Characteristics of
Estuaries
Introduction
 Estuary
= a semi-enclosed area where fresh
water and seawater mix

Where rivers meet the ocean
 Common
in areas with a wide continental
shelf
2
Formation of Estuaries
1. Coastal Plain
estuaries = formed
by rising sea level

Ex. Chesapeake
bay & Delaware
river mouth
2. Bar-built estuary
= sediments form
sandbars & miniislands

Ex. Texas Coast
3
Formation of Estuaries (cont)
3. Tectonic estuary
= land sinks due to
tectonic movement

Ex. San Francisco
Bay
4. Fjords = glaciers
create coastal
valleys

Ex. Alaska
4
Physical Characteristics: Salinity
 Influenced
by mixing of fresh and salt
water

salinity is between 0% and 3.5%
 “Salt
Wedge” = layer of denser, saltier
water that flows along the bottom

Changes with tides
5
Physical Characteristics: Substrate
 Substrate

Soft in estuaries (mud)
 Large


= type of bottom
amounts of sediment from rivers
Large particles settle first
Small particles carried out farther
 Mud
contains a lot of dead organic material
 Lack oxygen


Caused by aerobic bacteria
Black color, rotten egg smell
6
Water Temperature
 Shallow
water causes
more temperature change
Water Clarity
 Suspended
sediments
make water cloudy
7
Types of Estuaries
 Mudflats
= flat regions with a large tidal
range (exposed during low tide)

Bacteria, diatoms, burrowing animals, filter
feeders, worms, insects, crabs, fish, birds
 Salt
Marshes = grassy areas that extend
inland from mudflats

Salt-tolerant plants
 Mangrove
Forests = grow on coasts where
sediments accumulate

Plants form zones based on salt tolerance
8
Coping with Salinity
 Organisms
must
tolerate changing
salinity
 Osmoregulation
=
maintaining salt and
water concentrations
in the body

Fish, crabs, molluscs
9
Adapting to Mud
Constantly changing
environment
 Low oxygen levels
 Animals burrow into the mud
or live in tubes
 Many animals filter feed



Others feed from dead organic
matter
Less drastic salinity changes
than in water column
10
Plant Adaptations
 High

salt tolerance
Ex. Cordgrass,
seagrass
 Excrete

excess salts
Ex. Mangroves
 Succulents


accumulate water to
balance salt content
Ex. Pickleweed
11
Video Notes: Estuaries
1.
2.
3.
4.
5.
6.
What is an Estuary (2)
Tilamook Bay (2)
Mangrove Lagoon (2)
Tides & Life (4)
Bottom Dwelling Animals (6)
Pollution (2)
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