Dr Abe V Rotor
Paaralang Bayan sa Himpapawid with Ms Melly C Tenorio
738 DZRB AM Band, 8 to 9 evening class, Monday to Friday
A pond is a transient environment. Unlike a stream, river, or lake, it has feeble currents or none at all. It is surrounded by thick vegetation which, advances towards the pond as it grows older. As the pond fills up with sediments and muck, and its bottom gradually drains, higher plants become progressively abundant.
Hut by a Pond, painting by the author
At this stage, it is impractical to stratify the water into zones based on depth since the forces of wind and convection keep the whole volume of water in circulation so that at any depth the temperature is fairly uniform and the amount of gases, notably oxygen and carbon dioxide is equally distributed.
The relatively large ratio of surface to volume of ponds make them most susceptible to weather and climatic changes than large bodies of water. Because of their small size they are also susceptible to changes in physiographic conditions like erosion and deposition. Likewise they suffer much effect from pollution, changes in the chemical composition of the water, and the influence of the biota on their physical structure.
Like any community a pond grows, passes a relatively stable mature phase, and ultimately dies. This basic ecological cycle is a result of interplay between organisms and their environment. Organisms live in an environment where they are adapted, and remain in the most stable area or niche which best spells out their success as population and members of an interacting ecosystem.
The physical nature of the environment consequently determines what types of organisms can settle successfully. Temperature, rainfall, altitude, soil conditions and other abiotic factors decisively influence the kinds of plants that survive in a given locale. Vegetation in turn, as well as the animals, have selected effects on the kind of biotic community in that region. The presence of a set of organisms gradually alters the local conditions. Raw materials are withdrawn from the environment in large quantities, and metabolic wastes are returned together with dead organisms, but of another form and in different place, thus resulting to redistributions and alterations of vast quantities of substances.
This means that later generations of the original organisms may find the altered local environment no longer suitable for themselves so that the members of the community must resettle elsewhere or die out. Later a new community of different plants and animals arrive and settle down. Again this new community will alter the area according to its own specialization. Hence, it is said that the living and non-living parts of the environment are vitally interlinked, that changed in one produces change to the other.
As a typical ecosystem, a pond relates a classical story. Most ponds must have originated during the last ice age when the moving glaciers scraped out giant sinks. Others have been known to have originated from a portion of a bay or lake which was isolated by a sandbar by the action of waves and wind. Pirated rivers may also form into ponds. Most of the newly formed ponds may be wiped out days, months or years later, by storm or silt deposition. But a better-protected pond survives the drastic geologic fate. It must somehow face the slow process of ecological succession through which continuous dynamic processes take place that will ultimately lead to the accumulation of organic matter and silt.
On the functional aspect of ecological succession, like in any lentic communities, the progressive increase of organic matter which fills up the pond will lead into a heterotrophic conditions which means that the dependent organisms (heterotrophs) will increase in proportion to the increase of the producers (autotrophs). This results to an increased gross production of aquatic and semi-terrestrial organisms, and therefore, increased heterotrophy.
The placenta of life in a lentic environment is the fertile bottom. The mudflat is actually a part of the bottom of the pond that intermittently comes out for a quick drying only to be submerged like in a cycle, incubating impregnation of eggs and dormant lives. The mudflats are therefore exposed and submerged at intervals depending upon the amount of water that enters the pond from the headend and from the surrounding watershed. As the remaining aquatic zone further shrinks and the water flow meanders along the bottom, wider flats are formed.
No zone in the pond is richer in variety and in number of living things, and no types of interrelationships could be more complex, if not deceiving or unknown, than the aquatic zone where life continues on n some amazing and mystic ways. There are evidences that these dynamic changes shall go on until the pond has completely transformed into a terrestrial ecosystem, despite such threat of pollution which may had already marked the face of the pond, and had turned the tide of balance in nature.
But nature proves flexible with change. Normal changes would simply be dismissed by Nature’s own way of adjusting the role of it’s own creatures. Changes shape the conditions of the environment; Nature shape its organisms to fit better into it.
The bottom of the pond is directly affected by the amount of water and by water flow. It is the recipient of silt and other sediments from plant residues from the surrounding watersheds and from the immediate shoulders of the pond. The decreasing area occupied by water may indicate that age of the pond, and the changes which, undoubtedly lead towards an irreversible transition from aquatic to terrestrial state.
Typical of old ponds and lakes, the aquatic zone considerably decreases with the lack of water supply and by the steady deposition of silt and decomposing plant remains- not to mention the garbage and other wastes thrown into the pond by unscrupulous residents in the area. The black, spongy and fertile are an envy of many plant species and consequently of the dependent animal organisms. From time to time pioneer plants venture for a try to settle every time terrestrial conditions begin to prevail. But in many parts of the old exposed bottom left by the receding water, terrestrial plants can not settle down because time and again the water immediately submerges the previously baked flats to become once more a slosh of mud that readily shallows a wader to his knees. And so the outcome of the battle turns to the advantage of the water plants- Eichhhornia, Alternanthera, Jussiaea, and Pistia, and of course to the ever-present thick scums of blue-greens and green algae with their co-dependents. Ipomea, the adventuresome Brachiaria and other grasses on the other hand are pushed back to safer limits where they wait again for conditions to favor another invasion, that is when the mudflats shall come out to the sun again.
Henry David Thoreau's quote in Walden Pond where he lived for a year detached from 'civilization.' See complete quotation below.
The story of competition between the two groups continues indefinitely and all the while the sluggish water meanders against the shoulders of the pond and etches the old bottom. But all along, sediments are being arrested and piled upon the bottom until small isolated “islands” formed in the middle of the water zone. The isolation of these islands can not be for long, so their barrenness, for the dormant seeds under the warm rich soil suddenly come to life and together with air borne seeds and spores, and the stranded shoots and tillers, which altogether make these islands small lustful worlds in themselves.
No place in the aquatic zone is absolutely for a particular species. However the dominance of a species can be noted from one place to another. For example, the pseudo-islands in the middle of the aquatic zone may be dominated by Brachiaria, while the lower part of the pond adjacent to rear gate where water is impounded to some six inches deep, harbors the remnants of the once dominant Eichhornia. At the headend, the old bottom may be covered up with grass, except in places that may be occupied by Jussiaea repens, a succulent broad-leaf and a water-loving species.
Any decrease in area of the true aquatic zone a corresponding increase of the immediate zone. Terrestrial plant species continuously pursue the reclaimed flats. Ipomea and Alternanthera species appear at the front line of the invasion while the grasses stand by. The logic is that the former can better withstand the conditions of the waterline. Their roots bind the particles of silt and humus, which are suspended in the water, and when the plants die, organic matter is added, thus favoring the terrestrial species take over. It is as if these benefactors are robbed at the end by their own beneficiaries.
The aquatic and shore zones are more or less homogenous as far as their principal plant species are concerned. This could be explained by the fact that the newly established zone (aquatic zone invaded by plants) is but an extension of the shore zone, and was it not that the shore zone a part of the aquatic zone?
Hence, the close relationship of the two zones can be readily noted, although they can be divided by alterne, this demarcation is not steady as shore vegetation spreads out into the water zone.
The phytoplankton composed of countless green algae, flagellates, diatoms, desmids and a multitude of bacteria are the precursors of the food pyramid. In an illustration, they form the broad base of the structure, which is the foundation of a pyramid. If simplified, the phytoplanktons make up the larger link of a chain with which other links join---those of the zooplanktons to join first, then the insect larvae and nymphs,then the larger organism,and so on. The farthest link is made up of the decomposers that ultimately join with the link of organic matter and the humus upon which many phytoplankton and higher plants depend upon. Although the “food chain” is not really as clean-cut and orderly as this (there are short circuits and short-cuts of the chain), there is undoubtedly an existing order in the community, and that parasitism, predatism, saprophytism, commensalism, etc., are but “linking” relationship of a greater whole, the ecosystem.
In the pond, the rooted as well as the floating plants and the phytoplanktons are the “producers”. They support the herbivores (insects and fishes), and they add organic matter when parts or the whole of their bodies die. Zooplanktons generally feed upon the phytoplanktons, although some are dependent upon organic matter and humus. Small fishes, crustaceans and insects eat the zooplanktons in turn,, and these will be eventually eaten by carnivores. If not eaten, every plant and animal eventually die and decompose, its protoplasm reduced to the basic materials that green plants needed for growth.
The shores progressively widen following the drying of the mudflats. This area is usually dominated by Brachiaria mutica. Other plants belonging to Convulvolaceae, Amaranthaceae and Malvaceae may be next in number. During the rainy season the shores are waterlogged. The soil is black and it emits methane and ammonia gases, which show that anaerobic decomposition is taking, place. Muck is the product of this slow process. The soil is rather acidic but many plants tolerate it. High ferrous content can also be noted as rusty coloration, a characteristic of waterlogged soil.
Towards the end the shore becomes dry. Vegetation changes follow a dynamic pattern, the grass producing numerous secondary stalks, which become thick and bushy. The broad-loaf species tend to grow in clumps or masses. Some plants in the slope zones descend to join some plants in the shore zone, some are forced a prostate growth. Along the water line the grass is tall and verdant green.
Soon the pond will die.~
"I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived. I did not wish to live what was not life, living is so dear; nor did I wish to practise resignation, unless it was quite necessary. I wanted to live deep and suck out all the marrow of life, to live so sturdily and Spartan-like as to put to rout all that was not life, to cut a broad swath and shave close, to drive life into a corner, and reduce it to its lowest terms, and, if it proved to be mean, why then to get the whole and genuine meanness of it, and publish its meanness to the world; or if it were sublime, to know it by experience, and be able to give a true account of it in my next excursion."
— Henry David Thoreau, Walden, "Where I Lived, and What I Lived For"