Reducing Nitrate-N Losses to Achieve Water Quality Goals

Nutrient losses from agricultural systems in the Mississippi River basin have contributed to the hypoxic zone in the Gulf of Mexico. In 2008, in response to this challenge, the U.S. EPA‘s Hypoxia Task Force released an action plan for a national strategy to reduce, mitigate, and control hypoxia in the northern Gulf of Mexico and improve water quality in the Mississippi River basin (www.epa.gov/ms-htf). The action plan indicated that significant (i.e., 45%) reductions in riverine nitrogen and phosphorus loads are needed to achieve the goal of reducing the size of the hypoxic zone, and improve water quality in the basin. One of the main items in the 2008 action plan was the call for state-level nutrient reduction strategies. As a result, the twelve states bordering the Mississippi and Ohio Rivers have developed and begun implementing comprehensive nutrient reduction strategies (www.epa.gov/ms-htf/hypoxia-taskforce-nutrient-reduction-strategies). Iowa was one of the first states to conduct a scientific assessment of the potential nutrient reduction of different agricultural management practices and the level of implementation that might be needed to reach the goal of 45% reduction (www.nutrientstrategy.iastate.edu)

Technical Note: Hydraulic Property Determination of Denitrifying Bioreactor Fill Media

Denitrification bioreactors are one of the newest options for nitrate removal in agricultural drainage waters. Optimization of denitrification bioreactor design requires the ability to identify concrete values for the hydraulic properties of bioreactor fill media. Hydraulic properties, chiefly saturated hydraulic conductivity but also porosity and particle size, are not known for many types of possible bioreactor media though they have a significant impact upon bioreactor design and performance. This work was undertaken to more fully quantify the hydraulic properties of the major type of fill media used in Iowa denitrification bioreactors through a series of porosity, hydraulic conductivity, and particle size analysis tests. In addition, a particle size analysis was performed for two types of woodchips and one type of wood shreds in order to quantify and highlight the differences between what is commonly referred to as wood fill. Saturated hydraulic conductivity was determined for blends of woodchips, corn cobs, and pea gravel. For one of the most common types of woodchips used in bioreactors, the porosity varied from 66% to 78% depending on packing density and the average saturated hydraulic conductivity was 9.5 cm/s. It was found that additions of pea gravel significantly increased the hydraulic conductivity of woodchips though additions of corn cobs did not. Regardless of the fill mixture used, it is vital to design the bioreactor using the hydraulic properties for that specific media

Virtual Collaboration: Exploring New Frontiers

Librarians looking for professional development opportunities, especially in states like North Dakota where many serve small populations in rural areas, will benefit from thinking creatively about organizing a conference. Two sections of the North Dakota Library Association (NDLA) used Blackboard Collaborate Ultra as a platform to produce a fully online conference. This virtual “unconference” was interactive and robust, with speakers from across the state, interactive whiteboards, poster rooms, meeting space for special interest groups, and more. In this workshop, we will share what we have learned about Collaborate Ultra, including its strengths and weaknesses. We hope to brainstorm and discuss other potential applications, including classrooms, professional development, online meetings, group work, and supporting distance students and colleagues. Please bring your device and join us in a working session where you will experience Collaborate Ultra first-hand and discover how this tool can facilitate learning and collaboration and impact the work you do

Technical Note: The Potential of Municipal Yard Waste to be Denitrification Bioreactor Fill

The use of denitrification bioreactors to mitigate nitrate in agricultural drainage has recently gained much interest in the Midwestern United States and in similarly drained agricultural regions. However, as the number of bioreactor installations has increased, questions have been raised about the supply and consistency of denitrification carbon source material. In selecting such material, there is an important balance between optimal media properties (e.g., hydraulic properties, chemical composition), practicality, and material cost. The use of free material such as municipal yard waste may help minimize the cost of this voluntary water quality improvement strategy in the Midwestern United States, but may not provide other sufficient media properties. To investigate this, pilot-scale bioreactors were used to compare hardwood chips with free, chipped municipal yard waste in terms of nitrate removal potential and changes in the media. Sampling of bioreactor influent and effluent over a range of retention times showed the yard waste had higher removal efficiencies at a given retention time and higher removal rates than the woodchips. However, buried carbon media bags revealed the yard waste lost weight to a greater extent and more consistently than the woodchips meaning the woodchips had a half-life over two times greater than the yard waste. This, combined with the low carbon-to-nitrogen ratio of the yard waste, indicated yard waste material is not ideal for bioreactor installations that are intended to be low maintenance for at least ten years

Internal hydraulics of an agricultural drainage denitrification bioreactor

Denitrification bioreactors to reduce the amount of nitrate-nitrogen in agricultural drainage are now being deployed across the U.S. Midwest. However, there are still many unknowns regarding internal hydraulic-driven processes in these engineered treatment systems. To improve this understanding, the internal flow dynamics and several environmental parameters of a denitrification bioreactor treating agricultural drainage in Northeastern Iowa, USA were investigated with two tracer tests and a network of bioreactor wells. The bioreactor had a trapezoidal cross section and received drainage from approximately 14.2 ha at the North East Research Farm near Nashua, Iowa. It was clear from the water surface elevations and the continuous pressure transducer data that flow was attenuated within the bioreactor (i.e., reduction in peak flow as the hydrograph moved down gradient). Over the sampling period from 17 May to 24 August 2011, flow conditions and internal parameters (temperature, dissolved oxygen, oxidation reduction potential) varied widely resulting in early samplings that showed little nitrate removal ranging to complete nitrate removal (7–100% mass reduction; 0.38–1.06 g N removed per m3 bioreactor per day) and sulfate reduction at the final sampling event. The bioreactor\u27s non-ideal flow regime due to ineffective volume utilization was a major detriment to nitrate removal at higher flow rates. Regression analysis between mass nitrogen reduction and theoretical retention time (7.5–79 h) suggested minimum design retention times should be increased, though caution was also issued about this as increased design retention times and corresponding larger bioreactors may exacerbate detrimental by-products under low flow conditions. Operationally, outlet structure level management could also be utilized to improve performance and minimize detrimental by-products

Combining Environmental Monitoring and Remote Sensing Technologies to Evaluate Cropping System Nitrogen Dynamics at the Field-Scale

Nitrogen (N) losses from cropping systems in the U.S. Midwest represent a major environmental and economic concern, negatively impacting water and air quality. While considerable research has investigated processes and controls of N losses in this region, significant knowledge gaps still exist, particularly related to the temporal and spatial variability of crop N uptake and environmental losses at the field-scale. The objectives of this study were (i) to describe the unique application of environmental monitoring and remote sensing technologies to quantify and evaluate relationships between artificial subsurface drainage nitrate (NO3-N) losses, soil nitrous oxide (N2O) emissions, soil N concentrations, corn (Zea mays L.) yield, and remote sensing vegetation indices, and (ii) to discuss the benefits and limitations of using recent developments in technology to monitor cropping system N dynamics at field-scale. Preliminary results showed important insights regarding temporal (when N losses primarily occurred) and spatial (measurement footprint) considerations when trying to link N2O and NO3-N leaching losses within a single study to assess relationship between crop productivity and environmental N losses. Remote sensing vegetation indices were significantly correlated with N2O emissions, indicating that new technologies (e.g., unmanned aerial vehicle platform) could represent an integrative tool for linking sustainability outcomes with improved agronomic efficiencies, with lower vegetation index values associated with poor crop performance and higher N2O emissions. However, the potential for unmanned aerial vehicle to evaluate water quality appears much more limited because NO3-N losses happened prior to early-season crop growth and image collection. Building on this work, we encourage future research to test the usefulness of remote sensing technologies for monitoring environmental quality, with the goal of providing timely and accurate information to enhance the efficiency and sustainability of food production