Evolution Of Ponds Research Articles

Seasonal evolution of the albedo of multiyear Arctic sea ice

As part of ice albedo feedback studies during the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment, we measured spectral and wavelength‐integrated albedo on multiyear sea ice. Measurements were made every 2.5 m along a 200‐m survey line from April through October. Initially, this line was completely snow covered, but as the melt season progressed, it became a mixture of bare ice and melt ponds. Observed changes in albedo were a combination of a gradual evolution due to seasonal transitions and abrupt shifts resulting from synoptic weather events. There were five distinct phases in the evolution of albedo: dry snow, melting snow, pond formation, pond evolution, and fall freeze‐up. In April the surface albedo was high (0.8–0.9) and spatially uniform. By the end of July the average albedo along the line was 0.4, and there was significant spatial variability, with values ranging from 0.1 for deep, dark ponds to 0.65 for bare, white ice. There was good agreement between surface‐based albedos and measurements made from the University of Washington's Convair‐580 research aircraft. A comparison between net solar irradiance computed using observed albedos and a simplified model of seasonal evolution shows good agreement as long as the timing of the transitions is accurately determined.

Évolution d'un milieu littoral et remontée du niveau relatif de la mer à l'Holocène supérieur au nord de l'île du Cap-Breton, Nouvelle-Ecosse

The sedimentary sequence in a coastal pond on Cape Breton Island was examined by various analyses (pollen, plant macrofossils, diatoms, and rhizopods). The results allow for the reconstruction of different phases in the evolution of the pond in conjunction with relative sea-level rise during the late Holocene. Throughout the period studied the microflora and microfauna indicate that the pond was mainly freshwater, isolated from the sea by a continuous sand and gravel bar. Three phases in the pond evolution have been identified: (1) the lowermost part of the sequence is characterized by mineral detrital deposits and some marine fossils related to the reworking of bar sediment by storms and high tides washing over the rock sill; (2) this was followed by a rapid filling of the basin by organic detritus provided by shore washing processes; (3) a marsh evolving into a shallow lake completes the sequence up to the interruption by human occupation. The lake-level rise is linked to the formation of the bar, which was controlled by the highest storm-beach level. A submersion rate of 18 cm/century has been calculated using the beginning of the lacustrine phase, which was dated at 2680 years BP (UQ-616).

THE PRACTICE OF GRASS PRAWN (Penaeus monodon) CULTURE IN TAIWAN FROM 1968 TO 19841

ABSTRACTGrass prawn (Penaeus monodon) culture in Taiwan started more than 300 years ago as a by‐product of milkfish (Chanos chanos) culture. Since 1968, however, with the success achieved in larval rearing, prawn farming has developed into a major aquaculture industry.Fifty farmers were interviewed and the information obtained from them was compiled for this presentation. Prawn hatcheries have achieved a state of overproduction today, as postlarvae prices have been driven below cost due to the high number of commercial hatcheries now in operation. The evolution of culture ponds has also gone from a primitive lowdensity type to a well designed high‐density type. Formulated feed, its use and its role in the continuing development of the prawn industry, harvesting techniques and processing procedures are discussed. Prawn diseases remain a problem for some farms and this investigation suggests that further research is required in this area.An economic analysis of cost and profit of both family‐run and commercial farms is presented. A list of fixed and variable costs for operating all types of farms is provided and the relationship between each cost and the final profit is evaluated. The problems facing the grass prawn industry in Taiwan today as well as some future prospects are also discussed.

A Theory of Price Control

PRICE or rent control is but one of many forms of legislative action which interfere with private contracting in the market place. To delimit the scope of my analysis, I shall use the term "price control" to refer only to any set of regulations which satisfies the following three conditions. First, the control must fix the price (or income)' terms of private contracts; this categorically excludes any laws which regulate the distribution of income among the contracting parties on a share or percentage basis.2 Second, the control must involve no appropriation of proceeds to or from the government; taxation and subsidization are thus excluded. Finally, the fixing of price must not be associated with direct government sales, purchases, or manipulation of resources so as to maintain the regulated price;3 by this stipulation, price "support" is also excluded. Even on such terms, legal regulations to control price are still many and varied. To evaluate our understanding of the class of phenomena which we seek to explain it is essential that we discover implications refutable by facts. By this criterion the available body of economic theory pertaining to price control is deficient indeed: the massive literature on the subject offers few such implications.4 An alternative approach to analyzing the observable effects of price control is presented here.

STRATIGRAPHY OF FOSSIL PIGMENTS AS A GUIDE TO THE POSTGLACIAL HISTORY OF KIRCHNER MARSH, MINNESOTA1

Successional developments in the postglacial ecology and limnology of Kirchner Marsh revealed by concentration and diversity of sedimentary plant pigments include a peak of aquatic production (indicated by maximum pigment concentrations in sedimentary organic matter) reached during the early postglacial warm, humid interval at about 10,000 B.P. Production levels then declined. Very low levels of aquatic production (indicated by low pigment concentrations) seem indicated by about 6,000 B.P., in the middle part of a warm, dry interval following which pigment concentrations remained low (except for a brief interval about 5,000 B.P.), but with a marked rise in the ratio of chlorophyll derivatives to carotenoids, indicating an increase in allochthonous organic input accompanying the return of cooler moister conditions. These resulted in an encroachment of oak forest on the prairie, followed by the succession to reed‐swamp on the lake.A return to more truly aquatic conditions was reflected by an increase in sedimentary pigments from about 3,000 B.P. to a peak at 1,700 B.P., accompanied by a decline in the ratio of chlorophyll derivatives to carotenoids. Subsequently pigment concentrations fell, and their ratio increased sharply, as emergent aquatics became well established and caused a rapid evolution of pond to grass‐sedge meadow.The pigment data are generally in harmony with the ecological conclusions from pollen and macrofossils, but they provide much more information on changes in aquatic productivity at the site. Ratios of chlorophyll derivatives to carotenoids, along with measurements of pigment diversity, reveal changes in the balance between autochthonous and allochthonous organic contributions to the sediment and provide substantial evidence for the presence or absence of open‐water conditions.

Geology in tenth century Arabic literature

The Discourses of the Brothers of Purity, an Arabic classic written in the tenth century in Basra, includes remarkably modern geological ideas. An excellent and perfectly acceptable metamorphic cycle is described. The Discourses also contain the earliest known mention of peneplanation, pond evolution, epicontinental seas, weathering, and erosion and transport by streams and the wind.