PalaemonetesPalaemonetes – glass shrimp – glass shrimp

Boundary HabitatsBoundary HabitatsEstuariesEstuaries

Questions:Questions:

• What are estuaries?What are estuaries?– Physical parametersPhysical parameters– Biological classificationBiological classification

• What are patterns of mixing in What are patterns of mixing in estuaries?estuaries?

• What are the challenges of What are the challenges of estuaries?estuaries?

• How are estuaries and ocean How are estuaries and ocean systems linked?systems linked?

““Estuary” refers to a physical Estuary” refers to a physical conditioncondition

• A partially enclosed coastal area A partially enclosed coastal area where fresh and sea water mixwhere fresh and sea water mix

• Mixing creates high Mixing creates high variability in variability in salinitysalinity– Variable salinity is unusual in most other Variable salinity is unusual in most other

ocean systemsocean systems– Definition excludes inland, saline watersDefinition excludes inland, saline waters

• Geological derivationGeological derivation leads to finer leads to finer classification of estuariesclassification of estuaries

Drowned river valleysDrowned river valleys(Coastal plain estuaries)(Coastal plain estuaries)

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

• Usually in temperate zone, Usually in temperate zone, with low sediment loadswith low sediment loads

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

A drowned river valley estuaryA drowned river valley estuary

coastal plain estuarycoastal plain estuary

Bar-build EstuariesBar-build Estuaries

• Shallow basins, Shallow basins, with barrier islands with barrier islands & inlets& inlets

• Sedimentation=Sedimentation=

inundationinundation

• May be shallow May be shallow with extensive with extensive lagoons, marshes lagoons, marshes

FjordsFjords

• Once covered by Once covered by ice sheetsice sheets

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

• Norway, Canada, Norway, Canada, Chile, New ZealandChile, New Zealand

Tectonic estuariesTectonic estuaries

• Created by faulting and land subsidenceCreated by faulting and land subsidence

Patterns of mixing for fresh and sea Patterns of mixing for fresh and sea waterwater

• Mechanisms influencing patternMechanisms influencing pattern– Fresh water has lower Fresh water has lower densitydensity; floats on ; floats on

sea water if turbulence is lowsea water if turbulence is low– River flow is out, tidal flux is both out River flow is out, tidal flux is both out

and inand in

• Mixing patterns are sensitive to Mixing patterns are sensitive to flow flow ratesrates

• Salinity can be highly variable in Salinity can be highly variable in space and timespace and time

Fresh and salt water mixing Fresh and salt water mixing regimesregimes

““Positive” or “Salt-wedge” Positive” or “Salt-wedge” estuariesestuaries

• High flow of fresh water from riverHigh flow of fresh water from river

• Fresh water flows outward, over Fresh water flows outward, over deeper salt waterdeeper salt water

• Wedge of salt water changes position Wedge of salt water changes position with tideswith tides

• Moderately stratifiedModerately stratified

• Also called “river-dominated” Also called “river-dominated” estuariesestuaries

Marine-dominated estuariesMarine-dominated estuaries

• Very low flow of fresh waterVery low flow of fresh water

• Promotes more complete vertical Promotes more complete vertical mixingmixing

• Tidal flux, winds, and shape of basin Tidal flux, winds, and shape of basin influence mixinginfluence mixing

Negative/evaporite estuariesNegative/evaporite estuaries

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

• Creates hypersaline estuaries (higher Creates hypersaline estuaries (higher salinity than surrounding sea water)salinity than surrounding sea water)

Fluctuations in salinity in the water Fluctuations in salinity in the water column are buffered in sedimentscolumn are buffered in sediments

Other important physical Other important physical parametersparameters

• TurbidityTurbidity– Sediment load delivered by riverSediment load delivered by river– Dynamics of settling and resuspensionDynamics of settling and resuspension

• Temperature, which can be highly Temperature, which can be highly variable in shallow watervariable in shallow water

• Oxygen levels, also more variable Oxygen levels, also more variable than in typical ocean habitatsthan in typical ocean habitats

Interactions among physical Interactions among physical parametersparameters

Characteristics of biological Characteristics of biological communities: Marsh habitatscommunities: Marsh habitats

• Generally, high density but low diversityGenerally, high density but low diversity– Physiological stressesPhysiological stresses– Low topographic & substrate variabilityLow topographic & substrate variability– But very high potential for productivity due to But very high potential for productivity due to

nutrient inputnutrient input

ComponentsComponents

• Macrophytes (seagrasses, sedges, Macrophytes (seagrasses, sedges, rushes, cordgrasses)rushes, cordgrasses)

• Epiphytic algae (macro- and micro-)Epiphytic algae (macro- and micro-)

• Benthic macroalgae and microalgaeBenthic macroalgae and microalgae

• PhytoplanktonPhytoplankton

Estuary edge zonation in marshesEstuary edge zonation in marshes