Nutrient availability in support of Karenia brevis blooms on the central West Florida Shelf: What keeps Karenia blooming?

Identifying nutrient sources, primarily nitrogen (N) and phosphorus (P), sufficient to support high biomass blooms of the red tide dinoflagellate, Karenia brevis, has remained problematic. The West Florida Shelf is oligotrophic, yet populations >10⁶ cells L⁻¹ frequently occur and blooms can persist for months. Here we examine the magnitude and variety of sources for N and P that are available to support blooms. Annual average in situ or background concentrations of inorganic N in the region where blooms occur range 0.02–0.2 μM while inorganic P ranges 0.025–0.24 μM. Such concentrations would be sufficient to support the growth of populations up to ∼3×10⁴ cells L⁻¹ with at least a 1 d turnover rate. Organic N concentrations average 1–2 orders of magnitude greater than inorganic N, 8–14 μM while organic P concentrations average 0.2–0.5 μM. Concentrations of organic N are sufficient to support blooms >10⁵ cells L⁻¹ but the extent to which this complex mixture of N species is utilizable is unknown. Other sources of nutrients included in our analysis are aerial deposition, estuarine flux, benthic flux, zooplankton excretion, N₂-fixation, and subsequent release of organic and inorganic N by Trichodesmium spp., and release of N and P from dead and decaying fish killed by the blooms. Inputs based on atmospheric deposition, benthic flux, and N₂-fixation, were minor contributors to the flux required to support growth of populations >2.6×10⁴ cells L⁻¹. N and P from decaying fish could theoretically maintain populations at moderate concentrations but insufficient data on the flux and subsequent mixing rates does not allow us to calculate average values. Zooplankton excretion rates, based on measured zooplankton population estimates and excretion rates could also supply all of the N and P required to support populations of 10⁵ and 10⁶ cells L⁻¹, respectively, but excretion is considered as “regenerated” nutrient input and can only maintain biomass rather than contribute to “new” biomass. The combined estuarine flux from Tampa Bay, Charlotte Harbor, and the Caloosahatchee River can supply a varying, but at times significant level of N and P to meet growth and photosynthesis requirements for populations of approximately 10⁵ cells L⁻¹ or below. Estimates of remineralization of dead fish could supply a significant proportion of bloom maintenance requirements but the rate of supply must still be determined. Overall, a combination of sources is required to maintain populations >10⁶ cells L⁻¹.     

Pi 2 pulsations and the eastward electrojet: A case study

We report the results of a case study of two Pi 2 pulsations observed near the eastward electrojet by the Scandinavian Magnetometer Array. The power of the two Pi 2 pulsations, calculated using a standard Fast Fourier Transform method, peaks near the centre of the eastward electrojet. For both events there is a strong latitudinal gradient in the power poleward of the equatorward border of the electrojet. The sense of polarisation is predominantly clockwise at the northern stations and anticlockwise at the southern stations although the reversal from clockwise to anticlockwise does not occur at a constant latitude. For the first event the polarisation reversal occurs at higher latitudes in the western half of the array; for the second the polarisation reversal occurs at higher latitudes at the edges of the array. The polarisation reversal does not appear to be related to the location of the eastward electrojet. Equivalent current vectors of the Pi 2 pulsations, obtained by rotating the band pass filtered data through 90°, exhibit clear vortex structures in both events. The vortices change sense of direction at half the period of the Pi 2 pulsation. A simple model for the ionospheric electric field in accord with the field line resonance theory reconstructs the basic features of the observed Pi 2 equivalent current system. We thus conclude that Pi 2 signatures in the region of the eastward electrojet and far away from the auroral break-up region are governed by the field line resonance mechanism.     

Rapid incision of the Colorado River in Glen Canyon – insights from channel profiles,local incision rates,and modeling of lithologic controls

The Colorado River system in southern Utah and northern Arizona is continuing to adjust to the baselevel fall responsible for the carving of the Grand Canyon. Estimates of bedrock incision rates in this area vary widely, hinting at the transient state of the Colorado and its tributaries. In conjunction with these data, we use longitudinal profiles of the Colorado and tributaries between Marble Canyon and Cataract Canyon to investigate the incision history of the Colorado in this region. We find that almost all of the tributaries in this region steepen as they enter the Colorado River. The consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels, and their coincidence within a corridor of high local relief along the Colorado, suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem. This analysis makes testable predictions about spatial variations in incision rates; these predictions are consistent with existing rate estimates and can be used to guide further studies. We also present cosmogenic nuclide data from the Henry Mountains of southern Utah. We measured in situ ¹⁰Be concentrations on four gravel‐covered strath surfaces elevated from 1 m to 110 m above Trachyte Creek. The surfaces yield exposure ages that range from approximately 2·5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m/my. These incision rates are similar to other rates determined within the high‐relief corridor. Available data thus support the interpretation that tributaries of the Colorado River upstream of the Grand Canyon are responding to a recent pulse of rapid incision on the Colorado. Numerical modeling of detachment‐limited bedrock incision suggests that this incision pulse is likely related to the upstream‐dipping lithologic boundary at the northern edge of the Kaibab upwarp. Copyright © 2009 John Wiley & Sons, Ltd.     

Spatial and Temporal Variability in Estuary Habitat Use by American Alligators

Estuarine habitat occupied by Alligator mississippiensis, a primarily freshwater species, is spatially and temporally heterogeneous largely due to a salinity gradient that fluctuates. Using long-term night light survey data, we examined seasonal patterns in alligators’ habitat use by size classes in midstream and downstream estuary zones of Shark River, Everglades National Park, in southern Florida. We observed predominantly large-sized alligators (total length?≥?1.75 m); observations of alligators in the small size classes (0.5 m?≤?total length?<?1.25 m) were rare especially in the higher-salinity downstream zone. The density of alligators in the downstream zone was lower than that of the midstream zone during the dry season when salinity increases due to reduced precipitation. Conversely, the density of the large size alligators was higher in the downstream zone than in the midstream zone during the wet season, likely because of reduced salinity. We also found a significant declining trend over time in the number of alligators in the dry season, which coincides with the reported decline in alligator relative density in southern Florida freshwater wetlands. Our results indicated high adaptability of alligators to the fluctuating habitat conditions. Use of estuaries by alligators is likely driven in part by physiology and possibly by reproductive cycle, and our results supported their opportunistic use of estuary habitat and ontogenetic niche shifts.     

International solar terrestrial energy programme and the UK participation

The Solar Terrestrial Energy Programme (STEP) aims to improve our general understanding of how mass, energy and momentum are transferred between the various regions that form the Solar Terrestrial environment. STEP began in 1990 and will continue until 1997, during which time a number of major new spacecraft and ground-based projects will become operational. Six Working Groups form the basis of STEP, covering topics such as the Sun as a source of energy and disturbance, energy and mass transfer through the interplanetary medium and the magnetosphere-ionosphere system, ionosphere-thermosphere coupling and response to energy and momentum inputs, middle atmosphere responses to forcing from above and below, solar variability effects in the human environment, and informatics. A Royal Astronomical Society Geophysics Discussion meeting took place in March 1992 to draw to the attention of UK scientists the diverse nature of STEP and the opportunities offered by STEP. This paper consists of individual sections prepared by the speakers at the meeting and which cover most of the STEP Working Group topics. The main aims of each section are to provide a benchmark for the present status of the research area and to look ahead to the possible contributions that UK scientists can make during STEP.     

Butyltin compounds in a sediment core from the old Tilbury basin, London, UK

Sections from a sediment core taken from the River Thames were analysed for butyltin species using gas chromatography with species-specific isotope dilution mass spectrometry. Results demonstrated that in most samples tributyltin concentrations of 20–60 ng/g accounted for <10% of the total butyltin species present, which is in agreement with data from other sediment samples which were historically contaminated with tributyltin. Vertical distribution of the organotin residues with depth throughout the core, with data on organochlorine compounds and heavy metals allowed for the construction of a consistent hypothesis on historical deposition of contaminated sediments. From this it was possible to infer that the concentrations of tributyltin in sediments deposited during the early 1960s were in the order of 400–600 μg/g by using degradation rate constants derived by other workers. Such values fall well within the range quoted for harbour sediments in the literature.     

Adaptive Management of Urban Ecosystem Restoration: Learning From Restoration Managers in Rhode Island,USA

Urban aquatic restoration can be difficult to accomplish because of complications like industrial pollutants, population density, infrastructure, and expense; however, unique opportunities in urban settings, including the potential to provide benefits to many diverse people, can make urban restoration especially rewarding. The success of urban restoration projects—even those focused primarily on ecological targets—depends on community involvement and managers considering community needs. However, research on the social barriers to urban restoration and strategies managers use to overcome them is relatively rare. This work attempts to fill that gap by presenting barriers for aquatic restoration projects in urban settings and strategies to overcome them. Building from interviews with restoration managers involved in urban aquatic restoration projects in Rhode Island, we contribute through an adaptive management approach: identifying and synthesizing the lessons learned from managers’ work in urban settings. Ultimately, we suggest potential for double- and triple-loop learning by disentangling and critiquing the frames and policy/power structures that influence decision making in urban aquatic restoration.     

Initial backscatter occurrence statistics from the CUTLASS HF radars

A statistical study of the occurrence of ground and ionospheric backscatter within the fields-of-view of the CUTLASS HF radars, at an operating frequency of 10 MHz, during the first 20 months of operation has been undertaken. The diurnal variation of the occurrence of backscatter and the range at which such backscatter is observed is found to be highly dependent on seasonal changes of the ionospheric electron density in both the E and F region, determined from ionosonde observations. In general, ionospheric backscatter is observed at far ranges during the local day in winter months and at near ranges during the local night in summer months. The Iceland radar observes more near-range E region backscatter than the Finland radar as a consequence of its more zonal look-direction. The dependence of the occurrence of backscatter on geomagnetic activity and radar operating frequency are also investigated. The occurrence of ground and ionospheric backscatter is discussed in terms of HF propagation modes and ionospheric electron densities as well as geophysical processes. A brief assessment of the possible impact of solar cycle variations on the observations is made and frequency management is discussed. Such a study, with its focus on the instrumental aspect of backscatter occurrence, is essential for a full interpretation of HF coherent radar observations.     

SuperDARN: An example of a network approach to geospace science in the twenty-first century

The study of Earth's space environment, or geospace, has made considerable advances in the 50 years since the start of the Space Age, which was coincident with the 1957 International Geophysical Year. Space probes have visited most parts of that environment providing a wealth of in situ and remote-sensing measurements. Equally important in contributing to the advances made over the last 50 years have been the many instruments, which have been distributed on the surface of the Earth. In particular, the development of networks for the specific purpose of studying the dynamics of geospace, energy redistribution within geospace, and fundamental physical processes in plasmas has been hugely successful. Ground-based instruments remotely sense processes and phenomena in geospace and since this volume is large, networks of such instruments are the best way of measuring the global state of geospace and its dynamics. In this paper, I describe ways in which the Super Dual Auroral Radar Network (SuperDARN) has contributed to the success of ground-based networks, concentrating on science results, which have required the network approach so well demonstrated by SuperDARN. Such science includes the remote sensing of the reconnection electric field and its dynamics, the study of processes where asymmetries in the geospace system are induced by the external driving forces, and MHD waves, which play an important role in the transfer of energy and momentum within geospace. In addition, I discuss open science questions, which can be addressed by SuperDARN in the future, in particular in conjunction with current and future space missions as well as other ground-based networks.