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2017

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Full-Text Articles in Civil and Environmental Engineering

Induced Earthquakes And Public Safety, Lyndsey L. Dickson May 2017

Induced Earthquakes And Public Safety, Lyndsey L. Dickson

Civil Engineering Undergraduate Honors Theses

Like the number of earthquakes felt in Oklahoma, the number of media reports regarding large-magnitude earthquakes in Oklahoma has increased in recent years. News headlines that mention property damage and question who is responsible have sparked heated debated. In this document, a discussion is presented over the responsibility of engineers for the public’s safety in relation to earthquakes. Input from various groups is discussed, the action taken in Oklahoma is outlined, and ethical obligations presented by the American Society of Civil Engineers are considered. The United States Geological Survey (USGS) has reported a major grievance against building-code committees, but many …


Fatigue Analysis Of The Greenup Lock Gate On The Ohio River, Maggie Langston May 2017

Fatigue Analysis Of The Greenup Lock Gate On The Ohio River, Maggie Langston

Civil Engineering Undergraduate Honors Theses

This thesis analyzes damage due to fatigue of a typical lock gate on the United States waterway transportation system. Functioning lock gates are essential for this mode of transportation because they control water levels and provide access through dams for ships. Fatigue cracking is caused by cyclic loading and corrosion. Cyclic loading on a lock gate was imitated using a finite element model. This model was used to calculate stress ranges for a cycle so that the number of cycles to failure could be calculated. The proportion of cycles to cycles to failure is known as the fatigue capacity. A …


The Effects Of Aggregate Size On Shear Dynamic Modulus From Torsion Bar, Farida Mahmud May 2017

The Effects Of Aggregate Size On Shear Dynamic Modulus From Torsion Bar, Farida Mahmud

Civil Engineering Undergraduate Honors Theses

PavementME Design is based on mechanistic-empirical principles, which take the properties of layer materials into account in predicting pavement responses and performance. Of these principles, dynamic modulus is one of the most important. Dynamic modulus measures strain in response to the applied stress, which mimics loads from traffic and the corresponding deformation of the asphalt pavement. The traditional test for dynamic modulus in the uniaxial configuration cannot be performed on field cores due to lift thickness. Owing to that, the Indirect Tension and torsion bar configuration were developed. This research will focus on the torsion bar, which requires specimens that …


Predicted Vs Measured Initial Camber In Precast Prestressed Concrete Girders, Luke T. Freedle May 2017

Predicted Vs Measured Initial Camber In Precast Prestressed Concrete Girders, Luke T. Freedle

Civil Engineering Undergraduate Honors Theses

Prestressing of concrete is the introduction of permanent internal stresses in a structure or system in order to improve its performance. Concrete is strong in compression but weak in tension. The tensile strength of concrete is approximately 10% of the concrete’s compressive strength. Prestressing strands helps counteract this by introducing compressive stress in the area that will experience tensile stress because of the service load. In precast prestressed concrete girders, strands are placed in the bottom flange of the girder. These strands are tensioned to approximately 75% of their ultimate tensile capacity. After placing the concrete and after the required …


Effects Of Wash Water On The Compressive Strength Of Concrete, Gabriel W. Cook May 2017

Effects Of Wash Water On The Compressive Strength Of Concrete, Gabriel W. Cook

Civil Engineering Undergraduate Honors Theses

Due to the scale of concrete production throughout the world, there is potential for implementing methodologies that reduce the environmental impact of concrete processes. One intriguing solution is utilizing concrete wash water as mixing water. Concrete wash water is the water created by concrete production. If wash water can be reused, this would provide a safe disposal of the water and save millions of gallons of potable water per year (Indiana, 2014). For this to become a realistic option for concrete plants, it is important that the wash water does not decrease the compressive strength of concrete, otherwise the cost …


Effectiveness Of Small Strain Shear Wave Velocity As A Property For Assessing Damage Associated With Alkali-Silica Reaction In Concrete, Dillon K. Self May 2017

Effectiveness Of Small Strain Shear Wave Velocity As A Property For Assessing Damage Associated With Alkali-Silica Reaction In Concrete, Dillon K. Self

Civil Engineering Undergraduate Honors Theses

This research paper details the monitoring of expansion and shear wave velocity for fifteen concrete prisms cast in accordance with ASTM C1293 utilizing five mix designs with varying levels of ASR reactivity. Jobe sand and sodium hydroxide pellets were added in various quantities to increase the reactivity of the prisms. Strain measurements of the prisms were taken according to ASTM C129 and the shear wave velocity of the prisms was measured using ASTM C215. These measurements were taken weekly, then monthly for over a year. It was determined that shear wave velocity of the prisms decrease linearly as strain in …


Impacts Of Ozone Dose And Empty Bed Contact Time On Bulk Organic Removal And Disinfection Byproduct Mitigation In Ozone-Biofiltration Systems, Mayara Aquino May 2017

Impacts Of Ozone Dose And Empty Bed Contact Time On Bulk Organic Removal And Disinfection Byproduct Mitigation In Ozone-Biofiltration Systems, Mayara Aquino

UNLV Theses, Dissertations, Professional Papers, and Capstones

In areas where water shortages have compromised water supplies, potable reuse is a promising solution. However, additional research is needed to identify and/or optimize cost-effective treatment technologies to demonstrate compliance with potable reuse regulations. Treatment trains employing reverse osmosis (RO) and advanced oxidation, a combination known as ‘full advanced treatment’ (FAT), are required by the California Division of Drinking Water (CDDW) for surface water augmentation and direct injection of recycled water into local aquifers. A maximum concentration of 0.5 mg/L of wastewater-derived total organic carbon (TOC) is also required by CDDW in all groundwater recharge applications. This appears to be …


A Study On Human Evacuation Behavior Involving Individuals With Disabilities In A Building, Nirdosh Gaire May 2017

A Study On Human Evacuation Behavior Involving Individuals With Disabilities In A Building, Nirdosh Gaire

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The individuals with disabilities are disproportionately vulnerable to hazards. However, there is very little research inquiry focused on evacuation environments and the behavior of individuals with disabilities. The most widely applied computational method used to study how effective the built environment facilities emergency evacuations in individuals-based modeling. Current pedestrian evacuation models rarely include individuals with disabilities in their simulated populations due to there being very few empirical studies of the evacuation behavior of individuals with disabilities. As a result, the models do not replicate accurate patterns of pedestrian or evacuation behavior of a heterogeneous population, which results in the evacuation …


Short And Long-Term Structural Health Monitoring Of Highway Bridges, Navid Zolghadri May 2017

Short And Long-Term Structural Health Monitoring Of Highway Bridges, Navid Zolghadri

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Structural Health Monitoring (SHM) is a promising tool for condition assessment of bridge structures. SHM of bridges can be performed for different purposes in long or short-term. A few aspects of short- and long-term monitoring of highway bridges are addressed in this research.

Without quantifying environmental effects, applying vibration-based damage detection techniques may result in false damage identification. As part of a long-term monitoring project, the effect of temperature on vibrational characteristics of two continuously monitored bridges are studied. Natural frequencies of the structures are identified from ambient vibration data using the Natural Excitation Technique (NExT) along with the Eigen …


Impact Of Using Spatially Distributed Soils Information On Flood Hydrograph Simulation With Hec-Hms, Matthew J. Nelson May 2017

Impact Of Using Spatially Distributed Soils Information On Flood Hydrograph Simulation With Hec-Hms, Matthew J. Nelson

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Hydrologic rainfall-runoff models employ numerical equations to simulate the soil absorption of rainfall and resulting runoff. A number of methods have been developed to model these processes, but the parameters used to define these methods can be difficult to directly measure due to the variable nature of soil properties. They often rely on estimation of hydraulic and hydrologic parameters and calibration to produce accurate results.

A challenge with runoff method parameterization is the need for oversimplification using a lumped modeling approach. While distributed hydrologic modeling techniques are now available, distributed runoff methods are limited in use due to the tradition …


Durability Of Glass Fiber-Reinforced Polymer Bars In Seawater-Contaminated Concrete, Abdelrahman A. E. Alsallamin May 2017

Durability Of Glass Fiber-Reinforced Polymer Bars In Seawater-Contaminated Concrete, Abdelrahman A. E. Alsallamin

Theses

This research aims to investigate the durability performance and microstructure characteristics of two different types of glass fiber-reinforced polymer (GFRP) bars in severe environment. GFRP bars encased in seawater-contaminated concrete were immersed in tap water for 5, 10, and 15 months at temperatures of 20, 40, and 60°C. Half of the specimens were conditioned under a sustained load of 25% of their ultimate strength whereas the other half was conditioned without load. Following conditioning, the GFRP bars were retrieved then tested to failure under uniaxial tension. Microstructure analysis was performed by employing differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) …


Evaluating The Distributional Effects Of Regional Transportation Plans And Projects, Kristine Williams, Aaron Golub May 2017

Evaluating The Distributional Effects Of Regional Transportation Plans And Projects, Kristine Williams, Aaron Golub

TREC Final Reports

Metropolitan planning organizations (MPOs) have long been required to consider the equity implications of their regional transportation plans and processes. Funded by the National Institute for Transportation and Communities, this research aims to provide additional guidance to MPOs on how to evaluate distributional equity in regional plans and projects. The report begins with an overview of federal requirements related to equity in transportation planning. We then synthesize contemporary methods for measuring transportation equity and the distributional effects of plans and projects from a review of the literature and MPO plans and studies. The report concludes with exploratory case studies of …


Spatial And Temporal Study Of Heat Transport Of Hydrothermal Features In Norris Geyser Basin, Yellowstone National Park, Ruba A. M. Mohamed May 2017

Spatial And Temporal Study Of Heat Transport Of Hydrothermal Features In Norris Geyser Basin, Yellowstone National Park, Ruba A. M. Mohamed

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Monitoring thermal activity in Yellowstone National Park is required by the United States Congress to maintain the safety of the visitors and park service personnel and to protect the integrity of the park. This dissertation is part of a study initiated in the early 2000s to monitor the thermal activity in the park with focus on Norris Geyser Basin, the hottest geyser basin in the park. The study is considered the first multiple-year study in the basin which took place between August 2008 and October 2013. In this study, at least one thermal infrared image was acquired every year using …


Developing A General Methodology For Evaluating Composite Action In Insulated Wall Panels, Jaiden Thomas Olsen May 2017

Developing A General Methodology For Evaluating Composite Action In Insulated Wall Panels, Jaiden Thomas Olsen

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Precast Concrete Sandwich Panel Walls (PCSPW’s) have been in use for over 60 years. They provide a very efficient building envelope for many buildings. Characteristic PCSPW’s comprise an outer and inner layer (or wythe) of concrete separated by an insulating material. To use all of the material as efficiently as possible, the layers are attached by connectors which penetrate through the insulating layer and are embedded in either concrete wythe. These connectors make it possible for both layers of the wall to work together when resisting loads. The connectors are made out of plastic, or FRP, to prevent heat transfer …


High Early-Age Strength Concrete For Rapid Repair, Matthew O. Maler May 2017

High Early-Age Strength Concrete For Rapid Repair, Matthew O. Maler

UNLV Theses, Dissertations, Professional Papers, and Capstones

The aim of this research was to identify High Early-Age Strength (HES) concrete batch designs, and evaluate their suitability for use in the rapid repair of highways and bridge decks. To this end, two criteria needed to be met; a minimum compressive strength of 20.68 MPa (3000 psi) in no later than 12 hours, and a drying shrinkage of less than 0.06 % at 28 days after curing. The evaluations included both air-entrained, and non-air-entrained concretes.

The cement types chosen for this study included Type III and Type V Portland cement and “Rapid Set” − a Calcium Sulfoaluminate (CSA) cement. …


Statistical Models Of I-15 Bridge C-846: Changes In Natural Frequencies Due To Temperature, Gilbert Nichols May 2017

Statistical Models Of I-15 Bridge C-846: Changes In Natural Frequencies Due To Temperature, Gilbert Nichols

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Structural Health monitoring is to determine the condition of a bridge based on instrument measurements. The C-846 Bridge in Salt Lake City has such instrumentation. The bridge is located in Salt Lake City at about 2100 South and Interstate 15. This bridge has two kinds of instruments on it: accelerometers and thermocouples. The accelerometers measure the vibrations of the bridge. The accelerometers have been recording data on the bridge since 2001. The thermocouples, which measure temperature, were added as part of this thesis in April 2016.

In light of recent research, damage may be detected from measuring the change in …


Comparing The Effect Of Carbon Sources, Lactate And Whey, On Biological Reductive Dechlorination Of Tce In Laboratory Flow Through Columns, Sarah M. Kissell May 2017

Comparing The Effect Of Carbon Sources, Lactate And Whey, On Biological Reductive Dechlorination Of Tce In Laboratory Flow Through Columns, Sarah M. Kissell

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Trichloroethylene (TCE) is a chlorinated solvent most commonly used as an industrial degreaser for cleaning mechanical equipment. Historic improper management and disposal of TCE has resulted in contaminated soil and groundwater across the United States, including Hill Air Force Base in Utah. The abundance of TCE in the environment presents a public health risk because it is categorized as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC).

The purpose of this study was to improve the bioremediation techniques of biostimulation and bioaugmentation. A continuous flow-through column study was performed where columns packed with aquifer material …


Prestress Losses And Temperature Effects On A Deck Bulb Tee Girder Bridge, Phillip Powelson May 2017

Prestress Losses And Temperature Effects On A Deck Bulb Tee Girder Bridge, Phillip Powelson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

The Utah Transportation Center (UTC), in partnership with the Mountain Plains Consortium (MPC), sponsored a study to investigate the differences in prestress losses and temperature gradients in a concrete deck bulb tee girder bridge. The Millville Bridge was built as an access point to the Ridgeline High School in Millville, Utah. The bridge was built in 2016 and presently supports two lanes of traffic.

Changes in prestress were measured with a total of 16 vibrating wire strain gauges located at four cross-sections. Temperature gradients were measured with a total of 50 thermocouples located at five cross-section locations, four of which …


Estimation Of Groundwater Loads Into A Coastal Estuary Using Seawat, Antonio S. Berber Jr. May 2017

Estimation Of Groundwater Loads Into A Coastal Estuary Using Seawat, Antonio S. Berber Jr.

Theses and Dissertations

The research of regional groundwater flow is of vital importance at the Indian River Lagoon (IRL) due to the potential contribution groundwater flow has on nutrients into the IRL. If too many nutrients are introduced into the IRL, algal blooms could occur and impact the health of IRL system. The IRL is a coastal estuary located on the east coast of Florida. Submarine groundwater seepages (SGD) and groundwater loads into the IRL were numerically estimated by using SEAWAT, a program designed to simulate variable-density groundwater flow coupled with multi-species solute transport. Models were completed at three different study transects that …


Faculty Perceptions Of Student Recruitment And Retention In Stem Fields, Eshani Gandhi-Lee, Heather Skaza, Erica Marti, Peter G. Schrader, Marykay Orgill Apr 2017

Faculty Perceptions Of Student Recruitment And Retention In Stem Fields, Eshani Gandhi-Lee, Heather Skaza, Erica Marti, Peter G. Schrader, Marykay Orgill

Civil and Environmental Engineering and Construction Faculty Research

According to the President's Council of Advisors on Science and Technology (PCAST, 2012), there is a need to produce one million more STEM (Science, Technology, Engineering, and Mathematics) graduates in the U.S. over the next decade. Thus, more students must be recruited into and retained in STEM degrees of study. Because faculty are considered influential in students' choices to pursue and remain in STEM disciplines, we interviewed university STEM faculty in order to identify their perceptions of student recruitment and retention in STEM fields. Our data indicate that faculty are generally unaware of or not worried about the need to …


Transport Planning In Delft, Netherlands, Jan Nederveen Apr 2017

Transport Planning In Delft, Netherlands, Jan Nederveen

PSU Transportation Seminars

While the Netherlands is known today for the highest bicycling rates in the world, this movement only began in the 1970s. Transportation policy has been one of the critical keys to reducing automobile trips in the Netherlands.

Visiting scholar Jan Nederveen will present on transportation planning in the compact, densely populated city of Delft. Delft has been a city since 1246, and the historic street pattern is still visible today. The city has grown to 100,000 residents and covers an area of 5 square kilometers. Twenty years ago, the council decided to change the transportation philosophy from a car-oriented system …


Smartvid.Io, Purdue Ect Team Apr 2017

Smartvid.Io, Purdue Ect Team

ECT Fact Sheets Archive

The collection, organization, and retrieval of industrial media is a pervasive challenge that is especially glaring for companies in the AEC industry. Construction projects often generate large volumes of pictures & videos from the field for tracking progress and communicating between engineers, contractors, and subcontractors. It is not uncommon for field personnel to capture hundreds of photos per week on any given jobsite.

Smartvid.io is a cloud-based software solution designed for the specific needs of industrial media. The application’s internal deep-learning engines, collectively nicknamed VINNIE (for ‘Very Intelligent Neural Network for Insight and Evaluation’), use speech and image recognition to …


Hillman Composite Beam (Hcb®), Purdue Ect Team Apr 2017

Hillman Composite Beam (Hcb®), Purdue Ect Team

ECT Fact Sheets Archive

The Hillman-Composite Beam (HCB®), is an innovative structural member for use in highway and railroad bridges as well as marine facilities. The HCB is essentially a lightweight reinforced concrete beam strengthened and protected by a corrosion-resistant and resilient Fiberglass Reinforced Polymer (FRP) shell.

The beam is comprised of three main components, a concrete arch (compression reinforcement), an FRP bottom flange encapsulating steel strands tying the ends of the arch together (tension reinforcement) and the FRP shell. Galvanized Rebar “shear connectors” are used to make the beam composite with the concrete deck in the same manner as pre-stressed concrete beams.

The …


Taruc: A Topology-Aware Resource Utility And Contention Benchmark, Gavin Baker, Chris Lupo Apr 2017

Taruc: A Topology-Aware Resource Utility And Contention Benchmark, Gavin Baker, Chris Lupo

Civil and Environmental Engineering

Computer architects have increased hardware parallelism and power efficiency by integrating massively parallel hardware accelerators (coprocessors) into compute systems. Many modern HPC clusters now consist of multi-CPU nodes along with additional hardware accelerators in the form of graphics processing units (GPUs). Each CPU and GPU is integrated with system memory via communication links (QPI and PCIe) and multi-channel memory controllers. The increasing density of these heterogeneous computing systems has resulted in complex performance phenomena including nonuniform memory access (NUMA) and resource contention that make application performance hard to predict and tune. This paper presents the Topology Aware Resource Usability and …


A Conceptual Framework For Understanding Latent Demand: Accounting For Unrealized Activities And Travel, Kelly Clifton Apr 2017

A Conceptual Framework For Understanding Latent Demand: Accounting For Unrealized Activities And Travel, Kelly Clifton

PSU Transportation Seminars

Latent demand—the activities and travel that are desired but unrealized because of constraints—have been historically examined from the standpoint of understanding the impacts of proposed capacity or service improvements on travel demand.

Drawing on work from a variety of theoretical perspectives, this paper presents a broader conceptual view of latent demand that provides a useful framework for researching and understanding these unmet needs. This is important from an equity standpoint, as it provides insights into to questions of transport disadvantage, social exclusion and poverty.

The framework presented here is theoretical in nature and untested empirically. This study aims to promote …


Effects Of Tire Inclination (Turning Traffic) And Dynamic Loading On The Pavement Stress-Strain Responses Using 3-D Finite Element Modeling, Xiaodi Hu, Abu N.M. Faruk, Jun Zhang, Mena I. Souliman, Lubinda F. Walubita Apr 2017

Effects Of Tire Inclination (Turning Traffic) And Dynamic Loading On The Pavement Stress-Strain Responses Using 3-D Finite Element Modeling, Xiaodi Hu, Abu N.M. Faruk, Jun Zhang, Mena I. Souliman, Lubinda F. Walubita

Civil Engineering Faculty Publications and Presentations

In this study, ABAQUS finite element (FE) modeling in three-dimensional (3-D) loading mode was utilized to analytically investigate and quantify the effects of tire inclination and dynamic loading on the stress-strain responses of a pavement structure under varying loading and environmental conditions. The input variables for modeling consisted of actual laboratory and field data obtained from an in-service highway US 59 and included the in-situ pavement structure, material properties (i.e., modulus and shear strength), traffic, and climatic (i.e., temperature) data. Computational modeling and sensitivity analyses were conducted through variation of the following two input variables with a focus on the …


The Significance Of A High Resolution 2d Hydraulic Model Including Green Infrastructure For Assessment Of Coastal Community Vulnerability And Resilience, Katie M. Miller Apr 2017

The Significance Of A High Resolution 2d Hydraulic Model Including Green Infrastructure For Assessment Of Coastal Community Vulnerability And Resilience, Katie M. Miller

Theses and Dissertations

This paper outlines the development of an enhanced hydraulic flood model that uses a fine-scale grid to analyze significant areas of flooding for improved flood predictions and resiliency planning. This study modeled the extent of Atlantic City and Camden, New Jersey. The capabilities of the model were compared to coarser national models, HAZUS-MH and SLOSH, to understand the significance of fine-scale hydraulic modeling. The results illustrated that the HAZUS and SLOSH models showed gaps in some areas and lacked accuracy due to lower resolution. This paper also describes how these developed models show the impacts of severe storms, and the …


Comparison Of Chemical-Use Between Hydraulic Fracturing, Acidizing, And Routine Oil And Gas Development, Mary Kay Camarillo, William T. Stringfellow, J. K. Domen, S. B. Shonkoff Apr 2017

Comparison Of Chemical-Use Between Hydraulic Fracturing, Acidizing, And Routine Oil And Gas Development, Mary Kay Camarillo, William T. Stringfellow, J. K. Domen, S. B. Shonkoff

All Faculty Articles - School of Engineering and Computer Science

The potential hazards and risks associated with well-stimulation in unconventional oil and gas development (hydraulic fracturing, acid fracturing, and matrix acidizing) have been investigated and evaluated and federal and state regulations requiring chemical disclosure for well-stimulation have been implemented as part of an overall risk management strategy for unconventional oil and gas development. Similar evaluations for chemicals used in other routine oil and gas development activities, such as maintenance acidizing, gravel packing, and well drilling, have not been previously conducted, in part due to a lack of reliable information concerning on-field chemical-use. In this study, we compare chemical-use between routine …


Increased Span Length For The Mgs Long-Span Guardrail System Part Ii: Full-Scale Crash Testing, Dylan T. Meyer, John D. Reid, Karla A. Lechtenberg, Robert W. Bielenberg, Ronald K. Faller Apr 2017

Increased Span Length For The Mgs Long-Span Guardrail System Part Ii: Full-Scale Crash Testing, Dylan T. Meyer, John D. Reid, Karla A. Lechtenberg, Robert W. Bielenberg, Ronald K. Faller

Nebraska Department of Transportation: Research Reports

The objective of this research study was to design and evaluate the MGS long-span design for use with unsupported spans greater than 25 ft (7.6 m). Two full-scale crash tests were conducted to evaluate the MGS long-span system with increased span lengths and the use of UBSP posts adjacent to the long span. Both tests were conducted according to the TL- 3 criteria outlined in MASH. Both test nos. MGSLS-1 and MGSLS-2 were conducted with the 2270P vehicle impacting their respective critical impact points at a speed of 62 mph (100 km/h) and an angle of 25 degrees. Test no. …


Hyporheic Nitrate Uptake And Stoichiometric Limitations: Mesocosm Experiments Along A River Continuum., Vanessa A. Garayburu Caruso Apr 2017

Hyporheic Nitrate Uptake And Stoichiometric Limitations: Mesocosm Experiments Along A River Continuum., Vanessa A. Garayburu Caruso

Civil Engineering ETDs

Nutrient uptake in streams and rivers is controlled by complex transport dynamics and biogeochemical interactions, which together regulate nutrient export from watersheds. Decoupling the relative contributions of transport and biogeochemical processes to nutrient uptake at the watershed scale has been challenging due to the spatial and temporal heterogeneity of physicochemical properties. Furthermore, logistical constraints have resulted in solute-specific analyses, primarily concentrated in headwater streams, that disregard the role of stoichiometry in controlling biological uptake. We used experimental mesocosm (column experiments) along the Jemez River-Rio Grande continuum (1st-8th stream order) to isolate spatial differences in biological nitrate uptake. …