1. FRESHWATER ENVIRONMENT

2. The balance, continuation and overall equilibrium of a system based on a balance of a specific set of values considered normal in maintaining the specific system is referred as homeostasis All living things must maintain a level of homeostasis to survive The term homeostasis is often considered in science and in medicine as a means of maintaining the equilibrium of the body

3. Earth - about 97.5% of the water is saline, while the remaining 2.5% is fresh water The aquatic habitats together with their communities are called aquatic ecosystems Environment with water is called as aquatic ecosystem An ecosystem refers to all the living and non-living things of plants and animals of an area and their interactions Water - mother of life; liquid gold and is the universal solvent It occupies 71% of the earth surface

4. Freshwaters Freshwater ecosystems cover 0.8% of the earth's surface and contain 0.009% of its total water - generate nearly 3% of its net primary production Freshwater ecosystems contain 41% of the world's known fish species Freshwater is characterized by having low concentrations of dissolved salts and other total dissolved solids - less than 5 (ppt) of dissolved salts Water salinity based on dissolved salts in parts per thousand (ppt) FreshwaterBrackish waterBrackish waterSaline waterSaline waterBrine < 0.50.5 – 3030 – 50> 50

5. Health of an aquatic environment Health of an aquatic ecosystem is degraded as result of physical, chemical or biological alterations of the environment Physical alterations - Changes in water temperature, water flow and light availability Chemical alterations - Changes in the loading rates of bio stimulatory nutrients, oxygen consuming materials and toxins Biological alterations - Introduction of exotic species

6. Characteristics of freshwaters The river ecosystems are characterized by the river bed's, gradient or by the velocity of the current Fast moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving water of pools Eg. Rivers and streams.

7. TYPES OF FRESHWATER SYSTEMS Different types of freshwater systems viz. ponds and lakes, streams and rivers, and wetlands Based on the movement of water, it is generally grouped into lentic and lotic water systems The lentic water bodies include all standing water systems such as ponds, lakes and wet lands or swamps, The lotic systems include all flowing water systems such as small streams and rivers

8. Types of freshwater Lentic: slow-moving water, including pools, ponds, and lakes Lotic: rapidly-moving water, for example streams and rivers

9. LENTIC HABITATS Ponds and lakes are bodies of standing freshwater surrounded by land and are not having continuity or connection with the sea Lakes - larger and deeper Ponds - shallow enough that sunlight can reach the bottom allowing rooted plants to grow There is no clear cut difference between the lakes and ponds except for the size, but they very well behave differently in their ecology

10. PONDS Ponds - very shallow in nature and its average depth may be about 8-10 feet with some exceptions Light penetrates up to the very bottom Water temperature – uniform; changes with air temperature Bottom - covered with mud Dissolved oxygen - vary greatly during a single day The level of carbon dioxide and other gases is more in the bottom of the ponds - decomposition prevails in the bottom

11. Based on the origin, the ponds can be of natural types and artificial types Natural ponds - formed either due to the ageing of the lakes or filled with accumulation of rain water in the natural depressions that occur on the earth surfaces Artificial ponds are man-made ones Further, ponds are classified into temporary and permanent ponds depending on the duration of availability of water.

12. LAKES Lakes - bigger than ponds and too deep to support rooted plants except near the shore Some lakes are deep enough and wide enough for waves to form For example, the Lake Superior is the largest freshwater lake in the world, with a water spread area of 31,000 square miles Similarly, the Lake Baikal in the Southern Siberia, is the deepest lake in the world, which has a depth of 1,700 meters

13. ZONATION OF LAKES AND PONDS Lakes and ponds are divided into three different "zones” namely littoral, limnetic and profundal zones Are usually determined by depth and its distance from the shoreline COMMUNITIES OF LENTIC WATERS The lentic systems like lakes and ponds with their various zones have characteristic organisms and the following are the different communities

14. PRODUCERS: They include all primary producers such as phytoplankton and macro vegetations of the lakes and ponds. Phytoplankton:  Diatoms: Asterionella, Nitzschia, Navicula, Fragellaria, Synedra, Gomphonema, etc.;  Dinoflagellates: Ceratium, etc.  Blue green algae: Anabaena, Microcystis, etc.  Green algae: Spirogyra, Scenedesmus, Coelastrum, etc Macrophytes:  Floating plants: Pistia (water lettuce), Eichornia (water hyacinth), Lemna ( duckweed), Salvinia, etc.  Submerged plants: Valisneria (cord grass), Ceratophyllum (coon tail), Hydrilla, Chara (musk grass/ stone wort), Nitella, etc.  Rooted plants: Typha (cat tail), Scirpus (bulrush), Nelumbo, Nymphaea (water lily), Marsilia, Sagittaria (arrow-head), Potamogeton ( pond weed), etc.

15. CONSUMERS : The faunal components of lakes and ponds include organism such as benthos, periphyton, zooplankton, nekton and neuston. Benthos:  Molluscs - Lamellidens, Pila globosa, Planorbis  Insects - chironomids, stone-fly larva, black- fly larva, etc.  Polychaetes - Tubifex, earthworms, etc. Periphyton:  Protozoa - Arcella, Difflugia, Centropyxis  Ciliate protozoa – Vorticella  Sessile rotifers - Rotatoria, Philodina Zooplankton:  Cladocerans (water fleas) - Daphnia, Moina etc.  Copepods - Cyclops, Neodiaptomus, etc.  Cirripeds - Cypris  Rotifers - Brachionus etc. Nekton:  Fishes - Catla, common carp, Tilapia, Saccobranchus, Ophiocephalus, Clarius, Anabas, Mystus, etc.  Amphibians - frogs, tadepoles, etc;  Reptiles - Natrix natrix (water snake), turtles, etc and  Aquatic birds - pond herons, cattle herons, water ducks, cormorants etc. Neuston:  Plants: Pistia, Lemna, Eichornia,etc.  Animals: Ranatra sp.(water striders), Notonecta sp. (back swimmers), Gyrinus sp. ( whirligig beetle) etc.

16. LOTIC HABITATS Lotic habitats are called running water systems including streams and rivers These water bodies are different from the lentic systems by the following factors

17. FACTORS INFLUENCING RIVERS – Movement of water is the unique characteristic of lotic systems while the same is absent in the lentic systems. The flow of water is unidirectional. – The interchange between the soil and water is higher in the lotic waters than the lentic waters. – Dissolved oxygen content is more and uniformly distributed in running waters and there is no physical and chemical stratification. – Depending on the water movement in different zones, the nature of bottom materials is changing with sandy, muddy, rocky or pebbles. ZONATION IN RIVERS Three zones - crenine zone, rithron zone and potamon zone