Lotic Ecosystem : Types and Characteristics

The term lotic comes from Latin lotus meaning washing. It is a running water bodies such as streams and rivers. Lotic or flowing ecosystem is river channels and other related aquatic environments creek, brook, spring, or stream. They vary in size and shape. It includes small waterfalls to various big sized river water bodies. This ecosystem contains two main zones such as pools and rapids. In this case, the pools are the deeper water bodies where the currents are slower while the rapids are the areas where the water is fast with clear bottom. Moreover, in this ecosystem there is a difference between abiotic and biotic factors.

Characteristics of Lotic Ecosystem

Water flowing from lakes and ponds is of the following three main type:

(1) Currents: Currents are a controlling and limiting factor. Due to the smaller size and depth of the lake, the interaction of land and water is more in the flowing water body.

(2) With the exception of polluted areas, most lotic water bodies contain more dissolved oxygen than lakes.

(3) The temperature of water flowing from stagnant water is higher. Moreover, the specific feature of lotic water ecosystem is its speed or rate of water flow. The amount of water that passes through a particular unit is called the rate of water flow. It is expressed as meter³/ second water or acre-foot / second water (one acre foot of water is equal to the amount of water per acre volume and one foot depth). This velocity of water increases rapidly in the lower reaches of the river where the tributary river joins its main river.

Lotic water ecosystems can be divided in two parts based on the speed of water flow and the rate of flow. Namely:

(1) Fast flowing aquatic environment and

(2) Slow moving aquatic environment.

Fast Flowing Aquatic Environment

The part of the flowing river in which the current is more and the direction is changing rapidly, this part is called fast flowing aquatic environment. The objects that flow through the current are other things that look like animals and sediments. The effect of the current is that the stones and pebbles become round and smooth. These habitats are more diverse. Physical parameters such as the rate of water flow, the rate of water flow between the top and bottom of the rock blocks and the flow rate below them are completely different. Different species can live in these micro habitats. Moreover, aquatic plants are used as habitats for some fish that live in tidal environments. Phytoplankton are rarely seen in this region. Phytoplankton in this region are Diatom, Blue green algae, Green algae (e.g., Cladophora, Ulothrix) and water moss (e.g., Fontinalis).

(A) Plants Inhabiting Torrential Forms

Some fast-moving aquatic animals live in moss and flowering plants such as Eriocaulon miserum, Hydrolyum lichenoides and Duroea wallichii. These animal-inhabited plants become torpedo-shaped so that they are less obstructed by currents. Some animals such as the funnel-faced tadpoles of Megalophrys and the Tipulid larvae live in the roots of these trees. All of these creatures have a clinging technique and a limb. Some animals like Cephalopteryx, Heloides, Phalacrocera, Gammarus etc., live on the leaves and stems of aquatic plants. These animals have a hook-like structure through which they are attached to the leaves and stems. The larvae of Simulids and Chironomids live on the exposed surface of plants.

(B) Rock Inhabitant Forms

Animals that live on the surface of rocks have effective techniques for attaching them in a certain place. The creatures that live in this habitat are flattened. Some organisms such as freshwater shell Limpet, Ferrissia are flattened. Such anatomical structures are slightly obstructed by currents, and through strong legs existing throughout most of the space of the shell, they attach themselves to a place of rock. Other creatures, such as the reefy beetle larvae and the beetle larvae, are not only flattened but also have hooked claws on each leg, allowing them to be more firmly attached to the bottom of the pond. The larvae of Simulium and Chironomides are attached to the upper part of the rock by hooks on the back edges of their bodies. The caddisfly worm has both types of structures (hooks on the toenails and the hindquarters of the body). May Fly Nymphs,  and Psephenus are stuck with rocks through functional pads. 

Some animals, such as freshwater sponges, stick firmly to rocks. Other animals, such as the Caddis fly, build their nests on rotten organic matter or wood chips so that they can stick firmly to rocks. Some stationary algae and plants live on the exposed surface of the rock. Significant amounts of decomposed organic matter from upstream and river adjacent areas move into the fast flowing environment. So rotten organic matter is a source of energy for the fast flowing aquatic environment. Rotten organic matter is an important source of energy here compared to primary production. As a result, most of the primary consumers here are decaying organisms.

Organisms Living in the Space between the Rocks

Numerous different types of animals live in the space between the rocks. Many of them, such as the May Fly and the Stone Fly Naids, are flattened. Some of their behavioral adaptations are seen to hold the position of a particular place. One of these adaptations is thigmotaxis, which allows the animal to stick to a hard surface, such as rocks or other insect larvae. Another behavioral feature is rheotaxis through which the animal adapts to the current. 

Going against the current is another type of adaptation. These naids have different physical structures and behaviors through which they can take a stand against the current. The current wants to remove the insects from the rocks so that the animals also collide with its base surface. Other insect larvae have a large body size and their bodies are covered by thorns. Due to their physical size, they cannot easily go anywhere else through the current. The thorns help to keep the larvae in the middle of the rock. 

Inhabitants Occurring Beneath Rocks

Many species such as flattened worms, annelid worms, other insect larvae, oysters and some snails live under the rocks. The current cannot reach here much. Animals rarely move elsewhere. The animals that live here do not have special adaptations, but if the currents are low enough, some swimming creatures like fish can live. Stenothermal cool water fish live in fast flowing aquatic environments such as trout. In aquatic environments with high currents, fish are small in size and have a slender body. 

Trout and Tor tor can swim against the current of a stream or waterfall by expanding the muscles. Other fish in the aquatic environment live above or below rocks or boulders over which water flows slowly. Many Loaches  such as Nemacheilus and Amblyoceps olyra are found at the bottom, and limpet-like fish (such as Glyptosternum, Balitora) or specially adapted fish (Garra, Glyptosternum, Pseudechineis) live on the rocks. Loaches such as Balitora can be attached to rocks in the eastern part of the Himalayas and the hilly areas of Assam by forming succulent fins on the ventral side. 

Physico-chemically more aquatic environments tend to be cooler and more deep. Water temperature is low, low productivity is observed but biodiversity is high. In more current-rich aquatic ecosystems, currents are the main regulator of productivity. In such an environment, the production of carnivores is abnormally low.

Slowly Flowing Aquating Ecosystem

A slow-flowing aquatic environment tends to be different in many ways from a high-flowing environment. As the current level is low, such water flow has less capacity to erode the land. A small amount of sediment and decomposed organic matter accumulates at the bottom. Moreover, all these water flows have excessive temperature. As a result, such an environment contains a significant number of planktonic organisms, such as protozoa. Isopods, sowbugs, molluscs (Sphaenius, Pisidium and Anodonta dominata) and may fly, damsel fly, naids or tube, Chiromomus larvae and some other insect larvae and oysters, nemadodes, snails and rotifers. There is also an abundance of swimming organisms in such ponds. Notable fish species among these organisms are carp, catfish, suckers, spoonbill etc. In addition, these ponds contain larger crustaceans such as amphipods (freshwater shrimps).

Some insects spend most of their life cycle on the surface of water bodies. Notable among these insects are watet striders, water boatmen, back swimmers and predatory diving beetles. The region is also rich in zooplankton, especially, protozoa and smaller crustaceans such as Cladocera and Copepoda. Due to the abundance of food, a significant number of reptiles (water snakes, crocodiles, turtles) and amphibians are found in slow-moving ponds.

Such water bodies also have an abundance of plants. Besides, there are rooted vascular plants such as aquatic weeds, grasses, aquatic moss and fibrous algae. Open water contains an abundance of algae such as diatoms and flagellates. On the whole, the productivity of such reservoirs is higher than that of high-flowing reservoirs. Here the living communities depend on external food elements. In addition, in such an environment, rotten organic waste food chain organisms such as bacteria and fungi are more developed. Here in the muddy environment at the bottom partially decomposed organic matter is used as the main food source of bacteria and fungi.

Some slow-flowing ponds contain more organic matter than silt at the bottom. The concentration of oxygen in such reservoirs acts as the main limiting factor. Due to the high level of activity of the animal and the food chain that eats the active decomposed organic matter, a large amount of oxygen is removed from such reservoirs. Moreover, low water flow indicates less oxygen in the surface water. Dissolved oxygen is less in slow moving ponds than in fast flowing ponds. This amount of oxygen determines what kind of organism will live in the reservoir. Low-oxygen-tolerant fish such as carp and catfish can live comfortably in slow-moving ponds, while species with higher oxygen requirements, such as trout, are found in fast-flowing water.

Difference Between Lotic and Lentic Ecosystem

Lotic Ecosystem	Lentic Ecosystem
It has a continuosu water flow with definte direction.	Water flow is absent. In this case, water does not flow with a continuosu and definete direction.
Morphometrically, it has more complex perimeter with linear, narrower, longer and shallower basin.	It has less complex perimeter with circular and deeper basin.
Its  width is relatively narrow.	It has relativel broad width.
It can last for many thousands of years.	It can last for a few hundred to a few thousand years.
Water is fed by lower order streams, rains, precititation, melt, snow and springs.	Water is fed by higher order streams, lotic waters such as rivers, creeks, etc.
It contains high current velocity.	It contains low current velocity.
The water contains usually high dissolved oxygen due to fast flowing water.	The water contains low dissolved oxygen.
It has lower salt content.	It has higher salt content.
It has low speciation rates.	It has high speciation rates.
It contains higher species diversity.	It contains lower species diversity.
It has higher geographical range.	It has lower range of geography.
It has high stabilty.	It has low stability.