EEMB 142A Final - Wetlands

general characteristics of wetlands

extremely productive ecosystems - important habitats for biomass and energy transfer

wetland

an area of land whose characteristics are determined by the presence of water, either via permanent water-logging or through regular, usually seasonal, flooding

all wetlands share three basic criteria

1. hydrophytic vegetation (plant species that require/prefer wet soils)

2. undrained hydric soils (anoxic soils saturated with water)

3. wetland hydrology (inundated or wet at least part of year)

hydrophytic vegetation

hydrophyte: any species of plant that requires or prefers wet soils

• classes: submergent, floating, emergent

undrained hydric soils

hydric soils: usually saturated with water and deprived of oxygen

water table

height of saturated soil (high = lots of water on surface)

water table depth determines two things:

1. whether water-logging or flooding is seasonal or permanent

2. the oxygen concentration in the soil

decomposition of organic matter depletes oxygen (anaerobic/anoxic)

• decomposition typically slows in the absence of oxygen - decrease of pH

• leads to the formation of histosols (peats)

histosols

typically, acidic soils (pH = 4) which contain large amounts of organic material derived from decaying organisms

toxins

reducing conditions generates toxic chemicals (FeS, H2S, CH4)

aquatic marginal wetlands

created by rivers & lakes (marsh/swamp)

aquatic marginal wetlands: fringe wetland

hydrological connection with parent water body

aquatic marginal wetlands: flood wetland

hydrological separated from parent water body (only connected when flooded)

mires

fed by groundwater, overland runoff or precipitation

mires: minerotrophic / fens

water and nutrients from groundwater, high ions, alkaline

mires: ombrotrophic / bogs

above groundwater, fed by rainwater (quite acidic)

transitional wetland

transition between marginal and mire

AMW: marshes

• dominated by emergent plants

• vertical profile: moderate (1 m), frequently inundated

• soils/sediments: saturated, mostly anoxic, aerobic near root balls (diffusion out of the plants)

• diverse microbial community (bacteria and periphyton)

AWM: swamps

• dominated by trees/shrubs

• vertical profile: high (>1m), usually some standing water

• soils/sediment: saturated, mostly anoxic

• moderately diverse microbial community (bacteria- fungi, decreased periphyton)

• reduced photosynthesis and light

mires: fens

• dominated by grasses, sedges, rushes, wildflowers

• vertical profile: very low (<1m), fed by groundwater, higher nutrient levels

• soils/sediment: waterlogged, not as acidic as bogs

• low diversity microbial community (aerobic bacteria and periphyton)

• short growing season

mires: bogs

• dominated by moss

• vertical profile: low (<1m), rain fed, low in nutrients

• soils/sediments: saturated, highly acidic and anoxic, spongy peat

• low diversity microbial community (anaerobic bacteria, few periphyton)

nutrient cycling input

soluble inorganic nutrients: nitrates (NO3), ammonia (NH4), phosphates (PO4)

nutrient uptake by

trees, SAV, benthic algae, phytoplankton

nutrient cycling output

soluble and particulate matter: microbial, plant matter invertebrates

nutrient cycling loss

methanogenesis (CH4), denitrification (N2), sulfate reduction (H2S) to atmosphere

nutrient recycling

bacterial decomposition - peat to nitrogen (NH3) or sulfur (H2S)

productivity (typically nitrogen limited)

marsh > swamp > bog > fen

seasonal > permanent

detritus based food web

• most primary productivity “locked up” in hydrophytes

  • anti-grazing mechanisms like edges or toxins

• enters food webs as detritus processed by microbes or invertebrates

• oxygen consumption > oxygen production (P/R < 1)

• relatively few trophic levels supported: total primary production » unusable primary production

  • especially true in permanent wetlands

vertical plant zonation

changes in elevation creates range of different adaptive strategies & different species

• zones relate to height of water table with respect to sediment surface

coenocline

changes in plant community composition across an environmental gradient

zone #1: terrestrial

fully terrestrial environment (aerated soils)

zone #2: transitional

roots in aerated soil but anoxic / toxic at depth

zone #3-#6: species tolerant of permanently waterlogged sediments

• #3: hydrophytic, typically above ground parts are above water

• #4: emergent vegetation

• #5/#6: floating species and submergent vegetation

zone #7: none

behind littoral zone (no attached macrophytes)

assumptions of the predator/permanence model

1. permanence transition between temporary and permanent water habitats

2. predator transition between habits with and without fish

category 1: temporary without fish

• seasonal ponds

• R-selected species

• drought resistant or aerial dispersal

• invertebrate or amphibian predators

category 2: permanent without fish

• permanent ponds

• K-selected species

• large, active prey (advantage either too big to eat or can flea)

• invertebrate predators

category 3: permanent with fish

• permanent ponds, marsh, swamp

• K-selected species

• small, inactive prey (harder to find and hiding)

• fish predators

category 4: temporary with fish

• flood plains

• R-selected species

• drought resistant or dispersal via flood plains

• fish predators

high permanence

community structure is driven by predation pressure (biotic factors)

low permanence

community structure is driven by physiological tolerance to harsh environmental conditions (abiotic - desiccation)

predation and permanence effects on frogs

treatments: manipulated presence or absence of fish predators and hydroperiod

results: tadpoles respond to both predators and hydroperiod

• as water level declines, tadpoles increase development rates (R-selection)

• as predators increased, tadpoles decreased activity rates and developmental rates slowed (K-selected, inactive prey)

survival lowest in treatments with both fish and declining water predators

• both predator and hydroperiod transitions influence tadpoles physiological and behavioral responses (balanced R-selection vs K-selection)

ecosystem services: maintain water quality

filter/trap for nutrient, sediment, organic matter, other pollutants

ecosystem services: protection

storms, waves, floods, buffers strips, prevents erosion

ecosystem services: recharge groundwater

provide freshwater reserve (creates pure groundwater through depressions in ground)

ecosystem services: provide habitat

diversity hot spots, fisheries, nurseries, aquaculture

habitat destruction

development, pollution, changes in hydrology, recreational impacts and over harvesting of species