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Wetland ecosystems are controlled by their hydrology. Recent experimental and numerical investigations have suggested that flow pulses are needed to preserve sediment redistribution in some wetlands. In this study, the authors investigate the effect of pulsed-flow conditions on the hydrologic regime of low-gradient densely vegetated wetlands using a fine-resolution, two-dimensional depth-averaged numerical flow model. The model was applied to simulate flow depth and velocity within the Loxahatchee Impoundment Landscape Assessment (LILA) wetland located in Boynton Beach, Florida. Two pulsed-flow conditions with low-pulse and high-pulse flow magnitude were considered. The simulation results of low-pulse flow conditions reveal the areas within deep sloughs where flow velocities and directions change continuously, creating enhanced mixing areas within the deep slough. These mixing areas may have the potential to affect processes such as sediment redistribution and nutrient transport. Simulation of high-pulse flow magnitude, however, results in more uniform flow velocity inside deep slough. It also indicates that a pulse can only be detected when inflow discharge is at least 3.0 m ³/s. Lower inflow discharge values are too weak in magnitude to generate substantial changes in water surface elevation and velocity and they may not exhibit a flow wave propagation into the study area. [ABSTRACT FROM AUTHOR]

In the context of climatic uncertainty and potential climatic change, incorporating climatic variability and change in eco-hydrological analysis, as well as understanding the impact of such variability on ecosystems, is of crucial importance. The latter is particularly true for those complex ecosystems, such as wetlands, which cradle large varieties of species, many of which rare or endangered. Focusing on the Everglades wetlands, we investigate the presence of non-stationary elements in the seasonal cycle of precipitation, temperature and stage level and examine their correlation and potential impact on the ecosystem's flora and fauna. To this aim, we revisit demodulation techniques and demonstrate their validity for the diagnosis of long-term trends in the amplitude and phase of seasonal patterns of hydrologic series. We then analyse historical records of fauna and flora components of the Everglades in order to reveal potential relationships with hydrological trends. We observe that the seasonal patterns of all the time series analysed are non-stationary. In addition, we observe that the amplitude of seasonal oscillations of all hydro-climatic drivers is strongly correlated with anomalies in records of wading birds population and plant carbon assimilation. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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]

Tree islands in the Everglades wetlands are centers of biodiversity and targets of restoration, yet little is known about the pattern of water source utilization by the constituent woody plant communities: upland hammocks and flooded swamp forests. Two potential water sources exist: (1) entrapped rainwater in the vadose zone of the organic soil (referred to as upland soil water), that becomes enriched in phosphorus, and (2) phosphorus-poor groundwater/surface water (referred to as regional water). Using natural stable isotope abundance as a tracer, we observed that hammock plants used upland soil water in the wet season and shifted to regional water uptake in the dry season, while swamp forest plants used regional water throughout the year. Consistent with the previously observed phosphorus concentrations of the two water sources, hammock plants had a greater annual mean foliar phosphorus concentration over swamp forest plants, thereby supporting the idea that tree island hammocks are islands of high phosphorus concentrations in the oligotrophic Everglades. Foliar nitrogen levels in swamp forest plants were higher than those of hammock plants. Linking water sources with foliar nutrient concentrations can indicate nutrient sources and periods of nutrient uptake, thereby linking hydrology with the nutrient regimes of different plant communities in wetland ecosystems. Our results are consistent with the hypotheses that (1) over long periods, upland tree island communities incrementally increase their nutrient concentration by incorporating marsh nutrients through transpiration seasonally, and (2) small differences in micro-topography in a wetland ecosystem can lead to large differences in water and nutrient cycles. [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]