If the world depends on fossil fuels for its energy needs over the next two centuries, the U.S. National Academy of Sciences/National Research Council report Energy and Climate foresees the possibility of a peak atmospheric concentration of carbon dioxide of between 4 and 8 times the preindustrial level as occurring in A.D. 2150 to 2200. Climatic models of the general circulation of the atmosphere predict a 2–3°C rise in average temperature of the atmosphere for each doubling of the carbon dioxide content. Thus, a mean value of about 6°C increase in average atmospheric temperature would be anticipated if the models prove to be accurate and if the growth scenario used in the report were to be realized.

Carlyle Lake is typical of north-temperate Canadian Shield lakes both morphometrically and in its thermal and oxygen structure; however, the Lake is chemically unusual. Input of acidic melt-water in the spring of 1974 depressed the pH of the Lake to 4.5. The buffering capacity of the Lake has been reduced to such a degree that summer pH levels are about 5.0.

Despite this relatively high acidity, the biomass of the phytoplankton community is not low for an oligotrophic circumneutral lake. Although some evidence exists that phytoplankton community biomass is reduced in lakes of pH about 4.5 or below, no such reduction was observed in Carlyle Lake. However, as the numbers of phytoplankton species are reduced when lake pH levels fall below about 5.6, it would appear that community diversity is a more sensitive indicator of acidification of lakes than is community biomass.

The levels of four sets of pollutants (heavy-metals, artificial radionuclides, petroleum components, and halogenated hydrocarbons), have been measured in U.S. coastal waters, using bivalves as sentinel organisms. The strategies of carrying out this programme are outlined and the results from the first year's work are given. Varying degrees of pollution in U.S. coastal waters have been indicated by elevated levels of pollutants in the bivalves, which comprised certain species of mussels and oysters and were collected at over one hundred localities.

Increasing evidence indicates that a major portion of the enormous amount of polymorphism present in natural populations is maintained by natural selection. This polymorphism is necessary for adaptation. In the absence of a suitable amount of genetic diversity, a species will tend to die out in a changing environment.

The genetic diversity of most species has been considerably reduced in historical times. Breeding for uniformity, and reduction in the number and size of wild populations, are largely responsible for this loss. Replacement of a natural forest ecosystem by modern agriculture reduces the genetic diversity by three orders of magnitude at the very least. A comparison of the estimated prehistoric and present amount of genetic diversity leads to the alarming conclusion that we may already have lost as much as 90% of the total genetic diversity of the biosphere. Further loss is expected because of the rapid growth of human population.

Until very recently, knowledge of the feasibility of employing biocontrol against blackflies (Simuliidae) lagged far behind that concerning the prospects for mosquitoes (Culicidae). As recently an the overall review of biological control of vectors by Legner et al. (1974), the only field trial mentioned was an attempt in 1931 to use certain dragon-flies and a predacious chironomid against New Zealand blackflies. Apparently the results of this effort were not followed up. Jenkins's 1964 compilation included two reports of parasitoids (Braconidae, Scelionidae) from European and North American blackflies, yet other species of such entomophaga are known to be important biocontrol agents of certain economically significant arthropods. While neither predators nor parasitoids seem likely to be of practical significance as massproduced and field-liberated blackfly control agents, understanding of the role of such enemies in natural population limitation of Simuliidae (Service & Lyle, 1975) is clearly fundamental to the devising of selective integrated control methodologies that will minimize adverse effects to such already-operating agents.

The distribution of rainfall in Sudan, despite its generally low value, is also highly seasonal in character. The country is therefore dependent on its river system for perennial irrigation for reliable agricultural production. At present about 4.6 million acres (1.9 million ha) are under irrigated agriculture. In all these areas, the system of irrigation is achieved by a gravity-flow method based on hydraulic principles which take maximum advantage of land contours. It consists of hierarchies of supply and distributive canals. The lower stages of these hierarchies, called Minor-canals, produce ponding conditions and are thus very favourable for extensive growth of aquatic weeds (macrophytes).

Because future agricultural development will be based on gravity-flow, and for economic reasons, attention is focused on the increasing extent of this man-made aquatic habitat in the arid region of central Sudan.

The biological and geological importance of mangroves in coastal environs is well recognized. These halophytes contribute leaf-fall to marine food-webs, act as sediment stabilizers, and serve as a habitat for quite numerous organisms (Odum, 1971; Carlton, 1974; Walsh, 1974). They are consequently of considerable ecological and environmental significance. Attempts to revegetate coastal areas that have become denuded of valuable mangrove cover are also important environmentally and have involved two approaches: planting propagules (seedlings) or transplanting older, established plants (Teas, 1977).