estuaries

Question 1

How is an Estuary Defined?

Answer 1

drowned river valley where river meets ocean. filled with brackish sea water

Question 2

what are the patterns of circulation and salinity in estuaries?

Answer 2

CIrculation:
- river flow inputs
salt wedge estuaries: river flow dominates, little tidal mixing–>saline ocean water enters estuary as a wedge beneath freshwater
- highly stratified estuary: river flow still dominates, but tidal currents cause more mixing of saline upward: surface layer becomes progressively more saline
-well mixed estuaries; dominated by tidal currents; no salinity gradient

Question 3

What is the influence of a sill on an estuary?

Answer 3

A sill can act as a barrier to tidal flow, causing the water level on the upstream side of the sill to be higher than on the downstream side, leading to differences in salinity and circulation

Question 4

What mechanisms are responsible for the formation of a sill?

Answer 4

Deposition of sediments by rivers or waves

Question 5

What is the role of river runoff in the chemistry of an estuary?

Answer 5

• introduction of nutrients, sediments, organic matter
  -causes increased growth of primary producers

Question 6

What is the Halocline?

Answer 6

A vertical gradient in salinity

Question 7

What is the chemocline?

Answer 7

The boundary between the oxygenated and unoxygenated layers

Question 8

Residence time calculation?

Answer 8

Reservoir size/flow rate

Question 9

How does the water residence time affect the chemistry of estuary waters?

Answer 9

Longer residences times can lead to accumulation of nutrients and sediments, and higher levels of primary productivity

Question 10

What mechanisms may affect the depth of the chemocline in the Black Sea?

Answer 10

• incursions of very saline mediterranean water into the deeper anoxic layers
• interannual and decadal changes in the fresh riverine input to the surface layer
• changes in coastal currents due to storms
  internal waves in the chemocline
  -changes in both plankton productivity and species distribution due to changes in salinity

Question 11

What is the difference between conservative and non-conservative mixing?

Answer 11

conservative mixing: mixing of water with no change in the concentrations of dissolved species,

Non-conservative mixing: mixing that results in changes in the concentrations of dissolved species

Question 12

What is the flushing time of an estuary and how is it calculated?

Answer 12

The time it takes for the entire volume of fresh water in the estuary to be replaced
t=total volume of fresh water in an estuary/rate of rate of river discharge in estuary

Question 13

What is the flushing time for a vertically well-mixed estuary?

Answer 13

1-10 days

Question 14

How does flushing time influence net primary productivity?

Answer 14

Shorter flushing times can lead to higher levels of net primary productivity by increasing the availability of nutrients for primary producers

Question 15

Why is Cl- used as the x-axis in figure 7.3 in the text?

Answer 15

Cl- represents the salinity gradient along the length of the estuary

Question 16

What are the two groups of dissolved, inorganic, species in estuary water and how are they defined?

Answer 16

Conservative ions: have constant concentrations regardless of mixing
Non-conservative ions: which can change in concentration due to mixing or biological processes

Question 17

What estuary processes removed dissolved species from the water?

Answer 17

Flocculation, sedimentation, microbial activity

Question 18

What is the importance of flocculation in estuary waters?

Answer 18

flocculation is the process by which suspended particles aggregate and settle out of the water column.

Question 19

How does salinity affect flocculation?

Answer 19

salinity controls the ionic strength of the water, which affects the stability and mobility of suspended particles

Question 20

What are the possible fates of ‘flocs’ in estuaries?

Answer 20

settling, resuspension, erosion, and transport out of the estuary

Question 21

How do organic materials on clay surfaces affect flocculation?

Answer 21

organic materials on clay surfaces provide a surface for particle attachment and increasing particle stability

Question 22

What is the role of collision in the flocculation process?

Answer 22

collision between suspended particles can lead to flocculation by bringing particles into close proximity and promoting particle aggregation

Question 23

What is the importance of Fe-hydroxide minerals and the impact of their dissolution on estuary water?

Answer 23

they absorb and release dissolved species, and their dissolution can affect water chemistry

Question 24

What are the mechanisms controlling the concentrations of the major dissolved species in estuary water?

Answer 24

conservative and non-conservative mixing and sediment-water interactions

Question 25

What are the biogenic nutrients and what is their behaviour in estuaries?

Answer 25

essential elements, such as nitrogen and phosphorus, that are required for the growth of primary produces

Question 26

What are the net primary productivity of open ocean and estuaries? Why are they so different from one another?

Answer 26

Open ocean: low net primary productivity due to the limited availability of nutrients Estuaries: high net primary productivity due to the input of nutrients from land

Question 27

What is a nutrient trap?

Answer 27

an area in which nutrients are retained, often due to sedimentation or adsorption onto particles

Question 28

What are the internal and external nutrient sources in estuaries?

Answer 28

Internal: decomposition of organic matter, resuspension of sediments, nutrient regeneration from benthic organisms. External: river inflow, atmospheric deposition, ocean inputs

Question 29

What processes permanently remove dissolved nutrients from estuaries? which are the most important?

Answer 29

sedimentation, burial, denitrification and uptake by primary producers

Question 30

What is the redfield ratio and why is it important?

Answer 30

atomic ratio of carbon, nitrogen and phosphorus in phytoplankton and marine organic matter (106:16:1). it is important because it indicates the relative availability of these nutrients for primary production

Question 31

What is the definition of a limiting nutrient?

Answer 31

a nutrient in short supply relative to the requirements of primary producers, which limits their growth

Question 32

What is the common limiting nutrient in estuaries and why is it the limiting nutrient?

Answer 32

Nitrogen is commonly the limiting nutrient in estuaries 1. ratio of n:p in a number of rivers, especially polluted rivers, is lower than that of estuarine plankton, so there is excess P left over in the estuary upon consumption of all N 2. denitrification (reduction of NO3 to N2 and N2O) causes nutrient nitrogen to be selectively lost from estuary 3. N regenerated much slower than P after sedimentation

Question 33

What is an example of seasonal changes in the limiting nutrient and why does this occur?

Answer 33

changes in river flow and nutrient inputs

Question 34

What does the term 'reactive' mean when it is applied to elements (e.g., N and P)?

Answer 34

reactive: ability of elements to participate in biogeochemical cycles

Question 35

What is 'cultural eutrophication' and why is it important?

Answer 35

human caused eutrophication: excessive growth of algae

Question 36

Why does enhanced phytoplankton growth lead to oxygen depletion?

Answer 36

decomposition of dead phytoplankton takes up oxygen

Question 37

What is the effect of suspended particles on net primary productivity?

Question 38

What is the difference between hypoxia and anoxia?

Answer 38

hypoxia: low dissolved oxygen levels anoxia: complete absence of dissolved oxygen

Question 39

How do changes in annual precipitation affect the nitrate loading of an estuary (e.g., the Mississippi-Missouri river system)?

Answer 39

changes amount and timing of river flow--> affects nutrient inputs

Question 40

How is global change expected to affect the oxygen concentration in estuary waters?

Answer 40

increases water stratification and nutrient input, aiding in hypoxia,

Question 41

What is 'biochemical oxygen demand' and why is it important?

Answer 41

the amount of oxygen consumed by microbial decomposition of O.M in water. - high BOD levels can lead to oxygen depletion and hypoxia

Question 42

How can hypoxia and anoxia be ameliorated in estuaries?

Answer 42

- reducing nutrient inputs - restoring wetlands - improving wastewater treatment

Question 43

What are dinoflagellates and why are they important?

Answer 43

a group of important primary producing unicellular algae that can cause algal blooms

Question 44

WHy is most sediment deposited in deltas, estuaries and coastal marine environments?

Answer 44

these areas are where rivers meet the ocean and sediment transport processes change

Question 45

How are heavy trace metals removed from the water in estuaries?

Answer 45

adsorption, uptake by benthic organisms

Question 46

How does the type of estuary affect the transport of sediments from the river to the ocean?

Question 47

What role do floods play in the transport of sediments to and through estuaries?

Answer 47

increases sediment supply and alters the flow regime

Question 48

What is the importance of fecal pellets in estuaries?

Answer 48

they contribute to the nutrient cycling, productivity and food webs of the estuarine ecosystem

Question 49

Where are most sediments trapped?

Answer 49

intertidal zone where tidal currents and wave action are reduced - these zones have a high rate of sediment deposition

Question 50

What are antiestuaries and where can they be found?

Answer 50

saline coastal body of water where seawater flows into estuary in surface layer

Question 51

What are the mechanisms that create an antiestuary?

Answer 51

tectonic uplift, arid climate, restricted water exchange with the ocean

Question 52

What minerals form as the water in an antiestuary evaporates and what species do they remove from the water?

Answer 52

Halite (NaCl), gypsum (CaSO4*2H2O), and anhydrite (CaSO4) can form. - removes ions of Na, Cl, Ca, SO4 from water

Question 53

How do evaporite rocks differ from the minerals expected to form from evaporating seawater?

Question 54

What is a barred basin?

Answer 54

a basin separated from the open ocean by a narrow barrier, such as a sandbar or a reef. Barrier restricts water exchange and creates a shallow brackish environment

Question 55

What is the first mineral to form during seawater evaporation in a barred basin?

Answer 55

Aragonite (CaCO3), which is supersaturated in seawater and can precipitate rapidly

Question 56

What can cause a lateral variation in the mineralogy of evaporite deposits?

Answer 56

differences in the composition and concentration of the brines that precipitated the minerals, as well as by changes in the environmental conditions, such as temperatuer and salinity

Question 57

What is a sabhka?

Answer 57

a type of coastal salt flat that forms in arid and semiarid regions. - characterized by a flat, hard crust of evaporite minerals, such as gypsum and halite, often covered by a thin layer of windblown sand.