Estuaries Flashcards
What are estuaries?
Semi -enclosed bodies of water where freshwater mixes with seawater
Important factors that influence estuaries
Spatial gradient in abiotic conditions, like salinity
Experiences a lot of temporal variability (the changes or functions in a system over time) due to tides
4 types of estuaries
Drowned river valley (aka coastal plain) - formed when rising sea levels flood existing river valleys
Bar built - has a sand split
Tectonic - made by faults
Fjords - has steep walls
Drowned river estuaries
formed when rising sea levels flood existing river valleys. Most made at the end of the last ice age
Bar Built estuaries
Formed when barrier beaches or islands accumulate and create a separation between estuary and the ocean. Can be dynamic if the barrier beaches are unstable
Tectonic estuaries
When tectonic places run into fold up underneath each-other creating depressions
Fjords
Steep walled river valleys created by glaciers that became flooded with seawater. Long and narrow, often have a ‘sill’ which can prevent sea water inundation and decreases water exchange
5 characterizations of estuaries based on water circulation
- salt wedge
- fjord
- slightly stratified
- vertically mixed
- freshwater
Water circulation - salt wedge
Aka highly stratified. Occurs when rapidly flowing river water discharged into ocean with weak tidal currents. Density gradient creates clear boundary between body of water
Fjord water circulation
Restricts water circulation with open ocean, limiting the influx of seawater water. Very little tidal mixing, highly stratified
Slightly stratified water circulation
Fresh and salt water mix at all depths, but water is still saltier at depth. Typical of deep estuaries
Vertically mixed or well mixed
Occurs when river flow is low and tidal currents are moderate/strong. Similar salinity across depths, nice gradient.
Diversity and productivity of estuaries
High biomass and high productively. Not a lot of diversity
Allochthonous
Detritus production that happens outside estuary. Upland origin (sticks, leaves, ect.) or marine origin (marine plankton, seaweed, etc.)/
Autochotonous
Detritus production that happens inside estuary
- phytoplankton, benthic macro-algae, marsh, mangroves, seagrass
Organic matter varies in
- Deadness
- Size
- Lability
Labile - easily consumed or decomposed
Refractory - resistant to decomposition (tannins)
Labile vs refractory Organic matter
Labile - easily consumed or decomposed
Refractory - resistant to decomposition (tannins)
CDOM
Colored dissolved organic matter
Implications of CDOM in estuaries
Absorbs a lot of blue light, so the water ends up looking yellow/brown. This absorption of light can negatively impact photosynthesis
What can clear CDOM
Filter feeders and microbes
Stenohaline vs Euryhaline organisms
Stenohaline - narrow salinity range
Euryhaline - wide salinity range
Can vary based on life history stage
Remane diagram
Shows the hypothetical distribution of benthic invertebrate diversity along a marine -freshwater salinity gradient
