Topographic and meteorological influences on spatial scaling of heavy convective rainfall in mountainous regions

Characterizing the spatial scaling and dynamics of convective precipitation in mountainous terrain and the development of downscaling methods to transfer precipitation fields from one scale to another is the overall motivation for this research. Substantial progress has been made on characterizing the space-time organization of Midwestern convective systems and tropical rainfall, which has led to the development of statistical/dynamical downscaling models. Space-time analysis and downscaling of orographic precipitation has received less attention due to the complexities of topographic influences. This study uses multiscale statistical analysis to investigate the spatial scaling of organized thunderstorms that produce heavy rainfall and flooding in mountainous regions. Focus is placed on the eastern and western slopes of the Appalachian region and the Front Range of the Rocky Mountains. Parameter estimates are analyzed over time and attention is given to linking changes in the multiscale parameters with meteorological forcings and orographic influences on the rainfall. Influences of geographic regions and predominant orographic controls on trends in multiscale properties of precipitation are investigated. Spatial resolutions from 1 km to 50 km are considered. This range of spatial scales is needed to bridge typical scale gaps between distributed hydrologic models and numerical weather prediction (NWP) forecasts and attempts to address the open research problem of scaling organized thunderstorms and convection in mountainous terrain down to 1-4 km scales.

Discrete element methods for asphalt concrete : development and application of user-defined microstructural models and a viscoelastic micromechanical model

As an important Civil Engineering material, asphalt concrete (AC) is commonly used to build road surfaces, airports, and parking lots. With traditional laboratory tests and theoretical equations, it is a challenge to fully understand such a random composite material. Based on the discrete element method (DEM), this research seeks to develop and implement computer models as research approaches for improving understandings of AC microstructure-based mechanics. In this research, three categories of approaches were developed or employed to simulate microstructures of AC materials, namely the randomly-generated models, the idealized models, and image-based models. The image-based models were recommended for accurately predicting AC performance, while the other models were recommended as research tools to obtain deep insight into the AC microstructure-based mechanics. A viscoelastic micromechanical model was developed to capture viscoelastic interactions within the AC microstructure. Four types of constitutive models were built to address the four categories of interactions within an AC specimen. Each of the constitutive models consists of three parts which represent three different interaction behaviors: a stiffness model (force-displace relation), a bonding model (shear and tensile strengths), and a slip model (frictional property). Three techniques were developed to reduce the computational time for AC viscoelastic simulations. It was found that the computational time was significantly reduced to days or hours from years or months for typical three-dimensional models. Dynamic modulus and creep stiffness tests were simulated and methodologies were developed to determine the viscoelastic parameters. It was found that the DE models could successfully predict dynamic modulus, phase angles, and creep stiffness in a wide range of frequencies, temperatures, and time spans. Mineral aggregate morphology characteristics (sphericity, orientation, and angularity) were studied to investigate their impacts on AC creep stiffness. It was found that aggregate characteristics significantly impact creep stiffness. Pavement responses and pavement-vehicle interactions were investigated by simulating pavement sections under a rolling wheel. It was found that wheel acceleration, steadily moving, and deceleration significantly impact contact forces. Additionally, summary and recommendations were provided in the last chapter and part of computer programming codes wree provided in the appendixes.

Study of water use and supply in the district of Independencia, Peru

Peru is a developing country with abundant fresh water resources, yet the lack of infrastructure leaves much of the population without access to safe water for domestic uses. The author of this report was a Peace Corps Volunteer in the sector of water & sanitation in the district of Independencia, Ica, Peru. Independencia is located in the arid coastal region of the country, receiving on average 15 mm of rain annually. The water source for this district comes from the Pisco River, originating in the Andean highlands and outflowing into the Pacific Ocean near the town of Pisco, Peru. The objectives of this report are to assess the water supply and sanitation practices, model the existing water distribution system, and make recommendations for future expansion of the distribution system in the district of Independencia, Peru. The assessment of water supply will be based on the results from community surveys done in the district of Independencia, water quality testing done by a detachment of the U.S. Navy, as well as on the results of a hydraulic model built in EPANET 2.0 to represent the distribution system. Sanitation practice assessments will be based on the surveys as well as observations from the author while living in Peru. Recommendations for system expansions will be made based on results from the EPANET model and the municipality’s technical report for the existing distribution system. Household water use and sanitation surveys were conducted with 84 families in the district revealing that upwards of 85% store their domestic water in regularly washed containers with lids. Over 80% of those surveyed are drinking water that is treated, mostly boiled. Of those surveyed, over 95% reported washing their hands and over 60% mentioned at least one critical time for hand washing when asked for specific instances. From the surveys, it was also discovered that over 80% of houses are properly disposing of excrement, in either latrines or septic tanks. There were 43 families interviewed with children five years of age or under, and just over 18% reported the child had a case of diarrhea within the last month at the time of the interview. Finally, from the surveys it was calculated that the average water use per person per day is about 22 liters. Water quality testing carried out by a detachment of the U.S. Navy revealed that the water intended for consumption in the houses surveyed was not suitable for consumption, with a median E. coli most probable number of 47/100 ml for the 61 houses sampled. The median total coliforms was 3,000 colony forming units per 100 ml. EPANET was used to simulate the water delivery system and evaluate its performance. EPANET is designed for continuous water delivery systems, assuming all pipes are always flowing full. To account for the intermittent nature of the system, multiple EPANET network models were created to simulate how water is routed to the different parts of the system throughout the day. The models were created from interviews with the water technicians and a map of the system created using handheld GPS units. The purpose is to analyze the performance of the water system that services approximately 13,276 people in the district of Independencia, Peru, as well as provide recommendations for future growth and improvement of the service level. Performance evaluation of the existing system is based on meeting 25 liters per person per day while maintaining positive pressure at all nodes in the network. The future performance is based on meeting a minimum pressure of 20 psi in the main line, as proposed by Chase (2000). The EPANET model results yield an average nodal pressure for all communities of 71 psi, with a range from 1.3 – 160 psi. Thus, if the current water delivery schedule obtained from the local municipality is followed, all communities should have sufficient pressure to deliver 25 l/p/d, with the exception of Los Rosales, which can only supply 3.25 l/p/d. However, if the line to Los Rosales were increased from one to four inches, the system could supply this community with 25 l/p/d. The district of Independencia could greatly benefit from increasing the service level to 24-hour water delivery and a minimum of 50 l/p/d, so that communities without reliable access due to insufficient pressure would become equal beneficiaries of this invaluable resource. To evaluate the feasibility of this, EPANET was used to model the system with a range of population growth rates, system lifetimes, and demands. In order to meet a minimum pressure of 20 psi in the main line, the 6-inch diameter main line must be increased and approximately two miles of trench must be excavated up to 30 feet deep. The sections of the main line that must be excavated are mile 0-1 and 1.5-2.5, and the first 3.4 miles of the main line must be increased from 6 to 16 inches, contracting to 10 inches for the remaining 5.8 miles. Doing this would allow 24-hour water delivery and provide 50 l/p/d for a range of population growth rates and system lifetimes. It is expected that improving the water delivery service would reduce the morbidity and mortality from diarrheal diseases by decreasing the recontamination of the water due to transport and household storage, as well as by maintaining continuous pressure in the system to prevent infiltration of contaminated groundwater. However, this expansion must be carefully planned so as not to affect aquatic ecosystems or other districts utilizing water from the Pisco River. It is recommended that stream gaging of the Pisco River and precipitation monitoring of the surrounding watershed is initiated in order to begin a hydrological study that would be integrated into the district’s water resource planning. It is also recommended that the district begin routine water quality testing, with the results available to the public.

ISO 14001 in India: More than a certificate on the wall?

The growth of ISO 14001 certificates worldwide has led to much research on the role of voluntary standards in improving the environmental impacts of industry. Most of this research, however, has focused on industrialized countries, with very little research examining the effects of ISO 14001 and other voluntary initiatives in the developing world. This is especially unfortunate because it is in these very countries that proponents of ISO 14001 claim the largest benefits of the standard will occur, by helping polluting industries improve performance and by assisting environmental regulators in enforcing laws more effectively. Indian industries have begun adopting ISO 14001 at an accelerating pace, but there is little available information on what this means for the environmental performance of Indian firms. The research described here closes this gap by exploring the reasons for the increasing popularity of ISO 14001 in India, the ways in which firms use the standard and the benefits they obtain from it. Findings suggest that while the processoriented approach of ISO 14001 does offer important benefits, changing market demands towards cheaper certification and away from rigorous EMS implementation have devalued the standard for those interested in using it as an indicator of a firm’s environmental performance.

Exploration of the role of serum factors in maintaining bone mass during hibernation in black bears

Disuse osteoporosis is a condition in which reduced mechanical loading (e.g. bed-rest, immobilization, or paralysis) results in unbalanced bone turnover. The American black bear is a unique, naturally occurring model for the prevention of disuse osteoporosis. Bears remain mostly inactive for up to half a year of hibernation annually, yet they do not lose bone mechanical strength or structural properties throughout hibernation. The long-term goal of this study is to determine the biological mechanism through which bears maintain bone during hibernation. This mechanism could pinpoint new signaling pathway targets for the development of drugs for osteoporosis prevention. In this study, bone specific alkaline phosphatase (BSALP), a marker of osteoblast activity, and tartrate resistant acid phosphatase (TRACP), a marker of osteoclast number, were quantified in the serum of hibernating and active black bears. BSALP and TRACP decreased during hibernation, suggesting a balanced reduction in bone turnover. This decrease in BSALP and TRACP were correlated positively to serum adiponectin and inversely to serum neuropeptide Y, suggesting a possible role of these hormones in suppressing bone turnover during hibernation. Osteocalcin (OCN) and undercarboxylated OCN increased dramatically in the serum of hibernating bears. These increases were inversely correlated with adiponectin, glucose, and serotonin, suggesting that OCN may have a unique role in energy homeostasis during hibernation. Finally, MC3T3-E1 osteoblasts were cultured in the serum from active and hibernating bears, and seasonal cell responses were quantified. Cells cultured in serum from hibernating bears had a reduced caspase-3/7 response, and more living cells, after apoptotic threat. The caspase-3/7 response was positively correlated to serum adiponectin and to gene expression of OCN and Runx2, suggesting that reduced caspase-3/7 activity may be related to the reduced differentiation potential of osteoblasts in hibernation serum, and that adiponectin is a potential effector hormone. In summary, the activities of osteoblasts and osteoclasts are reduced during hibernation in bears. This reduced turnover is due, in part, to hormonal control. Further study of potential effectors adiponectin and neuropeptide Y may provide insight into the biological mechanism through which bears maintain bone throughout hibernation.

Electronic properties of zig-zag carbon nanotubes : a first-principles study

Carbon nanotube (CNT) is a one dimensional (1-D) nanostructured material, which has been the focal point of research over the past decade for intriguing applications ranging from nanoelectronics to chemical and biological sensors. Using a first-principles gradient corrected density functional approach, we present a comprehensive study of the geometry and energy band gap in zig-zag semi-conducting (n,0) carbon nanotubes (CNT) to resolve some of the conflicting findings. Our calculations confirm that the single wall (n,0) CNTs fall into two distinct classes depending upon n mod 3 equal to 1 (smaller band gaps) or 2 (larger gaps). The effect of longitudinal strain on the band gap further confirms the existence of two distinct classes: for n mod 3 = 1 or 2, changing Eg by ~ ±110 meV for 1% strain in each case. We also present our findings for the origin of metallicity in multiwall CNTs.

Dynamic modeling of active regeneration in catalyzed and non-catalyzed diesel particulate filters

Particulate matter (PM) emissions standards set by the US Environmental Protection Agency (EPA) have become increasingly stringent over the years. The EPA regulation for PM in heavy duty diesel engines has been reduced to 0.01 g/bhp-hr for the year 2010. Heavy duty diesel engines make use of an aftertreatment filtration device, the Diesel Particulate Filter (DPF). DPFs are highly efficient in filtering PM (known as soot) and are an integral part of 2010 heavy duty diesel aftertreatment system. PM is accumulated in the DPF as the exhaust gas flows through it. This PM needs to be removed by oxidation periodically for the efficient functioning of the filter. This oxidation process is also known as regeneration. There are 2 types of regeneration processes, namely active regeneration (oxidation of PM by external means) and passive oxidation (oxidation of PM by internal means). Active regeneration occurs typically in high temperature regions, about 500 - 600 °C, which is much higher than normal diesel exhaust temperatures. Thus, the exhaust temperature has to be raised with the help of external devices like a Diesel Oxidation Catalyst (DOC) or a fuel burner. The O2 oxidizes PM producing CO2 as oxidation product. In passive oxidation, one way of regeneration is by the use of NO2. NO2 oxidizes the PM producing NO and CO2 as oxidation products. The passive oxidation process occurs at lower temperatures (200 - 400 °C) in comparison to the active regeneration temperatures. Generally, DPF substrate walls are washcoated with catalyst material to speed up the rate of PM oxidation. The catalyst washcoat is observed to increase the rate of PM oxidation. The goal of this research is to develop a simple mathematical model to simulate the PM depletion during the active regeneration process in a DPF (catalyzed and non-catalyzed). A simple, zero-dimensional kinetic model was developed in MATLAB. Experimental data required for calibration was obtained by active regeneration experiments performed on PM loaded mini DPFs in an automated flow reactor. The DPFs were loaded with PM from the exhaust of a commercial heavy duty diesel engine. The model was calibrated to the data obtained from active regeneration experiments. Numerical gradient based optimization techniques were used to estimate the kinetic parameters of the model.

Improving learning by connecting chemistry curriculum to students' experiences

The purpose of the study was to design, implement, and assess the effects of a teaching unit about fuel sources and chemical energy on students’ learning. The unit was designed to incorporate students’ experiences in a way that was aligned with the Michigan High School Content Expectations. The study was completed with all of the students taking General Chemistry in a rural Michigan high school in the 2010-11 school year. There were 138 participants total. The participants were mostly Caucasian and the majority were in the 11th grade. Of these, 77 constituted the experimental group and were taught the unit. The additional 61 participants in the control group were given the posttest only. Data was derived from the results of pre/post tests, final assessment projects, and the researcher’s observations. A pretest that contained questions about the fuel sources was administered at the beginning of the unit. An identical posttest was administered at the completion of the unit. A final assessment project required students to choose the best fuel source for the area, and support their opinion with facts and data from their research or the learning activities and labs performed in class. The results of the study revealed that the teaching unit did produce significant learning gains in the experimental group. The results also indicated that the teaching unit added value to the current General Chemistry curriculum by expanding what students were learning. The instructional goals of the unit were aligned with the Michigan High School Content Expectations. The results also revealed that the students were able to learn to support their thinking and decisions with explanations based on the data and labs. These are essential science literacy skills. The study supported the view that connecting the required curriculum with students’ experiences and interests was effective, and that students can learn important science literacy skills, such as providing support for arguments and communicating scientific explanations, when given adequate teacher support.

Edge coloring BIBDS and constructing MOELRs

Chapter 1 is used to introduce the basic tools and mechanics used within this thesis. Some historical uses and background are touched upon as well. The majority of the definitions are contained within this chapter as well. In Chapter 2 we consider the question whether one can decompose λ copies of monochromatic Kv into copies of Kk such that each copy of the Kk contains at most one edge from each Kv. This is called a proper edge coloring (Hurd, Sarvate, [29]). The majority of the content in this section is a wide variety of examples to explain the constructions used in Chapters 3 and 4. In Chapters 3 and 4 we investigate how to properly color BIBD(v, k, λ) for k = 4, and 5. Not only will there be direct constructions of relatively small BIBDs, we also prove some generalized constructions used within. In Chapter 5 we talk about an alternate solution to Chapters 3 and 4. A purely graph theoretical solution using matchings, augmenting paths, and theorems about the edgechromatic number is used to develop a theorem that than covers all possible cases. We also discuss how this method performed compared to the methods in Chapters 3 and 4. In Chapter 6, we switch topics to Latin rectangles that have the same number of symbols and an equivalent sized matrix to Latin squares. Suppose ab = n2. We define an equitable Latin rectangle as an a × b matrix on a set of n symbols where each symbol appears either [b/n] or [b/n] times in each row of the matrix and either [a/n] or [a/n] times in each column of the matrix. Two equitable Latin rectangles are orthogonal in the usual way. Denote a set of ka × b mutually orthogonal equitable Latin rectangles as a k–MOELR(a, b; n). We show that there exists a k–MOELR(a, b; n) for all a, b, n where k is at least 3 with some exceptions.

Triggering of volcanic activity by large earthquakes

Statistical analyses of temporal relationships between large earthquakes and volcanic eruptions suggest seismic waves may trigger eruptions even over great (>1000 km) distances, although the causative mechanism is not well constrained. In this study the relationship between large earthquakes and subtle changes in volcanic activity was investigated in order to gain greater insight into the relationship between dynamic stresses propagated by surface waves and volcanic response. Daily measurements from the Ozone Monitoring Instrument (OMI), onboard the Aura satellite, provide constraints on volcanic sulfur-dioxide (SO2) emission rates as a measure of subtle changes in activity. Time series of SO2 emission rates were produced from OMI data for thirteen persistently active volcanoes from 1 October 2004 to 30 September 2010. In order to quantify the affect of earthquakes at teleseismic distances, we modeled surface-wave amplitudes from the source mechanisms of moment magnitude (Mw) ≥7 earthquakes, and calculated the Peak Dynamic Stress (PDS). We assessed the influence of earthquakes on volcanic activity in two ways: 1) by identifying increases in the SO2 time series data and looking for causative earthquakes and 2) by examining the average emission rate before and after each earthquake. In the first, the SO2 time series for each volcano was used to calculate a baseline threshold for comparison with post-earthquake emission. Next, we generated a catalog of responses based on sustained SO2 emission increases above this baseline. Delay times between each SO2 response and each prior earthquake were analyzed using both the actual earthquake catalog, and a randomly generated catalog of earthquakes. This process was repeated for each volcano. Despite varying multiple parameters, this analysis did not demonstrate a clear relationship between earthquake-generated PDS and SO2 emission. However, the second analysis, which was based on the occurrence of large earthquakes indicated a response at most volcanoes. Using the PDS calculations as a filtering criterion for the earthquake catalog, the SO2 mass for each volcano was analyzed in 28-day windows centered on the earthquake origin time. If the average SO2 mass after the earthquake was greater than an arbitrary percentage of pre-earthquake mass, we identified the volcano as having a response to the event. This window analysis provided insight on what type of volcanic activity is more susceptible to triggering by dynamic stress. The volcanoes with very open systems included in this study, Ambrym, Gaua, Villarrica, Erta Ale and, Turrialba, showed a clear response to dynamic stress while the volcanoes with more closed systems, Merapi, Semeru, Fuego, Pacaya, and Bagana, showed no response.

Great Lakes tributary phosphorus bioavailability

Information on phosphorus bioavailability can provide water quality managers with the support required to target point source and watershed loads contributing most significantly to water quality conditions. This study presents results from a limited sampling program focusing on the five largest sources of total phosphorus to the U.S. waters of the Great Lakes. The work provides validation of the utility of a bioavailability-based approach, confirming that the method is robust and repeatable. Chemical surrogates for bioavailability were shown to hold promise, however further research is needed to address site-to-site and seasonal variability before a universal relationship can be accepted. Recent changes in the relative contribution of P constituents to the total phosphorus analyte and differences in their bioavailability suggest that loading estimates of bioavailable P will need to address all three components (SRP, DOP and PP). A bioavailability approach, taking advantage of chemical surrogate methodologies is recommended as a means of guiding P management in the Great Lakes.

Four-window technique for measuring optical-phase-space-time-frequency tomography

A new approach, the four-window technique, was developed to measure optical phase-space-time-frequency tomography (OPSTFT). The four-window technique is based on balanced heterodyne detection with two local oscillator (LO) fields. This technique can provide independent control of position, momentum, time and frequency resolution. The OPSTFT is a Wigner distribution function of two independent Fourier transform pairs, phase-space and time-frequency. The OPSTFT can be applied for early disease detection.

Retrofitting boreholes contaminated with iron in rural Uganda

During my Peace Corps service as a community health liaison in rural Uganda I noticed that many improved water wells in our area had been abandoned. The communities described the water in these wells as being reddish in color, having a foul taste and odor, discoloring clothes and food, and not able to produce lather for washing. Personal investigations and an initial literature search suggested that the primary contaminant was iron. The water in these wells had a low pH and a rusty metallic smell. The water produced early in the morning appeared very red but the water became more transparent as pumping continued. The iron components of many of these wells experienced accelerated corrosion resulting in frequent pump failure. This rapid corrosion coupled with the timing of the onset of iron contamination (months to years after these wells were completed) suggests that the most likely cause of the poor quality water was iron related bacteria and/or sulphate reducing bacteria. This report describes a remedy for iron contamination employed at 5 wells. The remedy involved disinfecting the wells with chlorine and replacing iron pump components with plastic and stainless steel. Iron concentrations in the wells were less than 1 mg/L when the wells were drilled but ranged from 2.5 to 40 mg/L prior to the remedy. After the remedy was applied, the total iron concentrations returned to levels below 1 mg/L. The presence of iron related bacteria was measured in all of these wells using Biological Activity Reaction Tests. Although IRB are still present in all the wells, the dissolved iron concentrations remain less than 1 mg/L. This remedy is practical for rural areas because the work can be performed with only hand tools and costs less than US $850. Because the source of iron contamination is removed in this approach, substantial follow-up maintenance is not necessary.

Influence of traumatic impaction and pathological loading on knee menisci

Nearly half of the US population faces the risk of developing knee osteoarthritis (OA). Both in vitro and in vivo studies can aid in a better understanding of the etiology, progression, and advancement of this debilitating disorder. The knee menisci are fibrocartilagenous structures that aid in the distribution of load, attenuation of shock, alignment and lubrication of the knee. Little is known about the biochemical and morphological changes associated with knee menisci following altered loading and traumatic impaction, and investigations are needed to further elucidate how degradation of this soft tissue advances over time. The biochemical response of porcine meniscal explants was investigated following a single bout of dynamic compression with and without the treatment of the pharmaceutical drug, anakinra (IL-1RA). Dynamic loading led to a strain-dependent response in both anabolic and catabolic gene expression of meniscal explants. By inhibiting the Interleukin-1 pathway with IL-1RA, a marked decrease in several catabolic molecules was found. From these studies, future developments in OA treatments may be developed. The implementation of an in vivo animal model contributes to the understanding of how the knee joint behaves as a whole. A novel closed-joint in vivo model that induces anterior cruciate ligament (ACL) rupture has been developed to better understand how traumatic injury leads to OA. The menisci of knees from three different groups (healthy, ACL transected, and traumatically impacted) were characterized using histomorphometry. The acute and chronic changes within the knee following traumatic impaction were investigated. The works presented in this dissertation have focused on the characterization, implementation, and development of mechanically-induced changes to the knee menisci.

Mechanisms contributing to the deep chlorophyll maximum in Lake Superior

The seasonal appearance of a deep chlorophyll maximum (DCM) in Lake Superior is a striking phenomenon that is widely observed; however its mechanisms of formation and maintenance are not well understood. As this phenomenon may be the reflection of an ecological driver, or a driver itself, a lack of understanding its driving forces limits the ability to accurately predict and manage changes in this ecosystem. Key mechanisms generally associated with DCM dynamics (i.e. ecological, physiological and physical phenomena) are examined individually and in concert to establish their role. First the prevailing paradigm, “the DCM is a great place to live”, is analyzed through an integration of the results of laboratory experiments and field measurements. The analysis indicates that growth at this depth is severely restricted and thus not able to explain the full magnitude of this phenomenon. Additional contributing mechanisms like photoadaptation, settling and grazing are reviewed with a one-dimensional mathematical model of chlorophyll and particulate organic carbon. Settling has the strongest impact on the formation and maintenance of the DCM, transporting biomass to the metalimnion and resulting in the accumulation of algae, i.e. a peak in the particulate organic carbon profile. Subsequently, shade adaptation becomes manifest as a chlorophyll maximum deeper in the water column where light conditions particularly favor the process. Shade adaptation mediates the magnitude, shape and vertical position of the chlorophyll peak. Growth at DCM depth shows only a marginal contribution, while grazing has an adverse effect on the extent of the DCM. The observed separation of the carbon biomass and chlorophyll maximum should caution scientists to equate the DCM with a large nutrient pool that is available to higher trophic levels. The ecological significance of the DCM should not be separated from the underlying carbon dynamics. When evaluated in its entirety, the DCM becomes the projected image of a structure that remains elusive to measure but represents the foundation of all higher trophic levels. These results also offer guidance in examine ecosystem perturbations such as climate change. For example, warming would be expected to prolong the period of thermal stratification, extending the late summer period of suboptimal (phosphorus-limited) growth and attendant transport of phytoplankton to the metalimnion. This reduction in epilimnetic algal production would decrease the supply of algae to the metalimnion, possibly reducing the supply of prey to the grazer community. This work demonstrates the value of modeling to challenge and advance our understanding of ecosystem dynamics, steps vital to reliable testing of management alternatives.