what is an estuary an estuary is where freshwater from rivers merges with the ocean and is bordered...
TRANSCRIPT
Estuaries: Where Rivers Meet the Sea
What is an EstuaryAn Estuary is where freshwater from rivers merges with the ocean and is bordered by extensive wetlands (mudflats or saltmarshes)
Characteristics of Estuaries
Salinity varies spatially and over the course of a day as the tides move in and out
Nutrients from the rivers enrich estuarine waters making them one of the most biologically productive environments on earth
Salt marsh grasses, algae, and phytoplankton are the major producers
Many organisms are found in the muddy bottom
Estuaries rank among the environments most affected by humans
Functions and Values of EstuariesProvide open space and recreationProvide natural flood controlPurify the waterProduce oxygenAre outdoor laboratories for scientists and
educatorsProvide sediment traps and erosion controlServe as nurseries for marine fishesProvide homes for endangered speciesProvide habitat for migrating, wintering and
breeding birdsServe as repositories for native plants and
animals
Types of Estuaries – Four basic groups based on their origins
Drowned River Valley or Coastal Plain – Fig. 12.1 – formed as a result of the sea invading lowlands and river mouths. This is the most common type of estuary.
Types of EstuariesBar-built estuary – Fig. 12.1 – formed when a barrier
island or sand bar separates a section of the coast where freshwater enters. (Pictured below is an aerial view of Cape Hatteras, North Carolina.)
Types of EstuariesTectonic
Estuary – formed as a result from sinking land due to movements of the earth’s crust. San Francisco Bay formed in this way.
Types of EstuariesFjords – Fig. 12.2 – formed in a deep valley
created by a retreating glacier. (Kenai Fjord National Park, Alaska)
Physical Characteristics of Estuaries – unique because of mixing of salt and
freshwaterSalinity fluctuates as the tides move
seawater in and out of an estuary.Organisms are subjected to these
changes every day and therefore have adapted to these conditions.
Other factors that influence salinity include; the shape of the estuary, the bottom, wind and evaporation, and freshwater runoff
Salt Wedge – a layer of denser, saltier seawater that flows along the bottom
Physical Characteristic - Salinity
Salt Wedge
Sand and other coarse material settle out first near the river mouth
Finer particles settle out into “main” body of water, therefore most estuaries are soft mud (silt & clay) which is very dense and rich in organic material
Decomposition by bacteria depletes oxygen in the substrate and produces hydrogen sulfide (rotten egg smell)
Tidal flow keeps water in estuaries oxygen rich
Physical Characteristic - Substrate
Close up of Estuary Sand
Physical CharacteristicsTemperature – fluctuates widely because of tides,
organisms that are exposed at low tides also face seasonal temperature changes
Turbidity – estuaries usually have large amounts of suspended sediments which can reduce water clarity
Maintaining the proper salt and water balance is essential for all organisms.
Organisms that live in estuaries must cope with rapid changes in salinity.
Most estuarine organisms are marine species that have evolved to tolerate low salinities.
Coping with Salinity
Euryhaline species can tolerate a wide range of salinities.
Stenohaline species can only tolerate a narrow range of salinities (yellow fin tuna)
Osmoconformers (molluscs and worms) – osmotic balance is maintained by changing with the salinity of the water
Osmoregulators keep internal salt balances constant despite salinity levels of the water in which they live
Osmoconformer vs Osmoregulator
Osmoconformer vs Osmoregulator
Coping with SalinityMarine fish – have a lower salt concentration
than seawater, therefore tend to loose water; adaptations to maintain homeostasis include (Fig. 4.14)Drinks seawaterExcretes excess salt through gillsExcretes small volumes of concentrated salty
urine
Coping with SalinityAdaptations of other
marine organismsSea turtles/sea
gulls/sea lions have glands near the eyes that excrete “salty” tears (Fig. 4-15)
Mangroves/spartina grass – excrete excess salt through leaves
Salt crystals on spartina grass
Coping with Salinity – Pickleweed accumulates large amounts of water to dilute the salts they take up.
Most animals burrow or live in permanent tubes beneath the sediment
Inhabitants tend to be stationary or slow moving
Salinity fluctuations are less drastic than in the water column
Organisms overcome the depletion of oxygen by:Pumping oxygen rich water into their burrowsSome have blood that contains hemoglobin, an
oxygen carrying molecule
Adapting to the Mud
Adapting to the Mud
Different types of communities are associated with various estuaries
Open Water community includes those organisms that come and go with the tide (plankton, fishes, jellies).
Other types of communities are permanent parts of the ecosystem, these include:MudflatsSalt MarshesMangrove ForestsSea-grassesOyster Reefs
Estuarine Communities
Organisms in this type of community include phytoplankton, zooplankton, and marine fish that are flushed in and out by the tides.
Many types of marine fish and shrimp use estuaries as nurseries for their young.
Some fish migrate through estuaries.Anadromous – marine fish that live their
lives in the sea but return to freshwater to breed (salmon)
Catadromous – freshwater fish that migrate to the sea to breed (freshwater eels)
Open Water Community
Open Water CommunityZooplankton
Open Water CommunityPhytoplankton
Open Water CommunityAnadromous
Open Water CommunityCatadromous
Low tides expose organisms to desiccation, fluctuating temperatures and salinity, and predation.
Primary produces consist of diatoms, bacteria, and some algae
Consumers are typically burrowing deposit and suspension feeders that feed on detritus
Mudflat Communities
Mudflat Communities
Mudflat Communities
Mudflat Communities
Mudflat Communities
Mudflat Communities
Mudflat Communities
Mudflat Communities
Mudflat Communities
Salt Marsh CommunitiesSalt marshes are grassy areas that
extend along the shores of estuaries and sheltered coasts in temperate and subpolar regions.
Salt marshes are subject to the same fluctuations in salinity, temperature, and tidal changes that affect mudflats.
Pronounced zonation of vegetation in salt marsh communities is a result of fluctuations in salinity, height relative to the tide, and rate of evaporation
Cordgrass (Spartinia alterniflora) is the most common plant found where the marsh meets the mudflat. Helps to stabilize the bottom.
Salt Marsh CommunitiesZonation depends on several factors: two
important ones are salinity and nutrient availability.
Salinity changes depending on these conditions:a. frequency of tidal inundation
b. rainfall c. tidal creeks and drainaged. soil texture e. vegetation f. depth of water tableg. freshwater inflow
Nutrient availability varies considerably, especially the supply of usable nitrogen and phosphorous. Often there is not enough oxygen present in marsh soils to combine into useful nitrates and phosphates.
Salt Marsh Communities
Salt Marsh Communities
Salt Marsh Communities
Mangrove Forest CommunitiesMangrove forests are formed by
mangroves, tropical and subtropical trees and shrubs adapted to inundation by seawater.
Grow on protected coasts where muddy sediments accumulate.
The red mangrove is found along the coast of Florida. Can be identified by its prop roots.
Mangrove Forest Communities
Mangrove Forest Communities
Mangrove Forest Communities
Mangrove Forest Communities
Coral growing on amangrove root.
Mangrove Forest CommunitiesSnapper living among the mangrove roots.
Mangrove Forest CommunitiesCattle egret and nest in mangrove.
Sea Grass CommunitiesRoots help to stabilize the sediment and provide shelter to organisms
Florida lobster(yummy)
Oyster Reef Communities
Oyster Reef CommunitiesFriends of Hunting Island help resort oyster reefs.