Estuary

Where the River meets the Sea

Importance:Nursery GroundFilters PollutantsAbsorbs excess Rainfall (run-

off)Nutrient TrapSediment Trap (captured in

grasses)Overwintering (resting) Stop

for Birds

Mobile Bay:Bar-builtBarrier Island (Dauphin Island)

protects bay from wave actionMobile’s Delta- formed when

sediments from upstream are deposited at the mouth of the river as it enters the bay.

Physical CharacteristicsRiver flow slows as it enters

bay & nutrient rich sediments fall out of suspension

Flushing- time it takes to move water out to the seaRiver flow, tides, wind & salinity gradient affected by time

Nutrients, trash, young animals & detritus flushed

Salt Wedge:Salinity is higher on the bottom waters of an estuary (NaCl more dense than fresh water)

Water movement forms a wedge of high salinity water in the Estuary

Abiotic Environment of Estuary:

Nutrients: Phosphates, Nitrates, Sulfates from fresh water run-offFlocculation-nutrients dissolved in

fresh water become insoluble in salt water and precipitate out, clouding the water

BOD-Biochemical Oxygen Demand-high demand (low oxygen levels in water) when nutrients are too high

Abiotic Environment of Estuary

Sediment (benthos):Low oxygen levels or may even be ANAEROBIC in mud

Salinity is relatively constant, about 30 ppt

(Flushing doesn’t disturb the sediment)

Benthic organisms:Oysters:

Need solid substrate to attachMud suffocates oysters

Close shell & quits feeding when salinity drops…allowing bacteria to multiply in stomach…DANGEROUS to eat!

Clams & Annelid wormsLive buried in mud

MusselsByssal Thread used to attach to solid substrate

Marsh Periwinkle Snailseats algae growing on grasses

BacteriaDecomposerFood source

Descriptions of Organisms:

Stenohaline-require constant salinity near 30 ppt

Euryhaline-adapt to changes in salinity

Osmoregulator-able to regulate osmotic balance.Ex. fish

Osmoconformer-unable to control osmotic flooding of tissues. Ex. Sea Anemone

Partial Osmoregulator- Crab

Estuarine CommunitiesMudflats-exposed at low tide

Diatoms give mud “golden” colorNo grasses (or very few!)Anaerobic Atmosphere- bacteria

give off H2S (rotten)Provides shelter for clams & worms

Protects from sun (dessication)Protection from predatorsProvides constant salinity

Wetlands-partially flooded by tidesSaltmarsh- Temperate climate

Plants:Cord Grass (Spartina), Pickleweed (succulant)= halophytes

Bacteria- cyanobacteria= photosynthetic, nitrogen fixers

Animals- fiddler crabs, marsh snails

Wetlands continuedMangrove- Tropical climate

Mangrove shrubsProp roots & pneumatophores

Subtidal- Seagrass Beds Always underwater

Plants- Eel grass, Turtle grassHabitat for young fish & larvae

Nutrient pump- takes nutrients from sediments for growth & later releases them into the water when they die

Trap sediments

Uses & Abuses of Estuaries

2/3 of Commercial fish spend some part of their life in an Estuary!

Pollution-75% Estuaries have been destroyed in USA!!DevelopmentDredgingWastes DumpedPiers & Pilings altered flow of water

Food Chain in a Typical Estuary:Primary Producers –Consumers –Detritivores – Planktivores - Carnivores

Mobile Bay Environmental Issues:

Gas Wells~20 natural gas wells in Mobile Bay area

Fear of leaks hurt tourism… now not within 15 miles of shore

Artificial habitat for marine life

Growth on Eastern ShorePopulation increased >50% in past 20 yearsSewage treatment facilities above capacity(>160 gal treated water added to Bay DAILY)

Hypoxia caused by sewage in water….leads to fish kills

Sediment from building runs into Bay

Suffocates grassbeds (habitat & natural filter)

Biodiversity of BayAlabama ranked #1 in N.America for number of fish species

Alabama ranked #2 for number of extinct species…… due to dams and interference of water flow

Pollution of Alabama WaterDDT pesticide widely used in 1960’s, banned in 1972, caused death of Brown Pelican & ALL predatory birds

AL is the 5th MOST polluted stateHeavy metals such as Mercury and toxic chemicals have BIOACCUMULATED in the fish

Bay conditions monitored by Alabama Dept Enviromental Management (ADEM)

Alabama has adopted the EPA’s

MINIMUM

Water quality standards!

Nonpoint Source PollutionSource of pollutant can not be

identifiedDrainage from surface runoff within a WATERSHED (all the land that contributes runoff to a given point)Sediments,nutrients,chemicals (toxins), organic sewage