Estuaries

Question 1

How do we define and classify estuaries (4)

Answer 1

Salinity
Geomorphology
Sediment patterns
Oxygen

Question 2

Estuary Definiton

Answer 2

Where river meets ocean

Upper Limit: Defined as the point where the tidal influence begins in the river

Lower Limit: Defined as the point where the river “plume” ends. This is complex and subjective because the influence of the rivers extends over large spatial scales

Question 3

Estuary Classification Scheme (3)

Answer 3

Freshwater-seawater mixing: Determines longitudinal, and vertical salinity variability

Geomorphology: determines the shape of the estuary, habitat availability

Tidal range: determines emersion/submersion times

Question 4

Salinity

Answer 4

The measure of total dissolve inorganic solids

ppt: number of grams of inorganics per 1000 grams of water

PSU: electrical conductivity of seawater compared to standard potassium chloride solution

Question 5

Longitudinal salinity gradient

Answer 5

Oligohaline: 0.5-5 psu
Mesohaline: 5-18 psu
Polyhaline: 18-30 psu (very variable)
Euhaline: >30 psu

Question 6

How do tides affect salinity?

Answer 6

Receding tides decrease the amount of salinity

Rising tides increase the amount of salinity

Question 7

Osmoconformity

Answer 7

Maintain internal solutes = to medium
The salinity of body fluids same as surrounding waters
Most tolerance to salinity changes

Question 8

Osmoregulation

Answer 8

Can regulate/maintain internal salt levels
Some fish and invertebrates
Intermediate tolerance to salinity changes

Question 9

Stenohaline

Answer 9

Limited salinity tolerance

Question 10

Euryhaline vs Stenohaline

Answer 10

Euryhaline can tolerate salinity fluctuations (mostly osmoconformers)
Stenohaline cannot tolerate salinity fluctuations

Question 11

Tidal Classifications of Estuaries (4)

Answer 11

Microtidal estuaries (<2m)
Mesotidal estuaries (2-4m)
Macrotidal estuaries (4-6m)
Hypertidal estuaries (>6m)

Question 12

Estuary Sediment Size

Answer 12

The river deposits its sediments with larger particles appearing further upriver

The tides deposit its sediments with larger particles further from the shore

This means where they meet at the mouth of the river there are fine sediments that form mudflats

Question 13

Effect of sediment transport on benthic marine organisms

Answer 13

Water clarity and food availability

Sediments clog feeding mechanisms for filter feeders
Limit light available for photosynthesis
Organic rich particles fuel bacterial respiration, deplete oxygen levels
Organix rich particles/detritus might provide food for deposit feeders

Question 14

Estuaries are ephemeral on geological time scales (3)

Answer 14

Changes in sea level due to ice cap formation/thawing (sea level rises and falls, coastline moves)

Sedimentation (river-borne terrestrial materials from eroding continents can infill estuaries)

Tectonic activity (can create or eliminate estuarine basins )

Question 15

Estuary Characteristics that could affect benthic communities (5

Answer 15

Salinity variation: with distance from the river and from tides

Low oxygen conditions: especially in glacial fjords

Tides

Sediment transport

Geological age

Question 16

Remane Diagram

Answer 16

Developed in the Baltic sea
Assumes species diversity driven by salinity
Attempts to explain the distribution

Issues: 
Largely qualitative 
x and y axes are poorly defined 
Intertidal and subtidal 
Incorrectly labels "estuarine species"

Question 17

Atrill Model

Answer 17

The actual testable hypothesis which predicts that salinity capability, not an absolute value, is more important for predicting biodiversity in estuaries