ABSTRACTS-Toxicants: EvergladesHUB

(2009) Boyd, E.S., King, S., Tomberlin, J.K., Nordstrom, D.K., Krabbenhoft, D.P., Barkay, T. and Geesey, G.G. Methylmercury enters an aquatic food web through acidophilic microbial mats in Yellowstone National Park, Wyoming. Environmental Microbiology 11(4), 950-959.

Abstract
Microbial mats are a visible and abundant life form inhabiting the extreme environments in Yellowstone National Park (YNP), WY, USA. Little is known of their role in food webs that exist in the Park's geothermal habitats. Eukaryotic green algae associated with a phototrophic green/purple Zygogonium microbial mat community that inhabits low-temperature regions of acidic (pH similar to 3.0) thermal springs were found to serve as a food source for stratiomyid (Diptera: Stratiomyidae) larvae. Mercury in spring source water was taken up and concentrated by the mat biomass. Monomethylmercury compounds (MeHg+), while undetectable or near the detection limit (0.025 ng l(-1)) in the source water of the springs, was present at concentrations of 4-7 ng g(-1) dry weight of mat biomass. Detection of MeHg+ in tracheal tissue of larvae grazing the mat suggests that MeHg+ enters this geothermal food web through the phototrophic microbial mat community. The concentration of MeHg+ was two to five times higher in larval tissue than mat biomass indicating MeHg+ biomagnification occurred between primary producer and primary consumer trophic levels. The Zygogonium mat community and stratiomyid larvae may also play a role in the transfer of MeHg+ to species in the food web whose range extends beyond a particular geothermal feature of YNP.

(2009) Cohen, M.J., Lamsal, S., Osborne, T.Z., Bonzongo, J.C.J., Newman, S. and Reddy, K.R. Soil Total Mercury Concentrations across the Greater Everglades. Soil Science Society of America Journal 73(2), 675-685.

Abstract
Elevated Hg concentrations in the Everglades pose ecological and human health risks. We mapped soil total Fig concentrations per mass (THgM) and area THgA) across the Everglades, and investigated relationships with soil properties (total P [TP] and organic matter content), community type, and hydrologic compartmentalization. Samples (n = 600) from surface soils (0-10 cm) were selected from a Population of 1405 sites spanning the Everglades. Overall, 168 sites had THgM levels >0.2 mg kg(-1); interpolation suggests that 23% of the Greater Everglades exceeds this threshold. Hot spots (>0.4 mg kg(-1)) were observed in eastern Water Conservation Area (WCA) 1 and west-central WCA3A; parts of WCA2A, WCA3AN, and WCA3B were locally high. Despite significant global differences in THgM among plant Communities, differences evaluated using paired proximate sites were not significant, suggesting that large spatial scale depositional gradients govern ecosystem storage. Median THgA was 1.89 mg m(-2) (range 0.07-12.05 mg m(-2)), representing approximately 100 yr of atmospheric deposition at contemporary rates (similar to 19 mu g m(-2) yr(-1)). Correlation between TP and THgM was positive in unimpacted areas (TP < 500 mg kg(-1), r = 0.69), but negative in impacted areas (TP > 500 mg kg(-1), r = -0.47), probably due to accelerated peat accretion rates in P-enriched areas. Moreover, while reverse correlation with distance from a canal for THgM (0.70) and TP (-0.77) supports Hg enrichment via atmospheric deposition, THgM hotspots in WCA3AS, WCA1, and the Holeyland and Rotenberger tracts are suggestive of local enrichment mechanisms. Finally, despite dramatic regional emissions declines, the estimated mass of Hg in surface soils across the Everglades has increased similar to 20% (11,000 vs. 13,100 kg) since 1996; while the statistical significance of this change is unknown, it provides a useful benchmark for future surveys.

(2009) Covelli, S., Acquavita, A., Piani, R., Predonzani, S. and De Vittor, C. Recent contamination of mercury in an estuarine environment (Marano lagoon, Northern Adriatic, Italy). Estuarine Coastal and Shelf Science 82(2), 273-284.

Abstract
The Marano Lagoon, in the northern Adriatic Sea (Italy), has been affected by mercury (Hg) contamination from industrial and mining activities. It has been estimated that 186,000 kg of Hg were deliberately discharged into the main drainage system (Aussa-Corno River) by a chlor-alkali plant (CAP) from 1940s to 1984. The lagoon has also experienced a secondary long-term Hg input, originated from mining activity in Idrija (Slovenia), due to the supply of fluvial suspended particles carried by the Isonzo River in the Gulf of Trieste. Since local fishing activities are extensively conducted, there is great concern on the risk posed by potentially harmful effects of Hg to the trophic chain. Present inputs of this metal, both in dissolved (52.4-4.1 ng L-1) and particulate (130.8-3.4 ng L-1) phases, were preliminary investigated in the water column. Although direct discharge of Hg from the CAP no longer exists, the metal is still released from the source area into freshwaters, and its distribution and abundance is controlled by the salt-wedge circulation system, which is tide-influenced. Remobilization from bottom sediments can also be a secondary source of Hg into the aquatic environment. A speciation technique, used to investigate the main binding sites and phase associations of Hg in sediments (5.69-0.82 mu g g(-1)), evidenced the presence of mobile (1.8-11%) and potentially available species for methylation processes. The results are particularly important if related to resuspension effects caused by natural events and anthropogenic activities. Preliminary considerations on Hg behaviour in this estuarine environment are reported.

(2009) Herring, G., Gawlik, D.E. and Rumbold, D.G. Feather mercury concentrations and physiological condition of great egret and white ibis nestlings in the Florida Everglades. Science of the Total Environment 407(8), 2641-2649.

Abstract
Mercury contamination in the Florida Everglades has reportedly played a role in the recent decline of wading birds, although no studies have identified a mechanism leading to population-level effects. We assessed feather mercury levels in great egret (Ardea alba; n=91) and white ibis (Eudocimus albus; n=46) nestlings at breeding colonies in the Florida Everglades during a year (2006) with excellent breeding conditions (characterized by hydrology leading to concentrated prey) and a year with below average breeding conditions (2007). We also assessed the physiological condition of those nestlings based on levels of plasma and fecal corticosterone metabolites, and stress proteins 60 and 70. Mercury levels were higher in both species during the good breeding condition year (great egret=6.25 mu g/g +/- 0.81 SE, white ibis = 1.47 mu g/g +/- 0.41 SE) and lower in the below average breeding year (great egret=1.60 mu g/g +/- 0.11 SE, white ibis=0.20 mu g/g +/- 0.03 SE). Nestlings were in better physiological condition in 2006, the year with higher feather mercury levels. These results support the hypothesis that nestlings are protected from the harmful effects of mercury through deposition of mercury in growing feathers. We found evidence to suggest shifts in diets of the two species, as a function of prey availability, thus altering their exposure profiles. However, we found no evidence to suggest they respond differently to mercury exposure.

(2009) Wollenberg, J.L. and Peters, S.C. Mercury emission from a temperate lake during autumn turnover. Science of the Total Environment 407(8), 2909-2918.

Abstract
Lakes in temperate regions stratify during summer and winter months, creating distinct layers of water differentiated by their physical and chemical characteristics. When lakes mix in autumn and spring, mercury cycling may be affected by the chemical changes that occur during mixing. Sampling was conducted in Lake Lacawac, Eastern Pennsylvania, USA, throughout the autumn of 2007 to characterize changes in emission of gaseous elemental mercury (He) from the lake surface and dissolved mercury profiles in the water column during mixing. Water chemistry and weather parameters were also measured, including dissolved organic carbon (DOC), iron, and solar radiation which have been shown to interact with mercury species. Results indicate that emission of He from the lake to the atmosphere during turnover was controlled both by solar radiation and by surface water mercury concentration. As autumn turnover progressed through the months of October and November, higher mercury concentration water from the hypolimnion mixed with epilimnetic water, increasing mercury concentration in epilimnetic waters. Dissolved absorbance was significantly correlated with mercury concentrations and with iron, but DOC concentrations were essentially constant throughout the study period and did not exhibit a relationship with either dissolved mercury concentrations or emission rates. Positive correlations between dissolved mercury and iron and manganese also suggest a role for these elements in mercury transport within the lake, but iron and manganese did not demonstrate a relationship with emission rates. This research indicates that consideration of seasonal processes in lakes is important when evaluating mercury cycling in aquatic systems.

(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.

Abstract
Methyl mercury is a globally distributed neurotoxin, endocrine disruptor, and teratogen, the effects of which on wildlife at environmentally relevant levels are largely unknown. In birds, foraging efficiency and learning may be sensitive endpoints for sublethal methylmercury toxicity, and these endpoints also may be biologically relevant at the population level. In the present study, groups of wild-caught, prefledgling white ibises (Eudocimus albus) were raised in a free-flight, open-Air aviary on diets that approximated the measured range of methylmercury exposure in the Everglades ecosystem (0, 0.05, 0.1, and 0.3 mg/kg/d). The effect of methylmercury exposure on group foraging efficiency was exarrtined by allowing birds to forage on 200 fathead minnows (Pimephales promelas) in artificial ponds for 15 min by straining the arenas' contents through a seine net and counting all remaining prey. Additionally, we varied the difficulty of foraging by these tactile feeding birds by adding multiple levels of structural complexity (e.g., increased vegetation and prey refugia) to the pond. Structural complexity affected both foraging efficiency and the rate of increase in efficiency over time (improvement). Methylmercury exposure affected foraging efficiency (p = 0.03). It did not affect foraging improvement in the face of increasingly challenging environments, however, and the dose-response relationship was nonlinear (e.g., the control and high-exposure groups were the least efficient foragers). Evidence for an effect of methylmercury on foraging efficiency therefore was inconclusive because of unpredicted results and no interaction with time or habitat complexity. These data suggest a nonlinear dose-response relationship at low levels of methylmercury exposure; future research is needed to verify this hypothesis. This appears to be the first experimental demonstration of the effects of habitat complexity on foraging efficiency in long-legged wading birds.

(2008) Chumchal, M.M., Drenner, R.W., Fry, B., Hambright, K.D. and Newland, L.W. Habitat-specific differences in mercury concentration in a top predator from a shallow lake. Transactions of the American Fisheries Society 137(1), 195-208.

Abstract
We conducted a survey of mercury contamination in largemouth bass Micropterus salmoides from Caddo Lake, Texas, and found that fish collected from forested wetland habitat had higher concentrations of mercury than those collected from open-water habitat. Habitat-specific differences in largemouth bass size, age, absolute growth rate, trophic position (based on delta N-15), and horizontal food web position (based on delta C-13), characteristics known to influence mercury accumulation, did not explain the observed differences in mercury contamination. Rather, habitat-related differences in mercury concentration in a primary consumer, Mississippi grass shrimp Palaemonetes kadiakensis, indicated that food webs in forested wetland habitat were more contaminated with mercury than those in open-water habitat. Spatial variation in mercury contamination within lakes and elevated mercury concentrations in forested wetlands should be of special concern not only to researchers but also to public and environmental health officials dealing with mercury contamination in aquatic environments and human health risks associated with consumption of fish contaminated with mercury.

(2008) Delaune, R.D., Gambrell, R.P., Jugsujinda, A., Devai, I. and Hou, A. Total Hg, methyl Hg and other toxic heavy metals in a northern Gulf of Mexico estuary: Louisiana Pontchartrain basin. Journal of Environmental Science and Health Part a-Toxic/Hazardous Substances & Environmental Engineering 43(9), 1006-1015.

Abstract
Concentration of total Hg, methyl Hg, and other heavy metals were determined in sediment collected along a salinity gradient in a Louisiana Gulf Coast estuary. Surface sediment was collected at established coordinates (n = 292) along a salinity gradient covering Lake Maurepas, Lake Pontchartrain, Lake Borgne and the Chandeleur Sound located in the 12,170 km(2) Pontchartrain basin estuary southeastern coastal Louisiana. Lake Maurepas sediment with lower salinity contained higher levels of methyl Hg (0.80 g/kg) than Lake Pontchartrain (0.55 mu g/kg). Lake Maurepas sediment also had higher levels of total Hg (98.0 mu g/kg) as compared to Lake Pontchartrain (67.0 mu g/kg). Average total Hg content of Lake Borgne and the Chandeleur Sound sediment was 24.0 mu g/kg dry sediment and methyl Hg content averaged 0.21 mu g/kg dry sediment. Methyl Hg content of sediment was positively correlated with total Hg, organic matter and clay content of sediment. Methyl Hg was inversely correlated with salinity, sediment Eh and sand content. Total Hg and methyl Hg decreased with increase in salinity in the order of Lake Maurepas > Lake Pontchartrain > Lake Borgne/ the Chandeleur Sound. Lake Maurepas containing several times higher amount of methyl Hg in sediment as compared to Lake Pontchartrain and Lake Borgne and the Chandeleur Sound is an area that could serve as potential source of mercury to the aquatic food chain. Methyl Hg content of sediment in the estuary could be predicted by the equation: Methyl Hg = 0.11670-0.0625 Salinity + 0.05349 O.M. + 0.00513 Total Hg - 0.00250 Clay. Concentrations of other toxic heavy metals (Pb, Cd, Ni, Cu and Zn) in sediment were not elevated and was statistically correlated with sediment texture and iron and aluminum content of sediment.

(2008) Engle, M.A., Tate, M.T., Krabbenhoft, D.P., Kolker, A., Olson, M.L., Edgerton, E.S., DeWild, J.F. and McPherson, A.K. Characterization and cycling of atmospheric mercury along the central US Gulf Coast. Applied Geochemistry 23(3), 419-437.

Abstract
Concentrations of atmospheric Hg species, elemental Hg (Hg degrees), reactive gaseous Hg (RGM), and fine particulate Hg (Hg-PM2.5) were measured at a coastal site near Weeks Bay, Alabama from April to August, 2005 and January to May, 2006. Mean concentrat ions of the species were 1.6 +/- 0.3 ng m(-3), 4.0 +/- 7.5 Pg m(-3) and 2.7 +/- 3.4 pg m(-3), respectively. A strong diel pattern was observed for RGM (midday maximum concentrations were up to 92.7 pg m(-3)), but not for Hg degrees or Hg-PM2.5. Elevated RGM concentrations (>25 pg m-3) in April and May of 2005 correlated with elevated average daytime 03 concentrations (> 55 ppbv) and high light intensity (> 500 W m(-2)). These conditions generally corresponded with mixed continental-Gulf and exclusively continental air mass trajectories. Generally lower, but still elevated, RGM peaks observed in August, 2005 and January-March, 2006 correlated significantly (p < 0.05) with peaks in SO2 concentration and corresponded to periods of high light intensity and lower average daytime 03 concentrations. During these times air masses were dominated by trajectories that originated over the continent. Elevated RGM concentrations likely resulted from photochemical oxidation of Hg degrees by atmospheric oxidants. This process may have been enhanced in and by the near-shore environment relative to inland sites. The marine boundary layer itself was not found to be a significant source of RGM. Size segregation determination, using a limited dataset from two different methods, suggested that a significant fraction of particulate Hg was bound to coarse particles (> 2.5 pm). A potential source of the large fraction of coarse particulate Hg in the study area is sequestration of RGM within sea salt aerosols. The presence of rapidly depositing RGM and coarse particulate Hg may be important sources of Hg input along the Gulf Coast. However, the impact of these species oil deposition rates is yet to be determined.

(2008) George, B.M. and Batzer, D. Spatial and temporal variations of mercury levels in Okefenokee invertebrates: Southeast Georgia. Environmental Pollution 152(2), 484-490.

Abstract
Accumulation of mercury in wetland ecosystems has raised concerns about impacts on wetland food webs. This study measured concentrations of mercury in invertebrates of the Okefenokee Swamp in Georgia, focusing on levels in amphipods, odonates, and crayfish. We collected and analyzed total mercury levels in these invertebrates from 32 sampling stations across commonly occurring sub-habitats. Sampling was conducted in December, May, and August over a two-year period. The highest levels of mercury were detected in amphipods, with total mercury levels often in excess of 20 ppm. Bioaccumulation pathways of mercury in invertebrates of the Okefenokee are probably complex; despite being larger and higher in the food chain, levels in odonates and crayfish were much lower than in amphipods. Mercury levels in invertebrates varied temporally with the highest levels detected in May. There was a lack of spatial variation in mercury levels which is consistent with aerial deposition of mercury.

(2008) Hall, B.D., Aiken, G.R., Krabbenhoft, D.P., Marvin-DiPasquale, M. and Swarzenski, C.M. Wetlands as principal zones of methylmercury production in southern Louisiana and the Gulf of Mexico region. Environmental Pollution 154(1), 124-134.

Abstract
It is widely recognized that wetlands, especially those rich in organic matter and receiving appreciable atmospheric mercury (Hg) inputs, are important sites of methylmercury (MeHg) production. Extensive wetlands in the southeastern United States have many ecosystem attributes ideal for promoting high MeHg production rates; however, relatively few mercury cycling studies have been conducted in these environments. We conducted a landscape scale study examining Hg cycling in coastal Louisiana (USA) including four field trips conducted between August 2003 and May 2005. Sites were chosen to represent different ecosystem types, including: a large shallow eutrophic estuarine lake (Lake Pontchartrain), three rivers draining into the lake, a cypress-tupelo dominated freshwater swamp, and six emergent marshes ranging from a freshwater marsh dominated by Panicum hemitomon to a Spartina alterniflora dominated salt marsh close to the Gulf of Mexico. We measured MeHg and total Hg (THg) concentrations, and ancillary chemical characteristics, in whole and filtered surface water, and filtered porewater. Overall, MeHg concentrations were greatest in surface water of freshwater wetlands and lowest in the profundal (non-vegetated) regions of the lake and river mainstems. Concentrations of THg and MeHg in filtered surface water were positively correlated with the highly reactive, aromatic (hydrophobic organic acid) fraction of dissolved organic carbon (DOC). These results suggest that DOC plays an important role in promoting the mobility, transport and bioavailability of inorganic Hg in these environments. Further, elevated porewater concentrations in marine and brackish wetlands suggest coastal wetlands along the Gulf Coast are key sites for MeHg production and may be a principal source of MeHg to foodwebs in the Gulf of Mexico. Examining the relationships among MeHg, THg, and DOC across these multiple landscape types is a first step in evaluating possible links between key zones for Hg(II)-methylation and the bioaccumulation of mercury in the biota inhabiting the Gulf of Mexico region.

(2008a) Liu, G.L., Cai, Y., Kalla, P., Scheidt, D., Richards, J., Scinto, L.J., Gaiser, E. and Appleby, C. Mercury mass budget estimates and cycling seasonality in the Florida everglades. Environmental Science & Technology 42(6), 1954-1960.

Abstract
We estimated the mass budget for mercury (Hg) seasonally deposited into the Florida Everglades and investigated seasonality of Hg cycling by analyzing data obtained for water, soil, flocculent detrital material (floc), periphyton, and mosquitofish collected throughout the Everglades freshwater marshes in the 2005 dry and wet seasons. Higher wet season total Hg (THg) in soil, floc, and periphyton agreed with greater Hg amounts entering these compartments during the wet season, probably owing to substantially greater Hg deposition in the wet season than in the dry season. Seasonal differences were absent for THg in surface water. Methylmercury (MeHg) showed mixed seasonal patterns, with higher water and soil MeHg and lower periphyton MeHg in the dry season but no seasonality for floc MeHg. Seasonal variations in Hg deposition, MeHg production and transport, and mass of ecosystem compartments could be responsible for the seasonality of MeHg cycling. Higher mosquitofish THg, higher bioaccumulation factors, and higher biomagnification factors from periphyton to mosquitofish were observed in the wet season than in the dry season, indicating that the wet season is more favorable for Hg bioaccumulation. The mass budget estimation agreed with this result.

(2008b) Liu, G.L., Cai, Y., Philippi, T., Kalla, P., Scheidt, D., Richards, J., Scinto, L. and Appleby, C. Distribution of total and methylmercury in different ecosystem compartments in the Everglades: Implications for mercury bioaccumulation. Environmental Pollution 153(2), 257-265.

Abstract
We analyzed Hg species distribution patterns among ecosystem compartments in the Everglades at the landscape level in order to explore the implications of Hg distribution for Hg bioaccumulation and to investigate major biogeochemical processes that are pertinent to the observed Hg distribution patterns. At an Everglade-wide scale, THg concentrations were significantly increased in the following order: periphyton < flocculent material (floe) < soil, while relatively high MeHg concentrations were observed in floe and periphyton. Differences in the methylation potential, THg concentration, and MeHg retention capacity could explain the relatively high MeHg concentrations in floe and periphyton. The MeHg/THg ratio was higher for water than for soil, floe, or periphyton probably due to high dissolved organic carbon (DOC) concentrations present in the Everglades. Mosquitofish THg positively correlated with periphyton MeHg and DOC-normalized water MeHg. The relative THg and MeHg distribution patterns among ecosystem compartments favor Hg bioaccumulation in the Everglades.

(2008) Mao, Y.X., Liu, G.L., Meichel, G., Cai, Y. and Jiang, G.B. Simultaneous speciation of monomethylmercury and monoethylmercury by aqueous phenylation and purge-and-trap preconcentration followed by atomic spectrometry detection. Analytical Chemistry 80(18), 7163-7168.

Abstract
A new method for the detection of trace levels of organomercury species has been developed by combining the high enrichment capacity of purge and trap with aqueous phenylation derivatization. Phenylation products of monomethylmercury (MeHg) and monoethylmercury (EtHg) were first separated by capillary gas chromatography and then detected by atomic fluorescence spectrometry (AFS) or inductively coupled plasma mass spectrometry (ICPMS). Ibis combination made it possible to simultaneously quantify trace or ultratrace level of MeHg and EtHg in environmental samples. Method detection limits were 0.03 ng/L for both MeHg and EtHg when AFS was used as the detector and 0.02 and 0.01 ng/L for MeHg and EtHg with ICPMS, respectively. Certified reference materials, IAEA-405 and DORM-2, were analyzed and the results were in accordance with certified values. Both MeHg and EtHg were detected in sediment samples collected from the Florida Everglades and a Canadian wetland. This new method has been validated for the direct detection of trace organomercury species in freshwater samples and has the additional benefits of being free from interference by Cl- and dissolved organic matter.

(2008) Merritt, K.A. and Amirbahman, A. Methylmercury cycling in estuarine sediment pore waters (Penobscot River estuary, Maine, USA). Limnology and Oceanography 53(3), 1064-1075.

Abstract
Particulate mercury ( Hg) sequestered in coastal marine sediments may be efficiently methylated to highly toxic methylmercury ( MeHg), thereby placing exposed organisms at risk of MeHg bioaccumulation. The Penobscot River estuary in Maine, U. S. A., has been subject to Hg contamination from multiple industries including a recently closed chlor-alkali production facility. Pore-water depth profiles of total Hg, MeHg, and ancillary chemistry for the midestuary region were collected in August 2006 and June 2007. The profiles are divisible into kinetically discrete intervals with respect to MeHg dynamics. Dominant MeHg production occurs between,2 and 7 cm in August and similar to 2 and 8 cm in June, with similar net MeHg production rates between 0.35 x 10(-20) and 4.9 x 10(-20) mol cm(-3) s(-1). A significant decrease in pore-water MeHg concentration is observed in the vicinity of the sediment-water interface (SWI). For August, a minimum MeHg consumption rate constant of 1.1 d(-1) may be estimated equal to the diffusive transport rate within a depth interval < 0.75 cm. In June, the MeHg consumption zone extends from the SWI to a similar depth as for August, but the consumption rate is slower. MeHg consumption involves both sorption to sediment and demethylation. Intact sediment cores were incubated in the laboratory under various ponding regimes to study the influence of dominant geochemical parameters on in situ Hg methylation. The ponding regime changes the location of the redoxcline, which affects the depth of maximum methylation. Induced shoaling of the redoxcline brought about by the absence of any advective mixing of overlying water results in heightened MeHg efflux from the sediment.

(2008) Perry, W.B. Everglades restoration and water quality challenges in south Florida. Ecotoxicology 17(7), 569-578.

Abstract
This paper provides background information and a brief overview of water quality issues for the rest of the papers in this volume that are concerned with Everglades restoration. The Everglades of Florida have been diminished over 50% of their former extent. The Everglades are no longer a free-flowing wetland ecosystem, but are now subject to a complicated system of water management that is regulated primarily for flood control and consumptive use. Attempts to restore a more natural hydropattern to the remaining undeveloped Everglades are made more difficult by the natural extremes in rainfall, flat landscape, highly porous geology, and inaccessibility of the remaining natural areas. The Comprehensive Everglades Restoration Plan (CERP) seeks ecosystem restoration by adding water storage capacity, reducing groundwater seepage, improving regulatory delivery and timing of water to avoid environmental damage, and where feasible, improving the quality of water to be used for Everglades restoration. Water quality issues that currently exist for south Florida include eutrophication (especially phosphorus), mercury, and contaminants from agricultural production and the urban environment. Lands once in agricultural production that will be converted back to wetlands or will become reservoirs may contribute to the water quality concerns. Stormwater runoff from managed lands that will be used for restoration purposes will also present water quality challenges. The state continues to seek water quality improvement with a number of pollution reduction programs, and CERP attempts to improve water quality without sacrificing even more natural areas; however providing water quality sufficient for use in recovery of remaining Everglades wetlands and estuaries will remain a daunting challenge.

(2008) Rumbold, D.G., Lange, T.R., Axelrad, D.M. and Atkeson, T.D. Ecological risk of methylmercury in Everglades National Park, Florida, USA. Ecotoxicol. 17(7), 632-641.

Abstract
Dramatic declines in mercury levels have been reported in Everglades biota in recent years. Yet, methylmercury (MeHg) hot spots remain. This paper summarizes a risk assessment of MeHg exposure to three piscivorous wildlife species (bald eagle, Haliaeetus leucocephalus; wood stork, Mycteria americana; and great egret, Ardea albus) foraging at a MeHg hot spot in northern Everglades National Park (ENP). Available data consisted of literature-derived life history parameters and tissue concentrations measured in 60 largemouth bass (Micropterus salmoides), 60 sunfish (Lepomis spp.), and three composite samples of mosquitofish (Gambusia holbrooki) collected from 2003 to 2005. To assess risk, daily MeHg intake was estimated using Monte Carlo methods and compared to literature-derived effects thresholds. The results indicated the likelihood was very high, ranging from 98-100% probability, that these birds would experience exposures above the acceptable dose when foraging in northern ENP. Moreover, the likelihood that these birds would experience exposures above the lowest-observed-adverse-effect level (LOAEL) ranged from a 14% probability for the wood stork to 56% probability for the eagle. Data from this study, along with the results from several other surveys suggest that biota in ENP currently contain the highest MeHg levels in South Florida and that these levels are similar to or greater than other known MeHg hot spots in the United States. Given these findings, this paper also outlines a strategic plan to obtain additional measured and modeled information to support risk-based management decisions in ENP.

(2008) Valega, M., Lillebo, A.I., Pereira, M.E., Corns, W.T., Stockwell, P.B., Duarte, A.C. and Pardal, M.A. Assessment of methylmercury production in a temperate salt marsh (Ria de Aveiro Lagoon, Portugal). Marine Pollution Bulletin 56(1), 153-158.

Abstract
During the last two decades, restriction rules for the anthropogenic load of mercury have resulted in a substantial decrease of the inputs of this metal into aquatic systems. However the pool of mercury presently in sediments remains a problem due to its potential release to other environmental compartments such as the atmosphere, the overlying water column, and to living organisms through bioaccumulation and/or trophic transfer processes. The potential release of methylmercury from sediments to the overlying water column can harm the environment on a local or regional scale, particularly in areas highly dependent on fishery activities, endangering the system ecologically and economically as well as causing concern regarding human health.

(2008) Wiener, J.G. and Suchanek, T.H. The Basis for Ecotoxicological Concern in Aquatic Ecosystems Contaminated by Historical Mercury Mining. Ecological Applications 18(8), A3-A11.

Abstract
The Coast Range of California is one of five global regions that dominated historical production of mercury (Hg) until declining demand led to the economic collapse of the Hg-mining industry in the United States. Calcines, waste rock, and contaminated alluvium from inactive mine sites can release Hg (including methylmercury, MeHg) to the environment for decades to centuries after mining has ceased. Soils, water, and sediment near mines often contain high concentrations of total Hg (TotHg), and an understanding of the biogeochemical transformations, transport, and bioaccumulation of this toxic metal is needed to assess effects of these contaminated environments on humans and wildlife. We briefly review the environmental behavior and effects of Hg, providing a prelude to the subsequent papers in this Special Issue. Clear Lake is a northern California lake contaminated by wastes from the abandoned Sulphur Bank Mercury Mine, a U. S. Environmental Protection Agency Superfund Site. The primary toxicological problem with Hg in aquatic ecosystems is biotic exposure to MeHg, a highly toxic compound that readily bioaccumulates. Processes that affect the abundance of MeHg (including methylation and demethylation) strongly affect its concentration in all trophic levels of aquatic food webs. MeHg can biomagnify to high concentrations in aquatic food webs, and consumption of fish is the primary pathway for human exposure. Fish consumption advisories have been issued for many North American waters, including Clear Lake and other mine-impacted waters in California, as a means of decreasing MeHg exposure. Concerns about MeHg exposure in humans focus largely on developmental neurotoxicity to the fetus and children. Aquatic food webs are also an important pathway for MeHg exposure of wildlife, which can accumulate high, sometimes harmful, concentrations. In birds, wild mammals, and humans, MeHg readily passes to the developing egg, embryo, or fetus, life stages that are much more sensitive than the adult. The papers in this issue examine the origin, transport, transformations, bioaccumulation, and trophic transfer of Hg in Clear Lake, assess its potential effects on biota and humans, and provide information relevant to remediation of mine-impacted aquatic ecosystems.

(2008) Zhang, H. and Dill, C. Apparent rates of production and loss of dissolved gaseous mercury (DGM) in a southern reservoir lake (Tennessee, USA). Science of the Total Environment 392(2-3), 233-241.

Abstract
Apparent rates of dissolved gaseous mercury (DGM) concentration changes in a southern reservoir lake (Cane Creek Lake, Cookeville, Tennessee) were investigated using the DGM data collected in a 12-month study fromjune 2003 to May 2004. The monthly mean apparent DGM production rates rose from january (3.2 pgL(-1)/h), peaked in the summer months (June-August: 8.9, 8.0, 8.6 pg L-1/h), and fell to the lowest in December (1.6 pg L-1/h); this trend followed the monthly insolation march for both global solar radiation and UVA radiation. The monthly apparent DGM loss rates failed to show the similar trend with no consistent pattern recognizable. The spring and summer had higher seasonal mean apparent DGM production rates than the fall and winter (6.8, 9.0, 3.9, 5.0 pg L-1/h, respectively), and the seasonal trend also appeared to closely follow the solar radiation variation. The seasonal apparent DGM loss featured similar rate values for the four seasons (5.5, 4.3, 3.3, and 3.9 pg L-1/h for spring, summer, fall, and winter, respectively). Correlation was found of the seasonal mean apparent DGM production rate with the seasonal mean morning solar radiation (r=0.9084, p<0.01) and with the seasonal mean morning UVA radiation (r=0.9582, p<0.01). No significant correlation was found between the seasonal apparent DGM loss rate and the corresponding afternoon solar radiation (r=0.5686 for global radiation and 0.6098 for UVA radiation). These results suggest that DGM production in the lake engaged certain photochemical processes, either primary or secondary, but the DGM loss was probably driven by some dark processes.

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