Estuaries - Biology

choppedspleenΜηχανική

21 Φεβ 2014 (πριν από 3 χρόνια και 10 μήνες)

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Palaemonetes



glass shrimp

Boundary Habitats

Estuaries

Questions:


What are estuaries?


Physical parameters


Biological classification


What are patterns of mixing in estuaries?


What are the challenges of estuaries?


How are estuaries and ocean systems
linked?

“Estuary” refers to a physical condition


A partially enclosed coastal area where
fresh and sea water mix


Mixing creates high
variability in salinity


Variable salinity is unusual in most other
ocean systems


Definition excludes inland, saline waters


Geological derivation

leads to finer
classification of estuaries

Drowned river valleys

(Coastal plain estuaries)


Formed after the last ice age to
3000 years bp (before present)


Usually in temperate zone, with
low sediment loads


Process of sedimentation is
slower than inundation
(otherwise one finds deltas)

A drowned river valley estuary

coastal plain estuary

Bar
-
build Estuaries


Shallow basins, with
barrier islands & inlets


Sedimentation=


inundation


May be shallow with
extensive lagoons,
marshes

Fjords


Once covered by ice
sheets


Glaciers cut typical “U”
shaped valleys; rock
sills at mouths


Norway, Canada,
Chile, New Zealand

Tectonic estuaries


Created by faulting and land subsidence

Patterns of mixing for fresh and sea water


Mechanisms influencing pattern


Fresh water has lower
density
; floats on sea
water if turbulence is low


River flow is out, tidal flux is both out and in


Mixing patterns are sensitive to
flow rates


Salinity can be highly variable in space
and time

Fresh and salt water mixing regimes

“Positive” or “Salt
-
wedge” estuaries


High flow of fresh water from river


Fresh water flows outward, over deeper
salt water


Wedge of salt water changes position with
tides


Moderately stratified


Also called “river
-
dominated” estuaries

Marine
-
dominated estuaries


Very low flow of fresh water



Promotes more complete vertical mixing



Tidal flux, winds, and shape of basin
influence mixing


Negative/evaporite estuaries


In hot climates, high evaporation is
combined with low fresh
-
water flow



Creates
hypersaline

estuaries (higher
salinity than surrounding sea water)

Fluctuations in salinity in the water
column are buffered in sediments

Other important physical parameters


Turbidity


Sediment load delivered by river


Dynamics of settling and resuspension


Temperature, which can be highly variable
in shallow water


Oxygen levels, also more variable than in
typical ocean habitats


Interactions among physical parameters

Characteristics of biological communities:
Marsh habitats


Generally, high density but low diversity


Physiological stresses


Low topographic & substrate variability


But very high potential for productivity due to nutrient
input

Components


Macrophytes (seagrasses, sedges, rushes,
cordgrasses)


Epiphytic algae (macro
-

and micro
-
)


Benthic macroalgae and microalgae


Phytoplankton

Estuary edge zonation in marshes