Temporal fluctuations and anisotropy of the micrometeoroid flux in the Earth-Moon system measured by HEOS 2

The HEOS detector measures the mass and speed of micrometeoroids in the Earth-Moon system. They are detected by the plasma produced by particle impacts on the sensor. During 2 yr of data collection 384 particles have been registered. As shown earlier (COSPAR 1973), they can be divided into 3 categories according to their temporal distribution: particles that are (1) randomly distributed or (2) appear in “groups” or (3) appear in “swarms” In this paper the origin of the groups and swarms is discussed. For this purpose the article orbits with respect to the Earth and the Moon were traced back. The results imply a lunar origin of the groups, whereas the swarms are correlated with the vicinity of the Earth. In addition, the dependence of the cumulative flux upon the detector's viewing direction indicates clearly an anisotropic particle flux.     

Tidal hydrology and habitat utilization by resident nekton in<Emphasis Type="Italic">Pragmites</Emphasis> and Non-<Emphasis Type="Italic">Phragmites</Emphasis> Marshes

We compared nekton densities over a range of measured flooding conditions and locations withinPhragmites australis andSpartina alterniflora (salt marsh cordgrass) at the Charles Wheeler Salt Marsh, located on the lower Housatonic River estuary in southwestern Connecticut. Nekton were sampled on nine spring high tide events from May to October 2000 using bottomless lift nets positioned between 0–5 and 10–20 m from the creek edge. Flooding depth, duration, and frequency were measured from each vegetation type during each sampling month. Benthic macroinvertebrate density was also measured within each vegetation type in May, July, and September. Frequency of flooding was 52% lower and flooding depth and duration were also significantly reduced inP. australis relative toS. alterniflora. A total of 4,197 individuals representing 7 species, mostlyPalaemonetes pugio (dagger-blade grass shrimp) andFundulus heteroclitus (common mummichog), were captured.P. pugio densities were significantly greater inS. alterniflora as were benthic macroinvertebrate density and taxa richness during May, but not during June or October. Total fish density was not significantly different betweenP. australis andS. alterniflora and was independent of location on the marsh. Significantly more juvenileF. heteroclitus were collected withinS. alterniflora relative toP. australis in June and July, suggesting that recruitment of this species may be lower inP. australis habitat. Fish density generally did not vary predictably across the range of flooding depth and duration; there was a positive relationship between flooding depth and fish density inS. alterniflora. The measured reduction in flooding frequency (52%) withinP. australis at the Housatonic site would result in an average total monthly fish use, expressed as density, of 447 ind m⁻² forP. australis and 947 ind m⁻² forS. alterniflora. WhenP. australis expansion results in reduction of flooding frequency and duration, nekton community composition can change, access to the marsh surface is reduced twofold, and nursery habitat function may be impaired.     

The nature, extent and causes of land degradation in South Africa: legacy of the past, lessons for the future?

The aim of this paper is to reassess the land degradation and desertification problem in South Africa. The country has a wide range of interrelated environmental and development challenges existing in a socio–political context recently subject to substantial change. The paper outlines the fundamental environmental constraints and opportunities that underlie degradation phenomena and illustrates the nature, extent and geographical distribution of the major forms of soil and vegetation degradation in the country. The principal causes of degradation are identified and some important land use and land tenure questions that need to be addressed in the near future are posited.     

Instrumental neutron activation in geoanalysis

Theoretical aspects of instrumental neutron activation analysis (INAA) are discussed. Various applications of INAA to exploration geochemistry are described demonstrating its capabilities and its limitations.Cost, turnaround time, high sensitivity for certain elements, the non-destructive nature of analysis and its precision and accuracy have combined to make INAA an indispensible method for multielement determination on virtually all geological matrices. Humus, vegetation, heavy minerals, lake bottom sediments as well as rocks and soils comprise the major sample types analyzed by INAA. As many as 50 elements can be determined routinely and easily by INAA.     

New perspectives on the Negev continental bridge

In a paper written immediately after the reopening of the Suez Canal in 1975, a question was raised: is the Israeli Negev a viable alternative to the Suez Canal? (Geoforum, 8, 29–32, 1977). The answer posted then was pessimistic — the continental land bridge was seen as having failed to function as a real alternative.Now, two years after the reopening of the Canal, it appears that the land bridge seems to be a more economically viable venture than previously suggested. The amount of cargo in transit over the land bridge and its percentage of the total port of Eilat traffic is increasing despite competition from the Canal. This phenomenon and new perspectives on the Negev land bridge are discussed in this follow-up paper.     

Is the Israeli Negev a viable alternative to the Suez Canal?

The cargo movement over the continental bridge annually since 1970 is shown in Table 2. These figures should be compared with the (dry) volume of trade via Eilat annually (see third column of the same table) and they include the traffic via the continental bridge. From this table it is clear that the amount of cargo in transit over the bridge was not a major component of the total traffic through Eilat.     

Saving farmland,a Canadian program

This paper deals primarily with the steps followed by the Ontario government to save farmland. The development of policy responses to preserve Ontario farmland are not of long-standing duration. Although the Urban Development in Rural Areas (UDIRA) policy announced in 1966, could have led to greater provincial supervision no action was undertaken in the form of direct controls or guidelines until ten years later. In 1976 the government published documents which were to lead to the establishment of Food Land Guidelines. The Guidelines have been effective in preserving farm land but since they have been operative for such a short time it is probably too early to make a definitive statement. The results of hearings with respect to the urbanization of prime tender fruit land in Niagara have shown the Guidelines to be effective in setting boundaries between urban and agricultural uses. Further proof of the durability of the Guidelines in maintaining land in agriculture is evidenced by the low resale rate of farm related lots to non-farm uses.