6. Primary Production and Eutrophication

Definition and sources Process of eutrophication Eutrophication in Freshwater Ecosystems Eutrophication in Marine Ecosystems Ecosystem effects of eutrophication

Eutrophication

«The increase of nutrients in an aquatic ecosystem  that stimulates the growth of aquatic plants and algae»

Process of Eutrophication

biological oxygen demand is the amount of dissolved oxygen needed (i.e., demanded) by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.

Eutrophication in freshwater systems

Eutrophic State

Extremely high concentrations of phosphorus and chl a and poorer water clarity

Shallow lakes often muddy and contain an abundance of aquatic plants

Eutrophication of lakes

• natural

• cultural

Eutrophication in experimental lake systems

Bio-control of eutrohication in lakes

Types of Eutrophication in lakes

• dystrophic

• oligotrophic

• mixotrophic

• eutrophic

based on colour and level of phosphorous

Marine Eutrophication

• pycnocline forms causing stratification - preventing oxygen prnetration

• waves on surface reoxygenate surface water

• Nutrients from runoff and accumulation of dead orgainc matter on the bottom cause HYPOXIA

• leads to asyphixyation of low mobility or sessile organisms

• Called dead zones

Deoxygenation

• climate change - more intense thermoclines for longer

• increase of deadzones world wide

Costal Waters

• nitrogen is usually the limiting factor

• include deltas and salt marshes are naturally eutrophic but have become more intense and frequent

• coastal upwelling also increases the productivity of algae

examples: Mississippi delta , Black Sea

Dead Zones

areas in aquatic environments with low oxygen levels that can no longer support marine life

These regions, often caused by nutrient pollution and excessive algae growth, lead to hypoxia, making it difficult for fish and other organisms to survive. They can significantly impact biodiversity and local fisheries.

Harmful Algal Blooms

• algae that produce toxins

• Algae block light and suffocate fish

• Toxic species

  • Pseudo-nitzschia : Amnesic, Shellfish. Poisoning

  • Alexandrium: Paralytic, Shellfish, Poisoning

  • Dinophysis: Diarrhetic, Shellfish, Poisoning

Ecological Impacts of Eutrophication

• Toxic or non-edible phytoplankton species

• Increase of gelatinous zooplankton

• Decrease in biomass of benthic and epiphytic algae

• Changes in macroalgal composition and biomass

• Reduced water transparency

• Water colouration and odour

• Reduced Dissolved Oxygen – DO levels

• Fish mass mortality

• Loss of economically important fish stocks

• Reduced aesthetic value of ecosystem

Sargassum Belt

• in the middle of the atlanic

• free floating

• increase in surface temperature, and increase in nutrients from amazon river (caused by increased agriculture and deforestation)

Botswana Elephant Deaths

• caused by cyanobacteria blooms

• spillover - ripple effects

• eutrophication effects terrestrial organisms

Remediation of Eutrophication

• increase shellfish aquaculture - filter phytoplankton from water column

• Increase seaweed aquaculture