(M2) Lecture 11 - Eutrophication Flashcards
Definition of eutrophication and main effect
The process of nutrient enrichment, increased production of organic matter, and subsequent ecosystem degradation.
Excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis (primary production)
Definition of cultural eutrophication and sources
Increases in plant and algal growth due to anthropogenic nutrient inputs.
Sources
- Sewage
- Fertilizer runoffs
- Phosphorus-containing detergent (pre-1970s)
Difference between oligotrophic, mesotrophic, and eutrophic waters
Oligotrophic: low productivity of the primary producer
Mesotrophic: moderate productivity of the primary producer
Eutrophic: high productivity of the primary producer
Limiting factors vs nutrient excess: definitions, differences, and examples (N, P, Fe)
Principle of Limiting Factors: Certain ecological functions are controlled by whichever environmental factor is present in the least supply relative to demand. The most limiting factor determines the yield potential.
- Ex: light, water, nutrients, CO2
Nitrogen
- N is the main limiting nutrient in terrestrial ecosystems; plants compete
- human activities affect geochemical cycles
Phorphorus
- P is the main limiting nutrient in freshwater ecosystems
- found in ROCKS (very little in atmosphere)
- most natural sources from the weathering of rocks
- P molecules can attach to lake sediments once released from runoffs; affects food chains
Case Studies: In freshwaters- Lake Erie and the importance of the ELA
Lake Erie
- P loading
- has lowered since the 70s but P continues to enter the lake from rivers; due to agriculture
- causing seasonal algae blooms (summer; more sunlight and warmer, runoff from melting)
- even though we know the cause, despite the bans and restrictions blooms are happening; trying to at least control the intensity of the problem
- Harmful algal blooms formed
Case Studies: In coastal marine ecosystems- Gulf of Mexico (due to Mississippi River inputs)
- N concentration is the greatest, collected from terrestrial enviro (most crops using fertilizer high in N, instead of P)
- high concentration of N in the Mississippi = more N in the gulf of Mexico
- P has a greater impact but N still has an impact and causes a spike in primary production
- Hypoxic zone in the Gulf of Mexico
- every yr different concentrations of nutrients reach the gulf
- in order to see change we need to implement regulations on crop fertilization or waste water treatment
Interaction eutrophication- trophic cascade: how adding or removing a trophic level impacts eutrophication
Piscivore (top predator)
- ex. pike
Planktivore
- ex. minnows
Zooplankton
- herbivore
Phytoplankton
- autotroph
With top predator: less bad algae bloom bc there are more zooplankton feeding on the algae; with less algae the CO2 concentration did not decline as much
- pike increase
- minnows decrease
- zooplankton increase
- phytoplankton decrease
Without top predator: eutrophication is worse
- minnows increase
- zooplankton decrease
- phytoplankton increase
Controls on Primary Production
1. Top-down Controls (herbivores)
2. Bottom-up Controls (nutrients, water, light)
Main problems caused by eutrophication
- Harmful algal blooms
- Hypoxic dead zones
Harmful algal blooms: definition and how they are harmful (types of toxicity)
Cyanobacteria: phylum of bacteria that can photosynthesize
- Some produce toxins: neurotoxins, hepatotoxins, dermatotoxins
Microcystis sp.
- Most common bloom-causing cyanobacteria
- Can produce both neurotoxins and microcystins, a type of hepatotoxins
Nodularia sp.
- Brackish genus, produces potent hepatotoxins called nodularins that can greatly harm humans
You can be exposed through swimming but also through drinking. Limits are different depending on the Country.
Hypoxic dead zones: definition, how they form, and examples
Hypoxia: a reduced concentration of dissolved oxygen in a water body leading to stress and death in aquatic organisms.
Dead zones: hypoxic areas in aquatic ecosystems, typically a consequence of pollution, eutrophication, and high rates of decomposition, that are essentially devoid of life.
How the dead zone forms:
1. During the spring, sun-heated freshwater runoff from the Mississippi River creates a barrier layer in the Gulf, cutting off the saltier water below from contact with O2 in the air.
- Nitrogen and phosphorus from fertilizer and sewage in the freshwater layer ignite huge algae blooms. When the algae die, they sink into the saltier water below and decompose, using up oxygen in the deeper water.
- Starved of O2 and cut off from resupply, the deeper water becomes a dead zone. Fish avoid the area or die in massive numbers. Tiny organisms that form the vital base of the Gulf food chain also die. Winter brings respite, but spring runoffs start the cycle anew.
