Lecture 7 & 8 - Estuaries Flashcards by James Scott

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

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Name the four sections to the estaurry

River 
Upper
Middle
Lower
Open Sea

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Name the two areas with regards to tide

Intertidal - benthic zone

Palagic zone - subtidal

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Name the two habitats found at estuarine locations

Mudflats

Saltmarshes - network of drainage channels, residual water make decent feeding grounds

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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

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What are the three types of estaury mixing

Salt wedge
Partially mixed (most common)
well mixed (severn)

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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

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Example of salt wedge and fully mixed (most are partially mixed)

Salt wedge - Mississippi

well mixed - Severn

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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

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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

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What are the three types of sediment and their sizes

Muddle Cohesive Clays - 63µm (near sea)

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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

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What is the result of cohesive clays

Sticky sediment which is resistant to hydrological stresses and induced re-suspension of particles

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what is the biological polymers

diatoms producing piercing plates of biological polymer in cohesive clay sediments, further aiding binding of the sediment

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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

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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

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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

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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