L5 Factors determine the Primary Productivity

Factors That Determine Primary Productivity

  • Primary productivity in aquatic environments is influenced by a range of factors, including:

    • Light availability

    • Nutrient availability

    • Temperature

    • Salinity

Projection of Primary Productivity (IPCC 2019)

  • The Intergovernmental Panel on Climate Change (IPCC) provides projections for primary productivity under different climate scenarios (RCP8.5 and RCP2.6).

    • Data illustrated with ANPP (Above Net Primary Production) measured in grams of carbon per square meter per year (g C m² yr¹) over time from 1900 to 2100.

Limiting Factors of Primary Productivity

Open Ocean vs. Coastal Waters

  • Open ocean areas are generally oligotrophic, meaning they have low productivity due to:

    • High light penetration with less turbidity.

    • Limited nutrient availability, primarily nitrogen (N) and phosphorus (P).

  • Coastal and upwelling areas are eutrophic and are characterized by:

    • Higher productivity due to nutrient-rich waters (yellow-green.

    • Increased turbidity decreases light penetration.

Availability of Light

  • Solar radiation primarily consists of visible light, known as Photosynthetic Active Radiation (PAR), which ranges from 400 to 700 nm.

  • Blue-green wavelengths (~500 nm) penetrate the water most effectively.

Algal Accessory Pigments

  • Different algal phyla possess unique accessory pigments that facilitate photosynthesis:

    • Chlorophyta (Green algae): Chlorophyll b

    • Charophyta (Charophytes): Chlorophyll b

    • Euglenophyta (Euglenoids): Chlorophyll b

    • Ochrophyta (Brown algae): Chlorophyll c1 + c2, fucoxanthin

    • Chrysophyta (Yellow-brown algae): Chlorophyll c1 + c2, fucoxanthin

    • Rhodophyta (Red algae): Phycoerythrin, phycocyanin

    • Cyanophyta (Blue-green algae): Phycocyanin, phycoerythrin

    • Pigments can help differentiate algal taxonomic groups.

Euphotic Zone and Light Penetration

  • The euphotic zone is defined as the area in the water where enough light remains to support plant growth, typically extending to where light is 1% of surface PAR.

  • Different organisms have varying light needs; for example, seagrasses require more light compared to nanoplankton or cyanobacteria, which can survive with minimal light.

Photoinhibition

  • Defined as reduced photosynthesis rates due to high irradiance.

  • Plants adapted to high light conditions can better withstand photoinhibition.

  • Mechanisms to reduce damage include:

    • Structural adjustments and photosynthetic processes modification.

    • Changes in pigment composition.

Adaptation to Photoinhibition

  • Marine red algae experience photoinhibition at high light levels but recover quickly by evening.

  • Organisms such as Dictyota dichotoma adjust their orientation to minimize photodamage, protecting photosynthetic pigments from excess light.

Nutrient Availability

  • The major nutrients limiting primary productivity are nitrogen (N) and phosphorus (P), sourced from river runoff and atmospheric deposition.

    • Nitrogen is often the more limiting nutrient, with phosphorus being second, except in coral reef ecosystems.

  • Nutrient concentrations can vary widely across marine habitats.

    • N concentrations include nitrate (NO3−), nitrite (NO2−), and ammonium (NH4+).

    • Phosphorus is generally lower than nitrogen.

Temperature Effects

  • Temperature impacts the solubility and availability of gases such as CO2 in seawater, affecting marine photosynthetic organisms.

Seasonality of Primary Production

Tropical Regions

  • Consistent solar radiation means light is not a limiting factor, but high temperatures create stratified waters preventing nutrient mixing.

Temperate Regions

  • Seasonal stratification affects nutrient and light availability.

    • Spring bloom occurs when nutrients are replenished post-winter mixing.

Polar Regions

  • Cold water with consistent nutrient availability, light returns in spring leading to a spring/summer phytoplankton bloom.

High Nutrient Low Chlorophyll (HNLC) Regions

  • Areas of high nutrient availability but low phytoplankton biomass due to factors like low iron concentrations and grazing pressure.

Inorganic Carbon Dynamics

  • In marine environments, CO2 reacts with water to form carbonic acid, dissociating into bicarbonate and carbonate ions.

  • Bicarbonate is the primary inorganic carbon available for photosynthesis in many marine plants.

Ocean Acidification

  • Increased atmospheric CO2 leads to lower seawater pH, affecting marine organisms, particularly calcifiers like corals.

Measurement of Primary Production

  • Primary production can be challenging to measure compared to other water quality parameters.

  • Various methods include:

    • Direct: Plankton nets, oxygen evolution techniques, radiocarbon measurements.

    • Indirect: Satellite monitoring to estimate chlorophyll concentrations.

Conclusion

  • The understanding of primary productivity is crucial in the context of climate change and ecological assessments, emphasizing the interconnectedness of light, nutrients, temperature, and salinity in marine environments.