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