Productivity in Ecosystem

1.0What is Productivity? 

The productivity of an ecosystem refers to the speed at which new biomass is generated, measured in terms of energy or weight per unit area. Biomass, the total organic matter present in an ecosystem at a specific time, encapsulates this productivity. 

Several factors influence productivity, including sunlight, temperature, rainfall, nutrient availability, and the indirect effects of human activities. To compare different ecosystems, productivity is often assessed over the entire year, calculating annual production as the generation of new biomass per unit area within a year.

2.0Types Of Productivity

Productivity is of two types which are named as ; primary productivity and secondary productivity. 

1. Primary Productivity in ecosystem :

• Primary productivity revolves around the rate at which autotrophic organisms, notably plants, algae, and certain bacteria, harness solar energy to convert it into organic compounds through processes like photosynthesis. These primary producers play a pivotal role in capturing and transforming energy from the sun into a form accessible to other organisms in the ecosystem. Primary productivity is often quantified in terms of biomass or energy produced per unit area over a specific time, commonly expressed as grams per square meter per day (g m⁻² d⁻¹).
• There are two main aspects to primary productivity: Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).

Gross Primary Productivity (GPP) :

• This measures the total energy fixed by photosynthesis in an ecosystem, expressed as Kcal/m²/yr. GPP includes all the energy captured by plants. However, only a part of this energy is utilized for plant growth, while the rest is used in the plant's respiration and released as heat into the environment.

Net Primary Productivity (NPP) :

• NPP is a more specific measure as it subtracts the energy used by the plant in respiration (R) from GPP. This subtraction gives us the actual rate of production of new biomass available for consumption by other organisms. NPP represents the energy that contributes to the growth of plants and the sustenance of the ecosystem.

Net Primary Productivity (NPP) = Gross Primary Productivity(GPP) - Respiration(R)

2. Secondary Productivity in ecosystem :

• Secondary productivity relates to the rate at which heterotrophic organisms, such as herbivores (consumers). They convert the organic compounds produced by primary producers into their own biomass. This process illustrates the flow of energy through different trophic levels in the ecosystem's food web. Animals and other heterotrophs are key players in secondary productivity, and similar to primary productivity, it is measured in terms of biomass or energy produced per unit area over a specific time.
• Net Community Productivity Or Net Productivity : The rate of storage of organic matter not used by the heterotrophs
• Net community productivity (NCP) = net primary productivity (NPP) – Energy used by Heterotrophs (HR) 

3.0Movement Of Energy Between Trophic Levels 

• The movement of energy between trophic levels in an ecosystem follows the 10% law, a fundamental ecological principle. This law dictates that, on average, only about 10% of the energy from one trophic level is transferred to the next higher trophic level.
• At the base of the food chain, producers, such as plants, capture sunlight and convert it into chemical energy through photosynthesis. When herbivores consume these plants, they obtain energy, but only about 10% of the plant's energy is transferred to them. The rest is lost as heat or used in metabolic processes.
• Carnivores or omnivores that consume herbivores experience a similar energy transfer, with approximately 10% of the herbivore's energy passed on to them. This pattern continues up the trophic levels, resulting in a 90% loss of energy with each transfer.

4.0Factors Affecting Ecosystem Productivity

Ecosystem productivity is determined by many factors and can be very spatial and temporal in nature.

1. Solar Energy: The amount of light is what determines the rate of photosynthesis and therefore primary productivity. Tropical regions with abundant sunlight throughout the year are likely to have higher productivity as compared to polar or temperate regions with limited sunlight during certain seasons.
2. Availability of Nutrients: Some of the essential nutrients for plants growth are nitrogen, phosphorus, and potassium. Ecosystems with copious amounts of such nutrients, such as estuaries and wetlands, tend to have high productivity. Those with low nutrient levels are open oceans or deserts, and productivity is low in these regions.
3. Water Availability: Water is necessary for the photosynthesis process. Land systems in arid, semi-arid, and hot desert regions, such as deserts and grasslands, tend to have lower productivity than humid systems, like tropical rainforests.
4. Temperature: Temperature Influences both plants and animals' metabolic activities. The rate of productivity is enhanced when it is warm by accelerating photosynthesis and growth rates. Tundra-type cold conditions lead to low productivity because the sun energy is minimal, and biological processes are slow.
5. Carbon Dioxide (CO₂): CO₂ is an important input in photosynthesis. Increased CO₂ can enhance primary production, in an effect known as CO₂ fertilization, but this potentially may be constrained by other factors including nutrients.
6. Disruptions: Natural disturbances (such as fires, floods and hurricanes) and human activities (including deforestation and pollution) can have a very considerable impact on productivity in the ecosystem. Some of these disturbances can actually recycle nutrients and rejuvenate the ecosystem, while others can result in degradation and decreased productivity.

5.0Productivity in Different Ecosystems

Ecosystem productivity varies dramatically between biomes based on the interplay of factors listed above.

1. Tropical Rainforests: These are the most productive ecosystems on Earth, with high NPP due to warm temperatures and abundant rainfall and year-round growing seasons. They support great biodiversity and are the world's critical carbon sinks.

2. Temperate Forests: Temperate forests have average productivity, with seasonal fluctuations in NPP. During winters, these ecosystems are dormant, which alters their annual NPP.

3. Grasslands: Grasslands are of moderate productivity and highly reliant on seasonal rainfall. Often, water is the limiting factor to productivity in grasslands, and random fires work to maintain species balance by removing dead biomass.

4. Deserts: The deserts are of low productivity due to the scarcity of water and nutrients. There is some sparse vegetation that exists in deserts but these live in very harsh conditions, but an ecosystem it hosts only minimum primary and secondary productivity.

5. Oceans: Oceans take up more than 70% of Earth's surface; however, they generally tend to be low in productivity per unit area because of nutrient limitations in most open waters. However, ecosystems like coral reefs and coastal upwellings are highly productive due to nutrient cycling as well as sunlight availability.

6. Wetlands: Wetlands are highly productive systems, acting as ecological hotspots for biodiversity. In addition, they play an essential role in providing ecosystem services such as water filtration and flood regulation.

6.0Human Impacts on Ecosystem Productivity

Generally, human activities affect ecosystem productivity. They include agriculture, deforestation, urbanization, and industrialization; these activities have huge impacts on ecosystems. Often, they cause habitat destruction, soil degradation, and loss of biodiversity, which contributes to the inability of ecosystems to perform effectively.

1. Land Use Changes: Deforestation and land conversion for agriculture also reduces the total area available for primary production. Monoculture farming also cuts down further on productivity due to nutrient depletion in the soils, among other factors affecting biodiversity.
2. Pollution: Industrial pollution, including air, water, and soil contaminants, can also reduce both primary and secondary productivity through adverse health effects on organisms and disruption of nutrient cycles.
3. Climate Change: The changes in temperature and precipitation patterns due to climate change will, in turn, lead to changes in productivity in an ecosystem. In a few areas, the warmer temperatures would enhance productivity, but in others, it could decline sharply because of drought and extreme weather events.
4. Eutrophication: Over-enrichment of aquatic ecosystems can be attributed to excessive inputs of nutrients, primarily in the form of nitrogen and phosphorus from agricultural runoff. While it may initially enhance productivity, a surplus input of nutrients may result in harmful algal blooms, further decreasing oxygen levels and causing a collapse in secondary productivity.