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MARI201 > Estuaries (L7-8) > Flashcards

Estuaries (L7-8) Flashcards

1
Q

Why is the flow and ebb of the ocean important for estuaries?

A

It subjects the estuary to large changes in salinity, temperature, and turbidity

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2
Q

What are estuaries impacted by most strongly?

A

Anthropogenic activities

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3
Q

Why does reducing estuary size and changing estuaries into farmland have such a large impact?

A

It has large impacts on hydrodynamics, with less water going in, there is less water to flush out the sediment

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4
Q

How can water quality be determined?

A

By temperature, salinity, nutrients (nitrogen, phosphorus, and ammonia), turbidity, dissolved oxygen, pH, and pollutants

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5
Q

Estuaries importance to humans

A

Estuaries are important culturally and recreationally

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6
Q

What is a nutrient nexus?

A

Where nutrients run off both the land and the sea; coastal upwelling may provide macronutrients, runoff from the land may provide micronutrients

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7
Q

Why are estuaries so productive?

A

They have high levels of nutrients and organic matter, and have a lot of sunlight

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8
Q

Why are estuaries safe nursery habitats?

A

They contain a lot of weed and small plants, allowing for places for young organisms to hide and live

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9
Q

Why are filter feeders important to estuaries?

A

Bivalves filter feed and extract/filter the sediment from the water

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10
Q

What anthropogenic issue is most common around estuaries?

A

Sediment loading

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11
Q

Why are estuaries important for the climate?

A

The bottoms of estuaries are made of mud and detritus, which sequesters carbon as peet

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12
Q

What is an estuary?

A

A semi-enclosed coastal body of water having free connection to the open sea and within which sea water is measurably diluted with freshwater deriving from land drainage

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13
Q

How are estuaries formed?

A
  1. Rising sea level since the last glaciation drowns river valleys (Marlborough Sounds)
  2. Retreating glaciers get filled up with sea water (Fiordland)
  3. A bar built estuary is formed when a shallow lagoon or bay is protected from the ocean by a sand bar, island, or delta (West Coast)
  4. Tectonic estuaries are caused by the folding of land surfaces due to tectonic/volcanic activity (Manakau Harbour)
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14
Q

How are estuaries classified?

A

By geology, circulation, and salinity

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15
Q

What are the estuaries classified by geology?

A

Drowned river valleys, fiords, bar built, tectonic

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16
Q

What are the estuaries classified by circulation?

A

Salt wedge (high R:V), highly stratified, slightly stratified, vertically/well mixed (low R:V), and an inverse estuary

17
Q

Do estuaries stay as one classification their whole lifetime?

A

No, they can migrate between categories due to rainfall

18
Q

Salt wedge estuary

A

REFER TO IMAGE
River volume is much larger than tidal volume
Mixing is restricted to the thin layer between freshwater on top and a wedge of salt water below
There is friction between the salt and freshwater
Examples include the Whanganui and Taieri rivers (time dependent), as well as the Congo, Mississippi, and Swann river in WA (tide is small so has a lot of freshwater)

19
Q

Strongly stratified estuary

A

REFER TO IMAGE
River volume is comparable to tidal volume
Velocity shear at the interface produces internal wave motion causing the entrainment of saltwater upward
No freshwater is mixed downward
The upward mass flux of salt water leads to a significant increase in mass transport towards the sea
Examples include fiords in Doubtful Sound, high freshwater input (second largest) and a deep saltwater reservoir below

20
Q

Partially stratified estuary

A

REFER TO IMAGE
River volume is small compared to tidal volume
The tidal flow is turbulent through the entire water column
Salt water is stirred into the upper layer and freshwater down into the lower layer
This type of estuary is widespread in temperate and subtropical climates
Examples include New river (Invercargill) and James river in USA

21
Q

Vertically/well mixed estuary

A

REFER TO IMAGE
River volume is insignificant compared with the tidal volume
Tidal mixing dominates the entire estuary
Complete mixing erases all stratification
The flow speeds are low, usually measured in m/s rather than cumecs/s
These estuaries are prevalent in regions of strong tides
Examples of this include the Waikouaiti river, Otago Harbour, and Severn river in the UK

22
Q

Inverse estuary

A

REFER TO IMAGE
Have no freshwater input from rivers
High evaporation leads to a salinity increase at the inner end of the estuary
Examples of this include Spencer Gulf in SA and Port Augusta

23
Q

Salt plug estuary

A

REFER TO IMAGE
This estuary receives some freshwater but evaporation is so strong that at some intermediate position, the salinity becomes higher than the sea
Upstream from this position the circulation is normal, downstream it is inversed
Examples of this include Alligator river in the NT

24
Q

Classification by salinity

A

This is much easier than classification by circulation
The salinity at the surface has a ratio with the bottom salinity
Ss:Sb
The higher the ratio, the more mixed the estuary is

25
Q

What is the tidal range like in estuaries?

A

It is a large range, however the estuary shape modifies the tidal range by damping or amplifying the tidal wave

26
Q

What are the main methods for estimating flushing time and their issues?

A

Salinity - works well for a well mixed estuary
Tidal prism estimate - works well for a partially stratified estuary, a simple model but underestimates flushing time
Knudsen method - works well for a strongly stratified estuary but underestimates flushing time

27
Q

What is residence time?

A

The average time a dissolved or suspended matter resides in the estuary before it is carried out into the open sea

28
Q

What methods are used to calculate residence time?

A

Box models, particle models, and concentration models

29
Q

Why is residence time important for aquaculture?

A

Nutrients in the ecosystem can be a limiting factor in productivity, which changes the delivery of nutrients and food, the removal of waste, aeration (removal on O2 depleted water)

30
Q

How does the Coriolis force affect estuaries?

A

The Coriolis force deflects flows to the right in the Northern hemisphere and to the left in the Southern hemisphere
NH estuaries have stronger outflows on the the left side of the estuary due to this, and the opposite of this occurs in the SH
One side of an estuary will flush buoyant fluids and particles more efficiently than the other

31
Q

What effect does wind have on estuary circulation?

A

Water movement at the surface causes a circulation deeper down, forming a sashe (seen in Lake Wakatipu)

32
Q

What will affect estuaries in the future?

A

Deforestation, sea level rise, restoration, improved water quality

33
Q

Is an atoll lagoon an estuary?

A

No, as there is no freshwater input from the land and there is a connection to the sea

MARI201 (5 decks)

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