Carbon and Noble Gas Isotopes in the Tengchong Volcanic Geothermal Area, Yunnan, Southwestern China

Carbon and noble gas isotope analyses are reported for bubbling gas samples from the Tengchong volcanic geothermal area near the Indo-Eurasian suture zone. All samples contain a resolvable component of mantle-derived 3He. Occurrence of mantle-derived 3He coincides with surface volcanism. However, 3He occurs over a larger geographic areathan do surface volcanics. δ13C values for CO2 and CH4 vary from -33.4‰ to 1.6 ‰ and from -52.8‰ to -2.8‰, respectively. He and C isotope systematics indicate that CO2 and CH4 in the CO2-rich gases originated predominantly from magmatic component mixed with crustal CO2 produced from carbonate. However, breakdown of organic matter and near-surface processes accounts for the CH4 and CO2 in N2-rich gases. 3He/4He ratio distribution pattern suggests that mantle-derived He and heat sources of high-temperature system in central Tengchong originate from a hidden magma reservoir at subsurface. CO2-rich gases with the highest 3He/4He ratio (5.2 Ra) may be representative of the     

Pfiesteria shumwayae (Pfiesteriaceae) in New Zealand

Pfiesteria shumwayae Steidinger et Burkholder is now known to be present in New Zealand and occurs in estuaries around the country. The presence of Pfiesteria was initially determined by a polymerase chain reaction (PCR)‐based detection assay, using oligonucleotide primers targeted at ribosomal DNA extracted from estuarine water and sediments. Presence was confirmed by isolation from fresh sediments in the presence offish (Oreochromis mossambicus), followed by identification by scanning electron microscopy. The New Zealand isolates of P. shumwayae were ichthyotoxic in bioassays, but there is no historic evidence offish kills in New Zealand associated with the dinoflagellate.     

Variations in eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis> L.) morphology and internal nutrient composition as influenced by increased temperature and water column nitrate

In an experimental mesocosm system, we evaluated changes in morphology and tissue nutrient content (carbon [C], nitrogen [N], phosphorus [P]) of eelgrass (Zostera marina L.) as influenced by increased temperature and nitrate. During the late summer-fall growing season (14 weeks, August through mid-November), control plants were compared to plants grown at elevated temperatures (3°C to 4°C above ambient, based on 20-yr weekly means) and elevated water column nitrate enrichment (8 μM NO₃ ⁻, pulsed daily). Both increased temperature and increased nitrate led to declines in shoot density (by 40% and 48% for nitrate and temperature treatments, respectively), as well as decreased leaf and root production. High temperature promoted increased total C content of leaf tissues, whereas high nitrate increased the percentage of N in belowground tissues and depressed the C∶N ratio in aboveground tissues. The data indicated that increases in nitrate or temperature can significantly reduce the size ofZ. marine shoots and can also alter the internal C and N content. This reduction was not associated with significant increases in light-attenuating algae as we controlled epiphytic growth, so we suggest that a direct physiological mechanism or other mechanism was involved.     

MODFLOW 2000 head uncertainty,a first-order second moment method

A computationally efficient method to estimate the variance and covariance in piezometric head results computed through MODFLOW 2000 using a first-order second moment (FOSM) approach is presented. This methodology employs a first-order Taylor series expansion to combine model sensitivity with uncertainty in geologic data. MODFLOW 2000 is used to calculate both the ground water head and the sensitivity of head to changes in input data. From a limited number of samples, geologic data are extrapolated and their associated uncertainties are computed through a conditional probability calculation. Combining the spatially related sensitivity and input uncertainty produces the variance-covariance matrix, the diagonal of which is used to yield the standard deviation in MODFLOW 2000 head. The variance in piezometric head can be used for calibrating the model, estimating confidence intervals, directing exploration, and evaluating the reliability of a design. A case study illustrates the approach, where aquifer transmissivity is the spatially related uncertain geologic input data. The FOSM methodology is shown to be applicable for calculating output uncertainty for (1) spatially related input and output data, and (2) multiple input parameters (transmissivity and recharge).     

Temperature dependent absorption cross sections for formaldehyde (CH2O): The effect of formaldehyde on stratospheric chlorine chemistry

New measurements are reported of the absorption cross sections of formaldehyde at 296 K and 223 K. These measurements are significantly lower than those reported in the earlier literature at ca. 353 K. The implications of the lower absorption cross sections for stratospheric chlorine chemistry are considered using a one dimensional atmospheric model. A slight modification to ClX partitioning is predicted for the new cross sections, with only a small effect on estimated chlorine-catalyzed ozone perturbations.     

The stratospheric abundance of Hypochlorous Acid (HOCL)

New measurements of the absorption cross-section of HOCl suggest that this molecule may be more stable to photolysis than had been previously thought. These results, combined with recent measurements of the rate of formation, suggest that significant concentrations of HOCl could form in the stratosphere. In the present study, model calculations incorporating HOCl are discussed. The results are compared with available stratospheric measurements for chlorine species, and with calculations not including HOCl. It should be possible to detect HOCl in the stratosphere using i.r. techniques.     

Seasonal physical–chemical structure and acoustic Doppler current profiler flow patterns over multiple years in a shallow, stratified estuary, with implications for lateral variability

The overall goal of this study was to strengthen understanding of the hydrographic structure in shallow estuaries as influenced by seasonal and depth-dependent variability, and by variability from extreme meteorological events. The mesohaline Neuse Estuary, North Carolina, U.S.A., which was the focus, receives surface inputs from upriver and tributary freshwater sources and bottom inputs from downriver high-salinity sound water sources, resulting in varying degrees of stratification. To assess depth-dependent, estuary-wide changes in salinity, a multiple time series was created using data from four discrete depths (surface and 1, 2, and 3 m±0.25 m). The database was developed from weekly to biweekly sampling of the entire water column, and included side-channel as well as mid-channel data. We characterized seasonal differences in halocline depth affecting the hydrographic structure of the mesohaline estuary and site-specific variation in nutrient concentrations, based on a comprehensive eight-year physical/chemical database. The first two years of the record showed an expected seasonal signal and included events that impacted the surface layer from freshwater inputs. Remaining years had greater variability over seasons and depths, with freshening events that affected all depths. Halocline depth was compared at specific locations, and a “snapshot” view was provided of the relative depth of these water masses within the estuary by season. We also examined flow patterns at the same cross-estuary sites over a three-year period, using a boat-mounted acoustic Doppler current profiler (ADCP) with bottom-tracking capability. Composite visualizations constructed with single-transect ADCP data revealed a classical estuarine circulation pattern of outflow at the surface/southern shore and inflow at the bottom/northern shore. Although this pattern deviated under extreme climatological events and was sometimes variable, the estuary generally exhibited a high probability of direction of flow. Wind fields, hurricanes, and small-scale, high-precipitation events represented significant forcing variables.     

Low abundance of the dinoflagellates,Pfiesteria piscicida, P. shumwayae, andCryptoperidiniopsis spp., in South Carolina tidal creeks and open estuaries

The toxicPfiesteria complex are a group of dinoflagellates that have received considerable attention in recent years as causative factors in fish kill or lesion events in North Carolina estuaries and in the Pocomoke River of Chesapeake Bay. In response to the potentialPfiesteria threat, the South Carolina Task Group on Harmful Algae was formed in late 1997 and implemented programs to monitor harmful algal blooms and respond to fish kills or lesion events with particular emphasis on the Bushy Park (Cooper River, Charleston) region, a site of annually recurrent menhaden lesion events.Pfiesteria piscicida, Pfiesteria shumwayae, andCryptoperidiniopsis spp. were documented in South Carolina estuaries. Routine monitoring and fish kill or lesion event sampling consistently indicated low abundances compared to estimates from similar programs in North Carolina and Maryland that sampled areas with a history ofPfiesteria toxic activity. The finding thatPfiesteria-like organism (PLO) abundances were always low in samples collected during menhaden lesion events in Bushy Park suggested other causes for lesion progression, althoughPfiesteria spp. could not be ruled out as a factor in lesion initiation. Based on the previously demonstrated positive relationship between PLO abundance, chlorophylla, and inorganic nutrient concentrations (in laboratory experiments and North Carolina field observations), we hypothesized that the relatively low abundance ofPfiesteria spp. and other PLO (e.g.,Cryptoperidiniopsis) in South Carolina estuaries is related to the relatively low supply of phytoplankton prey, as supported by interstate comparisons in chlorophylla concentrations. Nitrate concentrations were generally much lower in South Carolina estuaries. Estuarine eutrophication may be an important consideration in explaining interstate differences in susceptibility toPfiesteria-related toxic events.     

Discovery of the “Phantom” dinoflagellate in Chesapeake Bay

Since its discovery in natural estuarine habitat of North Carolina in 1991, the widespread impact of the toxic dinoflagellate, Pfiesteria piscicida (gen. et sp. nov.), popularly called the “phantom” dinoflagellate, on North Carolina fish stocks has been established, yet little is known about its influence outside of North Carolina estuaries. Here, we document the presence of P. piscicida in Chesapeake Bay. A fish kill was observed after inoculating an aquarium containing mummichogs with sediment samples from Jenkins Creek, a brackish creek (salinity 11‰) of the Chesapeake Bay system. P. piscicida was the cause of the kill, as supported by morphological, physiological, and histological evidence. The appearance and behavior of the algae and symptoms associated with fish mortality were consistent with those previously observed in P. piscicida-associated aquaria fish kills in North Carolina. The discovery of P. piscicida in Chesapeake Bay supports the speculation that these toxic dinoflagellates have a dramatic and far-reaching impact on fish stocks in shallow, eutrophic estuaries along the eastern United States.