Developing Benthic Class Specific, Chlorophyll-a Retrieving Algorithms for Optically-Shallow Water Using SeaWiFS.

This study evaluated the ability to improve Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) chl-a retrieval from optically shallow coastal waters by applying algorithms specific to the pixels' benthic class. The form of the Ocean Color (OC) algorithm was assumed for this study. The operational atmospheric correction producing Level 2 SeaWiFS data was retained since the focus of this study was on establishing the benefit from the alternative specification of the bio-optical algorithm. Benthic class was determined through satellite image-based classification methods. Accuracy of the chl-a algorithms evaluated was determined through comparison with coincident in situ measurements of chl-a. The regionally-tuned models that were allowed to vary by benthic class produced more accurate estimates of chl-a than the single, unified regionally-tuned model. Mean absolute percent difference was approximately 70% for the regionally-tuned, benthic class-specific algorithms. Evaluation of the residuals indicated the potential for further improvement to chl-a estimation through finer characterization of benthic environments. Atmospheric correction procedures specialized to coastal environments were recognized as areas for future improvement as these procedures would improve both classification and algorithm tuning.

Modeling the impact of restoration efforts on phosphorus loading and transport through Everglades National Park, FL, USA.

Ecosystems of Florida Everglades are highly sensitive to phosphorus loading. Future restoration efforts, which focus on restoring Everglades water flows, may pose a threat to the health of these ecosystems. To determine the fate and transport of total phosphorus and evaluate proposed Everglades restoration, a water quality model has been developed using the hydrodynamic results from the M3ENP (Mike Marsh Model of Everglades National Park)--a physically-based hydrological numerical model which uses MIKE SHE/MIKE 11 software. Using advection-dispersion with reactive transport for the model, parameters were optimized and phosphorus loading in the overland water column was modeled with good accuracy (60%). The calibrated M3ENP-AD model was then modified to include future bridge construction and canal water level changes, which have shown to increase flows into ENP. These bridge additions increased total dissolved phosphorus (TP) load downstream in Shark Slough and decreased TP load in downstream Taylor Slough. However, there was a general decrease in TP concentration and TP mass per area over the entire model domain. The M3ENP-AD model has determined the mechanisms for TP transport and quantified the impacts of ENP restoration efforts on the spatial-temporal distribution of phosphorus transport. This tool can be used to guide future Everglades restoration decisions.

Fenton treatment of landfill leachate under different COD loading factors.

The application of Fenton treatment technology for treatment of landfill leachate greatly depends on the optimum Fenton operating conditions for a specific leachate. Determining optimum Fenton conditions requires multiple experiments using variable reaction parameters (pH, temperature, and H2O2 and Fe(2+) doses) and previous researches show a wide range of optimal operating conditions. In this study, the applicability of the dimensionless loading factor (LCOD), which is defined as the initial COD (COD0) of leachate with respect to available O2 for oxidation, was examined to derive optimum Fenton oxidant dose using reduced set of experiments. The Fenton experiments were conducted using leachates with three different COD0 concentrations, 1092, 546, and 273mgL(-1), LCOD in the range of 0.25-1.0, and H2O2/Fe(2+) 1.8 (w/w). The experimental data were analyzed to determine the correlation between the LCOD factor and selected feasibility parameters, amongst which were: (i) the COD removal kinetics, (ii) the total COD removal, (iii) the usability of H2O2 with respect to COD removal, (iv) leachate biodegradability, and (v) treatment cost incurred by chemical usage. The experimental COD removal with respect to the amount of O2 supplied by H2O2 was compared with respect to the optimum COD removal efficiency by the equation: η(FP(optimum)=0.733L(COD)-0.182 as developed by Singh and Tang (2013) and a LCOD of 0.75 was determined to be the optimum L(COD) for leachate treatment.

Estimation of the major source and sink of methylmercury in the Florida Everglades.

Mercury methylation and/or demethylation have been observed in several compartments [soil (saturated soils covered by standing water), floc, periphyton, and water] of the Everglades, a wetland with mercury as one of the major water quality concerns. However, it is still unclear which compartment is the major source or sink due to the lack of estimation and comparison of the net methylmercury (MeHg) production or degradation in these compartments. The lack of this information has limited our understanding of Hg cycling in this ecosystem. This study adopted a double stable isotope ((199)Hg(2+) and Me(201)Hg) addition technique to determine the methylation/demethylation rate constants and the net MeHg production rates in each compartment. This study improved the previous models for estimating these parameters by (1) taking into account the difference between newly input and ambient mercury in methylation/demethylation efficiency and (2) correcting the contribution of photodemethylation to Me(199)Hg concentration when calculating methylation rates in water. The net MeHg production rate in each compartment was then estimated to identify the major sources and sinks of MeHg. The results indicate that these improvements in modeling are necessary, as a significant error would occur otherwise. Soil was identified to be the largest source of MeHg in the Everglades, while the floc and water column were identified as the major sinks. The role of periphyton varies, appearing to be a source in the northern Everglades and a sink in the southern Everglades. Soil could be the largest source for MeHg in the water column, while methylation in periphyton could also contribute significantly in the northern Everglades.

Dispersion and stability of bare hematite nanoparticles: effect of dispersion tools, nanoparticle concentration, humic acid and ionic strength.

The aggregation and sedimentation of iron oxide nanoparticles (IONPs) can significantly affect the mobility and reactivity of IONPs and subsequently influence the interaction between IONPs and environmental contaminants. Dispersing bare IONPs into a stable suspension within nanoscale range is an important step for studying the interaction of IONPs with contaminants (e.g., toxic metals). In this study, different techniques to disperse bare IONPs (vortex, bath sonication and probe ultrasonication) and the effects of important environmental factors such as dissolved organic matter and ionic strength on the stability of IONPs dispersions were investigated. Vortex minimally dispersed IONPs with hydrodynamic diameter outside the "nano-size range" (698-2400 nm). Similar to vortex, bath sonication could not disperse IONPs efficiently. Probe ultrasonication was more effective at dispersing IONPs (50% or more) with hydrodynamic diameters ranging from 120 to 140 nm with minimal changes in size and sedimentation of IONPs for a prolonged period of time. Over the course of 168 h, considerable amounts of IONPs remained dispersed in the presence and absence of low ionic strength (0.1mM of NaCl) and 100mg/L of humic acid (HA). These results indicate that IONPs can be broken down efficiently into "nanosize range" by probe ultrasonication and a degree of stability can be achieved without the use of synthetic modifiers to enhance colloidal stability. This dispersion tool could be used to develop a laboratory method to study the adsorption mechanism between dispersed bare IONPs and toxic contaminants.

Degradation of methylmercury and its effects on mercury distribution and cycling in the Florida Everglades.

Methylmercury (MeHg) is recognized as one of the major water quality concerns in the Florida Everglades. Degradation of MeHg in the water is thought to be one of the most important processes to the cycling of MeHg, but there is a lack of quantitative estimations of its effect on the distribution and cycling of MeHg in this ecosystem. Stable isotope (Me201Hg) addition method was implemented to investigate the degradation of MeHg in the Everglades. By combining these results with the field monitoring data, effects of photodegradation on MeHg distribution and its contribution to MeHg cycling were estimated. The results indicate that degradation of MeHg in Everglades water is mediated by sunlight and that UV-A and UV-B radiations are the principal driver. The spatial pattern of MeHg photodegradation potential (PPD) generally illustrated an increasing trend from north to south in the Everglades, which was opposite to the distribution of MeHg in water column. Correlation analysis shows that MeHg concentration in the water had a significant negative relation to PPD, suggesting that photodegradation could play an important role in controlling the distribution of MeHg in Everglades water. Furthermore, about 31.4% of MeHg input into the water body was removed by photodegradation, indicating its importance in the biogeochemical cycling of MeHg in the Everglades. This percent reduction is much lower than that reported for other ecosystems, which could be caused by the higher concentration of DOC in the Everglades. The relatively slower degradation of MeHg could be one of the main reasons for the high ratio of MeHg to total mercury (THg) in this ecosystem.

Spatial variability in mercury cycling and relevant biogeochemical controls in the Florida Everglades.

Spatial patterns in mercury cycling and bioaccumulation at the landscape level in the Everglades were investigated by collecting and analyzing multimedia samples for mercury species and biogeochemical characteristics from 228 randomly located stations. Higher total mercury (THg) in environmental compartments (surface water, soil, flocculent detrital material (floc), and periphyton) generally occurred in the northern and central Everglades, but higher THg in water and periphyton in the Everglades National Park was an exception. Multiple biogeochemical characteristics, such as surface water dissolved organic matter (DOC(sw)), pH, chloride, and compositional properties of solid compartments (soil and floc), were identified to be important factors controlling THg distribution. Methylmercury (MeHg) was also higher in the northern Everglades for water, soil, and floc, but not for periphyton. Higher mosquitofish THg and bioaccumulation factor were observed in the central and southern Everglades, partially in accordance with periphyton MeHg distribution, but not in the "hot spot" areas of water, soil, or floc MeHg. The discrepancy in mercury bioaccumulation and mercury distribution in environmental compartments suggests that in addition to MeHg production, biogeochemical controls that make MeHg available to aquatic organisms, such as DOC(sw) and compositional properties of soil and floc, are important in mercury bioaccumulation.