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.
What abiotic components of lakes?
light
nutrients
which major nutrients cause eutrophication?
N and P from agricultural run off.
define
TP
TON
Total phosphorous - organic and inorganic. measure of P locked up in algae and other orgs within the water.
Total Oxidisable Nitrogen - nitrate and nitrite
Levels of TP and TON in many lakes fit with Vollenweider model, and deviations are due to composition of higher trophic levels.
what is euphotic depth
Vertical attenuation coefficient, k or E
Depth (m) where light falls below 1% of the surface irradiation
Measure of the attenuation of light with depth
What are 4 trophic state classes
Oligotrophic
mesotrophic
Eutrophic
Hypereutrophic
what effect does high/low macrophyte cover have
found in study of 27 finnish lakes:
higher: increased secchi depth
lower Phosphorous- 0-400microg Pl-1
low: lower transparency, range of P levels but mainly higher: 50 -1100
what is a direct driver of alternative equilibrium turbidities?
draw a graph of this.
macrophyte cover.
there is a critical turbidity level at which it can easity switch between states.
graph of nutrients on x and turbidity on y. 2 curves, for with and w/o vegetation.
what is the marble in a cup model?
shows alternative stable states
shows transition between macrophyte and phytoplankton dominated states as nutrients increase cause turbidity to increase. valleys show stable areas. hilltop represent a very quick switch which only a major disturbance can induce.
describe experiment in norfolk broads
Bure marshes national nature reserve
Balls et al 1989
Lakes were slowly deteriorating to turbidity
divided up small ponds to create mini ecosystems
with plants, water was clear, may be able to experimentally add nutrients to tell if nutrients driving turbidity.
what are 6 buffers of macrophyte dominated state?
- supression of eddy currents - vegetation on surface buffers water mixing by wind.
- water chemistry - can be harmful to fish
- structural refuges for zooplankton
- provision of habitat grazers of periphyton eg snails
- allelopathy - produce phenolic compounds to deter growth of pytoplankton
- firm sediment for plant germination and support.
what are 6 buffers of phytoplankton dominated state?
- Maintenance of open habitat and wind mixing
- early growth of algae
- lack of refugia
- lots of small phytoplankton
- High zooplanktivorous: piscivorous fish ratio
- Sediments unsuitable for growth of plants.
what are the main feedback loops creating existance of alternative equilibria in shallow lakes? scheffer et al
see diagram,
what can change a turbid lake into the alternative clear water state
Shock therapy (e.g. biomanipulation, pesticides, )
describe case study of Zwemlust
lake characteristics and action
Lake Zwemlust, netherlands, filled by seepage from river Vecht
Lake characteristics:
Surface area: 1.5 ha
Mean depth: 1.5 m
Max depth: 2.5 m
Secchi depth: 0.1-0.3 m
previously v popular swimming lake, became turbid.
1. March 1987- Fished out the lake with seine nets and electrofishing
2. drained lake
3. added: bundles of willow twigs attached to the bottom, 1kg daphnia magna and D. hyalina, 1600 pike fingerlings and 140 rudd, 200 waterlillies.
4. lake refilled by 3 days
Changes in Fish Community following Biomanipulation
of zwemlust
- rudd and pike not initially well established as not enough daphnia and lack of suitable habitat.
- tench and roach undesireable so not added,so caused increase in snails which became infected with parasite, Trichobilharzia ocellata, causing swimmers itch!
Changes in Phytoplankton Community following Biomanipulation
in zwemlust
- Chlorophyll a fell from summer maxima of 200 to < 10 µg l-1
- Cyanobacteria (Microcystis): replaced with green algae
- water remained transparent for a few years (Secchi 2.5 m)
Changes in Macrophyte Community following Biomanipulation
in zwemlust
Elodea nuttallii - very well initially, then declined after 1990, due to coot herbivory. large no. coot can clear vegetation v rapidly.
may have been better to make alternative sites for coot
Lessons learned from early Biomanipulation studies
- nutrient conc was too high
2. manipulation in isolation may not work. catchment considerations are important.
6 drivers of state switches
- eutrophication, nutrient induced changes
- storms
- water lavel changes
- fish stock management
- bird induced changes
- pesticides
case study of a successful biomanipulation
lake characteristics and problem
barton broad, East Anglia
Surface Area: 67 ha
High nutrients: connected to River Ant + 2 STW’s causing Internal loading of nutrients.
popular for boating - bankside erosion, ripping up macrophytes, reed beds and destabilising sediment. harmful antifowling paint on boats. coypu/marsh dog caused erosion
cause of internal loading of P
if anoxic, P in sediments becomes soluble - 1000x more P exchange. if high O2, binds to sediment.
seasonal thermal layering in lake, at depth O2 depletion, causing stratification.
Action in Barton broads to reduce P conc
why did initial attempts not work?
when condition became unuseable for recreation, authorities took action. Improvements in sewage treatment and dredging of sediment enriched P to sediment lagoons.
‘phosphate stripping’ - addition of iron salts to precipitate P.
Riplox method - inject Nitrates into sediments to create oxidised microzone at top of sediment to prevent release of P.
no effect of this reduction programme, due to internal loading of P.
second attempts to change barton broads? 2 methods
results
- dredge out sediment, removed 305000m3 sediment from 1996-2001, using pump, put in adjecent fields.
left to dry in sun then taken away. however, was very close tolake, so P just leached back in.
P reduced. - biomanipulation using PVS curtain to formfish barrier exclosures, as they were constantly entering from rivers. removed fish eating the zooplankton. exclosured had less circulation
measurements of chl conc, reduced to 16.4 micro g /L, from 70. 50% reduction in surface sediment, 3-20cm. phytoplankton changed from diatoms and cyanobacteria to green algae and cyanobacteia.
Fish stock reduced from 90,000 perha, to 4-7000.
plants reappeared in 3 years.
study of reducing P in Loch leven.
initially reduced point and diffuse sources of P by 60%, but took 15 years for full chemical recovery, due to release of P in chemical stores. evidence of recovery from presence of Pochard which feed on charophytes and other macrophytes.
left at reasonable conc to keep lake in ‘good ecological status’.
fish stocks recovered too.
lead to increased growth in depeer waters due to more light penetration, which is self stabilising.
methods of removing locked up P from sediment
Only released when the surface of the sediments, at the water interface, are anoxic.
plastic sheeting and fly ash to seal it away but only if you don’t want to restore plants.
Otherwise you can dredge to remove it.
how do reed beds act to reduce turbidity?
- Biosequestration of nutrients and heavy metals
- Binding of suspended solids (e.g. algae and bacteria within root biomass)
- Constructed wetlands
Can they be used to clean up sewage effluent before it reaches a lake? - reed beds were destroyed in barton broads by boats and encroaching shrubbery..
- good breeding ground for larval damselflies. also attract herbivorous birds so dont want too many.
Barley straw as a treatment to reduce algal/cyanobacterial blooms.
maybe, not fully convincing.
releases substances which reduce cyanobacteria.
study of phoslock
Lake Flemington
long history of eutrophication.
P input form pigfarm
cyano blooms in summer
natural recovery unlikely. no surface outflow.
25 tonnes Phoslock applied to seal sediment, potential to speed up ch recovery.
however ignored all the benthic biota. too early to know if really successful.
Lessons learned from three decades of lake restoration
Lakes can keep switching state - seen in lake Takern and Krankesjon.
must contantly monitor and biomanipulate where possible
