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Abstract: A numerical model has been developed to simulate the spatiotemporal patterning of the ridge and slough landscape in wetlands, characterized by crests (ridges) and valleys (sloughs) that are elongated parallel to the direction of water flow. The model formulation consists of governing equations for integrated surface water and groundwater flow, sediment transport, and soil accretion, as well as litter production by vegetation growth. The model simulations show how the spatial pattern self-organizes over time with the generation of ridges and sloughs through sediment deposition and erosion driven by the water flow field. The spatial and temporal distributions of the water depth, flow rates and sediment transport processes are caused by differential flow due to vegetation and topography heterogeneities. The model was parameterized with values that are representative of the Everglades wetland in the southern portion of the Florida peninsula in the USA. Model simulation sensitivity was tested with respect to numerical grid size, lateral vegetation growth and the rate of litter production. The characteristic wavelengths of the pattern in the directions along and perpendicular to flow that are simulated with this model develop over time into ridge and slough shapes that resemble field observations. Also, the simulated elevation differences between the ridges and sloughs are of the same order of those typically found in the field. The width of ridges and sloughs was found to be controlled by a lateral vegetation growth distance parameter in a simplified formulation of vegetation growth, which complements earlier modeling results in which a differential peat accretion mechanism alone did not reproduce observations of ridge and slough lateral wavelengths. The results of this work suggest that ridge and slough patterning occurs as a result of vegetation''s ability to grow laterally, enhancing sediment deposition in ridge areas, balanced by increased sediment erosion in slough areas to satisfy flow continuity. The interplay between sediment transport, water flow and vegetation and soil dynamic processes needs to be explored further through detailed field experiments, using a model formulation such as the one developed in this work to guide data collection and interpretation. This should be one of the focus areas of future investigations of pattern formation and stability in ridge and slough areas. [Copyright &y& Elsevier]

Abstract: The longevity and reactivity of nanoscale zerovalent iron (nZVI) and palladized bimetallic particles (BNP) were evaluated in batch and column experiments for remediation of a trichloroethene (TCE)-contaminated plume within a clayey soil from Oak Ridge Reservation (ORR). Comparative studies assessing the viability of BNP and nZVI confirmed that particle behavior is severely affected by clay sediments. Surface morphology and composition analyses using SEM and SEM–energy-dispersive spectroscopy spectrum revealed particle agglomeration through the formation of clay–iron aggregates of greater mass during the early phase of the experiment. Batch study results suggest that TCE degradation in ORR clayey soil follows a pseudo-first-order kinetic model exhibiting reaction rate constants (k) of 0.05–0.24 day−1 at varied iron-to-soil ratios. Despite high reactivity in water, BNP were less effective in the site-derived clay sediment with calculated TCE removal efficiencies of 98.7% and 19.59%, respectively. A column experiment was conducted to investigate particle longevity and indicator parameters of the TCE degradation process under flow conditions. It revealed that the TCE removal efficiency gradually declined over the course of the experiment from 86–93% to 51–52%, correlating to a progressive increase in oxidation–reduction potential (ORP) from −485 to −250 mV and pH drop from 8.2–8.6 to 7.4–7.5. The rate of nZVI deactivation reaction was found to be a first order with a k d value of 0.0058 day−1. SEM images of residual nZVI revealed heavily agglomerated particles. However, despite widespread oxidation and agglomeration, particles managed to maintain some capacity for oxidation. A quantitative analysis of nZVI deactivation has the potential of predicting nZVI longevity in order to improve the design strategy of TCE remediation. [Copyright &y& Elsevier]

Abstract Biofuels play a critical role in the Paris Agreement to help achieve climate change mitigation targets. However, a significant increase in production of biofuels might potentially be realized at the expense of overusing natural resources, particularly land and water. Understanding the tradeoffs between the impacts on land and water arises as a critical issue in the development of biofuels. This energy- water-land nexus might be particularly important for Brazil, which currently is the world's second largest producer and the largest exporter of biofuels. Furthermore, Brazil itself has set up its own Intended Nationally Determined Contribution agenda with a significant growth of biofuel production (18%) by 2030. Most studies on environmental impacts of biofuel production have either focused on land use or water use, but very few studies assessed both. Using an environmentally extended multiregional input-output (MRIO) approach, this study analyzes the current water-land nexus of bioenergy production in Brazil by quantifying the distribution of tradeoffs and synergies between land and water use for bioethanol production and its environmental consequences across Brazilian states. Our results show a clear tradeoff of water and land impacts and significant differences between irrigated and rainfed ethanol production. When including water and land scarcity in the analysis, the results are significantly different, uncovering very different tradeoffs and synergies between bioethanol producer and consumer states that could inform the expansion of bioenergy in Brazil. Compared to other crops, sugarcane has a higher comparative advantage relative to land than to water. Highlights • Biofuels play a critical role in the Paris Agreement to help achieve climate change mitigation targets. • This study analyzes the current water-land nexus of bioenergy production in Brazil. • Our results show a clear tradeoff of water and land impacts between irrigated and rainfed ethanol production. • Compared to other crops, sugarcane has a higher comparative advantage relative to land than to water. [ABSTRACT FROM AUTHOR]

Ecosystems of Florida Everglades are highly sensitive to phosphorus loading. Future restoration efforts, which focus on restoring Everglades water flows, may pose a threat to the health of these ecosystems. To determine the fate and transport of total phosphorus and evaluate proposed Everglades restoration, a water quality model has been developed using the hydrodynamic results from the M3ENP (Mike Marsh Model of Everglades National Park) — a physically-based hydrological numerical model which uses MIKE SHE/MIKE 11 software. Using advection–dispersion with reactive transport for the model, parameters were optimized and phosphorus loading in the overland water column was modeled with good accuracy (60%). The calibrated M3ENP-AD model was then modified to include future bridge construction and canal water level changes, which have shown to increase flows into ENP. These bridge additions increased total dissolved phosphorus (TP) load downstream in Shark Slough and decreased TP load in downstream Taylor Slough. However, there was a general decrease in TP concentration and TP mass per area over the entire model domain. The M3ENP-AD model has determined the mechanisms for TP transport and quantified the impacts of ENP restoration efforts on the spatial–temporal distribution of phosphorus transport. This tool can be used to guide future Everglades restoration decisions. [ABSTRACT FROM AUTHOR]

Abstract: We examined the relationships between two satellite-derived vegetation indices and foliar δ 15N values obtained from dominant canopy species in a set of tree islands located in the Everglades National Park in South Florida, USA. These tree islands constitute important nutrient hotspots in an otherwise P-limited wetland environment. Foliar δ 15N values obtained from a previous study of 17 tree islands in both slough (perennially wet) and prairie (seasonally wet) locations served as a proxy of P availability at the stand level. We utilized five cloud-free SPOT 4 multispectral images (20m spatial resolution) from different times of the seasonal cycle to derive two atmospherically corrected vegetation indices: the normalized difference vegetation index (NDVI) and the normalized difference water index (NDWI), averaged for each tree island. NDWI, which incorporates a shortwave infrared (SWIR) band that provides information on leaf water content, showed consistently higher linear fits with island foliar δ 15N values than did NDVI. In addition, NDWI showed greater variation throughout the seasonal cycle than did NDVI, and was significantly correlated with average water stage, which suggests that the SWIR band captures important information on seasonally variable water status. Tree islands in slough locations showed higher NDWI than prairie islands during the dry season, which is consistent with higher levels of transpiration and nutrient harvesting and accumulation for perennially wet locations. Overall, the results suggest that water availability is closely related to P availability in subtropical tree islands, and that NDWI may provide a robust indicator of community-level water and nutrient status. [ABSTRACT FROM AUTHOR]

Sharp boundaries typically separate the salinity tolerant mangroves from the salinity intolerant hardwood hammock species, which occupy the similar geographical areas of southern Florida. Evidence of strong feedback between tree community-type and the salinity of the unsaturated (vadose) zone of the soil suggests that a severe disturbance that significantly tilts the salinity in the vadose zone might cause a shift from one vegetation type to the other. In this study, a model based upon the feedback dynamics between vegetation and salinity of the vadose zone of the soil was used to take account of storm surge events to investigate the mechanisms that by which this large-scale disturbance could affect the spatial pattern of hardwood hammocks and mangroves. Model simulation results indicated that a heavy storm surge that completely saturated the vadose zone at 30ppt for 1 day could lead to a regime shift in which there is domination by mangroves of areas previously dominated by hardwood hammocks. Lighter storm surges that saturated the vadose zone at less than 7ppt did not cause vegetation shifts. Investigations of model sensitivity analysis indicated that the thickness of the vadose zone, coupled with precipitation, influenced the residence time of high salinity in the vadose zone and therefore determined the rate of mangrove domination. The model was developed for a southern Florida coastal ecosystem, but its applicability may be much broader. [Copyright &y& Elsevier]

Interferometric processing of JERS-1 L-band Synthetic Aperture Radar (SAR) data acquired over south Florida during 1993–1996 reveals detectable surface changes in the Everglades wetlands. Although our study is limited to south Florida it has implication for other large-scale wetlands, because south Florida wetlands have diverse vegetation types and both managed and natural flow environments. Our analysis reveals that interferometric coherence level is sensitive to wetland vegetation type and to the interferogram time span. Interferograms with time spans less than six months maintain phase observations for all wetland types, allowing characterization of water level changes in different wetland environments. The most noticeable changes occur between the managed and the natural flow wetlands. In the managed wetlands, fringes are organized, follow patterns related to some of the managed water control structures and have high fringe-rate. In the natural flow areas, fringes are irregular and have a low fringe-rate. The high fringe rate in managed areas reflects dynamic water topography caused by high flow rate due to gate operation. Although this organized fringe pattern is not characteristic of most large-scale wetlands, the high level of water level change enables accurate estimation of the wetland InSAR technique, which lies in the range of 5–10 cm. The irregular and low rate fringe pattern in the natural flow area reflects uninterrupted flow that diffuses water efficiently and evenly. Most of the interferograms in the natural flow area show an elongated fringe located along the transitional zone between salt- and fresh-water wetlands, reflecting water level changes due to ocean tides. [Copyright &y& Elsevier]