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Rockledge, FL, United States

Bae H.-S.,University of Florida | Dierberg F.E.,DB Environmental Inc. | Ogram A.,University of Florida
Applied and Environmental Microbiology | Year: 2014

The mechanisms and rates of mercury methylation in the Florida Everglades are of great concern because of potential adverse impacts on human and wildlife health through mercury accumulation in aquatic food webs. We developed a new PCR primer set targeting hgcA, a gene encoding a corrinoid protein essential for Hg methylation across broad phylogenetic boundaries, and used this primer set to study the distribution of hgcA sequences in soils collected from three sites along a gradient in sulfate and nutrient concentrations in the northern Everglades. The sequences obtained were distributed in diverse phyla, including Proteobacteria, Chloroflexi, Firmicutes, and Methanomicrobia; however, hgcA clone libraries from all sites were dominated by sequences clustering within the order Syntrophobacterales of the Deltaproteobacteria (49 to 65% of total sequences). dsrB mRNA sequences, representing active sulfate-reducing prokaryotes at the time of sampling, obtained from these sites were also dominated by Syntrophobacterales (75 to 89%). Laboratory incubations with soils taken from the site low in sulfate concentrations also suggested that Hg methylation activities were primarily mediated by members of the order Syntrophobacterales, with some contribution by methanogens, Chloroflexi, iron-reducing Geobacter, and non-sulfate-reducing Firmicutes inhabiting the sites. This suggests that prokaryotes distributed within clades defined by syntrophs are the predominant group controlling methylation of Hg in low-sulfate areas of the Everglades. Any strategy for managing mercury methylation in the Everglades should consider that net mercury methylation is not limited to the action of sulfate reduction. © 2014, American Society for Microbiology.

Juston J.M.,Juston Konsult | Kadlec R.H.,Chelsea Management | DeBusk W.F.,Water Resources Group LLC | Jerauld M.J.,DB Environmental Inc. | DeBusk T.A.,DB Environmental Inc.
Water Resources Research | Year: 2015

Upstream source control and Stormwater Treatment Areas (STAs) have reduced phosphorus (P) loads to Water Conservation Area 2A (WCA-2A), a northern Everglades wetland, by three quarters since year 2000. Nevertheless, large storages of P remain in enriched peat soils and it is unclear how legacy stores will impact spatial and temporal scales of recovery. We remeasured soil P enrichment along a well-studied eutrophication gradient in WCA-2A and applied a profile modeling approach with uncertainty analysis to assess changes in longitudinal soil P gradients 13 years after load reductions. We then analyzed existing internal water P data, using a novel data screening approach, for evidence of lowest possible water P concentrations independent from inflows. We interpret such water P limits as evidence of the strength of internal loading at a location. Results indicate that soil P enrichment persists in the ∼7.5 km long "impacted" zone, with no significant evidence of net advancement or recession, while a large pool of labile P in the flocculent layer consolidated and diminished. There is indeed evidence, both spatial and temporal, that this extensive zone of enriched soil P continues to elevate lowest achievable water P concentrations. The corresponding gradient of elevated water P limits is both receding and diminishing since load reductions, thus providing further evidence toward recovery. However, results also suggest that these "transitory P limits" due to internal loading are likely to persist for decades above water quality targets. These results advance our understanding of recovery in impacted wetlands and are relevant to Everglades restoration. © 2015. American Geophysical Union. All Rights Reserved.

DeBusk T.A.,DB Environmental Inc. | Dierberg F.E.,DB Environmental Inc. | DeBusk W.F.,Water Resource Group LLC | Jackson S.D.,DB Environmental Inc. | And 4 more authors.
Aquatic Botany | Year: 2015

Displacement of large areas of native Cladium jamaicense Crantz (sawgrass) by Typha domingensis Pers. (cattail) in the Everglades has occurred during the past several decades, and is widely attributed to phosphorus (P) enrichment. In addition, sulfide toxicity to marsh vegetation, particularly Cladium, has been cited as a possible consequence of increased loading of sulfate to the Everglades (USA) from anthropogenic sources, and a potential contributor to the shift from Cladium to Typha. We initiated a plant growth study at three "low P" sites in the Everglades with differing surface water sulfate (1-48mgL-1) and porewater sulfide (0.09-8.0mgL-1) concentrations. Leaf elongation (LE) rates of Cladium and Typha were monitored, along with surface and porewater concentrations of iron, nutrients, and inorganic sulfur species. During the course of the study, we observed no reduction in Cladium or Typha LE rates at the two sulfate-impacted locations, relative to LE at a sulfate-unimpacted site. Moreover, across all study sites, we observed a positive, instead of a negative, relationship between Cladium LE rates and porewater sulfide concentrations. This suggests overriding effects of other factors such as P availability and supply on plant growth in these low-P environments, which was supported by a positive relationship between dissolved porewater P concentrations and Cladium LE rates, and by the Typha to Cladium LE ratios. © 2015 Elsevier B.V.

Paudel R.,University of Florida | Grace K.A.,DB Environmental Inc. | Galloway S.,DB Environmental Inc. | Zamorano M.,South Florida Water Management District | Jawitz J.W.,University of Florida
Journal of Hydrology | Year: 2013

This work examined the potential effects of large-scale thinning of emergent vegetation on the stage dynamics in a very large (33.3km2) constructed treatment wetland in South Florida. Dense vegetative biomass in treatment wetlands may restrict water flow and increase water levels, which may in turn have adverse effects on vegetative community structure. Here, we developed a physically-based, spatially-distributed hydrodynamic model of Stormwater Treatment Area 2, Cell 2 (STA2C2) to investigate the spatio-temporal variability of water level (stage) in response to management for thinning of emergent macrophytes (e.g., burning and/or herbicide treatments). The model was calibrated against stage measured at six monitoring stations for 1year, and subsequently validated against 2years of stage data from eight stations. Finally, the validated model was extended to simulate various vegetation management scenarios. The model provided an excellent fit to observed stage data in both calibration and validation periods (median model efficiency indices of 0.82 and 0.83, respectively). Higher stages in the treatment cell were dominantly associated with peak inflow magnitude and the timing of event intervals. Prolonged periods of sustained deep water conditions were observed when one flow peak was followed by consecutive peaks. A gradual stage gradient from the inlet to outlet was observed during peak flow periods, with a shift to a sharp gradient at approximately two-thirds distance from the inlet. Stages in the wetland were found to be controlled less by the hydraulic resistance, as indicated by a low sensitivity of simulated water levels for a ±50% perturbation in flow resistance parameter. Water depths were reduced by a maximum of 12cm at the inlet region by thoroughly thinning the remaining emergent vegetation in STA2C2. Similarly, a maximum of only 2% of the total STA2C2 area was prevented from exceeding a water depth believed to be detrimental to Typha sp. (1.22m) after the highest peak inflow. Collectively, our findings suggested that vegetation thinning may not be effective for minimizing deep water conditions in STA2C2. © 2013 Elsevier B.V.

Juston J.M.,KTH Royal Institute of Technology | DeBusk T.A.,DB Environmental Inc. | Grace K.A.,DB Environmental Inc. | Jackson S.D.,DB Environmental Inc.
Ecological Modelling | Year: 2013

Engineered wetlands using submerged aquatic vegetation (SAV) are a cornerstone to the Stormwater Treatment Area (STA) project for stripping phosphorus from agricultural stormwater and lake water before entering protected Everglades marshes in south Florida, USA. However, recent efforts have suggested that the apparent lowest achievable outflow P (C*) in SAV systems (∼16 μg/l) may not be low enough for proposed regulatory criteria. Thus, deepened predictive understanding on the functionality of these systems is of critical importance. Here, we develop a steady-state mass balance model of intermediate complexity to investigate C* in SAV systems. The model focuses on the role of SAV biomass turnover and P release to the water column, drawing upon established principles from shallow lake studies. This study introduces several large and unique datasets collected from a single study site (STA-2 Cell 3) over a 10-year period and demonstrates coherence in these data through the modeling approach. The datasets included inflow-outflow values, P storage in accrued sediment at two intervals, annual surveys of SAV species composition, gradients of SAV tissue-P, and gradients of internal water column P concentration (previously published). The model was implemented and calibrated in an uncertainty framework with Monte Carlo methods, threshold screening, and multi-criteria limits of acceptability. Model calibration and validation appeared successful, resulting distributions of model parameters and accepted model simulations were relatively narrow, and results deepened perspectives on the previously identified C*. Rooted SAV species may be mining substantial P from underlying soils via root uptake and thus contributing internal loads. Steady turnover and decomposition of SAV biomass may be accounting for up to about a third of the background C*. These perspectives are relevant to STA optimization; our unique data, usage, and calibration strategy should be of interest to the aquatic ecosystem modeling community in general. © 2013 Elsevier B.V.

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