Mercury concentrations in red drum, Sciaenops ocellatus, from estuarine and offshore waters of Florida

Dorsal muscle tissue from 712 red drum, Sciaenops ocellatus, from Florida waters were analyzed for total mercury content. Mercury levels detected in these red drum varied but in most study areas were usually lower than regulatory threshold guidelines. Total mercury levels in individual fish from all study areas ranged from 0.020 to 3.6 ppm (wet weight). Total mercury levels detected in red drum from the Florida Keys-Florida Bay area were often higher than those in fish from all other estuarine study areas. Positive relationships between total mercury levels and fish size (length and weight) and fish age were observed in most Florida study areas, indicating that mercury levels tend to increase over time as red drum grow. The majority of large, mature red drum examined contained mercury levels greater than the 0.5-ppm threshold level set by the Florida Department of Health (DOH). Approximately 94% of all adult red drum from offshore waters adjacent to Tampa Bay contained mercury levels greater than or equal to the 0.5-ppm threshold level, and 64% contained levels greater than or equal to the DOH 1.5-ppm "no consumption" level. All fish from this area with mercury levels greater than 1.5 ppm were large individuals (670 mm SL). Eight percent of legal-size red drum from Florida waters contained total mercury levels greater than or equal to the 0.5-ppm threshold level. The majority (52%) of these legal-size fish greater than or equal to 0.5 ppm were from the Florida Keys-Florida Bay area. In the Florida recreational fishery, the current maximum size limit for this species is an effective filter that prevents humans from consuming those red drum with the greatest likelihood of containing high mercury levels.     

Copper bioavailability in a coastal environment of Northern Chile: comparison of bioassay and analytical speciation approaches

An integrated approach including chemical speciation analyses and microalgal bioassays was used to assess the impact of copper from copper mining on a coastal area in Northern Chile. Dissolved copper ranged from <1 microg l(-1) at reference sites to 48 microgl(-1) at sites close to the mine discharge. Dissolved copper at sites closest to the discharge always exceeded seawater complexing capacities determined by anodic stripping voltammetry (ASV), and consequently labile copper was always detected (1-37 microg l(-1)). Agreement between ASV-labile copper and copper retained by cation exchange (ALSA) columns was excellent. Measured labile copper also accurately predicted bioavailable copper determined by growth inhibition of Nitzschia closterium and enzyme inhibition in Dunaliella tertiolecta. Seawater from Caleta La Lancha had the highest dissolved and labile copper and was the most toxic to micro-algal growth and enzyme activity. Previous studies at this site confirmed it had the lowest level of biodiversity, suggesting that copper may have both direct and indirect effects on these communities.     

Water quality and phytoplankton as indicators of hurricane impacts on a large estuarine ecosystem

Three sequential hurricanes in the fall of 1999 provided the impetus for assessing multi-annual effects on water quality and phytoplankton dynamics in southwestern Pamlico Sound, North Carolina. Two and a half years of post-hurricane data were examined for short- and long-term impacts from the storms and >100 year flooding. Salinity decreased dramatically and did not recover until May 2000. Inorganic nitrogen and phosphorus concentrations were briefly elevated during the flooding, but later returned to background levels. Dissolved organic carbon concentrations declined through the whole study period, but did not appear to peak as was observed in the Neuse River estuary, a key tributary of the Sound. Light attenuation was highest in the fall to spring following the storms and was best correlated with chlorophylla concentrations. Phytoplankton biomass (chla) increased and remained elevated until late spring 2000 when concentrations returned to pre-storm levels and then cycled seasonally. Phytoplankton community composition varied throughout the study, reflecting the complex interaction between physiological optimal and combinations of salinity, residence time, nutrient availability, and possibly grazing activity. Floodwater advection or dilution from upstream maxima may have controlled the spatial heterogeneity in total and group-specific biomass. The storms produced areas of shortterm hypoxia, but hypoxic events continued during the following two summers, correlating strongly with water column stratification. Nitrogen loading to the southwestern sound was inferred from network analysis of previous nitrogen cycling studies in the Neuse River estuary. Based on these analyses, nutrient cycling and removal in the sub-estuaries would be decreased under high flow conditions, confirming observations from other estuaries. The inferred nitrogen load from the flood was 2–3 times the normal loading to the Sound; this estimate was supported by the substantial algal bloom. After 8-mos, the salinity and chla data indicated the Sound had returned to pre-hurricane conditions, yet phytoplankton community compositional changes continued through the multi-year study period. This is an example of long-term aspects of estuarine recovery that should be considered in the context of a predicted 10–40 yr period of elevated tropical storm activity in the western Atlantic Basin.     

Mutual neutralization rates of ionospherically important ions

Following our recently published measurements of the rate coefficients for mutual neutralization, α, of the ionospherically important reactions NO⁺ + NO₂^?(α₁) and NO⁺ + NO₃^?(α₂) carried out in ion-ion flowing afterglow plasmas at 300 K, we have determined the mutual neutralization rates for the water cluster ion H₃O⁺ · (H₂O)₃ with a mixture of several negative ions which are known to exist in the D region. The α coefficients for these cluster ion reactions do not differ significantly from alpha;₁ and α₂, all of these reactions having α ?6 × 10^?8 cm³/sec which is significantly smaller than values usually adopted in ionospheric calculations. Current information on the ionic composition of the D region and the implications of the present results to de-ionization rate calculations are discussed.     

Effects of maturation on the reflectance of the lunar regolith: Apollo 16 — A case study

Soils at the Apollo 16 site become progressively darker as the percentage of glassy agglutinates increases. Magnetic separates of the agglutinate fraction of a soil always are darker than the bulk soil, and darker than the non-agglutinate fraction that consists of rock and mineral fragments. Darkening of a soil with maturity is due mainly to the increasing proportion of agglutinates. Coating of rock and mineral fragments with thin deposits of glass aids darkening in a minor way, but most of these particles eventually are destroyed by melting as the soils mature.Present address: Dept. of Geological Sciences, University of Washington, Seattle, Wash., U.S.A.     

Origin of regional climate differences: role of boundary conditions and model formulation in two GCMs

Model differences in projections of extratropical regional climate change due to increasing greenhouse gases are investigated using two atmospheric general circulation models (AGCMs): ECHAM4 (Max Planck Institute, version 4) and CCM3 (National Center for Atmospheric Research Community Climate Model version 3). Sea-surface temperature (SST) fields calculated from observations and coupled versions of the two models are used to force each AGCM in experiments based on time-slice methodology. Results from the forced AGCMs are then compared to coupled model results from the Coupled Model Intercomparison Project 2 (CMIP2) database. The time-slice methodology is verified by showing that the response of each model to doubled CO₂ and SST forcing from the CMIP2 experiments is consistent with the results of the coupled GCMs. The differences in the responses of the models are attributed to (1) the different tropical SST warmings in the coupled simulations and (2) the different atmospheric model responses to the same tropical SST warmings. Both are found to have important contributions to differences in implied Northern Hemisphere (NH) winter extratropical regional 500 mb height and tropical precipitation climate changes. Forced teleconnection patterns from tropical SST differences are primarily responsible for sensitivity differences in the extratropical North Pacific, but have relatively little impact on the North Atlantic. There are also significant differences in the extratropical response of the models to the same tropical SST anomalies due to differences in numerical and physical parameterizations. Differences due to parameterizations dominate in the North Atlantic. Differences in the control climates of the two coupled models from the current climate, in particular for the coupled model containing CCM3, are also demonstrated to be important in leading to differences in extratropical regional sensitivity.     

Rock fragment distributions and regolith evolution in the Ouachita Mountains,Arkansas, USA

Rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls, erosion, deposition, bioturbation, and weathering. The distribution of rock fragments in regoliths of the Ouachita Mountains, Arkansas, shows that sandstone fragments are common in all layers, even if sandstone is absent in parent material. Shale and sandstone fragments are produced at the bedrock weathering front, but the shale weathers rapidly and intact fragments are rare in the solum. Sandstone is weathered from ridgetop outcrops and transported downslope. Some of these fragments are moved downward, by faunalturbation and by transport into pits associated with rotting tree stumps. Upward movement by treethrow is common, resulting in a net concentration of rocks near the surface. However, the highest fragment concentrations are in the lower regolith, indicating active production at the weathering front. The regolith is a dynamic feature, reflecting the influences of vertical and horizontal processes, of active weathering at the bedrock interface, and of surficial sediment movements. The role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities, and that forest soils have likely been extensively mixed within Holocene and historic time. Copyright © 2005 John Wiley & Sons, Ltd.