Optimal Distributed MQTT Broker and Services Placement for SDN-Edge Based Smart City Architecture.

A smart city is an urban area that collects data from various devices to effectively manage urban resources. The smart city IoT infrastructure connects numerous devices to an Internet-protocol-based low-power wireless network, shares massive amounts of data, and facilitates the development of new services. Message queuing telemetry transport (MQTT), a lightweight exchange protocol for the IoT environment, uses a publish and subscribe structure via a centralized broker to share data. The extent of edge computing provides distributed and closer resources to the data source while maintaining low transmission costs. However, a centralized MQTT data broker is unsuitable for distributed edge resources and could result in high latency, traffic, and bottleneck risk. Therefore, we proposed a distributed MQTT broker optimized architecture. A distributed MQTT broker for edge resources could reduce network traffic and data delivery latency by only managing consumed topics in the network. We formulate an integer non-linear program to optimize container placement and avoid wasting edge computing resources. We compared our proposed architecture to the existing distributed MQTT middleware architecture with greedy and random container placement through extensive simulation. Our methods show better performance in lowering deployment failure ratio, power consumption, network usage, and synchronization overhead.

A protocol for digitizing colors: the case of measuring color variables for forested wetland soils.

A procedure is presented and discussed that highlights the use of the Nix Pro Color Sensor ("Nix") in digitizing soil colors with applications for forested wetland soils. Informed by our soil color investigations using both the Munsell Soil Color Chart (MSCC) and the Nix in forested wetlands of the northern Virginia area, we crafted a standard operating procedure (SOP), adaptable to various locations and/or soil types, that guides users-regardless of knowledge of soil ecology or familiarity with the Nix-to successfully assess and monitor soil colors at various depths. Our SOP outlines steps for digitally collecting, storing, and sharing soil color data. Through the implementation of this procedure, soil color monitoring can enter the digital age, removing barriers of entry to soil color determination and enhancing individuals' interest in monitoring and understanding of the importance of soil color as an environmental and ecological indicator. With continued refinement and adaptation to intended use, the SOP herein presented has the potential to aid wetland/watershed assessment by providing data on soil colors that can be tracked over time while also encouraging public engagement in environmental monitoring of soils.

Predicting forested wetland soil carbon using quantitative color sensor measurements in the region of northern Virginia, USA.

Forested wetland soils within the Piedmont and Coastal Plain physiographic provinces of Northern Virginia (NOVA) were investigated to determine the utility of a handheld colorimeter, the Nix Pro Color Sensor ("Nix"), for predicting carbon contents (TC) and stocks (TC stocks) from on-site color measurements. Both the color variables recorded with each Nix scan ("Nix color variables"; n = 15) and carbon contents significantly differed between sites, with redder soils (higher a and h) at Piedmont sites, and higher TC at sites with darker soils (lower values of L, or lightness; p < 0.05). Nix-carbon correlation analysis revealed strong relationships between L (lightness), X (a virtual spectral variable), R (additive red), and KK (black) and log-transformed TC (Ln[TC]; |r| = 0.70; p < 0.01 for all). Simple linear regressions were conducted to identify how well these four final Nix variables could predict soil carbon. Using all color measurements, about 50% of Ln(TC) variability could be explained by L, X, R, or KK (p < 0.01), yet with higher predictive power obtained for Coastal Plain soils (0.55 < R2 < 0.65; p < 0.01). Regression model strength was maximized between Ln(TC) and the four final Nix variables using simple linear regressions when color measurements observed at a specific depth were first averaged (0.66 < R2 < 0.70; p < 0.01). While further study is warranted to investigate Nix applicability within various soil settings, these results demonstrate potential for the Nix and its soil color measurements to assist with rapid field-based assessments of soil carbon in forested wetlands.

Carbon Dioxide Emissions and Methane Flux from Forested Wetland Soils of the Great Dismal Swamp, USA.

The Great Dismal Swamp, a freshwater forested peatland, has accumulated massive amounts of soil carbon since the postglacial period. Logging and draining have severely altered the hydrology and forest composition, leading to drier soils, accelerated oxidation, and vulnerability to disturbance. The once dominant Atlantic white cedar, cypress, and pocosin forest types are now fragmented, resulting in maple-gum forest communities replacing over half the remaining area. In order to determine the effect of environmental variabes on carbon emissions, this study observes 2 years of CO2 and CH4 soil flux, which will also help inform future management decisions. Soil emissions were measured using opaque, non-permanent chambers set into the soil. As soil moisture increased by 1 unit of soil moisture content, CH4 flux increased by 457 µg CH4-C/m2/h. As soil temperature increased by 1 °C, CO2 emissions increased by 5109 µg CO2-C/m2/h. The area of Atlantic white cedar in the study boundary has an average yearly flux of 8.6 metric tons (t) of carbon from CH4 and 3270 t of carbon from CO2; maple-gum has an average yearly flux of 923 t of carbon from CH4 and 59,843 t of carbon from CO2; pocosin has an average yearly flux of 431 t of carbon from CH4 and 15,899 t of carbon from CO2. Total Cha-1year-1 ranged from 1845 kg of Cha-1year-1 in maple-gum to 2024 kg Cha-1year-1 for Atlantic white cedar. These results show that soil carbon gas flux depends on soil moisture, temperature and forest type, which are affected by anthropogenic activities.

Developing an ecosystem model of a floating wetland for water quality improvement on a stormwater pond.

An ecosystem model was developed to assist with designing and implementing a floating wetland (FW) for water quality management of urban stormwater ponds, focusing on nitrogen (N) removal. The model is comprised of three linked submodels: hydrology, plant growth, and nitrogen. The model was calibrated with the data that resulted from a FW constructed and implemented as part of an interdisciplinary pedagogical project on a university campus, titled "The Rain Project", which raised awareness of stormwater issues while investigating the potential application of green infrastructure for sustainable stormwater management. The FW had been deployed during the summer of 2015 (i.e., May through mid-September) on a major stormwater pond located at the center of the Fairfax Campus of George Mason University near Washington, D.C. We used the model to explore the impact of three design elements of FW (i.e., hydraulic residence time (HRT), surface area coverage, and primary productivity) on the function of FW. Model simulations showed enhanced N removal performance as HRT and surface area coverage increased. The relatively low macrophyte productivity observed indicates that, in the case of our pond and FW, N removal was very limited. The model results suggest that even full pond surface coverage would result in meager N removal (∼6%) at a HRT of one week. A FW with higher plant productivity, more representative of that reported in the literature, would require only 10% coverage to achieve similar N removal efficiency (∼7%). Therefore, macrophyte productivity appears to have a greater impact on FW performance on N removal than surface area coverage or pond HRT. The outcome of the study shows that this model, though limited in scope, may be useful in aiding the design of FW to augment the performance of degraded stormwater ponds in an effort to meet local water quality goals.

Carbon storage potential by four macrophytes as affected by planting diversity in a created wetland.

Wetland creation has become a commonplace method for mitigating the loss of natural wetlands. Often mitigation projects fail to restore ecosystem services of the impacted natural wetlands. One of the key ecosystem services of newly created wetlands is carbon accumulation/sequestration, but little is known about how planting diversity (PD) affects the ability of herbaceous wetland plants to store carbon in newly created wetlands. Most mitigation projects involve a planting regime, but PD, which may be critical in establishing biologically diverse and ecologically functioning wetlands, is seldom required. Using a set of 34 mesocosms (∼1 m(2) each), we investigated the effects of planting diversity on carbon storage potential of four native wetland plant species that are commonly planted in created mitigation wetlands in Virginia - Carex vulpinoidea, Eleocharis obtusa, Juncus effusus, and Mimulus ringens. The plants were grown under the four distinctive PD treatments [i.e., monoculture (PD 1) through four different species mixture (PD 4)]. Plant biomass was harvested after two growing seasons and analyzed for tissue carbon content. Competition values (CV) were calculated to understand how the PD treatment affected the competitive ability of plants relative to their biomass production and thus carbon storage potentials. Aboveground biomass ranged from 988 g/m(2) - 1515 g/m(2), being greatest in monocultures, but only when compared to the most diverse mixture (p = 0.021). However, carbon storage potential estimates per mesocosm ranged between 344 g C/m(2) in the most diverse mesocosms (PD 4) to 610 g C/m(2) in monoculture ones with no significant difference (p = 0.089). CV of E. obtusa and C. vulpinoidea showed a declining trend when grown in the most diverse mixtures but J. effusus and M. ringens displayed no difference across the PD gradient (p = 0.910). In monocultures, both M. ringens, and J. effusus appeared to store carbon as biomass more effectively than the other species, suggesting that the choice of plant species may play an important role in facilitating the development of carbon accumulation/storage in created wetlands. Plant community diversity provides many ecosystem services (e.g., habitat and floristic quality) other than carbon storage function. Thus, a further study is needed that will focus on investigating how other design elements such as microtopography and hydrologic connectivity may interact with PD in terms of enhancing the carbon storage potential of newly created wetlands.

ß-Isocyanoalanine as an IR probe: comparison of vibrational dynamics between isonitrile and nitrile-derivatized IR probes.

An infrared (IR) probe based on isonitrile (NC)-derivatized alanine 1 was synthesized and the vibrational properties of its NC stretching mode were investigated using FTIR and femtosecond IR pump-probe spectroscopy. It is found that the NC stretching mode is very sensitive to the hydrogen-bonding ability of solvent molecules. Moreover, its transition dipole strength is larger than that of nitrile (CN) in nitrile-derivatized IR probe 2. The vibrational lifetime of the NC stretching mode is found to be 5.5 ± 0.2 ps in both D2O and DMF solvents, which is several times longer than that of the azido (N3) stretching mode in azido-derivatized IR probe 3. Altogether these properties suggest that the NC group can be a very promising sensing moiety of IR probes for studying the solvation structure and dynamics of biomolecules.

Hydrologic connectivity to streams increases nitrogen and phosphorus inputs and cycling in soils of created and natural floodplain wetlands.

Greater connectivity to stream surface water may result in greater inputs of allochthonous nutrients that could stimulate internal nitrogen (N) and phosphorus (P) cycling in natural, restored, and created riparian wetlands. This study investigated the effects of hydrologic connectivity to stream water on soil nutrient fluxes in plots ( = 20) located among four created and two natural freshwater wetlands of varying hydrology in the Piedmont physiographic province of Virginia. Surface water was slightly deeper; hydrologic inputs of sediment, sediment-N, and ammonium were greater; and soil net ammonification, N mineralization, and N turnover were greater in plots with stream water classified as their primary water source compared with plots with precipitation or groundwater as their primary water source. Soil water-filled pore space, inputs of nitrate, and soil net nitrification, P mineralization, and denitrification enzyme activity (DEA) were similar among plots. Soil ammonification, N mineralization, and N turnover rates increased with the loading rate of ammonium to the soil surface. Phosphorus mineralization and ammonification also increased with sedimentation and sediment-N loading rate. Nitrification flux and DEA were positively associated in these wetlands. In conclusion, hydrologic connectivity to stream water increased allochthonous inputs that stimulated soil N and P cycling and that likely led to greater retention of sediment and nutrients in created and natural wetlands. Our findings suggest that wetland creation and restoration projects should be designed to allow connectivity with stream water if the goal is to optimize the function of water quality improvement in a watershed.

Soil properties predict plant community development of mitigation wetlands created in the Virginia Piedmont, USA.

The study investigated vegetative and soil properties in four created mitigation wetlands, ranging in age from three to ten years, all created in the Virginia Piedmont. Vegetation attributes included percent cover, richness (S), diversity (H'), floristic quality assessment index (FQAI), prevalence index (PI), and productivity [i.e., peak above-ground biomass (AGB) and below-ground biomass]. Soil attributes included soil organic matter (SOM), gravimetric soil moisture (GSM), pH, and bulk density (D(b)) for the top 10 cm. Species dominance (e.g., Juncus effusus, Scirpus cyperinus, Arthraxon hispidus) led to a lack of differences in vegetative attributes between sites. However, site-based differences were found for GSM, pH, and SOM (P < 0.001). Soil attributes were analyzed using Euclidean cluster analysis, resulting in four soil condition (SC) categories where plots were grouped based on common attribute levels (i.e., SC1 > SC2 > SC3 > SC4, trended more to less developed). When vegetation attributes were compared between SC groups, greater SOM, lower D(b), more circumneutral pH, and higher GSM, all indicative of maturation, were associated with higher H' (P < 0.05), FQAI (P < 0.05), and total and volunteer percent cover (P < 0.05), and lower AGB (P < 0.001), PI (P < 0.05), and seeded percent cover (P < 0.05). The outcome of the study shows that site age does not necessarily equate with site development with soil and vegetation developmental rates varying both within and among sites. The inclusion of soil attributes in post-construction monitoring should be required to enhance our understanding and prediction of developmental trajectory of created mitigation wetlands.

Analysis of soil color variables and their relationships between two field-based methods and its potential application for wetland soils.

While the Munsell Soil Color Chart (MSCC) is the most frequently used, well-established field method for reading soil color, the Nix Color Sensor (NCS) is an inexpensive, app-based alternative that can complement or potentially substitute for the MSCC. Soils were collected and their colors were measured from four forested sites across Northern Virginia within the Chesapeake Bay Watershed using both the MSCC and NCS. Three MSCC variables and 15 NCS variables were collected in the field; a methodology was established to use these "measured" (M) variables to derive 9 NCS calculated (C) variables. A stepwise correlation identified NCS variables most suitable for relating the NCS to each of the MSCC attributes: hue (H), value (V), and chroma (CM). Ultimately, H, V, and CM were deemed to be best represented by HRGB calculated from the RGB color space (ρ = 0.56), L from the CIE-Lab color space (ρ = 0.73), and z = Z/(X + Y + Z) from the XYZ color space (ρ = -0.80), respectively (p < 0.001). The corresponding explanatory powers of final NCS variables (i.e., HRGB, L, and z) for H, V, and CM were 26%, 54%, and 62%, respectively (p <0.01). Significant differences in z between soils identified as hydric and nonhydric, but lack of nonoverlapping ranges, indicate a potential for the NCS to complement the MSCC in assessing wetland soil color in an accessible and reproducible manner, including hydric soil identifications for wetland delineation practices. Further study with more data over various types of soils is necessary to establish stronger relationships between the NCS and MSCC. Nonetheless, the method of characterizing soil color variables from the two field methods presented in the study can serve as a template for future studies or environmental education programs desiring to use the NCS as a complement to the MSCC.

Planting richness affects the recovery of vegetation and soil processes in constructed wetlands following disturbance.

The resilience of constructed wetland ecosystems to severe disturbance, such as a mass herbivory eat-out or soil disturbance, remains poorly understood. In this study, we use a controlled mesocosm experiment to examine how original planting diversity affects the ability of constructed freshwater wetlands to recover structurally and functionally after a disturbance (i.e., aboveground harvesting and soil coring). We assessed if the planting richness of macrophyte species influences recovery of constructed wetlands one year after a disturbance. Mesocosms were planted in richness groups with various combinations of either 1, 2, 3, or 4 species (RG 1-4) to create a gradient of richness. Structural wetland traits measured include morphological regrowth of macrophytes, soil bulk density, soil moisture, soil %C, and soil %N. Functional wetland traits measured include above ground biomass production, soil potential denitrification, and soil potential microbial respiration. Total mesocosm cover increased along the gradient of plant richness (43.5% in RG 1 to 84.5% in RG 4) in the growing season after the disturbance, although not all planted individuals recovered. This was largely attributed to the dominance of the obligate annual species. The morphology of each species was affected negatively by the disturbance, producing shorter, and fewer stems than in the years prior to the disturbance, suggesting that the communities had not fully recovered one year after the disturbance. Soil characteristics were almost uniform across the planting richness gradient, but for a few exceptions (%C, C:N, and non-growing season soil moisture were higher slightly in RG 2). Denitrification potential (DEA) increased with increasing planting richness and was influenced by the abundance and quality of soil C. Increased open space in unplanted mesocosms and mesocosms with lower species richness increased labile C, leading to higher C mineralization rates.

Isonitrile as an Ultrasensitive Infrared Reporter of Hydrogen-Bonding Structure and Dynamics.

Infrared (IR) probes based on terminally blocked ß-isocyanoalanine (AlaNC) and p-isocyanophenylalanine (PheNC) amino acids were synthesized. These isonitrile (NC)-derivatized compounds were extensively characterized by FTIR and femtosecond IR pump-probe spectroscopies, and a direct comparison was made with popularly used nitrile (CN)- and azide (N3)-derivatized analogs. It is shown that the isonitrile stretch frequency exhibits extremely high sensitivity to hydrogen-bonding interactions. In addition, the IR intensity of the isonitrile group is much higher than that of the nitrile group and almost as intense as that of the azido group. Furthermore, its vibrational lifetime is much longer than that of the nitrile and azido groups. To elucidate the origin of such a high H-bond sensitivity and IR intensity observed for isonitrile, extensive quantum chemical calculations were performed. It is shown that the Coulombic contributions to the vibrational frequency shifts of the isonitrile and nitrile stretch modes have opposite signs but similar magnitudes, whereas the contributions of exchange repulsion and charge delocalization to their frequency shifts are comparable. Therefore, the isonitrile stretch frequency is much more sensitive to H-bonding interactions because the blue-shifting exchange-repulsion effects are additionally enforced by such electrostatic effects. It is also shown that the much higher IR intensity of the isonitrile group compared to that of the nitrile group is due to the configuration reversal of the atomic electronegativity between the NC and CN groups. Owing to these features, we believe that isonitrile is a much better IR reporter of H-bonding structure and dynamics than the widely used nitrile and azide.

Characterization of soil bacterial community structure and physicochemical properties in created and natural wetlands.

We used multi-tag pyrosequencing of 16S ribosomal DNA to characterize bacterial communities of wetland soils collected from created and natural wetlands located in the Virginia piedmont. Soils were also evaluated for their physicochemical properties [i.e., percent moisture, pH, soil organic matter (SOM), total organic carbon (TOC), total nitrogen (TN), and C:N ratio]. Soil moisture varied from 15% up to 55% among the wetlands. Soil pH ranged between 4.2 and 5.8, showing the typical characteristic of acidic soils in the Piedmont region. Soil organic matter contents ranged from 3% up to 6%. Soil bacterial community structures and their differences between the wetlands were distinguished by pyrosequencing. Soil bacterial communities in the created wetlands were less dissimilar to each other than to those of either natural wetland, with little difference in diversity (Shannon's H') between created and natural wetlands, except one natural wetland consistently showing a lower H'. The greatest difference of bacterial community structure was observed between the two natural wetlands (R=0.937, p<0.05), suggesting these two natural wetlands were actually quite different reflecting differences in their soil physicochemistry. The major phylogenic groups of all soils included Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Gemmatinomadetes, Nitrospira, and Proteobacteria with Proteobacteria being the majority of the community composition. Acidobacteria group was more abundant in natural wetlands than in created wetlands. We found a significant association between bacterial community structures and physicochemical properties of soils such as C:N ratio (ρ=0.43, p<0.01) and pH (ρ=0.39, p<0.01). The outcomes of the study show that the development of ecological functions, mostly mediated by microbial communities, is connected with the development of soil properties in created wetlands. Soil properties should be carefully monitored to examine the progress of functional wetland mitigation.