River VL 6 Flashcards
What are harmful algal blooms (HABs)?
Harmful algal blooms (HABs) are events characterized by the rapid and excessive growth of certain species of algae (phytoplankton) in aquatic environments, leading to harmful ecological, economic, and health impacts.
These blooms can occur in marine and freshwater ecosystems and are often associated with the proliferation (Wucherung) of toxic or nuisance (Plage) algae species.
What are common types of HABs?
- red tides (often inmarine waters)
- green blooms
- cyanobacterial blooms
Which river in Germany had recently been subject to a HAB? What did it result in?
- River Oder in 2022
- Mass die-off of fish, mussels and snails
- (fish density decrease by 60%; over 60% mussels killed in groine fields)
- Effects on food web
Which algae was causing the HAB in river Oder? How does this algae feed?
Prymnesium parvum
- Collective term “golden alga”
- Microscopic, single-celled flagellate organism belonging to the class Haptophyta. Prymnesium parvum has two flagella, for movement, and it is producing toxins.
- Mixotrophic: feed autotrophically (photosynthetic) and heterotrophically (on organic material, including bacteria, small algae, and dissolved organic compounds in the water).
What are ideal conditions fo Prymnesium parvum blooms?
- fast growth rte at 20-30°C
- High nutritient availability promotes growth
- Long water residence time (=low flow rate) > in lakes and brakisch water, reservoirs and groins
What initiated the mass development of Prymnesium parvum in river Oder?
Human made environmental disaster:
* High discharge of salt into the river by coal mining companies (salinity increased > 0.5 PSU)
* High nutrient input from agriculture and sewage plants
* River regulation
* Climate change
Toxin: “prymnesin”
- Conditions for producing toxins ≠ optimal growth conditions -> (unclear when produced)
- Destroys gills of aquatic organisms (fishes, mussels, some snail species) -> lack of oxygen
- Enter internal organs -> decomposition by e.g. destroying red blood cells
- Negative effects on reproduction of zooplankton and other phytoplankton species.
- Dead organisms release further nutrients into the water…
When was the first time, a red tide was mentioned?
In the bibel
HABs increase globally in…?
- Frequency
- Size (increase of expansion)
- Duration
- Time frame: These increases started gradually since 1995
Main cause of HABs is nutrient pollution. Where can the nutrients come from?
- Sewage plants (not filtering urea good enough)
- Agricultural fertilizers
- Discharge of waste or sewage by (mining) companies
What is a microalgae?
Informal term for photosynthetic, mainly eukaryotic (but sometimes prokaryotic) organisms, which lack multicellular specialized reproductive structures, roots, stems and leaves of plants.
Most harmful algal species of fresh waters and marine systems are…? Which other phytoplankton groups carry HA species?
Fresh water: Cyanobacteria (common in fresh water, but also marine systems)
Marine systems: Dinoflagellates (75% of marine HA species).
And then there are a phytoplankton groups carrying HA species, e.g.:
Diatoms, Hyptophytes
There are two types of HABs. Describe how the differ!
Type 1: Toxic algal blooms
* Production of toxins
* Toxins enter gills and eventually the food web (Bioaccumulation and Biomagnification).
Type 2: High-biomass HAB
* Can be non-toxic or toxic
* Kills fish and invertebrates due to oxygen depletion due to respiration & decomposition of high algal biomasses
* Decomposition needs lots of oxygen!
* Alters other conditions, e.g. light conditions
Explain bioaccumulation and biomagnification
Bioaccumulation
* Entering of toxins/pollutants into the food chain -> Accumulation of contaminants in biological tissues.
Biomagnification
* Pollutants concentrate in organisms as they move up from one trophic level to another.
Explain “hypoxia” and “anoxia”:
Hypoxia
* Low oxygen levels insuicient for aquatic organisms, reducing biodiversity and impacting fisheries.
Anoxia
* Complete absence of dissolved oxygen, causing severe harm to aerobic organisms and often leading to fish kills and mass mortality.
Terms “normoxia” and “hyperoxia” are self-explanatory then.
Explain mechanistically how harmful algal blooms can lead to hypoxia/anoxia and describe two negative impacts of hypoxia/anoxia on aquatic organisms!
Mechanism of Harmful Algal Blooms Leading to Hypoxia/Anoxia:
* Algal Bloom Growth: Excess nutrients (especially nitrogen and phosphorus) cause rapid growth of algae.
* Algae Death and Decomposition: When the algae die, they are decomposed by bacteria. This process consumes large amounts of dissolved oxygen.
* Oxygen Depletion: As bacterial decomposition continues, oxygen levels in the water drop, leading to hypoxia (low oxygen) or anoxia (no oxygen).
* Reduced light penetration is another factor leading to hypoxia/anoxia
Two Negative Impacts on Aquatic Organisms:
1. Fish and Invertebrate Death: Lack of oxygen causes fish and other aerobic organisms to suffocate, leading to mass die-offs.
2. Habitat Loss: Hypoxia/anoxia forces mobile organisms to leave the area, disrupting ecosystems and food chains. Stationary organisms (e.g., shellfish) often die due to prolonged oxygen deprivation.
