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In situ measurements by calcite and aragonite saturometry in the intermediate waters of the northeastern Pacific, indicate that these waters are close to saturation with respect to calcite. It is proposed that the carbonate compensation depth in this region is mainly controlled by the degree of carbonate saturation of ocean waters. If this suggestion is correct, then the carbonate compensation depth can be shown to be directly related to the alkalinity and nutrient cycles in the oceans. Three independent factors seem to control the depth of carbonate compensation: bottom topography, nutrient recycling rate (oceanic mixing) and a dependency factor relating biogenic CaCO 3 production to nutrient availability.

The ecological stability of Lake George is illustrated by the relatively small biomass fluctuations that occur in the fauna and flora of the lake. For the phytoplankton it is shown that the gradient of these oscillations is within the range depicted by a specific rate of population increase of +0.05 to -0.05 day -1 . The relative stability of the phytoplankton community is discussed in the terms of a mathematical model (Tailing 1957, 1971) which interrelates the variables, photosynthesis, respiration, biomass and the underwater light climate. Examples of the interrelationship, and the extreme susceptibility of either a positive or a negative increase rate to diurnal environmental changes, are drawn from both long and short term measurements in Lake George. The optical characteristics of the water column are shown to be very dependent upon the mixing regime sustained over the previous 24 h. The occurrence of negative or positive increase rates is dependent not only upon the incident radiation but also upon the wind induced turbulence. It is shown that, given measurements of the rates of photosynthesis and respiration and the other variables included in Tailing’s model, the biomass at which the Lake George phytoplankton will stabilize is predictable. Although light is likely to limit photosynthesis under all circumstances in Lake George, it is demonstrated that a more favourable photosynthetic response to the light climate may be induced by nutrient enrichment of the nutrient-poor phytoplankton. Because nutrient enrichment can induce increased photosynthetic capacity values, the rates of nutrient supply are thought to be major factors in controlling the ecological stability of the phytoplankton. The mixing regime of the lake is of paramount importance in the decomposition of the sediments and the rate of nutrient release from them. The importance of the nutrient recycling via zooplankton excretion is compared with the total input of nitrogen and phosphorus to the lake. That the ecological stability of the lake is a delicately balanced equilibrium between climate and biota is illustrated by calculations on the oxygen budget of the water column, and by the occurrence of fish-kills. The general characteristics of the lake are discussed in the context of the problems associated with eutrophication.

Inorganic and organic metabolites, including carbohydrates, amino acids, and organic acids, may be leached from the foliage of 125 diverse plant species by the action of rain, dew, and mist. Ca45, p32, and Sr89 absorbed by roots, and C14 absorbed as C1402 by foliage were leached from squash leaves and were subsequently reabsorbed by the roots and translocated to the aboveground parts of several plant species. This phenomenon of nutrient recycling is apparently a widespread natural phenomenon and has implications in plant nutrition. Bean plants were grown through 1 complete generation on the leachates from squash leaves. Leaching and reabsorption of the leachates are important in the distribution of fallout products, in the stimulation and suppression of plants beneath the spread of other plants, in plant competition, and in the development of

Sediments of deep Canadian shield lakes have a firm mud-water interface and an intricately structured, oxygenated surface. Surface relief is not uniform, but is broken by small ridges and upright chironomid tubes. The sedimentary material behaves like a weak jelly and becomes flocculent only when violently disturbed. Sculpins were observed to rest on and, when started, to hide in the oxygenated layers. Sequestering of nutrients in the bottom sediments is enhanced by the structuring of the substrate surface below 10 meters, and may inhibit nutrient recycling at overturn.