Aquatic Ecosystem • Water is a most important and essential abiotic factor of all kind of ecosystems and it also forms the habitat for an enormous variety of organisms. Aquatic ecosystem is the biggest ecosystem of the biosphere. • Global aquatic ecosystems fall into two broad classes and one mixed class:- • Fresh water ecosystem. • Salt water ecosystem. (marine) • Estuaries

FRESH WATER ECOSYSTEM

• Study of fresh water ecosystem is known as LIMNOLOGY. It is divided into two groups. • Lentic: - it includes standing water habitats. E.g. lakes, ponds, pool, wetlands (swamps, marsh, mangrove, fens etc). • Wetlands: areas where the soil is saturated or inundated for at least part of the time. • Lotic: - it includes running water habitats. E.g. rivers, springs, streams, ditch, (A stream is a body of water with a current, confined within a bed and banks.) etc.

LAKE AND POND ECOSYSTEMS • Lakes are inland depression containing standing water. Ponds are small bodies of standing water and shallow. Rooted plants can grow over most of the bottom. • Ponds may be seasonal with life span of few weeks and months, or perennial with age of several hundred years. Lakes date back as far as the ice ages. Lake Baikal of Russia and some others are very ancient.

Stratification: - the aquatic habitats of lake and ponds remain vertically stratified (depth or height from the surface) in relation to light intensity, temperature etc. [temperature vary--- O2, LIGHT VARY ----- organism vary] • Littoral zone: - shallow water near the shore forms the littoral zone. a belt close to shoreline, light reaching the bottom, supporting rooted plants; • It contains upper warm and oxygen rich circulating water later which is called epilimnion. This zone includes rooted vegetation. • Sublittoral zone: - it is non circulation cold water with poor oxygen zone called hypolimnion. • Limentic zone: - open water zone and away from the shore. It extends up to the compensation level. The compensation level is the point where the rate of photosynthesis is equal to the rate of respiration. In this zone light intensity is adequate. Due to availability of light, this zone contains enriched with plankton (free floating microscopic algae and animals); • Profundal zone: - deep water area found beneath limentic zone. It is beyond the depth of effective light penetration. light inadequate or absent. only heterotrophs occur. • The benthic zone is the lowest level of a body of water such as an ocean or a lake, it includes the sediment surface and some sub-surface layers. Organisms living in this zone are collectively called the benthos, e.g. the benthic invertebrate, crustaceans and polychaetes. • Abyssal zone: - it is found in deep lake/ocean.

Different zone of a deep freshwater lake Fresh water pond

Littoral zone Lake/Pond surface

Limentic Zone (Pelagic zone), Open water Zone Sublittoral (Photic/Euphotic Zone),

zone Compensation level (P=R) or LCP Profundal Zone, Deep Water Zone, Aphotic Zone, No photosynthetic organism

Benthic Zone

Thermal Stratification Lakes of temperate regions generally become thermally stratified due to differential heating and cooling.

In the summer thermal stratification, the upper layers of water become warm and do not mix with cooler water of deeper layers. because of difference in the density of water. The cool water has higher density than the warm water.

These two layers are separated by metalimnion, characterized by a steep decline in temperature and includes thermocline, that is the zone of sharp change in temperature, which checks the mixing of waters of the two zones.

Epilimnion – in summer, The warmer part of the lake with small temperature gradient. is called epilimnion (limnion = lake). water is warmer and typically has a higher pH and dissolved oxygen concentration than the hypolimnion. Freezes in winter

Metalimnion (thermocline) Temperature and oxygen changes rapidly with depth Hypolimnion In summer, the cooler part of the lake is called hypolimnion. Typically the coldest layer of a lake in summer and the warmest layer during winter 4 C throughout the year

Change in temperature in layer cause free mixing of water hence O2 and nutrient leading bloom of phytoplankton Warm (20 C) low density

Thermocline Mixing (10 C) Cool (4 C) high density

Summer (low growth) Autumn/Fall turn over

0 Cool (1-0 C)

Mixing (4 C) Thermocline 0 Warm 4 C

Winter (low growth) Spring turn over

Biotic components: -

• Types of aquatic organism • Macrophytes – large rooted plants, some submerged or emerged, hydrila, trapha, typha • Periphyton - Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. It serves as an important food source for invertebrates, tadpoles, and some fish. • freshwater organisms attached or clinging to plants and other objects projecting above the bottom sediments. • Plankton - Plankton are microscopic organisms that float freely with oceanic currents and in other bodies of water. Plankton is made up of tiny plants (called phytoplankton) and tiny animals (called zooplankton). • Nekton - Nekton or necton refers to the aggregate of actively swimming aquatic organisms in a body of water. • Benthos - Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. • Neustons - Neuston is the collective term for the organisms that float on the top of water (epineuston) or live right under the surface (hyponeuston). Trophic structure • Primary producer: - autotrophic plants, phytoplankton, some photosynthetic bacteria etc. • Primary consumer: - zooplanktons like Rotifers, Dafnia, Ostracods etc. the zooplanktons are found in littoral zone. • Secondary consumer: - chiefly insects and small fishes. • Tertiary consumers: - large fishes. • Decomposers: - bacteria, fungi etc found in profundal zone and benthic zone.

POND AND LAKE ECOSYSTEMS • Life Near Shore o Littoral zone: area of water closest to the edge of a lake or on o Sunlight reaches bottom of littoral zone, making it possible for algae and plants to grow ▪ •Beneath surface of water: algae ▪ •Near shore: cattails and rushes ▪ •Floating plants: water lilies ▪ •Small animals: snails, insects, clams, worms, frogs, salamanders, turtles, fishes, and snakes

• Life-Away-from-Shore o Open-water zone: area of lake or pond that ▪ extends from littoral zone across top of water ▪ Goes as deep as sunlight can reach ▪ Home to bass, trout, and other fishes ▪ Many photosynthetic plankton live in this area

• Deep-Water zone: o beneath open-water zone where no sunlight can reach Catfish, carp, worms, crustaceans, fungi, and bacteria live here o These organisms often feed on dead organisms that sink from above

Aquatic food chain

A food chain is a simple linkage of producers to consumers through feeding relationships. For example, when a small fish eats an aquatic insect, and a larger fish eats the small fish, the two fish and the insect are linked in a food chain. Food webs are more complex, and consist of a network of linked food chains.

http://www.biologydiscussion.com/essay/food-chain-in-ecosystem-explained-with-diagrams/1669

Abiotic Components DO2, DCO2, Temperature, Light, water, Minerals, Dissolve organic and inorganic compounds, Carbonates, bicarbonates, carbonic acids