1. Palaemonetes – glass shrimp

2. Boundary Habitats Estuaries

3. Questions: What are estuaries? What are estuaries? –Physical parameters –Biological classification What are patterns of mixing in estuaries? What are patterns of mixing in estuaries? What are the challenges of estuaries? What are the challenges of estuaries? How are estuaries and ocean systems linked? How are estuaries and ocean systems linked?

4. “Estuary” refers to a physical condition A partially enclosed coastal area where fresh and sea water mix A partially enclosed coastal area where fresh and sea water mix Mixing creates high variability in salinity Mixing creates high variability in salinity –Variable salinity is unusual in most other ocean systems –Definition excludes inland, saline waters Geological derivation leads to finer classification of estuaries Geological derivation leads to finer classification of estuaries

5. Drowned river valleys (Coastal plain estuaries) Formed after the last ice age to 3000 years bp (before present) Formed after the last ice age to 3000 years bp (before present) Usually in temperate zone, with low sediment loads Usually in temperate zone, with low sediment loads Process of sedimentation is slower than inundation (otherwise one finds deltas) Process of sedimentation is slower than inundation (otherwise one finds deltas)

6. A drowned river valley estuary

7. coastal plain estuary

8. Bar-build Estuaries Shallow basins, with barrier islands & inlets Shallow basins, with barrier islands & inlets Sedimentation= Sedimentation= inundation inundation May be shallow with extensive lagoons, marshes May be shallow with extensive lagoons, marshes

9. Fjords Once covered by ice sheets Once covered by ice sheets Glaciers cut typical “U” shaped valleys; rock sills at mouths Glaciers cut typical “U” shaped valleys; rock sills at mouths Norway, Canada, Chile, New Zealand Norway, Canada, Chile, New Zealand

10. Tectonic estuaries Created by faulting and land subsidence Created by faulting and land subsidence

11. Patterns of mixing for fresh and sea water Mechanisms influencing pattern Mechanisms influencing pattern –Fresh water has lower density; floats on sea water if turbulence is low –River flow is out, tidal flux is both out and in Mixing patterns are sensitive to flow rates Mixing patterns are sensitive to flow rates Salinity can be highly variable in space and time Salinity can be highly variable in space and time

12. Fresh and salt water mixing regimes

13. “Positive” or “Salt-wedge” estuaries High flow of fresh water from river High flow of fresh water from river Fresh water flows outward, over deeper salt water Fresh water flows outward, over deeper salt water Wedge of salt water changes position with tides Wedge of salt water changes position with tides Moderately stratified Moderately stratified Also called “river-dominated” estuaries Also called “river-dominated” estuaries

14. Marine-dominated estuaries Very low flow of fresh water Very low flow of fresh water Promotes more complete vertical mixing Promotes more complete vertical mixing Tidal flux, winds, and shape of basin influence mixing Tidal flux, winds, and shape of basin influence mixing

15. Negative/evaporite estuaries In hot climates, high evaporation is combined with low fresh-water flow In hot climates, high evaporation is combined with low fresh-water flow Creates hypersaline estuaries (higher salinity than surrounding sea water) Creates hypersaline estuaries (higher salinity than surrounding sea water)

21. Fluctuations in salinity in the water column are buffered in sediments

22. Other important physical parameters Turbidity Turbidity –Sediment load delivered by river –Dynamics of settling and resuspension Temperature, which can be highly variable in shallow water Temperature, which can be highly variable in shallow water Oxygen levels, also more variable than in typical ocean habitats Oxygen levels, also more variable than in typical ocean habitats

23. Interactions among physical parameters

24. Characteristics of biological communities: Marsh habitats Generally, high density but low diversity Generally, high density but low diversity –Physiological stresses –Low topographic & substrate variability –But very high potential for productivity due to nutrient input

25. Components Macrophytes (seagrasses, sedges, rushes, cordgrasses) Macrophytes (seagrasses, sedges, rushes, cordgrasses) Epiphytic algae (macro- and micro-) Epiphytic algae (macro- and micro-) Benthic macroalgae and microalgae Benthic macroalgae and microalgae Phytoplankton Phytoplankton

26. Estuary edge zonation in marshes