1. Pond and Lake Ecosystems

2. eco - environment System--- complex coordinated units. So system is a collection of interdependent parts of events that make up a complete structure. Energy from the sun, the input is fixed by green plants and transferred to animals. Nutrients are taken up by plants and animals where they are deposited, cycled from one feeding group to another, liberated by decomposition to the water, soil, and air (output). Thus, the nutrients and energy that comprising an integral part of the entire system, keeps the biosphere functioning. Water is a most essential and important abiotic factor of pond and lake ecosystems. It also forms the habitat for a large variety of plants and animals. These ecosystems are called as freshwater lentic ecosystems.

3. Freshwater pond and lake ecosystems involve a gradient from lakes to ponds to bogs (A bog is a wetland that accumulates peat, a deposit of dead plant material) marshes and swamps. Freshwater lentic ecosystems have low percentage of dissolved salts and subjected to the physical and chemical factors. Wide or slight fluctuations of factors significantly affect the fauna, altering their distribution, concentration, growth and existence.

4. Physico-Chemical Nature of Freshwater Fish has its own specific and unique set of environmental requirement for survival, growth and reproduction potentials. Unless environmental requirements are uniformly distributed, it is beyond possible to live fish in any ecosystem. Some important factors of pond and lake ecosystems are 1.Density 2.Pressure 3.Buoyancy 4.Temperature 5.Light 6.Oxygen 7.carbon dioxide 8.Salinity 9.pH of water

5. Density The density of water varies inversely with temperature and directly with the concentration of dissolved substances. Generally dissolved inorganic and organic salts increase the density of water. Thus, the density of a freshwater bodies is much less than that of the sea. The condition termed as Hypersalinity when evaporation of water from ponds and lakes takes place during summer season, the concentration of salts becomes higher. In contrast, salt concentration during rainy season becomes lower which is termed as hyposalinity.

6. Pressure In different freshwater environments, pressure is very less than in the sea, and aquatic animals appear to adjust them readily. The pressure of water on pond and lake- dwelling animals is combination of the weight of the water column and weight of the air.

7. Buoyancy The buoyancy of aquatic animals is equal to the weight of the water it displaces. It varies with the density of water and is influenced by viscosity and temperature of water. Fish keep stations by swimming movements by fins or by decreasing the specific gravity of the body with the help of air bladder.

8. Temperature Temperature of ponds and lakes exhibits an unique fluctuations and diurnal as well as seasonal fluctuations of temperatures are evident than in marine ecosystems. For example, a diurnal variation range of 4.8-5.0 °C is evident in tropical fish ponds with an average depth of 3 meters. On the other hand, in a polluted shallow moat with an average depth of 1.5 meters, the lowest and highest temperature at night and day times were 26.6 and 32.0°C, respectively.

9. Classification of ponds and lakes on the basis of thermal stratification 1)Temperate lakes/ponds: Surface temperatures differ below and above 4°C. 2) Tropical lakes/ponds: Surface temperatures are always maintained above 4°C. 3) Polar lakes/ponds: Surface temperatures never go above 4°C.

10. Thermal stratification phenomenon is controlled by the seasons and has a significant impact on the survival and existence of aquatic life. Increasing and decreasing temperatures cause a fall and rise in metabolism, respectively, resulting in decrease or increase rate of food consumption. The extremes of higher and lower temperature have lethal effects on aquatic animals. For example, temperature above 35°C or below 14 °C are reported to be lethal for Macrobrachium malcolmsonii and they prefer at temperature range below 29 and 31°C.

11. Light The influence of light on ponds and lakes is of considerable importance because light influences the productivity of these lentic environments. Since waters often have a lot of suspended materials, it is obvious that these materials obstruct the light and hence cannot able to reach the bottom. Thus, shallow lentic water bodies receive light to the bottom resulting in an 'abundant growth of phytoplankton and macrophytes. These ultimately form an excellent food chain. Moreover, light also controls the changes in position, nature of growth, and diurnal migration of different species of plankton.

12. Oxygen The oxygen is a most essential chemical composition of life processes and remain dissolved in freshwater environments. The freshwater ecosystems which remain in close proximity with air, contain an abundance of oxygen. This oxygen is mixed with the water either by wave action or water circulation or by diffusion. In this process, freshwater lentic water bodies dissolve about 5 per cent oxygen.

13. Other Gases The concentration of oxygen in freshwater ecosystems exhibits diurnal variation. Oxygen concentration remain very low at dawn and at peak between 12 noon and 4 PM. Oxygen is consumed by aquatic animals and decomposition of dead organisms in accelerated. Generally, the oxygen content of surface water remains high than in the deeper zone due to presence of phytoplankton population in significant amounts. Ponds and lakes have a lot of decaying vegetation and oxygen content remains in a stage of complete depletion. Reduction in the level of oxygen can be observed by the release of several gases due to decomposition of dead and decaying matters.

14. Carbon Dioxide Carbon dioxide gas diffuses directly from air and dissolved in water thus forming carbonic acid (H 2 C0 3 ) which ultimately affects the pH of water. It is also present in freshwater ecosystems as carbonates and bicarbonates of magnesium and calcium. Phytoplankton and aquatic plants require carbon dioxide for photosynthetic activity. Aquatic animals and decomposition process release and appreciable amounts of carbon dioxide. The high saturation levels of oxygen and carbon dioxide exhibit toxicity to aquatic life. In cases where freshwater lentic ecosystems have decaying vegetation, show an abundance of hydrogen sulphide. Nitrogen, ammonia, and sulphur dioxide are also found in freshwaters. All these gases are highly toxic to aquatic biota. Gradual increase in the concentration of these gases by any means results in complete or partial elimination of bottom fauna.

15. Salinity Salinity of freshwater bodies is mainly due to presence of common salt (sodium chloride) in significant amounts and the degree of salinity depends on the amount of salt present in dissolved condition. Since the concentration of salt in freshwater lentic water bodies is very low (about 2-5 ppt.), aquatic animals face the problem of osmoregulation. The salt concentration within the cell remains higher than the freshwater environment and therefore, the water tends to enter the body which should be removed. Fishes are above to remove extra amount of water by osmo- regulation. Many aquatic invertebrates possess excretory organs for elimination of excretory products along with water.

16. Dissolved Salts Freshwater ecosystems contain various types of dissolved salts such as compounds of nitrogen, phosphorus, calcium, magnesium, manganese, iron, sodium, zinc, sulphur, and potassium. Dissolved salts accumulate within the ecosystem by surface run-off and decay of aquatic organisms. Although ammonium salts, nitrates and nitrites are important for the growth of algae and aquatic macrophytes, the compounds are highly toxic to fish and fish food organisms. Phosphorus compounds are also important because plankton utilize this phosphorus as source of food. Thus, nitrogen and phosphorus concentrations gradually decreased. Compounds of salts greatly influence the composition of fauna, For example, deposition of calcium carbonate takes place by the activity of plants. This calcium carbonate is essential for external covering of arthropods and the shell of molluscs.

17. Hydrogen Ion Concentration or pH The pH of freshwater bodies is a determining factor for aquatic life and has a limiting factor. The pH values in a particular ecosystem fluctuate seasonally and annually. Although the range of pH is species specific, higher aquatic species (such as fishes) respond quickly to slight pH change, while lower aquatic species exhibited little reaction to changes in pH of water.

18. Characteristic Features of Ponds and Lakes

19. Ponds are considered as shallow standing water bodies of small or medium dimensions. They are so shallow that rooted plants are able to grow most of the bottom. On the other hand, lakes are inland depressions containing standing water. Although lakes may vary in size from less than acre to large seas covering thousands of square kilometer, the size of freshwater lakes generally vary from one to several hectares. Ponds and lakes possess outlet streams and are temporary features on the landscape.

20. The freshwater pond and lake habitats are vertically stratified into five distinct zones depending upon the intensity of light, temperature, hydrostatic pressure, and wave length absorption. 1. Littoral Zone: Shallow water having rooted vegetation near the shore that contains oxygen rich and upper warm circulating layer - called epilimnion. – It begins at about 6 meters from the surface. 2.Sublittoral Zone: This zone extends from littoral zone to non-circulating poor oxygen cold water zone - called hypolimnion. – This zone begins at about 10 meters from the surface.

21. 3Limnetic Zone: It is an open water zone away from the littoral zone and extends up to the depth where the rates of respiration and photosynthesis are equal. – This zone begins at about 50 meters from the surface. 4Profundal Zone: This zone is situated beneath the limnetic zone that extends beyond the depth of effective light penetration.. 5Abyssal Zone: This zone is found only in the deep water lakes. – It begins at about 2,000 meters from the surface of water.

23. In freshwater pond ecosystem, littoral zone is larger than the Iimnetic and profundal zones. Small ponds do not have the limnetic and profundal zones. Therefore, ponds have little vertical stratification. In general, freshwater ponds have three zones such as 1.littoral zone 2.limnetic zone 3.profundal zone.

24. Classification on the basis of the depth of light penetration 1.Trophogenic Zone: This zone includes littoral and sublittoral zones and is distinguished by growth of plants. 2.Tropholytic Zone: It includes the upper part of profundal zone and is characterized by the absence of aquatic plants. However, in between two zones, there is a compensation level which forms a boundary between the two zones. In this compensation level, the rates of respiration and photosynthesis remain in a state of perfect equilibrium.

25. Water Circulation in a Thermally Stratified Lakes The epilimnion is always heated by the sunshine and mixed by the wind and water currents. The hypolimnion is not heated and circulated by the wind and currents. The transition area between the two is called thermocline or metalimnion. The circulation layer of lake water is maintained by temperature. Whenever a metalimnion is formed, exchange of water does not takes place between hypolimnion and epilimnion.

26. Origin of Ponds and Lakes

27. In most regions, ponds occur due to rainfall in adequate amount. Permanent ponds have adequate depths and contain water all the year round. Temporary ponds are shallow, seasonal and most of them dried up during summer seasons. When a stream of water is flooded the plains, it shifts its position thus leaving the formed bed which is completely separated in the form of a lentic water area.

28. A lake is defined as an inland body of standing water, it is large and deeper than a pond. The term includes an expanded part of a river, a reservoir behind a dam, and a lake basin formerly or intermittently covered by water. Natural Lakes are formed in different ways as noted below: 1.By the deposition of silt, driftwood etc. in the beds of slow-flowing streams. 2.Gradual accumulation of rain and ground water in a volcanic crater or caldera. 3.Glacial abrasions of slopes in high mountain valleys impress deeply resulting in the formation of depressed areas with no surface outlets, which is filled with water from rain and melting snow. 4.Retreating valley glaciers are left behind as crescent- shaped ridges of rock debris and filled up with water.

29. Artificial lakes are man-made lakes which are constructed by damming rivers for power, irrigation and water storage or by constructing small marshes and ponds for wild life and fisheries. Artificial lakes are also called impoundments. Natural lakes differ from artificial lakes in thermal and oxygen variations and are characterized by high percentage of bottom organisms.

30. Coldwater Lakes and Ponds The term coldwater fish refers to those species which prefer thermal regime between the snow-melt waters of the greater Himalaya. These waters are generally characterized by dissolved oxygen contents high transparency low carbon dioxide inorganic soil Sparse (thin) biotic communities.

31. Benthic Communities of Lakes and Ponds On the basis of the dependence of water and soil, different organisms of the ponds and lakes can be classified into two forms: 1.Pedonic forms (depend on the substratum ) 2.Limnetic forms (free from any substratum) Moreover, according to the size of habitats, aquatic organisms are also divided into following types: 1.Plankton 2.Neusion 3.Nekton 4.Benthos

32. 1.Plankton: small animals (zooplankton) and plants phytoplankton) possess limited power of self- locomotion can move in such a way that they are able to control their vertical distribution.  Nekioplankton are the species of planktons that are very active move great distances very small distribution is controlled by water currents. 2.Nekton: large size animals powerful and active swimmers. The size vary from about 2 mm long (swimming insects) to the largest animal (the blue whale).

33. 3. Neusion : found in all freshwater ponds and lakes at the air-water interface. They include free-floating plants (such as Lemna, Azolia, Saluinia, Pistia.Spirodella, Eichornia, and Wolffia) and animals. Hyponeuston are the animals that spend most of their times below the water-air interface (such as back swimmers, diving beetles). Epineuston (water striders) live on the top of the air-water interface. 4.Benthos: Organisms living at the bottom of the freshwater ecosystem They either live above the soil-water interface-termed as benthic epifauna or within the soil-termed as infauna

34. Organisms of Littoral Zone Aquatic organisms are most prolific in this zone. Emergent vegetation is the most characteristic feature of the shore proper. These plants are deeply rooted in the shore but their tops remain exposed such as Sagiiaria (arrow heads), Scripus (bulrushes), Typha (cattails) etc. Some rooted plants with floating leaves such as Nelumbo, Nymphaea, Trapa, and Marsilea are found just slightly deeper part of the zone (Figure 3.3). Still deeper part of the zone, there are occurrence of rooted, submerged and thin stemmed aquatic weeds These are Vallisneria, Mycrophyllllm, Hydrila, Cham, Elodea etc.

36. Zooplankton of littoral zone: consists of Rotifers, Ostracods and Daphnids. The nekton includes Euglena, Paramecium, Corixa, Ranaira, Dytiscus, larvae of Gyrinus, Culex and Chaoborus (Figure 3.5). Neuston includes water spiders, protozoa, whirling beetles etc. Various types of pond fish such as sunfish, bass, pike, and top minnows spend much of their time in this zone for various purposes. Different species of animals of littoral zone live in association with plants or other objects. These include larvae of Dytiscus, Glossophonia (leech), Dragon fly and Damsel fly nymphs, Brachionus, Bryozoa, Lymnaea, Vorticellci, and Chironomus.

38. Organisms of Limnetic Zone This zone has autotrophs in abundance and because this zone is characterized by rapid variation of temperature, oxygen and water level, some species (such as Rotatoria, Philodina, Daphnia, Cyclops, Snails, Volvox, Euglena, and fishes) which are capable of encystment during unfavourable situations, live in this zone.

39. Organisms of Profundal Zone Generally autotrophs in this zone are not able to synthesize food and therefore detritus is the main source of energy for existence of several types of organisms such as clams, bacteria, fungi, annelids etc. that are capable of living in water having low oxygen and little light. Organisms are heterotrophs in nature and they are either carnivores or detritus feeder.

40. Organisms of Pond and Lake Bottom Most of the pond and lake bottoms are covered with sediment to form a uniform substratum of sand or mud. The most common benthic organisms include several species of insect larvae (Chaoborus, Chirononius etc.) oligochaetes (Aulodrillls, Btanchiura etc.), bivalves iPisidium, Parrevsia, Indonaia; Lanieliidensi, gastropods (Vivipl1rlls, Melalloides, GyratlillS, Planorbis) and crustaceans.