Leonard J. Scinto

Dissolved Organic Matter Characteristics Across a Subtropical Wetland’s Landscape: Application of Optical Properties in the Assessment of Environmental Dynamics

Wetlands are known to be important sources of dissolved organic matter (DOM) to rivers and coastal environments. However, the environmental dynamics of DOM within wetlands have not been well documented on large spatial scales. To better assess DOM dynamics within large wetlands, we determined high resolution spatial distributions of dissolved organic carbon (DOC) concentrations and DOM quality by excitation–emission matrix spectroscopy combined with parallel factor analysis (EEM–PARAFAC) in a subtropical freshwater wetland, the Everglades, Florida, USA. DOC concentrations decreased from north to south along the general water flow path and were linearly correlated with chloride concentration, a tracer of water derived from the Everglades Agricultural Area (EAA), suggesting that agricultural activities are directly or indirectly a major source of DOM in the Everglades. The optical properties of DOM, however, also changed successively along the water flow path from high molecular weight, peat-soil and highly oxidized agricultural soil-derived DOM to the north, to lower molecular weight, biologically produced DOM to the south. These results suggest that even though DOC concentration seems to be distributed conservatively, DOM sources and diagenetic processing can be dynamic throughout wetland landscapes. As such, EEM–PARAFAC clearly revealed that humic-enriched DOM from the EAA is gradually replaced by microbial- and plant-derived DOM along the general water flow path, while additional humic-like contributions are added from marsh soils. Results presented here indicate that both hydrology and primary productivity are important drivers controlling DOM dynamics in large wetlands. The biogeochemical processes controlling the DOM composition are complex and merit further investigation.

Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Natural, unenriched Evergladeswetlands are known to be limited by phosphorus(P) and responsive to P enrichment. However,whole-ecosystem evaluations of experimental Padditions are rare in Everglades or otherwetlands. We tested the response of theEverglades wetland ecosystem to continuous,low-level additions of P (0, 5, 15, and30 μg L−1 above ambient) in replicate,100 m flow-through flumes located in unenrichedEverglades National Park. After the first sixmonths of dosing, the concentration andstanding stock of phosphorus increased in thesurface water, periphyton, and flocculentdetrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 μg L−1: mean = 1916 μg P g−1, control: mean =149 μg P g−1), while the flocculentdetrital layer stored most of the accumulated P(30 μg L−1: mean = 1.732 g P m−2,control: mean = 0.769 g P m−2). Significant short-term responsesof P concentration and standing stock wereobserved primarily in the high dose (30 μgL−1 above ambient) treatment. Inaddition, the biomass and estimated P standingstock of aquatic consumers increased in the 30and 5 μg L−1 treatments. Alterationsin P concentration and standing stock occurredonly at the upstream ends of the flumes nearestto the point source of added nutrient. Thetotal amount of P stored by the ecosystemwithin the flume increased with P dosing,although the ecosystem in the flumes retainedonly a small proportion of the P added over thefirst six months. These results indicate thatoligotrophic Everglades wetlands respondrapidly to short-term, low-level P enrichment,and the initial response is most noticeable inthe periphyton and flocculent detrital layer.

Methylmercury Photodegradation in Surface Water of the Florida Everglades: Importance of Dissolved Organic Matter-Methylmercury Complexation

Photodegradation is the major pathway of methylmercury (MeHg) degradation in many surface waters. However, the mechanism of MeHg photodegradation is still not completely understood. Dissolved organic matter (DOM) is expected to play a critical role in MeHg photodegradation. By using several techniques, including N2/O2 purging and the addition of stable isotope (Me(201)Hg), scavengers, competing ligands, and a singlet oxygen ((1)O2) generator, the role played by MeHg-DOM complexation in MeHg photodegradation of Everglades surface water was investigated. DOM appeared to be involved in MeHg photodegradation via the formation MeHg-DOM complexes based on three findings: (1) MeHg was quickly photodegraded in solutions containing DOM extracts; (2) degradation of MeHg did not occur in deionized water; and (3) addition of competing complexation reagents (dithiothreitol-DTT) dramatically prohibited the photodegradation of MeHg in Everglades water. Further experiments indicated that free radicals/reactive oxygen species, including hydroxyl radical (·OH), (1)O2, triplet excited state of DOM ((3)DOM*), and hydrated electron (e(-)aq), played a minor role in MeHg photodegradation in Everglades water, based on the results of scavenger addition, (1)O2 generator addition and N2/O2 purging. A pathway, involving direct photodegradation of MeHg-DOM complexes via intramolecular electron transfer, is proposed as the dominant mechanism for MeHg photodegradation in Everglades water.

Landscape Patterns of Significant Soil Nutrients and Contaminants in the Greater Everglades Ecosystem: Past, Present, and Future

The primary goal of this review and synthesis effort is to summarize present landscape patterns of key soil constituents such as carbon (C), phosphorus (P), sulfur (S), and mercury (Hg), all of which are of historical and present interest with respect to Everglades restoration. A secondary goal is to highlight the importance of landscape scale monitoring and assessment of soils in the Everglades Protection Area (EPA) with respect to present and future restoration efforts. Review of present information derived from the two independent landscape scale studies revealed significant patterns of soil thickness, organic matter, and P in the EPA. Two soil constituents of concern, Hg (biological toxicity) and S (linked to increased P cycling), also exhibit spatial patterns at the landscape scale, suggesting a need for focused efforts of restoration. Significant patterns of soil enrichment and change suggest a dynamic interaction between environmental stressors and soil biogeochemical properties across the landscape. Trends and patterns at the landscape scale in the EPA suggest that landscape scale monitoring and assessment is necessary and critical to determining the success of restoration efforts. However, several key questions, surrounding appropriate temporal and spatial sampling scales, the standardization of sampling methods, and the significance of short range variability must be addressed to facilitate future landscape scale assessment efforts.

Growth of Calcareous Epilithic Mats in the Margin of Natural and Polluted Hydrosystems: Phosphorus Removal Implications in the C–111 Basin, Florida Everglades, USA

ABSTRACT The Florida Everglades is a fragile wetland system that is naturally depleted in phosphorus (P). This hydrosystem has been heavily impacted by human activities, including the draining of wetlands to provide water for agricultural and urban use. The result is a highly compartmentalized system with altered hydropatterns; wetlands receive canal discharges from diffuse agricultural/urban runoff containing high levels of pollutants, including P. Excess loading of P has induced ecological changes, including dramatic effects on periphyton, the dominant producer community. An Everglades rehabilitation plan has been established to restore natural hydropatterns and decrease P loads. On the southern edge of a large canal (C-111) draining the southern Everglades, levees have been removed to rehabilitate hydrology in the adjacent marsh. Levee removal resulted in exposure of limestone bedrock that, when flooded with shallow water from the canal, favors the development of thick calcareous epilithic mats. When flooded approximately 6 months a year, this margin area between the polluted and the natural hydrosystem functions as a Periphyton-based Stormwater Treatment Area(PSTA), a biological tool developed at the Southeast Environmental Research Center (Miami, FL), being considered in the Everglades as a means of P removal from enriched waters. Here, we evaluate the harvesting rates of periphyton that promote the most efficient removal of TP from the water entering the marsh. Results indicate that harvesting of periphyton at 3 month intervals provides the greatest TP sequestration.

Patterns of Soil Bacteria and Canopy Community Structure Related to Tropical Peatland Development

Natural environmental gradients provide important information about the ecological constraints on plant and microbial community structure. In a tropical peatland of Panama, we investigated community structure (forest canopy and soil bacteria) and microbial community function (soil enzyme activities and respiration) along an ecosystem development gradient that coincided with a natural P gradient. Highly structured plant and bacterial communities that correlated with gradients in phosphorus status and soil organic matter content characterized the peatland. A secondary gradient in soil porewater NH4 described significant variance in soil microbial respiration and β-1-4-glucosidase activity. Covariation of canopy and soil bacteria taxa contributed to a better understanding of ecological classifications for biotic communities with applicability for tropical peatland ecosystems of Central America. Moreover, plants and soils, linked primarily through increasing P deficiency, influenced strong patterning of plant and bacterial community structure related to the development of this tropical peatland ecosystem.

Nutrient Limitation in Two Everglades Tree Species Planted on Constructed Tree Islands

The Everglades is a low-nutrient ecosystem occupied by marsh plant species adapted to low availability of phosphorus. Recently, however, tree islands that are scattered throughout the marsh have been recognized as biogeochemical hotspots. The goal of this study was to determine the general patterns of response by common tree species when conditions limiting to optimal growth were improved by fertilization in an experimentally constructed and managed Everglades wetland. Thirty-six trees of two species, Annona glabra and Chrysobalanus icaco, were randomly selected on two peat- and two limestone-based islands. Each tree was treated with one of three nutrient regimes: Nitrogen (N), Phosphorus (P), or Control (no addition of nutrients). Positive highly significant P-treatment effects on leaf total P and leaf N:P were observed in both species in comparison to Control trees, but neither species exhibited a similar response to N-fertilization. However, among the two species, only A. glabra responded to P-fertilization with increased growth. Both fertilized and unfertilized trees of each species exhibited a highly significant growth response to hydrological condition, with growth enhanced on less persistently flooded sites. Our experimental results identify a clear difference in species growth responses to substrate type in the two species, but do not support the idea that a single critical N:P ratio can be used to indicate nutrient limitation for all wetland trees.

Fine spatial resolution simulation of two-dimensional modeling of flow pulses discharge into wetlands: Case study of loxahatchee impoundment landscape assessment, the everglades

AbstractWetland 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 hig...

Vegetation and soil response to hydrology in a re-created Everglades

Water depth and flow effects on growth and nutrient content of three marsh plants (Cladium jamaicense Crantz, Eleocharis cellulosa Torr., and Nymphaea odorata Aiton) and on soil-building were estimated in the Loxahatchee Impoundment Landscape Assessment where macrocosms contain habitats distinguished by relative water depth (deep slough, shallow slough, and mid-ridge) but that differ in flow. We hypothesized that optimal growth would vary with water depth and species, paralleling distributions in the natural environment, and that growth and tissue nutrients would be positively affected by flow. In addition, we hypothesized that plant morphology would influence sediment deposition with the dense growth of C. jamaicense supporting greatest accretion. Our hypotheses were partly supported. Cladium jamaicense unexpectedly grew best in deep sloughs at depths greater than previously reported. Eleocharis cellulosa had a wide depth tolerance and grew best in flowing conditions. Nymphaea odorata grew best in slough habitats. Nutrient contents differed among species and plant parts but were not affected by flow. Soil accretion did not vary with biomass but partially varied with depth and flow, both key factors in conceptual models of vegetation and soil dynamics in wetlands, especially in the Everglades ridge-and-slough topography.