Lecture 9 - Estuaries and Sandy Shores Flashcards

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1
Q

What is an estuary?

A

An inlet of the sea that reaches into a river (where freshwater meets saltwater).

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2
Q

What are the three sectors of an estuary?

A

1) Lower; free connection with open sea.
2) Middle; subject to salt water and freshwater mixing.
3) Upper; freshwater input from the river, but subject to daily tidal action.

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3
Q

Name and describe the three different types of estuary.

A

1) Ria; a drowned valley. Water comes in due to sea level rise.
2) Fjord; steep sided, glacial-cut estuary.
3) Bar-built estuary; estuary with a lot of sediment coming down, created by offshore deposits. Intermittently open to the sea.

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4
Q

What is the salinity of an estuary at the

a) Head?
b) Upper reaches?
c) Middle?
d) Lower reaches?
e) Mouth of the sea?

A

a) Head = less than 5ppt
b) Upper reaches = 5-18ppt
c) Middle = 18-25ppt
d) Lower reaches = 25-34ppt
e) Mouth of the sea = 34ppt.

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5
Q

What is the current focus of estuaries?

Give an example.

A

Using the tide to generate renewable energy.

In the Severn Estuary, could produce 4.4% of UK energy needs, but at a loss of 75% intertidal habitats.

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6
Q

What is a salt wedge estuary?

A

High river flow. Freshwater flows at high volume, floats over the top of the sea salt.

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7
Q

What is a partially-mixed estuary?

A

Between wedge and well-mixed.
More stable flows from both river and seawater.
At depth, constantly salinity.
Salinity increases from top to bottom.

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8
Q

What is a well-mixed estuary?

A

Low river flow.

Strong tides.

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9
Q

What is a fjord type salinity?

A

Freshwater sits on the top.

Seawater spills in and fills the deep bottom channels.

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10
Q

Describe how species diversity changes with the salinity gradient.

A
  • Freshwater; high species diversity.
  • 5ppt; much lower species diversity.
  • Middle reaches (5-18ppt); begins to slowly increase.
  • Diversity increases greatly as you enter salty water.
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11
Q

True or false:
Saltwater species have better abilities to cope with increased salinity than marine species have to cope with reduced salinity.

A

FALSE.
Marine species have better abilities to cope with reduced salinity than freshwater species have to cope with increase salinity.

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12
Q

What are brackish animals?

A

Freshwater species at the edge of their salinity tolerances.

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13
Q

What did Attril (2002) argue?

A

That salinity is the primary factor determining distribution and species diversity.
Proposed a two-ecocline model for estuaries (where an ecocline is a gradual ecological gradient).

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14
Q

Where do mudflats form in estuaries?

A

In the middle reaches

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15
Q

How much mud is accumulated each year in estuaries?

A

2mm

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16
Q

Explain why fine mud is found in the middle of the estuary.

A

The faster the water moves, the bigger the particles it can carry.
As it slows down, large particles begin to drop first.
When it moves very slowly, it no longer carries fine silty mud.
When river meets tide, water hardly moves, and fine silty mud drops out at the centre of the estuary.

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17
Q

Why do you get a Dissolved Oxygen (DO) sag in the middle of an estuary?

A
  • High organic load of estuaries leads to high levels of bacterial salinity
  • When mud sinks out, brings organic matter with it.
  • A lot of respiratory processes happen in the top layer of mud
  • The middle of the estuary has the largest amount of mud.
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18
Q

Where in the estuary has the highest oxygen content?

A

The top of the estuary.

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19
Q

Why are estuaries heterotrophic systems?

A

Contain mostly secondary producers rather than primary producers.

20
Q

What are the three main types of primary production in temperature estuaries? Where is each found?

A

1) Diatoms - much higher in abundance near marine input.
2) Large macroalgae
3) Seagrasses; occur at mouth by the sea.

21
Q

Where in the estuary are phytoplankton mostly seen?

A

At the mouth where salinity is high.

Found in shallow surface of the water column, where light penetrates.

22
Q

Why are seagrasses under threat in the UK?

A

From boating activities.

23
Q

Where in an estuary might seagrass beds form?

A

At the mouth.

24
Q

What is blue carbon?

A

CO2 in the marine environment.

25
Q

Where does most of the food available for organisms in the estuarine mud come from?

A

The detritus pathway

26
Q

Organic carbon in estuarine mud flat can support a community of detritivores how much higher than in offshore sediments?

A

10 times.

27
Q

Describe a polychaete found at the mouth of an estuary.

A

Arenicola marina.

Respiratory structures cannot cope in fine silty muds found at the centre of the estuary.

28
Q

Describe an adaptation of polychaete.

A

Good at anaerobic respiration when required, when burying in sediment where oxygen is low.

29
Q

Name three things that sediment reworking by infauna can do.

A

1) Increase oxygen available to deeper sediment layers.
2) Redistribute particulate organic matter deposited not he sediment surface
3) Increase nutrient release

30
Q

What percentage of fixed nitrogen needed for photosynthesis is released back into the water column by sediment remineralisation?

A

80%

31
Q

Name an arthropod that engages in bioturbation.

A

Corophium volutator

32
Q

How much is oxygen uptake increased with high densities of Corophium present/

A

Oxygen uptake is doubled.

33
Q

a) Nitrification needs ____ bacteria

b) Denitrification needs ____ bacteria

A

a) Nitrification needs aerobic bacteria.

b) Denitrification needs anaerobic bacteria.

34
Q

Describe two adaptions of the ragdowm (Hediste diversicolor).

A
  • Euryhaline; wide range of salinity tolerance.

- Able to cope with diluted blood; does not disturb its functions.

35
Q

When is the ragworm an ionic conformer?

A

At salinities above 25-25%

36
Q

Are molluscs osmoconformers or osmoregulators?

A

Osmoconformers.

37
Q

At what point do oysters and mussels switch to anaerobic respiration?

A

When they close their shell.

38
Q

What do osmoregulators do in

a) Low salinity?
b) High salinity?

A

a) Low salinity = lose salts and gain water.

b) High salinity = lose water and gain salts.

39
Q

What is

a) Euryhaline?
b) Stenohaline?

A

a) Euryhaline - can cope with a wide range of salinities.

b) Stenohaline = can cope with a narrow range of salinities.

40
Q

Describe the reproduction of Carcinus maenus.

A

Females produce up to 185,0000 eggs.

Larvae develop offshore in several stages before their final moult to juvenile crabs in the intertidal zone.

41
Q

What is the key physical factor controlling crabs?

A

Temperature

42
Q

In what sense is there a high biomass of fish in estuaries?

A

In numbers, not species.

43
Q

Give two groups of estuarine specialist fish.

A
  • Mummichog

- Flounder

44
Q

Give a group of fish whose juveniles use estuaries for nursery grounds.

A

Flounder

45
Q

How are estuaries important for birds?

A

Act as a feeding ground.

46
Q

Describe the work of Emmersen et al (2001).

A

Studied nitrogen flux as an indicator of functioning.
Only Nereis diversicolor was important.
Functioning was less variable with increasing species richness.
Diverse systems are more stable.

47
Q

Give and describe two types of sand found at estuaries.

A
  • Dilatend sand; well drained, difficult to move through.

- Thixotropic sand; easy to move through.