A percent-of-flow approach for managing reductions of freshwater inflows from unimpounded rivers to Southwest Florida estuaries

The Southwest Florida Water Management District has implemented a management approach for unimpounded rivers that limits withdrawals to a percentage of streamflow at the time of withdrawal. The natural flow regime of the contributing river is considered to be the baseline for assessing the effects of withdrawals. Development of the percent-of-flow approach has emphasized the interaction of freshwater inflow with the overlap of stationary and dynamic habitat components in tidal river zones of larger estuarine systems. Since the responses of key estuarine characteristics (e.g., isohaline locations, residence times) to freshwater inflow are frequently nonlinear, the approach is designed to prevent impacts to estuarine resources during sensitive low-inflow periods and to allow water supplies to become gradually more uvailable as inflow increases. A high sensitivity to variation at low inflow extends to many invertebrates and fishes that move upstream and downstream in synchrony with inflow. Total numbers of estuarine-resident and estuarine-dependent organisms have been found to decrease during low-inflow periods, including mysids, grass shrimp, and juveniles of the bay anchovy and sand seatrout. The interaction of freshwater inflow with seasonal processes, such as phytoplankton production and the recruitment of fishes to the tidal-river nursery, indicates that withdrawal percentages during the springtime should be most restrictive. Ongoing efforts are oriented toward refining percentage withdrawal limits among seasons and flow ranges to account for shifts in the responsiveness of estuarine processes to reductions in freshwater inflow.     

Titan's surface and rotation: new results from Voyager 1 images

We present an analysis of images of Saturn's moon Titan, obtained by the Voyager 1 spacecraft on November 8-12, 1980. Orange filter (590-640 nm) images were photometrically corrected and a longitudinal average removed from them, leaving residual images with up to 5% contrast, and dominated by surface reflectivity. The resultant map shows the same regions observed at 673 nm by the Hubble Space Telescope (HST). Many of the same albedo features are present in both datasets, despite the short wavelength (600 nm) of the Voyager 1 images. A very small apparent longitudinal offset over the 14 year observation interval places tight constraints on Titan's rotation, which appears essentially synchronous at 15.9458±0.0016 days (orbital period =15.945421±0.000005 days). The detectability of the surface at such short wavelengths puts constraints on the optical depth, which may be overestimated by some fractal models.     

Do Stable Isotope Data from Calcrete Record Late Pleistocene Monsoonal Climate Variation in the Thar Desert of India?

Late Pleistocene terrestrial climate records in India may be preserved in oxygen and carbon stable isotopes in pedogenic calcrete. Petrography shows that calcrete nodules in Quaternary sediments of the Thar Desert in Rajasthan are pedogenic, with little evidence for postpedogenic alteration. The calcrete occurs in four laterally persistent and one nonpersistent eolian units, separated by colluvial gravel. Thermoluminescence and infrared- and green-light-stimulated luminescence of host quartz and feldspar grains gave age brackets for persistent eolian units I–IV of ca. 70,000–60,000, ca. 60,000–55,000, ca. 55,000–43,000, and ca. 43,000–25,000 yr, respectively. The youngest eolian unit (V) is <10,000 yr old and contains no calcrete. Stable oxygen isotope compositions of calcretes in most of eolian unit I, in the upper part of eolian unit IV, and in the nonpersistent eolian unit, range between −4.6 and −2.1‰ PDB. These values, up to 4.4‰ greater than values from eolian units II and III, are interpreted as representing nonmonsoonal¹⁸O-enriched “normal continental” waters during climatic phases when the monsoon weakened or failed. Conversely, 25,000–60,000-yr-old calcretes (eolian units II and III) probably formed under monsoonal conditions. The two periods of weakened monsoon are consistent with other paleoclimatic data from India and may represent widespread aridity on the Indian subcontinent during isotope stages 2 and 4. The total variation in δ¹³C is 1.7‰ (0.0–1.7‰), and δ¹³C covaries positively and linearly with δ¹⁸O. δ¹³C values are highest when δ¹⁸O values indicate the most arid climatic conditions. This is best explained by expansion of C₄grasses at the expense of C₃plants at low latitudes during glacial periods when atmosphericpCO₂was lowered. C₄dominance was overridingly influenced by global change in atmosphericpCO₂despite the lowered summer rainfall.     

The Decay of Supersonic and Super-Alfvénic Turbulence in Star-Forming Clouds

Supersonic and super-Alfvénic turbulent motions generate an intricate pattern of shock waves through which the turbulence decays. We here illustrate the spatial structure during shock formation and decay. This revised version was published online in July 2006 with corrections to the Cover Date.     

Supersonic Ambipolar Diffusion: Estimating the Magnetic Field Strength in Protostellar Outflows

The magnetic field plays a crucial role in star formation. It is involved in rotational braking, collapse braking, outflow formation and jet collimation. Direct observations of the field are difficult. However, the field can be indirectly estimated through the field-cushioned C-shocks which produce strong infrared molecular emission lines. In particular, a high field in the outflows will generate the ‘shock absorber’ signature: very broad H₂lines. Such lines are indeed observed. Here we summarise recent progress in C-shock formation and stability. We demonstrate numerically that the Shock Absorbers are evolutionary and stable. The widths of H₂lines then limit the magnetic field strength. A field of 6 mG is suggested for HH 212. This revised version was published online in July 2006 with corrections to the Cover Date.     

The impact-theory interpretation of the distribution of Maria on the lunar surface

The satellite impact interpretation of the surface distribution of lunar maria is presented according to Barricelli and Metcalfe (1969). It is emphasized that the formation of molten rock (lava) which, according to the Apollo 11 findings, seems to have been the origin of the material of which maria are composed, can be the result of heat developed by the impacts which created the respective maria (Gilbert 1893) and does not necessarily imply a volcanic or internal origin of this material.The distribution of mascons and some of its possible interpretations are discussed.Present address: Oslo Universitet, Dept. of Mathematics, Blindern, Norway.     

Corporate management of the Northwestern Hawaiian Islands lobster fishery

Limited entry and biological quotas were implemented in the lobster fishery of the Northwestern Hawaiian Islands in 1991, during a period of declining stock abundance. A companion use-it-or-lose-it permit provision has had the perverse effect of increasing fishing effort during times of declining stocks. Despite its unfavorable short-term prospects, the fishery has the potential to be very lucrative for a small number of boats over the long term. This paper introduces a dramatically different management regime that would create ownership rights in a private management corporation for the current limited-entry permit holders. This corporation would function within a renewable operating contract with the government to protect the public interest in the conservation of the lobster population and its associated ecosystem. Published by Elsevier Science Ltd.