Yallop 7-10 Flashcards
what is the result of anthropogenic eutrophication in lakes?
loss of biodiversity
toxicity from cyanobacterial blooms
poor light penetration
loss of architecture
what accelerated eutrophication?
post 1930s agricultural intensification
what ecosystem services do plants in shallow lakes provide?
high plant biomass,
ph oxygenates water
food source for herbivores
surface for epiphyte growth - mainly bacteriaand algae which make a biofilm.
architecture provides refuge for small animals
main photosynthetic plants and algae
- Elodea nuttallii - Nuttall’s pondweed, rooted/floating.
- Potamogeton pectinatus - fennel pondweed, grassy.
- Potamogeton natans - broad-leaved pondweed, leaves float on surface.
- Ceratophyllum demersum- Rigid hornwort
- Chara aspera - rough stonewort
- Duckweed - Lemna gibba
what instruments can be used to quantify aquatic vegetation?
Bathyscope
Underwater camera
Ekman grab
Hydroacoustic methods
How does Hydroacoustic mapping of lake vegetation work?
sends down signal, tells you whether bottom is silt, sand or vegetation.
gives PVI - percent volume infested
can measure at diff time points, eg after herbivores introduced, diff seasons, or just long term.
common phtyoplankton in shallow lakes
Diatoms
green algae
cyanobacteria
sample by dragging net of 40micrometre mesh size around.
concerns that climate change may favour cyanobacteria over other phytoplankton.
3 key cyanobacterial bloom forming genera
Anabena - spiral shape
Microcystis - round, contain potent neurotoxins which kill cattle in australia.
Aphanizomenon - long filaments
what forms the benthic component of autotrophic community?
Biofilms
grow on hard and soft substrates in FW lakes, made of diatoms and green algae, cyanobacteria and small heterotrophic protists.
imp for microbial loop/nutrient recycling
what forms the grazing community in shallow lakes?
Zooplankton
rotifers: filter 0.8 ml d-1
Daphnia/Cladoceran: filter 1-60 ml d-1
Copepods: 1-20 ml d-1
can effectively clear water bodies by consuming large numbers of algae.
Herbivorous snails:
Effectively prevent build up of biofilms on plant surfaces which cause plant death.
Provide food source
5 feeding classes of fish in shallowlakes?
- Zooplanktivore eg Juvenile perch
- Piscivore - Pike, Mature perch
- Benthivore- Tench, Bream, Roach, Carp
- Molluscivore - Tench
- Omnivore/herbivore - Rudd, Roach, Grass Carp.
which are some desireable and undesireable fish
desireable - Tench and rudd, not zoo planktivorous for the longer periods of their lives.
Undesireable - Bream, creates turbidity
what are some periphyton processes?
biofilms oxyenate water by ph.
herbivores inc snails, grazing and clean surfaces,lessen effect of heavy metals and toxins which would adsorb to sediments and be taken up by plants.
sediments get anoxic quickly below surface due to bacteria.
what effects can removing and introducing fish species have?
increasing piscivores will decrease zooplanktivorous fish, allowing increase in other planktivores such as Chaoborus, key invert pred.
If piscivores removed, more zooplanktivores, reducing zooplankton, increasing phytoplankton, which can result in turbidity.
what has caused selection for larger zooplankton and smaller phytoplankton species in some lakes?
comp between invert and fish planktivores has lead to dominance by larger zooplankton species. they can ingest larger range of phytoplankton sizes, but excrete more slowly leading to reduced phytoplankton biomass.
study of Crystal lake in connecticut
Introduction of zooplanktivorous Alosa (shad) shifted the zooplankton community to smaller species.
Brookes and dodson, 1964
study by pace et al 1999 of nutrient addition.
2 lakes:
A - dominated by planktivorous minnows
B - dominated by piscivorous bass.
B has much larger crustaceans due to reduction in planktivory, whereas in A, minnows eat larger xooplankton. nutrient enrichment had no effect on length of crustaceans *indicator of grazing potential)
nutrient enrichment increased bacterial and primary production in both lakes, but much more in A.
the fact that no change was seen in grazing community, but the bacterial and primary production increased upon nutrient addition, shows that nutrient addition is an important bottom up effect in structuring the community.
example of top down control, and vollenweider model.
as P loading rate increases:
- increase in chl. conc (measure of algal biomass)
- a control lake matches the rate of increase, but minnow and piscivore dominated lakes deviate form model.
- Piscivores are exerting a top down supression on planktivores which are controlling zooplantkon, meaning more phytoplankton in piscivore lake, which is why it is further away from model.
large cladocera in planktivore lake = top down effect on phytoplankton.
large cladocera reclycle nutrients more slowly which is why its also lower.
