Aquatic Ecosystems UPSC

Aquatic Ecosystems

Ecosystem consisting of water as the main habitat are known as aquatic ecosystem.

Classification Based on Salt Concentration:

1. Freshwater Ecosystem: 5 ppt (Lakes, ponds, springs, streams, rivers).

2. Marine Ecosystem: Equals to sea level; Approx. 35 ppt (Ocean).

3. Brackish Water Ecosystem: 5-35 ppt; (Estuaries, Salt marshes, mangrove swamps).

Aquatic Organisms:

Classification on Zone of occurrence and their ability to cross these zones,

1. Neuston: That rest or swim on the surface e.g. water striders.

2. Periphyton: That are attached or clinging to other plants or any other surface. e.g. Algae.

3. Plankton: That float on the surface of the waters e.g. phytoplankton like algae and zooplankton like rotifers.

4. Nekton: That swim on the surface e.g. fish.

5. Benthos: That are attached to bottom sediments e.g. sea grass.

Zones of Aquatic ecosystem

Factors limiting the productivity of Aquatic Life:

Sunlight:

1. Photic Zone:

Layer where sunlight penetrates and photosynthesis can take place.

2. Aphotic Zone:

Layer where sunlight penetration is too low and no photosynthesis but respiration takes place.

Dissolved Oxygen:

• Fresh water - 10 ppm. Oxygen enters through air water interface, and photosynthesis.

• It is influenced by temperature - warm water - Less O2 and vice versa.

• If it falls to 5 ppm or below then organisms will die.

Transparency:

Turbidity because of suspended particulate matter like clay or silt can limit productivity of life.

Temperature:

Water has higher specific heat than air. So temperature change will be slower. Temperature fluctuation can be fatal to aquatic organisms.

Ageing of lakes

Eutrophication

• Eutrophication is the ecosystem’s response to addition of artificial or natural substances, mainly phosphates, through detergents, fertilisers, or sewage to an ecosystem.

• Physical identification: Can see excess growth of green algae on the surface due to enrichment of the aquatic system by the addition of nutrients.

• Reason: leaching of phosphates and nitrates containing fertilisers from agricultural lands into lakes and rivers.

Results in:

• Algal bloom - unsustainable population explosion due to nutrient enrichment.

• Light penetration: This restricts the penetration of sunlight.

• Oxygen depletion: resulting in no/less photosynthesis since decomposition of the dead algae uses more oxygen. This process results in suffocation and death of aquatic animals.

• New anaerobic conditions: Clostridium botulinum, that produce toxins, come up in these conditions.

• Degradation of aquatic ecosystem.

Eutrophication can be natural or manmade (waste water effluent, runoff from agriculture).

Effects:

• Change in ecosystem - formation of Detritus layer, since algal blooms die and settle at the bottom resulting in marshy land.

• Decreased biodiversity: Algal blooms decrease oxygen availability and reduce penetration of sunlight.

• New species invasion: since aerobic conditions give way to anaerobic conditions.

• Toxicity - Neuro and hepatotoxins, O2, loss of coral reefs, changes in colour of water, and increases gelatinous zooplankton (toxic)

Mitigation 

• Riparian buffer.

• Interfaces between a flowing body of water and land created near the waterways, farms, roads, etc. in an attempt to fi lter pollution.

• Sediments and nutrients are deposited in the buf f er zones instead of deposition in water.

• Minimizing the non-point pollution.

• Nitrogen testing & modeling.

• N-Testing is a technique to find the optimum amount of fertilizer required for crop plants. It will reduce the amount of nitrogen lost to the surrounding area.

• Treatment of Industrial effluents.

• Organic farming & Integrated Farming System.

• Reduction in livestock densities • Improving the efficiency of use of fertilizer.

• Increase in efficiency of nitrogen & phosphorous removal from municipal waste water.

Measurement of Quality of water

Presence of organic and inorganic wastes in water decreases the dissolved Oxygen (DO) content of the water. 

Water having DO content below 8.0 mg L-1 may be considered as contaminated. Water having DO content below. 4.0 mg L-1 is considered to be highly polluted. 

DO content of water is im-portant for the survival of aquatic organisms. 

A number of factors like surface turbulence, photo-synthetic activity, O2 consumption by organisms and decomposition of organic matter are the fac-tors which determine the amount of DO present in water.

• The higher amounts of waste increases the rates of decomposition and O2 consumption, thereby de-creases the DO content of water. The demand for O2 is directly related to increasing input of organic wastes and is empressed as biological oxygen de-mand (BOD) of water. 

• Water pollution by organic wastes is measured in terms of Biochemical Oxygen Demand (BOD). BOD is the amount of dissolved oxygen needed by bac-teria in decomposing the organic wastes present in water. It is expressed in milligrams of oxygen per litre of water.

• The higher value of BOD indicates low DO content of water. Since BOD is limited to biodegradable materials only. Therefore, it is not a reliable method of measuring pollution load in water. 

• Chemical oxygen demand (COD) is a slightly better mode used to measure pollution load in water. It is the measure of oxygen equivalent of the require-ment of oxidation of total organic matter (i.e. bio-degradable and non-biodegradable) present in water.

Coral Reefs

▪ These are submarine morphological creatures with organic calcium’s structure.

▪ These are very beautiful, natural, wonder and among world’s oldest, most diverse and most productive ecosystem.

▪ In terms of biodiversity, they are the marine equivalents of tropical rainforest.

Mutualistic Relationship:

▪ They represent mutualistic relationship between coral animals and blue green algae called zooxanthellae.

▪ Corals obtain part of their livelihood from seawater and the remainder comes from the algae that live on the corals tissue.

▪ The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis. Corals live in huge colonies and their body is attached to one another.

▪ When corals die, the other corals grow on the dead calcareous debris.

▪ The coral reefs form along coast, islands or sea mountains, winds provide the foundation.

▪ Corals growth depends upon the calcium carbonate obtained from the sea.

Ideal Conditions for their Growth:

▪ Temperature: 25°C to 30°C limited to tropical belt, less than 18°C or 33°C - Corals tend to die

▪ Salinity: Corals need saline water. Average salinity 27 - 40 PPM (parts per million)

▪ Need shallow water, less than 60-65 metres

▪ Need submarine platforms

▪ Need Sediment free, clear water.

▪ Water which is disturbed by currents and waves is beneficial and it ensures supply of oxygen. 

Benefits of Corals to Mankind:

▪ Coral reef provides sites for diverse variety of plants and animals.

▪ It is Storehouse of living resources like fish. Reef fish accounts for about 15% of the worldwide fish catch

▪ They are a source of tourism revenue.

▪ Coral reefs help moderate atmospheric temperature by removing CO2 from atmosphere.

▪ Coral reefs protect coastlines from wave erosion.

Types of Reefs:

1. Fringing Reef: A reef grows out from the land and is connected to it.

2. Barrier Reef: A reef which is separated from land by a lagoon (part of sea which is cut off from rest of sea)

3. Atoll Reef: Formed away from coast in deep waters. Generally elliptical or circular in shape as it uses top of sea mountains to grow. Encloses a lagoon in the centre.

4. Patch Reef: Patch Reefs are isolated outcroppings (Patches) of coral that are in close proximity to each other but are physically separated by sand rings. They are typically found in shallow lagoons within a larger collective reef, or atoll.

Coral Bleaching:

▪ Natural disturbances which cause damage to coral reefs include violent storms, flooding, high and low temperature extremes, El Nino Southern Oscillation (ENSO) events, sub aerial exposures, predatory outbreaks and epizootics.

▪ Coral reef bleaching is a common stress response of corals to disturbances mentioned above.

▪ Bleaching occurs when,

• The densities of zooxanthellae decline and/or the concentration of photosynthetic pigments within the zooxanthellae fall. 

• If the stress-causing bleaching is not too severe and if it decreases in time, the affected corals usually regain their symbiotic algae within several weeks or a few months.

• If zooxanthellae loss is prolonged, i.e. if the stress continues and depleted zooxanthellae populations do not recover, the coral host eventually dies.

Causes of coral Bleaching:

• Increase in Ocean temperature due to climate change is causing coral bleach.

• Runoff water and Polluted water can dilute ocean water and bleach near shore corals.

• Overexposure to Sunlight and irradiance can bleach shallow corals

• Extreme Low tides causes corals get exposed to air and bleach.

Mangrove

• Mangroves are various large extensive types of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics - mainly between latitudes 25 N and 25 S.

• Mangroves are salt tolerant trees (halophytes) adapted to live in harsh coastal conditions. They contain a complex salt filtration system and complex root system to cope with salt water immersion and wave action. They are adapted to the low oxygen (anoxic) conditions of waterlogged mud.

Characteristics of Mangroves:

▪ Evergreen land plants growing on sheltered shores (deltas, estuaries, bays, creek, and barrier islands)

▪ Physiological adaptation to salinity stress and to waterlogged anaerobic mud.

▪ Need abundant sunlight, has the ability to absorb fresh water from saline water source.

▪ Pneumatophores (Blind Roots): They have special roots like Prop root, pneuma-tophores, stilt roots which help to impede water flow and stabilises the coastal shores.

▪ They act as breeding ground for fish.

▪ Moderates monsoonal tidal floods and reduces inundation of coastal lowlands. Prevent coastal soil erosion.

▪ Protects coastal land from Tsunami, hurricane, floods etc.

▪ Enhances natural recycling of nutrients.

▪ Supports numerous flora, fauna, and avifauna. Edge effect can be seen here.

▪ Supplies raw materials - wood, medicinal plants, edible plants

▪ Recreation and tourist attractions.

Threat from Human Interference:

▪ Approximately 35% of the mangrove area was lost during the last several decades of the 20th century.

▪ The UNEP (United Nations Environment Program) & Hamilton (2013), estimate that shrimp farming causes approximately a quarter of the destruction of mangrove forests.

▪ Likewise, the 2010 update of the WMA (World Mangrove Atlas) indicated a fifth of the world’s mangrove ecosystems have been lost since 1980.

▪ They are also destroyed for conversion of area for agricultural purposes, fuel fodder, mining, oil spills, aquaculture (shrimp), use of fertiliser industrial purposes.

Mangroves in India

Wetland Ecosystem

Is a land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem.

Ramsar Convention Definition:

▪ Wetlands are areas of marsh, fen, peatland, or water whether natural or artificial, permanent, or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres.

▪ It’s an intermediate stage between deep water habitats and terrestrial habitats.

▪ Habitat experience periodic flooding from adjacent deep-water habitat and plants and animals are adapted to shallow flooding.

▪ For Ex: Lake littorals, floodplains, marshy, swampy areas, bogs, fens, mangroves.

Functions of wetlands

• Habitat - for a variety of flora and fauna

• Filters sediments and nutrients from surface water

• Nutrient recycling

• Water purification

• Flood mitigation

• Ground water recharging

• Controlling rate of runoff in urban areas

• Buffer shoreline against erosion

• Stabilisation of local climate

• Tourism, recreation and cultural heritage.

Reasons for depletion

• Conversion of lands for agriculture

• Overgrazing

• Removal of sand from beds

• Aquaculture

• Habitat destruction and deforestation

• Pollution

• Domestic waste

• Agricultural runoff

• Industrial effluents

• Climate change

Mitigation measures

• Proper survey and demarcation

• Protection process of natural 

regeneration

• Artificial regeneration

• Afforestation

• Weed control

• Wildlife conservation

• Removal of encroachments

• Eutrophication abatements

• Environmental awareness