Estuarine Ecology

Estuary - costal, semi-enclosed extended interface between marine and lotic system. Dynamic, noise and geographically emphemeral

Streams do not produce estuaries - not strong enough

Different definitions though based on tidal regime and infulence, salinity profiles, geomorphology

Fjord type (U) - glacier formation

Ria type (V) - river formation

Coastal plain type - formed by rivers at end of life, create marshes

Bar built - sand/silt bars build up due to offshore deposits

Blind - system closed off by offshore deposits

Delta front - riverine deposit formation

Tectonic - earthquake/tectonic driven

Caused by balance between river flow volume and strength of tides. Salt water denser than freshwater so sinks. Tides mix so stronger the tide the less variation in water salinity

Salt wedge - strong river flow, little mixing

Partially mixed - graduation of salt to freshwater

Well mixed - vertical mixing leading o horizontal change in salinity

Affects salinity profile development - higher tidal range means more mixing

Higher wave amplitude means stronger tidal currents

Tidal resonance = amplification due to tidal waves - high high tide

Global variation in tidal amplitude:

• Microtidal - <2m
• Mesotidal - 2-4m
• Macrotidal - 4-6m
• Hypertidal - >6m

Tides infuenced by regional and local topography e.g. flow channels

Semi-diurnal (1 a day)

Diurnal (2 a day)

Both terrestrial and marine sediment inputs

Water reaching an estuary = reduced sediment carrying capacity

• Heavier sediments deposited first e.g. mud
• Coarser material deposited at head and mouth e.g. sand
• = diverse range of habitats and nutrient-rich waters

Micronutrients e.g. Fe, Mn, interact with fresh/marine waters = change oxidiation states

Reduced state = metal ions dissolved (freshwater), then precipitate (marine)

• Increase deposition rates on flats - reduces water flow and creates habitats
• Reduces erosion rates - biofilms bind sediments
• High nutrient loading - fuels primary and secondary production
• Increase turbidity - reduces light and photosynthesis
• Increases bacterial activity - reduced oxygen and eutrophication

Multiple primary production sources - diverse habitats

Upper areas - freshwater marshes + phytoplankton

Mid to lower areas - more benthic algae, marine phytoplankton, sea grass beds, salt marshes

Estuaries mostly dominated by secondary production - terrestrial detritus (leaves), marine allochthonous particulate organic matter

Bacterial production from sediments in extensive mud flats - large SA for growth

Black mud - reduced due to increased bacterial activities

Combo of primary and secondary production similar to rainforests and coral reefs

Salinity varies depending on time of day - high and low tides

Most organisms cannot cope with large salinity variation - adaptations prevent adverse effects - cell crenation/lysis

Osmoconformers - osmotic pressure body matches surrounding areas

Osmoregulators - expend energy actively excreting water

Euryhaline - tolerate large salinity ranges

Stenohaline - tolerate narrow salinity ranges

Fish - lower internal osmotic body pressure than environment 

• Marine fish actively secrete salts
• Freshwater fish swallow lots of water w/ little ions - actively transported into the body

Organisms move in and out of estuary with tide - prevent salt variation effects

Organisms bury in sand - reduce salinity fluctuations in interstitial fluids than overlying water

Ramane diagram shows steep reduction in freshwater species with salinity

Steep drop in diversity in upper to mid estuary

Then brackish animals dominate

Didromous species common in estuaries - fish spending part of lifes in freshwater and part in salt water

Invertebrates - dominate epifauna and infauna

• Crabs, shrimps, gastropods, polychaetes, bivalves

Fish - use as nursery groups or move with tides

• Flounder, bass, whiting, herring, salmon, eels

Birds - migratory visitors

• Geese, ducks, waders, gulls, cormorants

Plankton

• Phytoplankton - diatoms, dinoflagellates
• Zooplankton - copepods, scyphozoans, larval stages

Estuaries easy access to sea, very sheltered - hotspot for human settlement

Harbour construction and dredging - large scale mods impacting ecosystem

Damage to sea beds and removing habitats

Effluent from harbours - nutrient rich so eutrophication

Pollutants - anti-fouling agens and industrial/agri runoff - accumulation

Large enclosed seas with limited water exchange to oceans and large freshwater inputs

Baltic Sea, White Sea, Black Sea, Sea of Azov

Sea of Azov - shallowest sea in world (14m max), very high but variable salinity and high evaporation rates, easy to mine salt