estuary where the river meets the sea. importance: nursery ground filters pollutants absorbs...
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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