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Epsc 325 > estuaries > Flashcards

estuaries Flashcards

1
Q

How is an Estuary Defined?

A

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

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2
Q

what are the patterns of circulation and salinity in estuaries?

A

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

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3
Q

What is the influence of a sill on an estuary?

A

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

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4
Q

What mechanisms are responsible for the formation of a sill?

A

Deposition of sediments by rivers or waves

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5
Q

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

A
  • introduction of nutrients, sediments, organic matter
    -causes increased growth of primary producers
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6
Q

What is the Halocline?

A

A vertical gradient in salinity

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7
Q

What is the chemocline?

A

The boundary between the oxygenated and unoxygenated layers

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8
Q

Residence time calculation?

A

Reservoir size/flow rate

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9
Q

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

A

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

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10
Q

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

A
  • 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
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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

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

A

1-10 days

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14
Q

How does flushing time influence net primary productivity?

A

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

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15
Q

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

A

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

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16
Q

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

A

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

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17
Q

What estuary processes removed dissolved species from the water?

A

Flocculation, sedimentation, microbial activity

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18
Q

What is the importance of flocculation in estuary waters?

A

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

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19
Q

How does salinity affect flocculation?

A

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

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20
Q

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

A

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

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21
Q

How do organic materials on clay surfaces affect flocculation?

A

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

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22
Q

What is the role of collision in the flocculation process?

A

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

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23
Q

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

A

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

24
Q

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

A

conservative and non-conservative mixing and sediment-water interactions

25
Q

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

A

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

26
Q

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

A

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

27
Q

What is a nutrient trap?

A

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

28
Q

What are the internal and external nutrient sources in estuaries?

A

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

29
Q

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

A

sedimentation, burial, denitrification and uptake by primary producers

30
Q

What is the redfield ratio and why is it important?

A

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

31
Q

What is the definition of a limiting nutrient?

A

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

32
Q

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

A

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

33
Q

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

A

changes in river flow and nutrient inputs

34
Q

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

A

reactive: ability of elements to participate in biogeochemical cycles

35
Q

What is ‘cultural eutrophication’ and why is it important?

A

human caused eutrophication: excessive growth of algae

36
Q

Why does enhanced phytoplankton growth lead to oxygen depletion?

A

decomposition of dead phytoplankton takes up oxygen

37
Q

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

A
38
Q

What is the difference between hypoxia and anoxia?

A

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

39
Q

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

A

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

40
Q

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

A

increases water stratification and nutrient input, aiding in hypoxia,

41
Q

What is ‘biochemical oxygen demand’ and why is it important?

A

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

42
Q

How can hypoxia and anoxia be ameliorated in estuaries?

A
  • reducing nutrient inputs
  • restoring wetlands
  • improving wastewater treatment
43
Q

What are dinoflagellates and why are they important?

A

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

44
Q

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

A

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

45
Q

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

A

adsorption, uptake by benthic organisms

46
Q

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

A
47
Q

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

A

increases sediment supply and alters the flow regime

48
Q

What is the importance of fecal pellets in estuaries?

A

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

49
Q

Where are most sediments trapped?

A

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

50
Q

What are antiestuaries and where can they be found?

A

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

51
Q

What are the mechanisms that create an antiestuary?

A

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

52
Q

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

A

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

53
Q

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

A
54
Q

What is a barred basin?

A

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

55
Q

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

A

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

56
Q

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

A

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

57
Q

What is a sabhka?

A

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.

Epsc 325 (12 decks)

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