The proposed research tests the hypothesis that sediment transport dynamics play a role in controlling the topographic patterning that is crucial to the ecology of the ridge and slough landscape in the Florida Everglades. Namely, under historical flow conditions, it is hypothesized that sediment redistribution from open-water slough to vegetated ridge regulated ridge width but that, with drainage and compartmentalization of the Everglades, the magnitude of redistribution has decreased, permitting expansion of ridges into open-water sloughs and loss of topographic heterogeneity. Project hypotheses will be tested through a combination of field and laboratory experimentation and numerical modeling of the mass and momentum balance equations governing flocculent sediment transport dynamics and flow in vegetated environments. Experimental analysis of floc transport mechanics will describe the critical shear stresses and turbulence intensities that entrain size classes of floc in a deposited bed, equilibrium aggregate size distributions and concentrations resulting from flow with different shear parameters, aggregate settling velocities, and changes in turbulence and flow profiles that occur across a ridge/slough cross-section as a result of vegetation and microtopography. To this end, flow monitoring and a series of transport experiments and tracer tests using natural floc will be performed in laboratory and field flumes. Funds will also sponsor the execution of complementary science fair projects by Forest Hill High School environmental science magnet program students, which will focus on using a rapid-assessment optical technique for developing an organic matter mixing model across a ridge/slough transect (which can be used as a validation measure for the sediment transport model) and on elucidating the effects of ambient water quality on flocculent organic sediment transport properties. Intellectual merit. The proposed research builds upon previous research showing the existence of sediment redistribution from open-water channels to vegetated environments by producing a model to predict the magnitude and spatial distribution of sedimentation as a function of flow velocity and water level. In the Everglades, sediment occurs primarily in the form of organic floccules, the mechanics of which are not well understood. Similarly, although flocculation plays a dominant role in the suspended sediment dynamics of rivers, wetlands, and estuaries throughout the world, studies on the impacts of flow through vegetated environments on sedimentation and transport of floccules and predictive models of floc dynamics on landscape morphology and evolution are nonexistent. This research develops a set of laboratory and field experiments designed to address the critical questions about floc transport mechanics required for model development and an original model of how these mechanics influence landscape evolution. Thus, the proposed research will set a precedent for improved predictions of sediment transport and landscape dynamics that will have implications for estuarine science, fluvial geomorphology, wetlands science, and contaminant transport. Broader impacts - Results of this project will be broadly disseminated to (1) researchers in the field, through organization of a special session at an ASLO meeting on implications of flocculant sediment transport for landscape dynamics and subsequent publication of a special journal issue, to (2) policy makers involved in implementation of the Comprehensive Everglades Restoration Plan through regular participation of the PIs in Landscape Subteam meetings and the Greater Everglades Ecosystem Restoration conference, and to (3) the general public, through publication of a popular science article on Everglades landscape dynamics. Further, model results will impact policy and society by leading to improved recommendations of flow velocities and hydroperiods that should be implemented to restore the ridge and slough landscape. Enhanced infrastructure resulting from the purchase of a laser diffraction particle size analyzer will benefit classroom demonstrations, laboratory, and field research at the K-12, undergraduate, and graduate levels. Research efforts will also enhance collaborative efforts between the USGS, University of Colorado, and K-12 education and will synergistically complement an existing USGS project on biogeochemical feedback mechanisms and nutrient transport within the ridge and slough landscape. Finally, this research enhances the knowledge transfer to future generations of scientists through a committed partnership with the environmental science magnet program at Forest Hill High School in West Palm Beach, Florida and by providing research support to a current Ph.D student.
The objective of this research was to more fully understand the role that sediment transport plays in evolution of the Everglades landscape. Historically, over a third of the Everglades landscape area comprised the ridge and slough landscape, a patterned ecosystem consisting of elongated, elevated peat ridges interspersed among lower sloughs through which most of the flow occurred. The alignment of these striped landscape features with the flow direction is ecologically important because it provides corridors for fish migration. The patterned landscape also provides a mosaic of different habitat types in sharp juxtaposition, which supports high biodiversity in wading bird and fish populations. Several other large wetlands throughout the world exhibit the same type of striped patterning present in the Everglades, making this feature of interest for worldwide wetland conservation. However, the Everglades ridge and slough landscape is currently in the spotlight because of its prominence in Everglades restoration. Despite its stability for millennia, the Everglades ridge and slough landscape has been degrading rapidly over the past century (predominantly through a loss of sloughs) concurrent with numerous human-induced changes including drainage, compartmentalization of the Everglades through the construction of levees and canals, and nutrient enrichment. However, the specific reasons for its degradation were poorly understood. Understanding the drivers of Everglades landscape evolution remained a prominent research need, as restoration of the ridge and slough landscape became a goal of the Comprehensive Everglades Restoration Plan. This project tested the hypothesis that redistribution of sediment from fast-flowing sloughs to slowly flowing ridges was a critical process maintaining the ridge and slough landscape pattern. Studying sediment transport in the Everglades pushes the boundaries of current knowledge, as, in contrast to most rivers and estuaries, the sediment in the Everglades is almost completely organic, originating from partially decayed plants and microorganisms. In flowing water it forms aggregates (also known as floc) that vary in size and settling speed, and its physical properties depend on the flow speed and the microbial communities that colonize the aggregates. The principal investigators (PIs) conducted field and laboratory experiments to better understand the transport properties of that floc and then incorporated the results into a numerical model that simulated the evolution of the ridge and slough landscape from an initially unpatterned state. They found that the model was able to produce realistic ridge and slough landscapes only when flow speeds were sufficient to transport and redistribute organic sediment. In subsequent modeling experiments, simulated ridge and slough landscapes were perturbed in ways similar to the human disturbances to the system of the past century. These experiments suggested that decreased mean water levels cause the most rapid degradation of the ridge and slough landscape. Decreased flow velocities also induce a loss of sloughs but at a slower rate. Products of this research benefited basic and applied science. The PIs chaired two sessions at international technical meetings about the dynamics of flocculent sediment transport and about the hydrological and ecological mechanisms influencing landscape development, the latter of which resulted in the publication of a special issue of the journal Geomorphology. Research products also included publications that have informed Everglades restoration decisions. For instance, the modeling resulted in recommended target flow speeds for pulsed flow releases that form part of the Everglades restoration strategy. It also led to the first recognition that the abundance of spikerush, a type of vegetation that has become more populous within sloughs over the past century, may need to be reduced if the pulsed flow releases are to be successful in achieving target flow speeds. The model simulates processes that occur in many wetlands throughout the world and is therefore not specific to the Everglades. Broad application of the model showed that these processes can produce a variety of different wetland landscape patterns in different environments and suggested that these patterns are particularly sensitive to changes in water levels and flow speeds. This project also contributed in substantial ways to education at the K-12, undergraduate, and graduate student levels. It formed the central focus of a Ph.D dissertation and provided a research experience for several undergraduate and high school students. A mentoring/research partnership was formed between the PIs and Forest Hill Community High School, in which the PIs worked with several groups of students in completing related science fair projects and provided guest lectures for environmental science courses. In addition, the project produced a nonfiction children’s book, titled One Night in the Everglades, with accompanying curricula targeted for fourth and fifth graders. The book provides information about Everglades restoration science while profiling a day in the life of a young scientist and is currently in press.
