Lecture 9 - Estuaries and Sandy Shores

Question 1

What is an estuary?

Answer 1

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

Question 2

What are the three sectors of an estuary?

Answer 2

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.

Question 3

Name and describe the three different types of estuary.

Answer 3

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.

Question 4

What is the salinity of an estuary at the

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

Answer 4

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.

Question 5

What is the current focus of estuaries?

Give an example.

Answer 5

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.

Question 6

What is a salt wedge estuary?

Answer 6

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

Question 7

What is a partially-mixed estuary?

Answer 7

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

Question 8

What is a well-mixed estuary?

Answer 8

Low river flow.

Strong tides.

Question 9

What is a fjord type salinity?

Answer 9

Freshwater sits on the top.

Seawater spills in and fills the deep bottom channels.

Question 10

Describe how species diversity changes with the salinity gradient.

Answer 10

• 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.

Question 11

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

Answer 11

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

Question 12

What are brackish animals?

Answer 12

Freshwater species at the edge of their salinity tolerances.

Question 13

What did Attril (2002) argue?

Answer 13

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).

Question 14

Where do mudflats form in estuaries?

Answer 14

In the middle reaches

Question 15

How much mud is accumulated each year in estuaries?

Answer 15

2mm

Question 16

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

Answer 16

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.

Question 17

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

Answer 17

• 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.

Question 18

Where in the estuary has the highest oxygen content?

Answer 18

The top of the estuary.

Question 19

Why are estuaries heterotrophic systems?

Answer 19

Contain mostly secondary producers rather than primary producers.

Question 20

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

Answer 20

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

Question 21

Where in the estuary are phytoplankton mostly seen?

Answer 21

At the mouth where salinity is high.

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

Question 22

Why are seagrasses under threat in the UK?

Answer 22

From boating activities.

Question 23

Where in an estuary might seagrass beds form?

Answer 23

At the mouth.

Question 24

What is blue carbon?

Answer 24

CO2 in the marine environment.

Question 25

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

Answer 25

The detritus pathway

Question 26

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

Answer 26

10 times.

Question 27

Describe a polychaete found at the mouth of an estuary.

Answer 27

Arenicola marina.

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

Question 28

Describe an adaptation of polychaete.

Answer 28

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

Question 29

Name three things that sediment reworking by infauna can do.

Answer 29

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

Question 30

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

Answer 30

80%

Question 31

Name an arthropod that engages in bioturbation.

Answer 31

Corophium volutator

Question 32

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

Answer 32

Oxygen uptake is doubled.

Question 33

a) Nitrification needs ____ bacteria

b) Denitrification needs ____ bacteria

Answer 33

a) Nitrification needs aerobic bacteria.

b) Denitrification needs anaerobic bacteria.

Question 34

Describe two adaptions of the ragdowm (Hediste diversicolor).

Answer 34

• Euryhaline; wide range of salinity tolerance.

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

Question 35

When is the ragworm an ionic conformer?

Answer 35

At salinities above 25-25%

Question 36

Are molluscs osmoconformers or osmoregulators?

Answer 36

Osmoconformers.

Question 37

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

Answer 37

When they close their shell.

Question 38

What do osmoregulators do in

a) Low salinity?
b) High salinity?

Answer 38

a) Low salinity = lose salts and gain water.

b) High salinity = lose water and gain salts.

Question 39

What is

a) Euryhaline?
b) Stenohaline?

Answer 39

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

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

Question 40

Describe the reproduction of Carcinus maenus.

Answer 40

Females produce up to 185,0000 eggs.

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

Question 41

What is the key physical factor controlling crabs?

Answer 41

Temperature

Question 42

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

Answer 42

In numbers, not species.

Question 43

Give two groups of estuarine specialist fish.

Answer 43

• Mummichog

- Flounder

Question 44

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

Answer 44

Flounder

Question 45

How are estuaries important for birds?

Answer 45

Act as a feeding ground.

Question 46

Describe the work of Emmersen et al (2001).

Answer 46

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.

Question 47

Give and describe two types of sand found at estuaries.

Answer 47

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

- Thixotropic sand; easy to move through.