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...
Crawford, John T.; Butman, David; Loken, Luke; Philipp Stadler; Catherine Kuhn; Striegl, Robert G. Controls on methane concentrations and fluxes in streams draining human-dominated landscapes
Streams and rivers are active processors of carbon, leading to significant emissions of CO2 and possibly CH4 to the atmosphere. Patterns and controls of CH4 in fluvial ecosystems remain relatively poorly understood. Furthermore, little is known regarding how major human impacts to fluvial ecosystems may be transforming their role as CH4 producers...
Crawford, John T.; Stanley, Emily H. 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...
Turner, P.A.; Griffis, T.J.; Baker, J.M.; Lee, X.; Crawford, John T.; Loken, Luke C.; Venterea, R.T. 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...
Stanley, Emily H.; Casson, Nora J.; Christel, Samuel T.; Crawford, John T.; Loken, Luke C.; Oliver, Samantha K. 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...
Crawford, John T.; Loken, Luke C.; Stanley, Emily H.; Stets, Edward G.; Dornblaser, Mark M.; Striegl, Robert G. Source limitation of carbon gas emissions in high-elevation mountain streams and lakes
Inland waters are an important component of the global carbon cycle through transport, storage, and direct emissions of CO2 and CH4 to the atmosphere. Despite predictions of high physical gas exchange rates due to turbulent flows and ubiquitous supersaturation of CO2—and perhaps also CH4—patterns of gas emissions are essentially undocumented for...
Crawford, John T.; Dornblaser, Mark M.; Stanley, Emily H.; Clow, David W.; Striegl, Robert G. 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...
Crawford, John T.; Loken, Luke C.; Casson, Nora J.; Smith, Collin; Stone, Amanda G.; Winslow, Luke A.