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Estuaries Coastal embayment where fresh and salt water mix: connection of sea to fresh water source at least part of the year Geomorphology, geologic history.

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Presentation on theme: "Estuaries Coastal embayment where fresh and salt water mix: connection of sea to fresh water source at least part of the year Geomorphology, geologic history."— Presentation transcript:

1 Estuaries Coastal embayment where fresh and salt water mix: connection of sea to fresh water source at least part of the year Geomorphology, geologic history and climate create differing chemical and physical m conditions. dictate types of estuaries


3 Types of Estuaries Coastal plain – most common, rising SL flooded river valleys [chesapeake, hudson] Tectonic – similar: sea invades subsiding land [SF Bay] Lagoon - sandbars parallel coastline and cut off embayment; salinity varies (river? climate: evap/rainfall?) [NC, NL TX] Fjord – valley cut by glaciers then flooded by sea, characteristic sill at mouth restricts bottom water exchange [chile, scotland, alaska, bc, hudson]

4 Salinity classification
Gradient from FW to SW Density differences – FW < SW Shape, tides, rainfall:evap , river discharge, affect FW-SW mixing Also seasonal changes in climate


6 Estuary Continuum Types form a continuum from
little mixing (salt wedge), to moderate mixing, weak wedge (partially mixed) to Fully mixed or homogenous, marine dominated or neutral estuaries Negative (reversed salt wedge) Where on continuum depends on Mixing Tidal regime, basin geometry, river flow Seasonal variations in rainfall, wind regimes, evap rate


8 Fjord

9 Positive or Salt Wedge estuary
Where FW input >>evap, FW moves across the surface, mixing with SW, dec salinity but leaving deep water unmixed Isohalines slant upstream at bottom Vertical profile: salinity always least at surface Horizontal – decreasing upstream

10 Partially mixed and homogenous estuaries
Partial – indistinct or variable salt wedge Homogenous - Complete mixing or where evap rate = FW inflow

11 Negative or Evaporate Estuary
Deserts, where FW input low, evap high, SW enters and mixes with limited FW. Evap causes hypersalinity at surface Sinks, moves out as bottom current Isohalines slant opposite: downstream at bottom Vertical profile reversed: salinity always greatest at surface Horizontal – increased salinity upstream


13 Seasonal or Intermittent Estuary
Where marked wet and dry seasons occur Wet – rainfall, open to sea Dry - little or no inflow, outlet often blocked Salinity varies temporally not spatially

14 Physical Characteristics: Salinity
Fluctuation dominant feature Gradient always occurs but varies w/tide, basin topography, amt of freshwater Affects water column salinity much more than interstitial water

15 Tide – isohalines displaced up and down stream, region with max salinity fluctuation

16 Coriolis effect – No. hemisphere, deflects outflow of FW to right looking down a N-S oriented estuary; SW flowing in deflected to right looking up estuary from sea

17 Seasonal effect - Change in evaporation or FW inflow or both
Seasonal effect - Change in evaporation or FW inflow or both. Change in FW moves salt wedge down or upstream Flushing time – water entry and exit: amt of time for a given mass of FW to be discharged


19 Substrate Net depositional environment (dredging)
Highly variable, most soft and muddy characteristic Depends on geology and recent sediment transport (eg. fjord) Suspended particles in FW mix with SW, ions cause flocculation and settling SW: estuary is sheltered, less energy, suspended particles settle out

20 Currents and particle size:
larger settle out faster than smaller, currents=energy: more keeps larger particles suspended SW and FW drop coarse particles first: coarse sediments at mouth and upper reaches Mixing zone with finest mud Terrestrial and marine organic material: food reservoir Fine particles high surface:volume ratio bacterial substrate. Catastrophic events important deposition and removal of sediment Permanent alteration of volume, topography Prolonged salinity change

21 Temperature Smaller volume, large surface: heats, cools more rapidly (not fjords) Surface waters most variable FW inflow – FW more temperature variable than sea Estuary colder in winter and warmer in summer than nearby sea Tidal change – vary temperature between river and sea temp range Mid estuary greatest tidal temp effect Annual temp. variation least at mouth, increases up estuary to max at head

22 WAVES: Limited fetch and shallow depth limits size of potential waves;
Narrow mouth and shallows dissipate sea waves Calm promotes sediment deposition and rooted SAV

23 CURRENTS tides and river flow, limited to channels
Velocity highest in middle of channel where friction least, and where flows constricted Flow regimes control sediment and larval distribution High velocity areas – erosion, not deposition; high larval recruitment, high productivity High flows = flux of food for filter feeders, inc. gas exchange

24 Turbidity Particles in suspension, max at mouth, at time of max river inflow, decreases down estuary, lowest at mouth Phytoplankton concentration and wind speed are factors in lagoon systems Ecol effect - reduce light penetration, reducing primary production Severe – primary production by emergent plants only

25 Down estuary: Turbidity decline Nutrients still elevated Algal bloom

26 Oxygen FW, SW influx, mixing – usually sufficient
Hypoxia -summer thermocline and vertical salinity stratification, little vertical mixing Isolation of deep water, plus high organic loading, long flushing times may lead to hypoxia, anoxia Substrate also low oxygen – organics plus high bacterial numbers, fine particles, low exchange rate – anoxic (also fertilizer) Key - Bioworking by Callianassa, Balanoglossus oxygenates sediment


28 Substrate also low oxygen – organics plus high bacterial numbers, fine particles, low exchange rate – anoxic Key - Bioworking oxygenates sediment

29 Biota Marine – most species; stenohaline (>25 psu) and euryhaline (15-30 psu) Brackish – 5-18 psu, mid region only; both physical and biotic factors limit distribution Freshwater - < 5 psu, upper only Transitional – Migratory fishes (salmon, eels) Part of life in estuary (penaeid shrimp) Feeding only - bull sharks, birds


31 Fewer species than FW or SW
Origin marine, not FW – like other transitional zones: Intertidal fauna origin marine, not terrestrial No true estuarine species, low species richness Why? Theories: Extreme salinity range difficult to adapt to Estuaries are “young” environments Both??


33 Vegetation Subtidal - Limited by substrate availability, turbidity
Sea grasses L imited green algae Intertidal Mud flats – abundant benthic diatoms, blue green algae mats Emergent – salt marshes, mangroves

34 Morphological adaptation
Highly variable oxygen, temperature, salinity Burrowing – setae stop silt clogging Fish - Smaller body size Plants – Aerenchyma - anoxia salt glands – excess salt root carbohydrate stores – energy “succulance strategy” – buffer water loss form osmosis Small leaves, few stomata, photosyn stems Reduce water loss

35 Physiological adaptation
Maintain ionic balance when salinity fluctuates Marine - most osmoconformers, internal salt conc. > estuarine envt. ; barrier Estuarine – osmoregulators, function with varying internal salt conc., barriers to salinity Osmoregulators move water Move ions Adjust internal water-ion balance

36 Behavior Burrowing – less change, buffered from salinity and temp change Osmoregulatroy adults but vulnerable larva – reproduce in or migrate to SW (crabs) Burrowing and ability to tolerate low salinity- predator avoidance Adaptable larvae- high nutrient sources up estuary

37 Ecology of estuaries Internal primary production not high
Role of primary production reduced: few herbivores Sink for primary production elsewhere – terrestrial, salt marsh Detritus carbon system

38 European type - – large mud flats, little vegetation
Large benthic, plankton diatom primary production Energy from outside (allocthonous) – sea or river source Support large populations because they are effective detritus sinks Net energy receivers

39 American estuary – dominated by extensive emergent vegetation
Huge marsh productivity (~6850 kcal/m²/yr vs diatoms - ~1600 kcal/m²/yr Excess carbon producer –

40 Detritus based food web
Organic particles, bacteria, protozoa, algae Estuary water – 110 mg dry organic mater per liter vs 1-3 open ocean Bottom up - salt marsh plant detritus production controlled by physical factors Top down – consumers control production Sea grass contribution, nutrients – human factor

41 Nutrients Fertilizer use, coastal development (loss of buffers), organic wastes Promotes macro algae growth, loss of other productivity Excess phytoplankton growth - stops light transmission, loss of sea grass

42 Structure and salinity
Horizontal banding – assume physical control but untested Plant communities distribution – each does best in own salinity Research - All marsh plants do better in FW, but salt marsh plants poor competitors (comp exclusion, salt adaptation a “refuge “)

43 Currents Obstructions – accelerate flow, increase flux of larvae to site, influx of particles for filter feeders, increase efficiency of gas exchange on leaves Increases photosynthesis and metabolic rates of vascular plants, algae Decreases importance of consumers Predators ineffective – hard to move, poor olfactory cues

44 Oyster beds, mussels, sea grass
High flow rates – less deposition, coarse substrate, high density of organisms with fast growth rates. Oyster beds, mussels, sea grass Low flow – low larvae, low food availability, low gas exchange, more effective predators Maine – high flow= mussel beds, low flow = unpalatable algae canopy, bare understory


46 Food webs primarily detritus based ? – low water column productivity, few herbivores, large amts of detritus Small detritus consumed by suspension feeders, deposit feeders (size selected) Both consumed by predators – Invertebrates: polychaetes, blue crabs, Busycon whelks - keystone Fish and birds – consume detritus feeders and predators Trophic relay – move estuarine production offshore

47 Consumer control Fish – specialize on prey type and size, and specialize with age Shore Birds – consume huge numbers of prey (4-20% of invertebrate production) Shore bird predation keeps benthic density down

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