Lecture 7 & 8 - Estuaries Flashcards
Define an estuary
A semi-enclosed body of water with a free connection to the open sea, within which the marine seawater input is partially diluted by freshwater from terrestrial sources. Benthic organisms key for primary productivity
Name the four sections to the estaurry
River Upper Middle Lower Open Sea
Name the two areas with regards to tide
Intertidal - benthic zone
Palagic zone - subtidal
Name the two habitats found at estuarine locations
Mudflats
Saltmarshes - network of drainage channels, residual water make decent feeding grounds
Explain mixing processes in the estaury
Isohalines are present and indicative of a salt wedge, salt water is is dense so freshwater floats on top
What are the three types of estaury mixing
Salt wedge Partially mixed (most common) well mixed (severn)
What are the four factors that control water mixing
Wind - turbulent mixing
Heating / cooling - stratification and turnover
Tide - speed of flood and ebb
Gravitation circulation - salinity gradient, density dependent mixing
Example of salt wedge and fully mixed (most are partially mixed)
Salt wedge - Mississippi
well mixed - Severn
What is the salt water (or tidal) excursion
The distance up the estuary that the salt water reaches, which depends on tide and gravitational mixing of water column
What dictates sediment accretion and erosion in estuaries
Energy of the shore if no wave energy the accretion occurs but erosion can occur in tides, storms and size of sediment depends on water column energy
What are the three types of sediment and their sizes
Muddle Cohesive Clays - 63µm (near sea)
Explain the formation of Cohesive clays
Clay particales become bound through Van der Waals forces of attraction between +/- charged particles. The clay particles are -ve and +ve ions from the water column bind from hydrogen bonding. In additional biological polymers aid this cohesiveness
What is the result of cohesive clays
Sticky sediment which is resistant to hydrological stresses and induced re-suspension of particles
what is the biological polymers
diatoms producing piercing plates of biological polymer in cohesive clay sediments, further aiding binding of the sediment
Explain sandy sediments and their inability to bind
These are larger particles (>63µm), these are from weather rock and they are uncharged particles so dont bind to organic material and nutrients, therefore they are unconsolidated and may rest on the surface of a polymer layer
what is the influence of sediment size on biological zonation
different species require a different sediment size and therefore can only live in the location in which sediment size is appropriate
What is Floc Formation
Saline water (+ve) reduce repulsion of clays, aiding in the binding of particles. Bio-polymers and algae aid this process leading to the formation of aggregations of sediment particles known as Floc
What do Flocs control?
These Flocs flow on the flood and ebb tide and determines erodability, resuspension / sedimentation and therefore transport in and out of the sediment
Six stages to salt marsh formation
Accretion of sediment to form salt marsh
Colonisation and growth of microaglea
Colonisation by saltmarsh species (facilitated by above)
Stabilises substratum and allows for more accretion
Forms a raised habitat partially covered by MHWS
Then plant colonisers occur - pioneer species
Do a flow diagram from the colanisers of an estuary
Cynobacterias >
1 - cord grass, reproduces through a rhizome system asexually to cover large area. this stabilises and rises the sediment making it more terrestrial
2 - Other less salt tolerant grasses invade, leads to vertical zonation of grasses
Explain nutrient limitation in an estuarine environment, and the main two
Limits primary production, and is an example of bottom up dependant growth of algea. Nitrogen and Phosphorous
Explain Phosophrous as limiting nurtients
binds well to iron compounds in freshwater - transported to estuary by river run off. Released by diffusion into water column and via sediment pore water from sediment stored nutrients
Explain nitrogen as a limiting nutrient
mostly from riverine sources but usually used up by the time it reaches the estuary, therefore it is often the limiting nutrient and availability controlled by bacterial mineralisation
What are primary producers in the benthic mudflat zone
Macroalgae - primary diatoms (Bacillariophyta) which can form the polymer on the surface
What are the three ecosystem functions of the Diatoms
a) carbon supply to estuarine environment (grazing)
b) produce extracellular polymers
c) grazed by many invertebrate macrofauna
How does this diatoms move in the sediment?
this organisms temporary migrate (xmigrate) vertically through the substratum, their height depends on tide and light availability
what are two other types of primary producers in the mud flat
Cyanobacteria
Seagrasses (higher plant grazed by wildfowl)
What are Limnetic organisms
freshwater organisms which just hate salt, cannot tollerate salinities >0.5
What are olgiohaline organisms
freshwater organisms that dont mind a bit of salt but up to < 5
what are true estuarine organisms
brackish water organisms, which are found in salinities 2-25
What are Euryhaline marine organisms
marine organisms which extend into estuaries reach areas with salinities as low as 5, most common in estuaries
What are stenohaline marine organisms
true marine organisms from the sea, occur in > 18
Explain the difference between an osmoregulator and and osmoconformer
Osmoregulators use energy to transport salt or stop salt entering the cell, the do this due to the osmotic potential, ions and salts want to move down the concentration gradient. Osmoregulators don’t control it but they put up with it
Explain osomoregulators in depth
Maintain a constant internal osmotic potential irrespective of the external changes. This has metabolic energy costs (from active transport)
Explain osmoconformers in depth
Internal osmotic pressure changes depending on the external osmotic pressure, body tissues must be tolerant to these changes
What are hyper and hypo osmoregulators
Hyper is active uptake if ions and loss of water at LOW salinities, hypo is water uptake and active excretion of ions at HIGH salinities
What are most species in reality a mix of? (with regards to osmotic pressure
normally a mix of a regulator and conformer depending on external conditions
Explain the difference between the niches of osmoregulators and osmoconformers
Osmoregulators can colonise a wider range of habitats through the estuary whereas osmoconformers are greatly restricted in range due to large flux in salinity
Name the 1 type of benthic organism found her as well some juicy facts
Meiofauna - 0.1 to 1.0mm in size, temporary or permanent are they are important grazers and recyclers of nutrients through detrital feeding
What are the three types of macrofauna found in this enviroment
Grazers and deposit feeders
Filter feeders
Predators
Some info about birds in estuarine systems
Can be wading or sediment feedingm over winter and migratory populations are of high importance, may take a high proportion of benthic invertebrate population (top down control)
What is Palegic estuarine biota
These are primary produces such as the phytoplankton can be limited by turbidity in the water column and cause red tides
Give some details on estuarine fish
These can be benthic feeders or juvenile fish that use saltmarsh systems as a nursery
Give some details on fauna (other) in a salt marsh
see latin names but stuff like worms, snails etc
