Browsing by Author "Bock, Emily"

Now showing 1 - 10 of 10
  • Thumbnail Image
    Artificial sinks to treat legacy nutrients in agricultural landscapes
    Bock, Emily; Stephenson, Stephen Kurt; Easton, Zachary M. (2019-06-05)
    Legacy nutrients introduce a critical time lag between changes in nutrient application or implementation of best management practices (BMPs) and observable reductions in loads delivered to downstream waters. Nitrogen and phosphorus leached through soils into groundwater may take decades to eventually be discharged to surface waters and, consequently, often prevent the attainment of water quality improvement goals. For example, the National Resource Council has cautioned that in the Chesapeake Bay watershed legacy nutrients, particularly nitrogen (N), could delay achievement of nutrient load reductions needed to meet Total Maximum Daily Load (TMDL) requirements.. Groundwater discharge transporting legacy N has been identified specifically as a significant nutrient source to the Bay. Unfortunately, most existing BMPs cannot remediate these nutrient reservoirs and the Chesapeake Bay Program has not active policy to address legacy nutrients; better management options are needed...
  • Thumbnail Image
    Challenges and Opportunities for Denitrifying Bioreactors in the Mid-Atlantic
    Bock, Emily (Virginia Tech, 2018-01-18)
    Sustaining the global population depends upon modern agricultural practices reliant on large inputs of nitrogen (N) fertilizer, but export of excess N from agroecosystems has negative environmental consequences, such as accelerated eutrophication and associated water quality degradation. The challenges posed by diffuse and widespread nutrient pollution in agricultural drainage waters necessitate cost-effective, adaptable, and reliable solutions. In this context, enhanced denitrification approaches developed over the last several decades have produced denitrifying bioreactors that harness the ability of ubiquitous soil microorganisms to convert bioavailable N into inert N gas, thereby removing bioavailable N from an ecosystem. Denitrifying bioreactors are edge-of-field structures that consist of organic carbon substrate and support the activity of denitrifying soil bacteria that remove N from intercepted nutrient-enriched drainage waters. The potential to improve bioreactor performance and expand their application beyond the Midwest to the agriculturally significant Mid-Atlantic region was investigated with a three-pronged approach: 1) a pilot study investigating controls on N removal, 2) a laboratory study investigating controls on emission of greenhouse gases nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2), and 3) a field study of one of the first denitrifying bioreactors implemented in the Atlantic Coastal Plain. The pilot and laboratory studies tested the effect of amending woodchip bioreactors with biochar, an organic carbon pyrolysis product demonstrated to enhance microbial activity. The pilot-scale study provides evidence that either hardwood- of softwood-feedstock biochar may increase N removal in woodchip bioreactors, particularly under higher N loading. The results from the laboratory experiment suggest the particular pine-feedstock biochar tested may induce greater greenhouse gas emissions, particularly of the intermediate product of denitrification and potent GHG nitrous oxide. The field study evaluated performance of a biochar-amended woodchip bioreactor installed on a working farm. Two years of monitoring data demonstrated that the bioreactor successfully removed N from drainage waters, but at relatively low rates constrained by low N loading that occurred in the absence of fertilizer application during continuous soy cropping at the site (10.0 kg NO3--N ha-1 yr-1 or 4.86 g NO3- -N m-3 d-1 on the basis of bed volume reached the bioreactor.) Removal rates averaged 0.41 g m-3 d-1 (8.6% removal efficiency), significantly lower than average rates in systems receiving greater N loading in the Midwest, and more similar to installations in the Maryland Coastal Plain. Greenhouse gas fluxes were within the range reported for other bioreactors, and of the N removed an average of only 0.16% was emitted from the bed surface as N2O. This case study provides useful measurements of bioreactor operation under low N loading that informs the boundaries of bioreactor utility, and may have particular regional relevance. The pilot and field studies suggest that wood-based biochars may enhance N removal and may not produce problematic quantities of greenhouse gases, respectively. However, the laboratory study raises the need for caution when considering the costs and benefits amending woodchip bioreactors with biochar and accounting for the effect on greenhouse gas emissions in this calculation, because the tested pine biochar significantly increased these emissions.
  • Thumbnail Image
    Comparison of short-term streamflow forecasting using stochastic time series, neural networks, process-based, and Bayesian models
    Wagena, Moges B.; Goering, Dustin; Collick, Amy S.; Bock, Emily; Fuka, Daniel R.; Buda, Anthony R.; Easton, Zachary M. (2020-04)
    Streamflow forecasts are essential for water resources management. Although there are many methods for forecasting streamflow, real-time forecasts remain challenging. This study evaluates streamflow forecasts using a process-based model (Soil and Water Assessment Tool-Variable Source Area model-SWAT-VSA), a stochastic model (Artificial Neural Network -ANN), an Auto-Regressive Moving-Average (ARMA) model, and a Bayesian ensemble model that utilizes the SWAT-VSA, ANN, and ARMA results. Streamflow is forecast from 1 to 8 d, forced with Quantitative Precipitation Forecasts from the US National Weather Service. Of the individual models, SWAT-VSA and the ANN provide better predictions of total streamflow (NSE 0.60-0.70) and peak flow, but underpredicted low flows. During the forecast period the ANN had the highest predictive power (NSE 0.44-0.64), however all three models underpredicted peak flow. The Bayesian ensemble forecast streamflow with the most skill for all forecast lead times (NSE 0.49-0.67) and provided a quantification of prediction uncertainty.
  • Thumbnail Image
    Enhanced Denitrification Bioreactors Hold Promise for Mid-Atlantic Ditch Drainage
    Christianson, L. E.; Collick, A. S.; Bryant, Ray B.; Rosen, T.; Bock, Emily; Allen, A. L.; Kleinman, P. J. A.; May, E. B.; Buda, A. R.; Robinson, J.; Folmar, G. J.; Easton, Zachary M. (2017-12)
    There is strong interest in adapting denitrifying bioreactors to mid-Atlantic drainage systems to help address Chesapeake Bay water quality goals. Three ditch drainage-oriented bioreactors were constructed in 2015 in Maryland to evaluate site-specific design and installation concerns and nitrate (NO3-N) removal. All three bioreactor types removed NO3-N, as measured by load and/or concentration reduction, showing promise for denitrifying bioreactors in the mid-Atlantic's low gradient Coastal Plain landscape. The ditch diversion bioreactor (25% NO3-N load reduction; 0.97 g NO3-N removed m(-3) d(-1)) and the sawdust denitrification wall adjacent to a ditch (> 90% NO3-N concentration reduction; 1.9-2.9 g NO3-N removed m(-3) d(-1)) had removal rates within range of the literature. The in-ditch bioreactor averaged 65% NO3-N concentration reduction, but sedimentation is expected to be one of the biggest challenges. A robust water balance is critical for future assessment of bioreactors' contribution to water quality improvement in low gradient mid-Atlantic landscapes.
  • Thumbnail Image
    Factors When Considering an Agricultural Drainage System
    Easton, Zachary M.; Bock, Emily; Collick, Amy S. (Virginia Cooperative Extension, 2017-02-23)
    A well designed drainage system can improve crop yield, and lower the variation in crop yield by removing excess water in the soil.
  • Thumbnail Image
    Greenhouse Gas Production and Nutrient Reductions in Denitrifying Bioreactors
    Bock, Emily (Virginia Tech, 2014-06-11)
    The global nitrogen cycle has been disrupted by large anthropogenic inputs of reactive nitrogen to the environment. Excess nitrogen underlies environmental problems such as eutrophication, and can negatively affect human health. Managing the natural microbial process of denitrification is advocated as a promising avenue to reduce excess nitrogen, and denitrifying bioreactors (DNBRs) are an emerging technology harnessing this biochemical process. Previous DNBR research has established successful nitrate removal, whereas this study examines the potential to expand DNBR functionality to address excess phosphorus and mitigate the production of nitrous oxide, a potent greenhouse gas. Results from a laboratory experiment supported the hypothesis that the addition of biochar, a charcoal-like soil amendment and novel organic carbon source in DNBR research, would increase nitrate and phosphorus removal as well as decrease the accumulation of nitrous oxide, an intermediate product of microbial denitrification. In order more closely examine the ratio of the products nitrous oxide and inert dinitrogen, development of a novel analytical method to quantify dissolved gases in environmental water samples using gas chromatography mass spectrometry was undertaken. Although static headspace analysis is a common technique for quantifying dissolved volatiles, the variation in sample preparation has recently been revealed to affect the determination of dissolved concentrations of permanent gases and convolute comparison between studies. This work demonstrates the viability of internal calibration with gaseous standard addition to make dissolved gas analysis more robust to variable sample processing and to correct for matrix effects on gas partitioning that may occur in environmental samples.
  • Thumbnail Image
    Hydrology Basics and the Hydrologic Cycle
    Easton, Zachary M.; Bock, Emily (Virginia Cooperative Extension, 2020-11-04)
    This fact sheet summarizes complex relationships and highlights important applications of hydrologic concepts in agroecosystems, including conservation of soil water in the vadose zone1 to support crop production and water quality.
  • Thumbnail Image
    Hydrology Basics and the Hydrologic Cycle
    Easton, Zachary M.; Bock, Emily (Virginia Cooperative Extension, 2015-11-09)
    Presents and explains some concepts in hydrology and the hydrologic cycle, with emphasis on some concepts of importance in agroecosystems.
  • Thumbnail Image
    Managing Drainage from Agricultural Lands with Denitrifying Bioreactors in the Mid-Atlantic
    Bock, Emily; Collick, Amy S.; Easton, Zachary M. (Virginia Cooperative Extension, 2018-11-05)
    Discusses the use of denitrifying bioreactors (trenches or beds with organic carbon material) to remove nitrates from drainage water, and convert them to inert nitrogen. Results of this use include improved water quality.
  • Thumbnail Image
    Soil and Soil Water Relationships
    Easton, Zachary M.; Bock, Emily (Virginia Cooperative Extension, 2016-03-22)
    Discusses the relationships between soil, water and plants. Discusses different types of soil, and how these soils hold water. Provides information about differences in soil drainage. Discusses the concept of water balance.