Use of Cell-Specific PAM-Fluorometry to Characterize Host Shading in the Epiphytic Dinoflagellate Gambierdiscus toxicus

Abstract. Cell‐specific fluorescence characteristics were used to characterize the light tolerance of the toxic benthic dinoflagellate Gambierdiscus toxicus. The fluorescence parameter F_v : F_m was measured using pulse amplitude modulation (PAM) fluorometry on individual cells collected from foliose red algae growing in the sub‐tidal margin of South Water Cay, Belize. Samples were collected over several days during sunny and cloudy conditions and compared to samples incubated in situ. The data from individual cells were used to generate both F_v : F_m frequency histograms and averages. Maximum individual cell values of F_v : F_m reached 0.81 in pre‐dawn samples, a value near the theoretical maximum for PAM fluorometry. In field samples from macroalgal hosts, average F_v : F_m values declined only slightly during the day, but cells incubated in bottles under 47 % incident sunlight showed a significant mid‐day depression. In freshly collected samples, near‐maximum F_v : F_m values could be found in individual cells during the entire day; however, the frequency histograms indicated a greater range in F_v : F_m values during the afternoon than in the morning. In contrast, cultures of G. toxicus showed a tight distribution around a mean. Field samples showed a rapid recovery to near‐maximum F_v : F_m within 2 min when assayed using a standardized actinic light series. Similar results were obtained in laboratory cultures of G. toxicus grown at 73 µmol photons · m^‐2 · s^‐1, but not at 383 µmol photons · m^‐2 · s^‐1. These data provide empirical support for suggestions that G. toxicus exploits the three‐dimensional structure of the algal host thallus to minimize light exposure. This strategy permits G. toxicus, a high‐light intolerant species in culture, to thrive in shallow, well‐lit tropical seas. It may also partially explain the observed preference of G. toxicus for complex, foliose macroalgae as hosts.     

Factors regulating benthic food chains in tropical river deltas and adjacent shelf areas

Benthic food chains of the Amazon (Brazil) and Fly (Papua New Guinea) river deltas and adjacent shelves are compared. Abundance patterns of the major trophic groups (bacteria, meiofauna, and macroinfauna) are similar between regions, with very low densities, or the absence of benthos, within and near the deltas. For muds in the more quiescent areas, benthic abundance and productivity are highest, commonly coinciding with maximum pelagic primary production. Episodes of physical disturbance, erratic food supply, and dilution of river-derived, particulate organic matter foster the development of opportunistic benthic communities of variable diversity and low biomass, dominated by bacteria. These pioneering assemblages are the main food of penaeid shrimp, which dominate the demersal trawl fisheries of both fluvial-dominated regions.     

Modelling the population dynamics of Calanus in the Fair Isle current of northern Scotland

The population dynamics of a marine zooplankton species in the Fair Isle Current off northern Scotland have been investigated by modelling and field study. An age- and weight-structured model of a population of the copepods Calanus finmarchicus and Calanus helgolandicus was embedded in a biomass based ecosystem model comprising nutrients, phytoplankton, and other non-Calanus zooplankton. The model was configured to represent a Lagrangian water column drifting in the Fair Isle Current off the north of Scotland during June 1988, with physical characteristics derived from the results of a three-dimensional hydrodynamic model of the northwest European shelf. The time-series results from the model were compared to data from a semi-synoptic field study by assuming the system to be short-term steady state and transposing the spatially resolved field observations into pseudo-time series along the modelled column drift track. The hydrodynamic model correctly reproduced the general physical characteristics of the system which were destratification of an initially stratified water column as a result of advection through a tidally energetic mixing zone, and subsequent re-establishment of stratification with distance downstream. The biological components of the model were broadly successful at reproducing the main features of the phytoplankton biomass response to the physical processes. The field data indicated that, despite the short-term changes in phytoplankton abundance along the drift track, the stage composition and biomass of the Calanus population was relatively stable. However, the model revealed that the main diagnostic features of the response were at the individual level, reflected in the weight at age distribution and reproductive output. The study highlights the difficulty of obtaining adequate data for testing complex models of zooplankton responses to short-term spatio-temporal variations in physical forcing.     

Technical considerations in extracting and regulating springwater for public consumption

Many states within the United States as well as many other countries have promulgated regulations addressing public health, consumer protection, and truthin-labeling aspects of the extraction, bottling, and labeling of commercially bottled springwater intended for public consumption. Many of these regulations are inconsistent, suggesting a need for more uniform standards in acceptable extraction methods and legal/technical definitions of spring and springwater. An objective of the extraction or collection method is protecting the quality and integrity of the springwater, especially against microbial contamination. A summary of microbiological issues associated with groundwater and springwater is presented. Acceptable extraction methods can be either surface collection boxes/houses at the discharge point of the spring or a subsurface borehole or gallery interception system. Although extraction wells can provide total protective isolation of the water, a potential concern with that method is providing assurance that the extracted water is in fact the same water that feeds the adjacent spring. Criteria for testing this requirement are suggested in the paper.     

A powerful new infrared array camera for the NASA Infrared Telescope Facility

We have just finished building a 1.0–5.5 m infrared array camera for the NASA Infrared Telescope Facility based upon the SBRC 256×256 InSb array. After a brief overview of the capabilities of the camera (named NSFCAM), we present some of the first images obtained with this new camera, including results obtained with our realtime shift & add speckle imaging mode.     

Stabilisation of the Stanton Lees Landslip Using an Embedded Pile Retaining Wall

A landslip occurred near the village of Stanton Lees, Derbyshire, UK, in November 2000 following a prolonged period of heavy rainfall. The slip resulted in the gradual, progressive down-slope movement of a steep embankment that was supporting an existing gabion retaining wall and a minor road which was subsequently closed to vehicular traffic. This paper describes the site; the sequence of events leading up to the start of the landslide; an interpretation of the ground conditions and onsite monitoring data; and the engineering works carried out in order to stabilise the slip and return the road to serviceability. The landslip occurred due to the superficial deposits moving over the weathered bedrock after the groundwater levels had been elevated following a prolonged period of heavy rainfall. A stability analysis indicated that the embankment was at a state of limiting equilibrium and its factor of safety on slope instability was found to be particularly sensitive to fairly minor changes in the groundwater levels. The remedial works replaced the existing gabion wall with a new cantilevered, bored pile retaining wall that comprised two rows of piles (600-mm in diameter), which were staggered in plan arrangement.     

锚杆锚固体系中的波系特征研究

采用凝固过程中的混凝土模拟不同物理力学特性的锚固介质,用数值模拟和试验的方法研究了锚固锚杆中的波系及锚固锚杆中界面波的形成过程。数值模拟和试验模拟都表明随着锚固介质力学性质的改变锚杆中传播的波的特性发生改变。锚杆中传播的P波对锚固介质的力学特性非常敏感,随着锚固强度的增加,界面波产生,P波逐渐衰减消失。锚杆中传播的波由原来的P波占主导成为界面波占主导,波在锚固段的传播速度也由杆速度成为界面波波速。界面波的波速与锚固介质的力学性质相关,因此可以用界面波的波速来评价锚杆锚固质量以及计算锚杆锚固段长度。     

The role of terrestrial snow cover in the climate system

Snow cover is known to exert a strong influence on climate, but quantifying its impact is difficult. This study investigates the global impact of terrestrial snow cover through a pair of GCM simulations run with prognostic snow cover and with all snow cover on land eliminated (NOSNOWCOVER). In this experiment all snowfall over land was converted into its liquid–water equivalent upon reaching the surface. Compared with the control run, NOSNOWCOVER produces mean-annual surface air temperatures up to 5 K higher over northern North America and Eurasia and 8–10 K greater during winter. The globally averaged warming of 0.8 K is one-third as large as the model’s response to 2 × CO₂ forcing. The pronounced surface heating propagates throughout the troposphere, causing changes in surface and upper-air circulation patterns. Despite the large atmospheric warming, the absence of an insulating snow pack causes soil temperatures in NOSNOWCOVER to fall throughout northern Asia and Canada, including extreme wintertime cooling of over 20 K in Siberia and a 70% increase in permafrost area. The absence of snow melt water also affects extratropical surface hydrology, causing significantly drier upper-layer soils and dramatic changes in the annual cycle of runoff. Removing snow cover also drastically affects extreme weather. Extreme cold-air outbreaks (CAOs)—defined relative to the control climatology—essentially disappear in NOSNOWCOVER. The loss of CAOs appears to stem from both the local effects of eliminating snow cover in mid-latitudes and a remote effect over source regions in the Arctic, where −40°C air masses are no longer able to form.     

Defining probability of saturation with indicator kriging on hard and soft data

In humid, well-vegetated areas, such as in the northeastern US, runoff is most commonly generated from relatively small portions of the landscape becoming completely saturated, however, little is known about the spatial and temporal behavior of these saturated regions. Indicator kriging provides a way to use traditional water table data to quantify probability of saturation to evaluate predicted spatial distributions of runoff generation risk, especially for the new generation of water quality models incorporating saturation excess runoff theory. When spatial measurements of a variable are transformed to binary indicators (i.e., 1 if above a given threshold value and 0 if below) and the resulting indicator semivariogram is modeled, indicator kriging produces the probability of the measured variable to exceed the threshold value. Indicator kriging gives quantified probability of saturation or, consistent with saturation excess runoff theory, runoff generation risk with depth to water table as the variable and the threshold set near the soil surface. The probability of saturation for a 120 m × 180 m hillslope based upon 43 measurements of depth to water table is investigated with indicator semivariograms for six storm events. The indicator semivariograms show high spatial structure in saturated regions with large antecedent rainfall conditions. The temporal structure of the data is used to generate interpolated (soft) data to supplement measured (hard) data. This improved the spatial structure of the indicator semivariograms for lower antecedent rainfall conditions. Probability of saturation was evaluated through indicator kriging incorporating soft data showing, based on this preliminary study, highly connected regions of saturation as expected for the wet season (April through May) in the Catskill Mountain region of New York State. Supplementation of hard data with soft data incorporates physical hydrology of the hillslope to capture significant patterns not available when using hard data alone for indicator kriging. With the need for water quality models incorporating appropriate runoff generation risk estimates on the rise, this manner of data will lay the groundwork for future model evaluation and development.     

Modelling the DC electrical response of fully and partially saturated Permo-Triassic sandstone

Results from a laboratory investigation into the electrical properties of fully and partially saturated Wildmoor Triassic Sandstone have been modelled using the Archie, Waxman–Smits and Hanai–Bruggeman equations. The results demonstrate the limitation of using simple relationships to describe samples when the matrix resistivity ρ_r is not significantly greater than the saturating electrolyte resistivity ρ_w. In these situations Archie's parameters m and n are not accurately determined. Conversely, the more sophisticated Waxman–Smits and Hanai–Bruggeman models provide parameters that better describe the electrical properties of the rock and are able to identify heterogeneity between samples that would otherwise be missed. The ranges of values for matrix resistivity (49 < ρ_r < 161 Ωm) and cementation factor (1.6 < m < 2.1) obtained from the Hanai–Bruggeman model indicate significant variation between samples. Comparison of laboratory‐determined values for cation exchange capacity (0.06 < Q_v < 0.51 meq/mL) and those obtained from the Waxman–Smits model (0.09 < Q_v < 0.55 meq/mL) indicates a very strong correlation, suggesting this model is appropriate for describing the rock. There is good agreement between parameters modelled using fully and partially saturated versions of both the Hanai–Bruggeman and Waxman–Smits equations, indicating that the data are consistent with these models and that the assumptions made are appropriate.