Estuaries

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. Partiallymixed and homogenousestuaries • 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 orboth. 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 insuspension, 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. 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