Water requirements for cultivatingSalicornia bigeloviiTorr. with seawater on sand in a coastal desert environment

The forage and oilseed halophyte,Salicornia bigeloviiTorr., was grown in gravity-drained lysimeters set in open plots of the same crop over two seasons in a coastal desert environment in Sonora, Mexico. The lysimeters were irrigated daily with seawater (40 g l⁻¹salts) at rates ranging from 46–225% of potential evaporation. Biomass and seed yields increased with increasing irrigation depth over the range of treatments. Biomass yields ranged from 13·6–23·1 t DM ha⁻¹, equivalent to conventional forage crops, on seasonal water application depths of 2·3–3·8 m, but were markedly lower at lower irrigation depths. Increasing the irrigation depth lowered the soil solution salinity, resulting in greater growth and water use, and hence leaching fractions that were nearly even over irrigation treatments, averaging 0·5. Evapo-transpiration rose in direct proportion to the irrigation depth. Potential evaporation was estimated by site pan evaporation and by the Blaney-Criddle and Penman models using climatological data; the methods agreed within 15%. The ratio of evapo-transpiration to potential evaporation increased over the growing season and approached 1·5 by pan on the highest irrigation treatment due to the combined effects of high transpiration and high evaporation from the permanently moist soil surface. The best field predictor of biomass yield was the salinity of the soil moisture in the top 15 cm of soil profile, which constitutes the root zone for this crop. Root zone salinity must be kept at 70–75 g l⁻¹for high yields. Although irrigation and drainage requirements were high compared to conventional crops, seawater irrigation appears to be feasible in medium sand and could augment crop production along coastal deserts. The possibility of using this crop for animal production is discussed.     

Examples of ice pack rigidity and mobility characteristics determined from ice motion

A method has been developed to determine ice pack rigidity and mobility using observed ice motion. Using this method, one may determine how solidly the ice pack is frozen in near real-time. In addition, spatial and temporal variations in the freezing and thawing of the ice pack can be studied. Various degrees of ice rigidity were considered using remotely-sensed ice motion off the N coast of Alaska during 1975 and 1979. Summer-time ice rigidities were detected first in late June 1975 and lasted through September 1975. However, in 1979 considerably higher rigidities were found in August while summer-like rigidities were detected into late November. Analyses of atmospheric pressure distributions suggest that less mechanical breakup occurred in the summer of 1979, resulting in the greater rigidities during August of that year. In addition, minimum ice coverage was 21% less in the Beaufort Sea in 1979 than in 1975. The result was a relatively large percent of thinner ice for November of 1979 than for 1975, the likely cause of the less rigid conditions detected during the fall of 1979.Nomenclature D deviation in height (m) of a pressure level from the standard atmosphere (Huschke 1959). - e_T time lag (h) at which the autocorrelation of ice speed drops to e^–1 - SL the large-scale disturbance or longwave component of a scalar field; in this study, the 500 mb circulation (Holl 1963). - U mean ice speed over a given time interval - V variance of ice speed over a given time interval     

Rural settlements,mission settlements and rehabilitation in Transkei

During the 19th century the predominant form of rural settlement in Transkei was that of dispersed homesteads. The form of the homesteads tended to differ from tribe to tribe, while the homesteads of various tribal groups were separated from each other by uninhabitated areas, or buffer zones. During the 19th century mission settlements were introduced to Transkei, some of which developed into towns.In the 20th century, mainly as a result of government action, homesteads have been nucleated into rural settlements and villages and much of the land has been fenced. A few peri-urban and industrial villages also exist in Transkei. Over 95% of the population of Transkei in 1980 were still rural dwellers.     

Chlorite-illite/muscovite interlayered and interstratified crystals: A TEM/STEM study

Phyllosilicates in rocks which are transitional from mudstone to slate from Lehigh Gap, Pa., have been studied by a variety of techniques, including high resolution Transmission Electron Microscopy and Analytical Electron Microscopy. The principal minerals are white mica which is transitional from illite in mudstone to ordered twolayer mica in slate, and chlorite. 7Å berthierine occurs more rarely. Dioctahedral and trioctahedral layers are shown to be interleaved in individual crystals at all scales between the following two end members: (1) both random and regular 11 interlayering at the scale of individual layers, as shown, in part, by lattice fringe images. (2) packets of trioctahedral and dioctahedral layers up to a few thousand Ångstroms or microns in thickness, detectable with ordinary optical techniques. The complete range of intermediate structures is represented in samples which are in transition to slate. Bulk analytical (EMPA), X-ray diffraction or other measurements are shown to result in averages over both kinds of layers when TEM techniques are not used.Contribution No. 400 from the Mineralogical Laboratory, Department of Geological Sciences, The University of Michigan     

The relationship between dissolved humic acids and soluble iron in estuaries

Dissolved humic acid and soluble iron appear to be chemically unassociated in estuaries despite their coincident removal. This conclusion is supported by differences in the aggregation kinetics of soluble iron and dissolved humic acid, the inability of extracted humic acid to stabilize laboratory preparations of ferric hydroxide, and decreasing ratios of humic acid carbon to soluble iron along the axes of some estuaries.     

Latitudinal patterns in seagrass epifauna: Do patterns exist,and can they be explained?

Seagrass-associated epifauna of several taxa constitute a major parallel element of seagrass communities over a range of latitudes. Hypotheses relating to latitudinal variation of several factors (e.g., predation, competition, primary production, habitat structure, stability and time) have been proposed to explain geographic variation in the structure of biological systems. We have summarized available information to firstly determine whether any latitudinal patterns exist for the seagrass-associated epifauna, and secondly to examine hypotheses which might explain observed patterns. Diversity and density of various seagrass epifaunal groups showed inconsistent latitudinal patterns. Diversity of decapod and amphipod crustaceans increased significantly with decreasing latitude, while diversity of isopods and fishes showed nonsignificant trends with latitude. Amphipod diversity was highly correlated with seagrass biomass over the range of latitudes. However, density of amphipods showed no pattern with either latitude or seagrass biomass; large within-site differences may have overwhelmed latitudinal patterns. For seagrass-associated amphipods, two parameters presumably related to predation intensity showed contradictory patterns. Size of individuals generally decreased toward the tropics, yet susceptibility to predators showed weak trends of increasing in the tropics. We found little support for the assumed gradients of those hypotheses proposed to explain latitudinal patterns in biota. Only a weak trend of increasing seagrass production toward the tropics was found; there was no relationship between latitude and seagrass biomass (=habitat complexity in part), epiphyte species richness (=habitat heterogeneity in part), or predator abundance. No data were available comparing actual intensity of predation on seagrass fauna or on proposed gradients of stability and competition. The patterns found were not consistent with the predictions of any single hypothesis. Contrary to evidence from other biological systems, it appears that latitude is, in general, an inconsistent predictor of differences in structure of the epifaunal component of seagrass communities. Although we did find some latitudinal patterns of increasing diversity and susceptibility to predators and decreasing size of individual amphipods toward the tropics, we were astonished by the lack of data supporting the assumptions of hypotheses concerning primary productivity, stability, time, competition, predation and habitat heterogeneity and complexity.     

The pitfalls of thresholding atmospheric dispersion data

Atmospheric dispersion data are invariably corrupted by random noise and perhaps baseline drift giving rise to unreal negative values. This paper shows that the indiscriminate use of thresholding can give rise to large errors in estimates of some key statistical parameters.