Submergence Conditions Research Articles

Reclaiming a saline-sodic, sandy loam soil under rice production

A field-plot reclamation experiment was conducted on a virgin saline-sodic, sandy loam, permeable soil while growing rice with pre- and post-planting leaching under conditions of continuous and intermittent submergence. The soil studied contained very high amounts of soluble salts and exchangeable sodium throughout the profile. The chief salts were Cl − and SO 2− 4 of Na +, Ca 2+ and Mg 2+. The data obtained showed that post-transplanting leaching under intermittent submergence alone progressively decreased salinity and sodicity throughout the top 100 cm of the soil to levels safe for cultivation of relatively deep-rooted crops. The surface few centimetres of soil were essentially reclaimed within a few hours after leaching so that young rice seedlings established and survived to give good yield. It was concluded, therefore, that reclamation of these types of soil in arid and semi-arid regions, where good quality water is not available for leaching prior to transplanting rice, would not require any such pre-planting leaching. The results further indicated that there is no need to apply an amendment such as gypsum, mainly because Ca 2+ and Mg 2+ present in such soils are adequate to replace the initially high exchangeable sodium during leaching. Leaching efficiency was high under conditions of intermittent submergence. It was shown that leaching curves could be useful in determining the amount of leaching water required for a given mode of application in order to decrease harmful levels of salinity and sodicity to safer levels for a particular crop.

Field studies on leaching behaviour of a highly saline-sodic soil under two modes of water application in the presence of crops

SummaryThe leaching behaviour of a highly saline-sodic, moderately permeable, sandy-loam soil was evaluated under continuous and intermittent submergence conditions in a longterm field study in the presence of rice and subsequent wheat and sesbania crops. Leaching curves with respect to both desalinization and desodification showed that leaching efficiency was considerably higher with intermittent than with continuous submergence. The curves were useful in determining the amount of leaching water needed for a given mode of water application to reduce harmful levels of salinity and sodicity to acceptable ones. Empirical equations were determined to fit the experimental data. Their comparison with another empirical equation from published bare-field data of this site showed that leaching efficiency under crops was higher than under fallow. From the desodification leaching curve, it is concluded that in reclamation of these soils there is no need of the application of any amendment like gypsum. The soil salinity and sodicity data recorded at different growth stages and crop yields showed that leaching during the rice growing season, under intermittent submergence without previous leaching, decreased salinity and sodicity throughout the top 100 cm of the soil to levels safe for the successful cultivation of rice and subsequently the relatively deep-rooted crops of wheat and sesbania.

Emergence of Crown Roots from the Elongated Culm in Several Floating Rice Varieties under Submerged Conditions

Emergence of Crown Roots from the Elongated Culm in Several Floating Rice Varieties under Submerged Conditions

Geomorphic and hydraulic evolution of tidal creeks on a subsiding beach ridge plain, North Inlet, S.C.

We describe stratigraphic and geomorphic features of a small marsh basin that is in an early stage of evolution under conditions of slow submergence. These features suggest that the tidal creek draining this basin was originally a freshwater stream that has gradually adjusted its hydraulic geometry to an increasing volume of tidal discharge imposed by submergence. A generalized model of the evolution of hydraulic geometry in response to submergence is presented as a complement to the classical Mudge—Davis model of marsh evolution.

Laminated Algal Mats from a Coastal Lagoon, Laguna Mormona, Baja California, Mexico

ABSTRACT Laminated algal mats are well developed at Laguna Mormona, a closed hypersaline lagoonal complex on the west coast of Baja California, Mexico. These mats and underlying organic accumulations attain a maximum thickness of 30 cm. Their morphology is controlled mainly by the degree of desiccation: mound-shaped structures develop under conditions of permanent submergence; flat-topped mounds and horizontal mats broken by desiccation cracks occur in settings where the mats have grown up to the water surface; and mats curved into concave-upward saucers develop under conditions of extreme desiccation. The accumulation rate in these mats is several millimeters per year, with one to several laminae forming per year. Filamentous cyanophytes (viz., Microcoleus chthonoplastes and several species of Lyngbya), a coccoid cyanophyte (Entophysalis sp.), and diatoms contribute to the primary organic deposit which is subsequently degraded and modified by bacterial activity. Sheaths, rather than trichomes, of the oscillatoriacean cyanophytes occur at depth in these mats: this is due largely to the motile nature of the trichomes which glide upward leaving empty sheaths behind. However, it also appears that the sheaths of M. chthonoplastes and Lyngbya aestuarii are more resistant to degradation than are the trichomes, and sheaths of the colonial coccoid Entophysalis are more resistant to degradation than are their cellular contents. Although these modern mats are not being permineralized by silica, many aspects of their macro-structure, lamina structure, and biology are applicable to the interpretation of silicified Proterozoic mats and their contained microbiotas.

Buoyancy and ventilation in Aedes aegypti (L.) pupae (Diptera: Culicidae).

Various aspects of buoyancy in Aedes aegypti (L.) pupae were studied. Gas in the ventral air space is necessary for a pupa to be buoyant and maintain its normal position at the air-water interface. Pupae, under conditions of forced submergence, and commonly spontaneously, lose their buoyancy and reach or exceed the density of water. Contact with the atmosphere usually results in an immediate recovery of buoyancy. These changes in buoyancy are considered to be caused by changes in volume and/or gas pressure in the tracheal system. An hypothetical explanation for the observed changes in buoyancy is presented and aspects of the functional and adaptive significance of buoyancy and changes in buoyancy are discussed.

Stability of Floating Ice Blocks

The critical conditions at which buoyant blocks on a flowing stream are swept under a downstream floating cover are investigated analytically and experimentally. The mathematical model of block stability is based on a one-dimensional hydrodynamic analysis of the flow passing beneath the upstream end of a floating cover, and the force and moment equilibrium of the block. It is argued that the condition of incipient submergence is reached when the block sinks and rotates until the stagnation water surface elevation equals that of the top upstream edge of the block. Experiments to verify the analysis were conducted in a 1-ft wide laboratory flume using right parallelpiped blocks with three different specific gravities and a range of length-thickness ratios. The moment coefficient which arises in the analysis was evaluated by means of the experimental data, which were found to be in good agreement with the analytical results.

Spartinas kolonisation og udbredelse langs Ho Bugt

Spartina sp. (“townsendii” and anglica) was introduced in the Ho Bugt area at Esbjerg in 1931. The investigation is based on a study of a sample area on the peninsula Skallingen during the years 1957, 1960, 1965 and 1970, on litterature and on a survey of the whole bay in 1971. The colonization in the different parts of the bay is described. “Spartina shows an extremely plastic morphological response to the varying conditions of tidal submergence and exposure on different parts of the marsh. This enables it to occupy a wide range of zones occupied in other areas by a series of different plant communities.” (Ranwell, 1964). “It has, in fact, not only taken possession of a vacant ecological niche, but has spread from this to form a serious competition to other salt marsh species of long standing.” (Goodman a.o., 1959).

Communication between Divers in Deep Submergence Atmospheres

There are two obvious peculiarities of divers' speech in deep submergence conditions. At any depth, a diving mask, when worn, has an acoustic reaction on the vocal tract, deteriorating the intelligibility. For depths below 400 ft, the helium atmospheres used, either in a mask or in a habitat, shift the frequency band associated with speech intelligibility upward by as much as a factor of 3. The effects of both can be overcome if a microphone is suitably designed. The upward shift of “Mickey Mouse Effect” is generally credited with destroying intelligibility to such an extent that a downward shifting compensator becomes necessary. By itself, the upward shift does not destroy intelligibility, but there are other effects associated with diving and deep submergence that may make a compensator necessary even for face-to-face conversation in a habitat. At the present time, the performance of compensators is limited by the microphones available.

Spartina Salt Marshes in Southern England: V. Tidal Submergence and Chlorinity in Poole Harbour

An account of the physiography of Poole Harbour in relation to the development of Spartina x townsendii agg. marsh has been given in an earlier paper in this series (Bird & Ranwell 1964). The present paper records the conditions of tidal submergence and chlorinity within which Spartina marshlands are found in Poole Harbour and considers how Spartina and other common marsh plants are distributed in relation to these factors. In spite of its lagoon-like appearance (Bird & Ranwell 1964, Fig. 1), Poole Harbour is a tidal estuary where fresh and sea water meet and mix. It is unusual, not only in its shape and in the fact that it is fed by twin rivers (the Piddle and the Frome), but also in the double high water phenomenon of its tides which are a feature of this part of the south English coast. Consequently, Poole Harbour is an estuarine environment of great complexity. A full investigation of the variations of chlorinity in relation to tides and the weather in the harbour would require intensive studies lasting many years, but limited observations at selected sites are of interest in the absence of detailed information, and it was with this in mind that the present survey was carried out. With the exception of the pioneer studies of Green (1940) and Green, Ovington & Madgwick (1952) on the tidal regime, we know of no other basic work on the estuarine environment in Poole Harbour. Nomenclature is in accordance with Clapham, Tutin & Warburg (1962).

The Effect of Light on the Growth Rate of Two Barnacles Balanus balanoides (L.) and B. crenatus Brug. under Conditions of Total Submergence

The Effect of Light on the Growth Rate of Two Barnacles Balanus balanoides (L.) and B. crenatus Brug. under Conditions of Total Submergence