(2009) Harvey, J.W., Schaffranek, R.W., Noe, G.B., Larsen, L.G., Nowacki, D.J. and O'Connor, B.L. Hydroecological factors governing surface water flow on a low-gradient floodplain. Water Resources Research 45, Art.No.W03421.

Abstract
Interrelationships between hydrology and aquatic ecosystems are better understood in streams and rivers compared to their surrounding floodplains. Our goal was to characterize the hydrology of the Everglades ridge and slough floodplain ecosystem, which is valued for the comparatively high biodiversity and connectivity of its parallel-drainage features but which has been degraded over the past century in response to flow reductions associated with flood control. We measured flow velocity, water depth, and wind velocity continuously for 3 years in an area of the Everglades with well-preserved parallel-drainage features (i.e., 200-m wide sloughs interspersed with slightly higher elevation and more densely vegetated ridges). Mean daily flow velocity averaged 0.32 cm s(-1) and ranged between 0.02 and 0.79 cm s(-1). Highest sustained velocities were associated with flow pulses caused by water releases from upstream hydraulic control structures that increased flow velocity by a factor of 2-3 on the floodplain for weeks at a time. The highest instantaneous measurements of flow velocity were associated with the passage of Hurricane Wilma in 2005 when the inverse barometric pressure effect increased flow velocity up to 5 cm s(-1) for several hours. Time-averaged flow velocities were 29% greater in sloughs compared to ridges because of marginally higher vegetative drag in ridges compared to sloughs, which contributed modestly (relative to greater water depth and flow duration in sloughs compared to ridges) to the predominant fraction (86%) of total discharge through the landscape occurring in sloughs. Univariate scaling relationships developed from theory of flow through vegetation, and our field data indicated that flow velocity increases with the square of water surface slope and the fourth power of stem diameter, decreases in direct proportion with increasing frontal area of vegetation, and is unrelated to water depth except for the influence that water depth has in controlling the submergence height of vegetation that varies vertically in its architectural characteristics. In the Everglades the result of interactions among controlling variables was that flow velocity was dominantly controlled by water surface slope variations responding to flow pulses more than spatial variation in vegetation characteristics or fluctuating water depth. Our findings indicate that floodplain managers could, in addition to managing water depth, manipulate the frequency and duration of inflow pulses to manage water surface slope, which would add further control over flow velocities, water residence times, sediment settling, biogeochemical transformations, and other processes that are important to floodplain function.

(2009) Knickerbocker, C.M., Leitholf, S., Stephens, E.L., Keellings, D.J., Laird, H., Anderson, C.J.R., Fauth, J.E. and Quintana-Ascencio, P.F. Tree Encroachment of A Sawgrass (Cladlum jamaicense) Marsh within an Increasingly Urbanized Ecosystem. Natural Areas Journal 29(1), 15-26.

Abstract
Fire suppression and altered water drainage often change community structure and species composition in human-dominated ecosystems. We describe the decline of sawgrass marshes between 1940 and 2002, and assess the current condition of remnant marshes within the MacKay Tract, an isolated wetland embedded within rapidly developing eastern Orlando, Florida. We tested the correlation between live sawgrass and presence of adult hardwood trees and seedlings (primarily red maple, Acer rubrum) and describe vegetation in plots with different levels of tree encroachment. Total area occupied by open sawgrass in the MacKay Tract has declined dramatically the last 60 years, in 2006, open sawgrass comprised only 12% of the area covered in 1940. Tree basal cover was negatively associated with live sawgrass and positively related to red maple seedling density, but not associated with dead sawgrass tussocks. Sawgrass was positively correlated with the second axis of a non-metric multidimensional scaling ordination on understory plant assemblage, while red maple seedlings and several species associated with disturbed areas were significantly negatively cot-related with this axis. Another nine plant species were positively correlated with the first axis, while Osmunda cinnamomea (cinnamon fern) was negatively associated with it. We suggest that woody species are continuing to colonize what is left of the sawgrass marsh. Without intervention (e.g., restoring hydrologic flow and fire), the sawgrass (Cladium jamaicense Crantz) area within the marsh will continue being replaced by woody and exotic species.

(2009) Larsen, L.G., Harvey, J.W., Noe, G.B. and Crimaldi, J.P. Predicting organic floc transport dynamics in shallow aquatic ecosystems: Insights from the field, the laboratory, and numerical modeling. Water Resources Research 45, W01411.

Abstract
Transport of particulate organic material can impact watershed sediment and nutrient budgets and can alter the geomorphologic evolution of shallow aquatic environments. Prediction of organic aggregate ("floc'') transport in these environments requires knowledge of how hydraulics and biota affect the entrainment, settling, and aggregation of particles. This study evaluated the aggregation and field transport dynamics of organic floc from a low-gradient floodplain wetland with flow-parallel ridges and sloughs in the Florida Everglades. Floc dynamics were evaluated in a rotating annular flume and in situ in the field. Under present managed conditions in the Everglades, floc is not entrained by mean flows but is suspended via biological production in the water column and bioturbation. Aggregation was a significant process affecting Everglades floc at high flume flow velocities (7.0 cm s(-1)) and during recovery from high flow; disaggregation was not significant for the tested flows. During moderate flows when floc dynamics are hydrodynamically controlled, it is possible to model floc transport using a single "operative floc diameter'' that accurately predicts fluxes downstream and to the bed. In contrast, during high flows and recovery from high flows, aggregation dynamics should be simulated. When entrained by flow in open-water sloughs, Everglades floc will be transported downstream in multiple deposition and reentrainment events but will undergo net settling when transported onto ridges of emergent vegetation. We hypothesize that net transport of material from open to vegetated areas during high flows is critical for forming and maintaining distinctive topographic patterning in the Everglades and other low-gradient floodplains.

(2009) McCormick, P., Newman, S. and Vilchek, L. Landscape responses to wetland eutrophication: loss of slough habitat in the Florida Everglades, USA. Hydrobiologia 621(105-114.

Abstract
Much of the historical Everglades has been either lost or degraded as a result of human activities. Among the aquatic habitats that comprise the Everglades landscape mosaic, open-water sloughs support critical ecological functions and appear especially sensitive to both hydrologic and water-quality perturbations. We used a combination of remote sensing and on-the-ground sampling to document spatial changes in the extent and vegetative composition of sloughs along a phosphorus (P) gradient in the northern Everglades. Increasing levels of water and soil P were associated with a decline in slough coverage, loss of the abundant native periphyton community, and a shift in dominant macrophyte species. The characteristic slough macrophyte species Eleocharis cellulosa and Nymphaea odorata exhibited different sensitivities to P enrichment, but both species declined with enrichment as slough habitats were invaded by Typha domingensis, a species that is known to expand aggressively in response to enrichment. A limited amount of open-water habitat occurred in highly enriched areas, but these habitats were maintained largely as a result of airboat disturbance and did not contain characteristic slough vegetation. Many changes in slough coverage and composition occurred in areas where water and soil P concentrations were only marginally higher than background levels. Our findings support the need for Everglades hydrologic restoration efforts to adhere to strict water-quality standards for P to avoid further degradation of this key landscape feature.

(2009) Miao, S.L. and Zou, C.B. Seasonal variation in seed bank composition and its interaction with nutrient enrichment in the Everglades wetlands. Aquatic Botany 90(2), 157-164.

Abstract
In the Florida Everglades, nutrient enrichment from agricultural outflow and the change in hydrology have collectively contributed to the expansion of cattails (Typha spp.). To assess the effectiveness of prescribed fire in controlling cattails and to predict vegetation dynamics after the fire, it is important to understand the seasonal variation of the soil seed bank and how the seed bank is affected by nutrient enrichment and fire. This paper investigates the effects of season, nutrient enrichment, and fire on soil seed bank species composition, richness, and density along a nutrient gradient in Water Conservation Area 2A (WCA 2A) of the Florida Everglades. Species richness was significantly affected by nutrient enrichment and season but not their interaction. Total seed density, however, was significantly affected by the interaction between nutrient enrichment and season. Yet, at species level, the relationship between seed density, nutrient enrichment and season varied. The highest seed density of cattail occurred in summer at highly enriched sites, but that of sawgrass occurred in fall regardless of enrichment; the seed density of water lily was very low regardless of season and nutrient enrichment, and the highest Amarathus seed density occurred at highly enriched sites year round. Moreover, germination timing differed greatly among species. While cattail seeds had a short incubation period and started to germinate 2-3 days after initiation of the germination assay, sawgrass seeds generally started to germinate 4 weeks later. Further, both the prescribed summer fire at the highly enriched site and the natural winter fire at the moderately enriched site reduced the seed density of cattail but not of sawgrass. Our results suggest that fire application for vegetation recovery in WCA 2A would benefit from explicitly considering seasonal dynamics of the seed bank.

(2009) Miao, S.L., Zou, C.B. and Breshears, D.D. Vegetation Responses to Extreme Hydrological Events: Sequence Matters. American Naturalist 173(1), 113-118.

Abstract
Extreme hydrological events such as flood and drought drive vegetation dynamics and are projected to increase in frequency in association with climate change, which could result in sequences of extreme events. However, experimental studies of vegetation responses to climate have largely focused on responses to a trend in climate or to a single extreme event but have largely overlooked the potential for complex responses to specific sequences of extreme events. Here we document, on the basis of an experiment with seedlings of three types of subtropical wetland tree species, that mortality can be amplified and growth can even be stimulated, depending on event sequence. Our findings indicate that the impacts of multiple extreme events cannot be modeled by simply summing the projected effects of individual extreme events but, rather, that models should take into account event sequences.

(2009) Min, J.H. and Wise, W.R. Simulating short-circuiting flow in a constructed wetland: the implications of bathymetry and vegetation effects. Hydrological Processes 23(6), 830-841.

Abstract
Short-circuiting flow, commonly experienced in many constructed wetlands, reduces hydraulic retention times in unit wetland cells and decreases the treatment efficiency. A two-dimensional (2-D), physically based, distributed modelling approach was used to systematically address the effects of bathymetry and vegetation on short-circuiting flow, which previously have been neglected or lumped in one-dimensional wetland flow models. In this study, a 2-D transient hydrodynamics with advection-dispersion model was developed using MIKE 21 and calibrated with bromide tracer data collected at the Orlando Easterly Wetland Cell 7. The estimated topographic difference between short-circuiting flow zone and adjacent area ranged from 0.3 to 0.8 m. A range of the Manning roughness coefficient at the short-circuiting flow zone was estimated (0.022-0.045 s m(-1/3)). Sensitivity analysis of topographical and vegetative heterogeneity deduced during model calibration shows that relic ditches or other ditch-shaped landforms and the associated sparse vegetation along the main flow direction intensify the short-circuiting pattern, considerably affecting 2-D solute transport simulation. In terms of hydraulic efficiency, this study indicates that the bathymetry effect on short-circuiting flow is more important than the vegetation effect.

(2009) Qian, Y., Miao, S.L., Gu, B. and Li, Y.C. Effects of Burn Temperature on Ash Nutrient Forms and Availability from Cattail (Typha domingensis) and Sawgrass (Cladium jamaicense) in the Florida Everglades. Journal of Environmental Quality 38(2), 451-464.

Abstract
Plant ash derived from fire plays an important role in nutrient balance and cycling in ecosystems. Factors that determine the composition and availability of ash nutrients include fire intensity (burn temperature and duration), plant species, habitat nutrient enrichments and leaf type (live or dead leaf). We used laboratory simulation methods to evaluate temperature effects on nutrient composition and metals in the residual ash of sawgrass (Cladium jamaicense) and cattail (Typha domingensis), particularly on post-fire phosphorus (P) availability in plant ash. Live and dead leaf samples were collected from Water Conservation Area 2A in the northern Everglades along a soil P gradient, where prescribed fire may be used to accelerate recovery of this unique ecosystem. Significant decreases in total carbon and total nitrogen were detected with increasing fire temperature. Organic matter combustion was nearly complete at temperatures >= 450 degrees C. HCl-extractable P (average, 50% of total P in the ash) and NH4Cl-extractable P (average, 33% of total P in the ash) were the predominant P fractions for laboratory-burned ash. Although a low-intensity fire could induce ail elevation of P availability, an intense fire generally resulted in decreased water-soluble P. Significant differences in nutrient compositions were observed between species, habitat nutrient status, and leaf types. More labile inorganic P remained in sawgrass ash than in cattail ash; hence, sawgrass ash has a greater potential to release available P than cattail. Fire intensity affected plant ash nutrient composition, particularly P availability, and the effects varied with plant species and leaf type. Therefore, it is important to consider fire intensity and vegetation community when using a prescribed fire for ecosystem management.

(2009) Smith, T.J., Anderson, G.H., Balentine, K., Tiling, G., Ward, G.A. and Whelan, K.R.T. Cumulative Impacts of Hurricanes on Florida Mangrove Ecosystems: Sediment Deposition, Storm Surges and Vegetation. Wetlands 29(1), 24-34.

Abstract
Hurricanes have shaped the structure of mangrove forests ill the Everglades via wind damage, storm Surges and sediment deposition. Immediate effects include changes to stern size-frequency distributions and to species relative abundance and density. Long-term impacts to mangroves are poorly Understood at present. We examine impacts of Hurricane Wilma oil mangroves and compare the results to findings from three previous storms (Labor Day, Donna, Andrew). Surges during Wilma destroyed 1,250 ha of mangroves and set back recovery that started following Andrew. Data from permanent plots affected by Andrew and Wilma showed no differences among species or between hurricanes for % stern mortality or % basal area lost. Hurricane damage was related to hydro-geomorphic type of forest. Basin mangroves suffered significantly more damage than riverine or island mangroves. The hurricane by forest type interaction was highly significant. Andrew did slightly more damage to island mangroves. Wilma did significantly more damage to basin forests. This is most likely a result of the larger and more spatially extensive storm surge produced by Wilma. Forest damage was not related to amount. of sediment deposited. Analyses of reports from Donna and the Labor Day storm indicate that sonic sites have recovered following catastrophic disturbance. Other sites have been permanently converted into a different ecosystem, namely intertidal mudflats. Our results indicate that mangroves are not in a steady state as has been recently claimed.

(2009) Tipping, P.W., Martin, M.R., Nimmo, K.R., Pierce, R.M., Smart, M.D., White, E., Madeira, P.T. and Center, T.D. Invasion of a West Everglades wetland by Melaleuca quinquenervia countered by classical biological control. Biological Control 48(1), 73-78.

Abstract
The population dynamics of Melaleuca quinquenervia were monitored over a 5-year period in a cypresspine wetland while subjected to two levels of herbivory. The trees had been recruited during 1998-1999 after a destructive crown fire. Half of 26 experimental plots were sprayed every 4-6 weeks with an insecticide to reduce herbivory by the biological control agents Oxyops vitiosa and Boreioglycaspis melaleucae. After only 1-year melaleuca density increased by 26% in sprayed plots and by 7% in unsprayed plots. However, over the entire 5-year period melaleuca density increased in sprayed plots by 0.1% while decreasing by 47.9% in unsprayed plots when compared to initial densities. Annual mortality of melaleuca never exceeded 6% in any year in sprayed plots but ranged from 11% to 25% in unsprayed plots. There was a significant year by treatment interaction indicating the importance of the environment on tree mortality. Limited seed production occurred on sprayed trees but never on unsprayed trees. Mean tree height increased by 19.6% in sprayed plots while declining by 30.6% in unsprayed plots. Coverage by native vegetation did not increase with decreasing melaleuca density. This is the first study with controls that quantifies the population level regulation of melaleuca by introduced biological control agents and corroborates other correlative studies that documented significant changes in melaleuca communities after the introduction and establishment of biological control agents.

(2009) Utescher, T., Ivanov, D., Harzhauser, M., Bozukov, V., Ashraf, A.R., Rolf, C., Urbat, M. and Mosbrugger, V. Cyclic climate and vegetation change in the late Miocene of Western Bulgaria. Palaeogeography Palaeoclimatology Palaeoecology 272(1-2), 99-114.

Abstract
A late Miocene paludal to lacustrine sequence from a carbonate basin in NW Bulgaria (Staniantsi Basin) is analysed displaying up to 27 rhythmically bedded sedimentary cycles. In the lower part of the sequence, the cycles consist of alternating autochthonous brown coal and marls containing diverse mollusc assemblages. The upper part of the sequence is characterized by alternating dark to light grey clays and calcareous silts. A palynomorph record comprising 163 samples is analysed by statistical means to reconstruct vegetation changes. The Coexistence Approach is used to calculate quantitative palaeoclimate records for 6 parameters. The studied section displays hierarchical cyclicity patterns. Longer-term cycles possibly related to eccentricity (period similar to 100 kyr) are present in the palynomorph record and show climate changes of warmer/wetter and cooler/drier periods in combination with frequency oscillations of thermophilous elements. Short-term cycles most probably related to precession (period similar to 21.7 kyr) are expressed by alternations of brown coal and marl/shell beds and show cyclic change in peat-forming vegetation related to oscillations of the groundwater level. As a triggering mechanism, wetter/warmer and drier/cooler climate phases related to orbital precession are probable. In addition, sections sampled at high resolution display small scale climate and vegetational variability. As is shown by the analysis ferns were an important component of the peat-forming vegetation, while outside the mire, a wetland vegetation consisting of pioneers and a mixed mesophytic forest with evergreen shrubs existed. An oligo- to mesotrophic slightly alkaline lake became repeatedly established with a diverse mollusc fauna and a dense hydrophytic vegetation with characean meadows. In the upper part of the section, a spreading of herbaceous vegetation is observed, also known from other contemporaneaous palynomorph records in Bulgaria and surrounding areas. The increase of Asteraceae in the upper part of the section, combined with a marked decrease in woody taxa, points to an opening of habitats and a decrease in mean annual precipitation. This trend is paralleled by the mollusc fauna which yields several terrestrial, partly xerophilous taxa.

(2009) Webb, J., Miao, S.L. and Zhang, X.H. Factors and mechanisms influencing seed germination in a wetland plant sawgrass. Plant Growth Regulation 57(3), 243-250.

Abstract
Sawgrass (Cladium jamaicense) is the predominant plant and vegetation community in the Florida Everglades. Germination of sawgrass seeds in the laboratory or nursery has been difficult and problematic, yet little is known about the physiological mechanistic regulation of the sawgrass seed germination process. In the present study, we examined the factors and mechanisms that influence sawgrass seed germination. We found that removal of seed husk and bracts, pre-soaking with bleach (hypochlorite), breaking the seed coat, or combinations of these treatments promoted the rate and success of germination, whereas presence of seed-encasing structures or treatment with husk/bract extract inhibited germination. We further detected the presence of abscisic acid (ABA) in the husk and bract. Experiments with ABA and gibberellin biosynthesis inhibitors fluridone and tetcyclacis suggested that ABA already presented in the pre-imbibed seeds, and not derived through post-dormancy de novo synthesis, contributed to the inhibition of seed germination. Examination of bleach and mechanical treatments indicated the physical barrier presented by the seed-encasing structures provided additional mechanism for the long-term delay of seed germination. Based on the results of this study and others, we discussed the implications of sawgrass seed dormancy and germination in relation to its natural habitat and proposed a hypothesis that the protracted seed dormancy in sawgrass offered an adaptive advantage in the pre-anthropogenic Everglades environment, but may become a liability in the current man-managed Everglades water system.

(2008) Adams, E.M. and Frederick, P.C. Effects of methylmercury and spatial complexity on foraging behavior and foraging efficiency in juvenile white ibises (Eudocimus albus). Environmental Toxicology and Chemistry 27(8), 1708-1712.