Limnic Ecosystem (Freshwater)
Limnic ecosystem is a unit consisting of various organisms that function together in a collection of fresh water masses in a certain area, both flowing (lotic) and still water (lentik), which allows the flow of energy and the cycle of matter between biotic and abiotic components.
A river is a running water ecosystem, while lakes, ponds and ponds are still water ecosystems. In this plengdut.com post, the limnic ecosystem to be discussed is rivers ecosystem and lakes ecosystem.
River Ecosystem
A river is a mass of water that flows in large quantities and is long. Based on the velocity of the water flow, several groups of rivers are known, namely rivers with fast currents, moderate currents, and weak currents, while based on their size there are known names of large river, tributaries, and ditches.
In addition, based on the physical condition it is known that a river is ecosystem rocky, sandy or muddy, or even a combination of all these elements. Each is inhabited by different groups of flora and fauna, depending on the quality and quantity of existing water conditions.
The river ecosystem is unique because it is a corridor extending from upstream to downstream which can be up to tens or hundreds of kilometers in length. The condition of the area ecosystem on either side of the river differs from one river to another, as well as between the upstream, middle and downstream areas.
The upstream part of the river which is still surrounded by relatively good forest cover will have better water quality than the river body in the middle or downstream. In general, the middle or downstream parts are more likely to bear the environmental burden due to forest clearing, pollution from mining, household, agricultural and factory waste.
Watershed (DAS) in various regions in Indonesia generally experience a serious threat due to, among others, narrowing of river boundaries due to erosion and density of settlements on river boundaries and pollution.
Several watersheds, especially in the middle and downstream areas and also tributaries, have experienced a decline in the chemical and physical quality of the waters due to forest encroachment, gold mining, nickel, copper, lime, sand and industrial waste disposal. Ecosystem disturbance in the upstream part of the river is the cause of flooding in the middle and downstream. In addition, damage in the upstream area can also lead to reduced water discharge, causing drought during the dry season in the downstream area.
Disturbed river ecosystems will affect the quality and quantity of groundwater which is beneficial for healthy drinking water sources. In addition, it will directly or indirectly affect the aquatic biota in it, such as fish, shrimp, plankton, benthos, and crabs as well as various types of snails and shells.
Lake Ecosystem
The characteristics of the lake are closely related to the history of its formation. Generally, tectonic, volcanic, crater, and caldera lakes are located on the plateau around mountains or mountains and have deep and relatively stable bases. On the other hand, floodwaters are located in lowlands and are relatively shallow and tend to be shallow due to silting and the development of invasive aquatic plants.
Lakes are large natural bodies of water surrounded by land and are not connected to the sea, except through rivers (Figure). Lakes can be in the form of basins that occur due to natural events which then collect and store rainwater, springs, seepage, and / or river water (KLH 2010). Indonesia has about 840 lakes and 735 lakes (small lake) with a total area of about 500,000 ha.
The largest lake in Indonesia is Toba (110,260 ha), while the deepest lake is Matano (600 m). A total of 521 of the 840 lakes have an area of more than 10 ha (Table), are scattered in almost all islands, especially in Sumatra, Sulawesi, Kalimantan and Papua (Nontji 1991) and have 3 of the 20 deepest lakes in the world (> 400m) (KLH 2008 ).
Based on its depth, the lake ecosystem has four zones:
- Mintakat Litoral, is a shallow area so that sunlight can penetrate the lake bottom optimally and the water on the edge of the lake feels warm. The vegetation in the zodiac is in the form of rooted plants with leaves sticking out of the water surface. The types of biota in this zone ecosystem vary, including types of attached algae (especially diatoms), various snails and mussels, insects, crustaceans, fish, amphibians, reptiles such as turtles and snakes, ducks, and geese as well as some mammals that forage in Lake.
- Mintakat Limnetik, is an area of free water that is far from the edge and can still be penetrated by the sun. This area is inhabited by a variety of phytoplankton, including algae and cyanobacteria; zooplankton which mostly includes rotifers, and various small shrimp that predate phytoplankton and various types of fish.
- Mintakat Profundal, is a deep area, namely the afotic lake area. Microbes and other organisms use very limited oxygen for cellular respiration after decomposing detritus that has fallen from the limnetic region. This area is inhabited by worms and microbes.
- Mintakat Bentik, is the bottom area of the lake where benthos live and the remains of dead organisms are buried.
Based on the production of organic material, lakes can be grouped into:
- Oligotrophic lakes, namely deep lakes and lack of nutrients so that the phytoplankton in limnetic areas are not productive. The characteristics of this lake include very clear water, inhabited by very few organisms, and at the bottom of the water there is a lot of oxygen throughout the year.
- Eutrophic lakes, which are shallow lakes and rich in nutrients so that phytoplankton is very productive. The characteristics of this lake are that the water is cloudy, there are various kinds of organisms, and oxygen is present in the deep area.
Oligotrophic lakes can develop into eutrophic lakes due to the presence of organic material that enters excessively and is deposited. This change can be accelerated by human activities, for example from the residue of man-made fertilizers, from agricultural activities, and from the landfill of the surrounding municipal waste which enriches the lake with the waste of nitrogen and phosphorus.
As a result of the accumulation of excess fertilizer and waste, there was an explosion in the algae population resulting in excessive detritus production which eventually depleted the lake's oxygen intake. Enrichment of lakes like this is called "eutrophication" which causes water to no longer be used and reduces the value of the beauty and function of the lake ecosystem.
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| Image of Limnic ecosystem Lake Tomohon, North Sulawesi |
Table. Number and Area of Lakes (Limnic ecosystem ) in Indonesia
|
Island |
Number of Lakes (Area> 10 Ha) |
Total Area (Ha) |
|
Sumatra |
170 |
190,043 |
|
Borneo |
139 |
84,231 |
|
Java
and Bali |
31 |
6,270 |
|
NTT
and NTB |
14 |
6,041 |
|
Sulawesi |
30 |
141,871 |
|
Maluku |
10 |
3,438 |
|
Papua |
127 |
59,830 |
|
AMOUNT |
521 |
491,724 |
Source: Nontji 1991