7 Wetlands and Saltmarshes Flashcards
Definition: Wetland
- an ecosystem that arises when inundation by water produces soils
- soils dominated by anaerobic processes
- that forces the biota, particularly rooted plants, to adapt to flooding
examples of coastal wetlands
- Marshes
- Swamps
- Mangroves
- Fens
- Ponds
- Wet meadows
- Bogs
Importance of coastal wetlands
- Coastal protection
- Food and material production
main factors that control wetland types
- Hydrology
- Fertility
- Disturbance
- Competition
- Herbivory
- Burial
key factor that distinguishes between coastal and interior wetlands?
salinity
Definition: Coastal wetland
- transitional systems between the land and the sea
- waters are stagnant or running, brackish or saline
- dominated by halophytic vegetation with morphological or physiological adaptations to salinity
e.g.
-estuaries
- bays
- salt marshes
- coastal lagoons
- coastal lakes
- swamps
dynamic environment of coastal wetlands
- Geologically unstable environments
- influenced by sea level changes, subsidence / uplift and silting up
- Overlap with terrestrial habitats → upward expansion caused by sea level rise
- Overlap with previously subtidal habitats (downward expansion) due to progressive sediment entrapment, colonization of sediment deposited by storm surges or colonization of exposed sediments in uplifted areas
- Most of the current transitional ecosystems were formed after the last glaciation
- they were following the retreat of glaciers and rapid sea level rise → 1000 - 10000 years of age
variability of coastal wetlands
great variability in
- size
-hydrological and topographical characteristics
–> estuaries, deltas, lagoons, coastal ponds, bays
- may even include diluted closed seas (Baltic, Adriatic and Black Seas = inner estuaries)
- some coastal wetlands also include open sea areas with low salinity (= outer estuaries)
hydrology - tidal regimes
- lower estuaries are dominated by waves and tides
- middle estuaries are dominated by tides
- upper estuaries are dominated by river action
hydrology - salinity
sediment deposition
(Sedimentablagerung)
- controlled by current velocity
- finest sediment components deposit at low energy
parameters (gradients)-of coastal wetlands
- Cohesiveness
- Porosity
- Permeability
- Density
- Erodibility
- Oxygen content
- Hydrogen sulphide
- Organic content
vegetation in coastal wetlands?
- dominant intertidal halophilous vegetation
salt marshes
- intertidal systems colonised by halophilous vegetation (adapted to salt and anoxia)
- salt marshes develop favorably on gently sloping shores with low wave energy and sufficient sediment supply
- they are typically found in estuaries and in protected bays with shallow water
- common salt marsh plants are glassworts (Salicornia spp.) and the cordgrasses (Sporolobus in the past named Spartina spp.), which have worldwide distribution
adaptations in halphilous vegetation
- roots: superficial adventitious roots to facilitate oxygenation
- Aerenchyma: tissue with cells interspaced with large intercellular spaces that allow gas circulation
- metabolism: anaerobic
- salt accumulation or excretion capacity
- great tolerance to variations in salinity
- very efficient osmoregulation system
Eelgrass (Zostera marina)
Glasswort (Salicornia dolichostachya)
Sea Lavender (Limonium Vulgare)
Sea pow (Puccinellia Maritima)
Sea Aster (Aster tripolium)
Cord grass (Spartina Anglica)
Sea purslane (Halimione portulacoides)
very halophilous species in po delta lagoons
tolerance to salinity variations
(tidal effect)
the salt wedges in typical estuaries move in and out with the tide
- at high tide (a) the crab is covered by water with a salinity 35%
- at low tide (b) by water with a low salinity between 5-15%
stenohaline and euryhaline species?
- stenohaline species tolerate a narrow range of variations
- euryhaline species tolerate a wide range of variations
Osmoregulation in coastal wetlands
- Osmoconformer: osmotic balance maintained in equilibrium between organism and external environment
(in environments with increasing salinity of water) - Osmoregulators: constant internal fluid concentration regardless of the external environment (organisms with increasing salinity of blood)
anadromous fish
- born in fresh water
- spends most of its life in the sea
- return to fresh water to spawn
e.g. salmon and sturgeon
catadromous fish
- lives in fresh water
- enters salt water to spawn
e.g. eels
typical zonation in salt-marshes
- biological communities (zonation) change along the strong gradients of physical factors
- species along the tidal elevation gradient (Gezeiten-Höhengradient) are adapted to the inundation frequency (Überschwemmung), including extreme flooding and srorm events
graph:
- MHT = mean high tide
Definition: salt marshes
salt marshes are hierarchically organized communities structured by both positive and negative forces
interactions of physical and biotic factors in salt-marshes
- physical stress increases, the farther down the zonation goes
(vice versa: physical stress decreases landwards)
–> “more attractive” to grow where less stress is –> competition
- landwards: plants have an increased competitive ability
role of positive interactions in salt marshes
1) Sediment stabiliiation
- mussel-plant interaction
- mussel stabilize and fertilize soil, benefiting plants
- plants provide sites for mussels to attach and contribute detritus to diet
2) Substrate oxygenation
- plants trap sediment and create low-marsh habitat
- they oxygenate soil which stimulates further plant growth
3) Soil shading that limits the salt build-up (due to plants)
4) Refugee from consumers
- plants support burrows
- they shelter crabs from predators
–> crabs aerate soil and stimulate plant growth
Stress gradient hypothesis
trophic cascade
(snail, crabs, biomass)
- crabs or turtles forage on snails
- snails forage on plants
- plants produce biomass
trophic cascade
(fishermen, fish, crabs, plants)
Societal values of wetlands
they provide many ecosystem services
- provisioning (food, fresh water, fiber and fuel…)
- regulating (climate, erosion, water purification and regulation)
- cultural
- supporting
EEV (estimated economic value) for coastal wetlands
“how much would you pay, if you had to build the infrastructure?”
foundation for wetland ecosystem?
plants (primary production, oxygenation, shelter…)
commercially valuable species in wetlands
- e.g. bivalves, shrimps and fish species such as eel, sea bream etc.
- they live part of their lives in these transitional aquatic environments
- wetlands are habitat, nursery and forage areas
primary production in wetlands
- very high primary production
- g/m^2 per year is higher than g/m^2 per year in tropical rainforest
- most of biomass produced is processed by decomposers
Carbon sequestration in Wetlands
- anoxic soils let organic matter degrade slowly
- wetlands store carbon in the soil and don’t release it in the atmosphere
how is carbon stored in soils in wetlands?
- the water flow leads to sediment accretion
- in that way the sediment works as a trap for runoff –> carbon held here for up to thousand years
- soils are very anoxic and therefore decompose slowly
–> accumulation of organic matter (storage in soil)
role of wetlands as flood defense
- can reduce the height of damaging waves as e.g in storm conditions by up to 20%
- vegetation reduces the water energy flow:
strong tidal currents –> hit vegetation –> weak tidal currents
- the extent of area in salt marshes that are present in an estuary determine the probability of flooding
- close to rivers there are more floods expected –> reduced by salt marshes
role of salt marshes in water purification
1) Denitrification
- bacteria in anoxic conditions use nitrogen as substrate for chemical reactions
- leads to denitrification and subsequent (anschließender) release of N2
2) wetlands are being built manmade to reduce nutrient levels in waters
Threats to salt marshes
- Settlement
- Agriculture & farming
- Ports, transport and commercial activities
- Source of food, water and raw materials
- Aquaculture
- Landfills –> leads to habitat loss and invasive species
marsh losses in italy
- 7000 km^2 at the end of 1800
- since then to today < 1000 km^2
- in Po delta > 70% of wetlands have been reclamed (zurück kultiviert)
- currently the marshes in Italy are severely degraded and altered systems
threats of marshes
- chemical pollution
- urban runoff
- nutrient
- invasive species
- hypoxia
- high population and urbanization
eutrophication effects on salt marshes (excess of nutrients)
- alters salt marsh community structure
- influences biomass allocation in plants
eutrophication effects on salt marshes (climate change)
- marsh elevation and sea level rise
- salt marshes can keep peace with sediment IF enough sediment is supplied
- climate changes leads to shift in plant communities: perennial (more than one year) grasses to annual succulents
coastal squeeze
- prevents the landward transgression resulting from sea level rise and other anthropogenic activities
Definition: functional trait
any morphological, physiological or phenological feature measurable at the individual level, from the cell to the whole organism
trait-based ecology in salt marshes
- approach to understand how trait can respond to an environment
- traits respond to environmental gradients
- traits effect on ecosystem functioning
–> trait based ecology is an approach to link changes in environmental condition to ecosystem functioning, through organisms trait
Response - Effect framework
left: natural system
right: effect
- due to change different species survive
- species have different traits
- the community structure changes and therefor the ecosystem property
traits- decomposition relationship in salt marshes
- salt marshes have a broad plant economic spectrum (PES) from a low stressful habitat to a high stressful habitat
- at low stressful habitat: conservation of resources –> specific resistance traits (e.g. leaf protein content)
- at high stressful habitat: fast resources acquisition
traits guiding management
- future climatic conditions may differ from the current or past ones
- managers could favor species with traits capable to withstand future conditions
