Biogeomorphology Flashcards
Betard - year?
2021
Betard 2021
Insects as biogeomorphic agents
insects can have constructional or erosional impacts
they also can have direct and indirect impacts on landforms and geomorphic processes
Role of termites in geomorphology?
produce largest and strongest mounds
come in variety of shapes and allow identification of different species operating in the area
burrowing insects protect sediment from erosion through creation of macropores underground that increase infiltration capacity of soil reducing surface runoff
simultaneously bioerosive - berrowing relies on displacement of sediment material that then lies on the surface becomes vulnerable to erosion
net effect of erosion or protection is dependent on type of mounds and nest density
Example of location of termite mounds?
Semi - Arid region of north Brazil
- approx. 200 million earth mounds that reach up to 2-4m high
Termites indirect control on geomorphic processes - study
McCarthey et al (1998) - Okavongo Delta in Botswana finding that activity of termites resulted in altered physio-chemical properties of surrounding soil
creating optimum environment for pioneer shrubs and trees that could then trap sediment resulting in lateral and vertical island growth
Bio constructional process
How do aquatic insects often participate in bioerosion?
during foraging activity aquatic insects can increase suspension of sediment material by removing it from interstitial space
Example of aquatic insect in geomorphology
Stonefly - can erode 200-400kgm-2 of sand per year through feeding on organic matter attached to the river bed
During feeding the stonefly scrape along the river bed dislodging small sediments which are carried down the rivers course
Bioconsolidation insect example - With researcher (Date)
Rice - 2021
Caddis flies - consolidate bed sediments
flies spin silk that used to build filter feeding nets on riverbeds that bind together rock and sand resulting in the need for a greater shear stress to be exerted on the river bed in order to entrain sediment
Beavers research
Brazier et al (2021)
Beavers as bioconstructional
through creation of dams that slow the force of water and reduce peak flow downstream.
dams trap sediment and biotic material that is then deposited and broken down to build up the riverbed.
Beavers as bio erosional
,beavers can act as agents of erosion, they excavate bank burrows to live in displacing significant volumes of sediment and creating weakened riverbanks that are more vulnerable to hydraulic erosion and collapse
also sites of channel avulsion
Explain process of channel avulsion and beavers
beaver dams build up, they divert water flow into a wider area of floodplains creating multi-thread channels.
This results in the sudden abandonment of the river from its original channel in favour of the more efficient route.
Further downstream the river re-joins the original channel at a knickpoint where there is a difference in elevation creating a ‘waterfall- like’ structure that forms a site of high intensity erosion
crustaceans as bioerosive agents - example
crayfish - destabilising riverbeds during foraging and fighting
decrease the amount of shear stress needed to entrain sediment from river bed by 50-75%
widespread and can be found in central and south America, Europe, western Asia, Madagascar and Australia
salmon as bio-destructive agents - study name and date?
Wilkes et al - 2019
effects of salmon on river bed
during spawning season female salmon create redds (nests) through strong undulations of their tails
causes suspension and the mixing of gravels and sediments that make the river bed unstable
result in a lower shear stress needed to entrain sediment
changes in river width and depth
Explain how vegetation is bioprotective and bio constructive in fluvial landscapes-
because sediment is so easily mobilised in rivers
dependent on plants ability to retain sediment
plants with greater resistance to flow result in greater retention of sediment
stabilise sediment by forming root networks that extend wide and deep across floodplains and river beds - decreases rate of erosion + helps build up river channels, banks and floodplains
example of fluvial vegetation
name and date of study and explain
seagrass- in morro Bay California
rapidly declined in last decade due to increased pollution and land clearing.
led to shift from previously accretion dominated system to an erosional landscape (Viles & Coombes, 2022)
Viles and Coombes - date
2022
how do trees effect bioconstruction along rivers ?
through large wood cycle
whole trees or branches fall into rivers = accumulate and form dams
unmanaged material accumulates behind these dams causes mass deposition that can create floodplains and vegetation landforms that further reinforce tree growth
Positive feedback cycle = bioconstruction along the river
How does tree type effect rate of sediment erosion?
Different trees grow different types of root network
In temperate areas in the northern Hemisphere high abundance of willow and poplar trees can grow at root depths of several metres leading to high sediment reinforcement - slow rates of erosion
what are biofilms?
communities of microorganisms made up of fungi, bacteria, and algae
Secretion of extracellular polymeric substances (EPS) create a matrix
what role do biofilms play in bioconstruction?
EPSs trap sediment and alter the physio-chemical composition leading to increased cohesion between fine sediment grains = bioflocculation
= increase in deposition and reduces rate of suspension
study to support biofilms as bioprotective-
Valentine et al (2014) - found that when biofilms are allowed to grow for longer undisturbed periods of time
able to withstand higher shear stresses
protecting rock beneath from erosion
Biofilms as bio-erosional?
secretion of EPSs can also chemically erode rock surfaces producing sediment that can then more easily be transported away from the site
what determines the net bio-erosional or protective effect of biofilms?
other abiotic factors, e.g.. climate
explain the biogeomorphological window (Viles 2019)
within a bio geomorphic succession there are particular conjunctions of conditions that permit feedbacks to establish and operate
within these windows biogeomorphology exerts its clearest signatures on the landscape
