Estuaries

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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 and climate create differing chemical and physical m conditions. dictate types of estuaries. Types of Estuaries.
Transcript
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
  • 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]
  • 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
  • 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
  • FjordPositive 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 upstreamPartiallymixed and homogenousestuaries
  • Partial – indistinct or variable salt wedge
  • Homogenous - Complete mixing or where evap rate = FW inflow
  • 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
  • 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
  • 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
  • Tide – isohalines displaced up and down stream, region with max salinity fluctuation 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 seaSeasonal 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • Down estuary:Turbidity declineNutrients still elevatedAlgal bloomOxygen
  • 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
  • Substrate also low oxygen – organics plus high bacterial numbers, fine particles, low exchange rate – anoxicKey - Bioworking oxygenates sedimentBiota
  • 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
  • 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??
  • 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
  • Morphological adaptationHighly 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
  • Physiological adaptationMaintain ionic balance when salinity fluctuates Marine - most osmoconformers, internal salt conc. > estuarine envt. ; barrierEstuarine – osmoregulators, function with varying internal salt conc., barriers to salinityOsmoregulatorsmove waterMove ionsAdjust internal water-ion balance 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
  • 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
  • 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
  • American estuary – dominated by extensive emergent vegetation
  • Huge marsh productivity (~6850 kcal/m²/yr vs diatoms - ~1600 kcal/m²/yr
  • Excess carbon producer –
  • 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
  • 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
  • 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 “)
  • 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
  • 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
  • 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
  • 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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