The case study farm produces 66% of its biogas from off-farm food waste sources, highlighting the... more The case study farm produces 66% of its biogas from off-farm food waste sources, highlighting the potential to increase the circularity of food and agricultural systems when farms capture and recycle external waste sources. • The farm can meet 78% of its crop nitrogen needs from waste products recycled in digestion, assuming a 37% nitrogen use efficiency (NUE). However, phosphorus in the imported food waste creates an excess relative to crop needs. • The farm creates an excess of energy that is returned to the electric grid, providing broader off-farm benefits through a circular economy approach. • Widespread commercial implementation of circular economy principles in the U.S. dairy sector requires more measured data about how farms successfully implement circularity within the constraints of market incentives and farm operations. ABSTRACT. Coupling agricultural production with sustainable bioenergy systems may help us improve the circular economy of the food system and work within planetary boundaries for climate stabilization. However, leading sustainable dairies often do not have data to support that claim. As a result, practical case studies of circular economies with measured data from commercially operating farms are lacking in the literature, which is instead dominated by hypothetical and theoretical analyses. To grow and scale commercial implementation of circular economy and sustainability principles, it is important to understand how commercial farms implement these principles within the constraints of market incentives and actual farm operations. We conducted a case study of a commercial dairy farm in Pennsylvania, where a well-managed anaerobic digester system serves as the basis for a circular farm economy and allows the next generation to grow the farm business and expand the portfolio of revenue streams. The farm recycles food and agricultural waste into heat, renewable electricity, and fertilizer to heat and power the farm, amend the soil, and reduce farm costs. We also highlight the potential to scale the case study farm's circular economy approach in Pennsylvania using the state's projected 2030 manure, corn stover, winter double crops, switchgrass, and food waste resources to produce energy via biogas or renewable natural gas (RNG). We estimate the state could generate 40 million MJ annually from such integrated anaerobic digestion systems, meeting 3% of its electricity consumption. Circular economies like this case study can be designed in food and agricultural systems to operate within the constraints of an operating farm and recycle waste, produce nitrogen-and phosphorus-rich soil amendments and reduce imports of synthetic fertilizers, reduce and offset fossil energy consumption and greenhouse gas emissions associated with crop and livestock production, regenerate natural ecosystems, help ensure agricultural resilience and sustainability, and provide economic benefits.
Elements of Bed Load Particle Diffusion Based on a Large, High-Resolution Data Set Obtained from High-Speed Imaging: Toward a Physical Interpretation of Particle Kinematics
Earth Surface Processes and Landforms, Aug 9, 2016
Bedload sediment transport is the basic physical ingredient of river evolution. Formulae exist fo... more Bedload sediment transport is the basic physical ingredient of river evolution. Formulae exist for estimating transport rates, but the diffusive contribution to the sediment flux, and the associated spreading rate of tracer particles, are not clearly understood. The start-and-stop motions of sediment particles transported as bedload on a streambed mimic aspects of the Einstein-Smoluchowski description of the random-walk motions of Brownian particles. Using this touchstone description, recent work suggests the presence of anomalous diffusion, where the particle spreading rate differs from the linear dependence with time of Brownian behavior. We demonstrate that conventional measures of particle spreading reveal different attributes of bedload particle behavior depending on details of the calculation. When we view particle motions over start-and-stop timescales obtained from high-speed (250 Hz) imaging of coarse-sand particles, high-resolution measurements reveal ballistic-like behavior at the shortest (10 2 s) timescale, followed by apparent anomalous behavior due to correlated random walks in transition to normal diffusion (> 10 1 s)-similar to Brownian particle behavior but involving distinctly different physics. However, when treated as a 'virtual plume' over this timescale range, particles exhibit inhomogeneous diffusive behavior because both the mean and the variance of particle travel distances increase nonlinearly with increasing travel times, a behavior that is unrelated to anomalous diffusion or to Brownian-like behavior. Our results indicate that care is needed in suggesting anomalous behavior when appealing to conventional measures of diffusion formulated for ideal particle systems.
Observation of incomplete particle hops in imaging-based experiments with bed-load transport does... more Observation of incomplete particle hops in imaging-based experiments with bed-load transport does not just occur with hops that are longer than an area of observation. Even short hops can be in fact incompletely measured if they cross the boundaries of the focus area. Experimental censorship biases the statistical distribution and moments of bed-load particle hops. This paper presents: a theoretical quantification of an expected effect of experimental censorship; based on this quantification, a method to correct the statistical distribution of hop lengths; an application of the method to experimental data. Applying the correction leads to significantly different values of the mean hop length, compensating the biasing effect of censorship. By contrast, nothing can be done for experimental truncation that is associated with hops longer than an applied area of observation. Experimental truncation must be avoided a priori, by appropriate design of the measurement method.
Journal Of Geophysical Research: Earth Surface, Nov 1, 2015
A high-resolution data set obtained from high-speed imaging of coarse sand particles transported ... more A high-resolution data set obtained from high-speed imaging of coarse sand particles transported as bed load allows us to confidently describe the forms and qualities of the ensemble distributions of particle velocities, accelerations, hop distances, and traveltimes. Autocorrelation functions of frame-averaged values (and the decay of these functions) support the idea that the forms of these distributions become time invariant within the 5 s imaging interval. Distributions of streamwise and cross-stream particle velocities are exponential, consistent with previous experiments and theory. Importantly, streamwise particle velocities possess a "light" tail, where the largest velocities are limited by near-bed fluid velocities. Distributions of streamwise and cross-stream particle accelerations are Laplace in form and are centered on zero, consistent with equilibrium transport conditions. The majority of particle hops, measured start to stop, involve short displacements, and streamwise hop distances possess a Weibull distribution. In contrast to previous work, the distribution of traveltimes is exponential, consistent with a fixed temporal disentrainment rate. The Weibull distribution of hop distances is consistent with a decreasing spatial disentrainment rate and is related to the exponential distribution of traveltimes. By taking into account the effects of experimental censorship associated with a finite sampling window, the relationship between streamwise hop distances and traveltimes, L x ∼ T p , likely involves an exponent of ∼ 2. These experimental results-an exponential distribution of traveltimes T p and a Weibull distribution of hop distances L x with shape parameter k < 1-are consistent with a nonlinear relationship between these quantities with > 1.
Macroecology strives to identify ecological patterns on broad spatial and temporal scales. One su... more Macroecology strives to identify ecological patterns on broad spatial and temporal scales. One such pattern, Rapoport's rule, describes the tendency of species' latitudinal ranges to increase with increasing latitude. Several mechanisms have been proposed to explain this rule. Some invoke climate, either through glaciation driving differential extinction of northern species or through increased seasonal variability at higher latitudes causing higher thermal tolerances and subsequently larger ranges. Alternatively, continental tapering or higher interspecific competition at lower latitudes may be responsible. Assessing the incidence of Rapoport's rule through deep time can help to distinguish between competing explanations. Using fossil occurrence data from the Palaeobiology Database, we test these hypotheses by evaluating mammalian compliance with the rule throughout the Caenozoic of North America. Adherence to Rapoport's rule primarily coincides with periods of intense cooling and increased seasonality, suggesting that extinctions caused by changing climate may have played an important role in erecting the latitudinal gradients in range sizes seen today.
Highlights The case study farm produces 66% of its biogas from off-farm food waste sources, highl... more Highlights The case study farm produces 66% of its biogas from off-farm food waste sources, highlighting the potential to increase the circularity of food and agricultural systems when farms capture and recycle external waste sources. The farm can meet 78% of its crop nitrogen needs from waste products recycled in digestion, assuming a 37% nitrogen use efficiency (NUE). However, phosphorus in the imported food waste creates an excess relative to crop needs. The farm creates an excess of energy that is returned to the electric grid, providing broader off-farm benefits through a circular economy approach. Widespread commercial implementation of circular economy principles in the U.S. dairy sector requires more measured data about how farms successfully implement circularity within the constraints of market incentives and farm operations. . Coupling agricultural production with sustainable bioenergy systems may help us improve the circular economy of the food system and work within pla...
Elements of Bed Load Particle Diffusion Based on a Large, High-Resolution Data Set Obtained from High-Speed Imaging: Toward a Physical Interpretation of Particle Kinematics
Journal of Geophysical Research: Earth Surface, 2019
This article has been accepted for publication and undergone full peer review but has not been th... more This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
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