4US Outer Coast Estuaries Cape Flattery – Cape Mendocino 24 - Washington49 – Oregon15 – N. California________________89 - totalMost are small(< 10 km2)Lee et al. 2006
5WHY ARE ESTUARIES IMPORTANT? Juvenile fish traveling from the river to the ocean can adapt to salt waterEel grass beds provide refuge or nurseries for many fish and invertebratesInvertebrate and their larva provide food for many species of fish (including salmon)Provide a stop over for migratory birdsProvides a buffer against floods and tsunamis for the surrounding land
6PARTS OF AN ESTUARY (based on the proportion of time under water) Channel under water all the timeEelgrass beds under water most of the timeMud flat exposed mid to low tideSalt marsh covered only at high tideUplands always out of the water
7ESTUARY CLASSIFICATION HOW THEY WERE FORMED1. Drowned river valleys2. Fjord3. Sand bar (or bar built)4. Delta (Nile river)WATER MIXING1. Salt wedge2. Partially mixed3. Well mixed
8DROWNED RIVER VALLEYSLess then 10,000 years in age Branching structure of old river systems Contain large areas of mud flats and salt & marshes (wetlands) Great deal of biomass and biodiversity
9SAND BAR ESTUARYAt river mouths where sand or shingle accumulates off shore to form islands or spits May be interlinked islands & estuary systems Generally shallow Siletz bay is and example of a sand bar estuary
11FJORDSFormed as sea bed rose above glaciated valleys after the last ice age Narrower and straighter then drowned river valleys Less biomass & biodiversity Greater Tsunami hazard May be anoxic at depths
13SALT WEDGE ESTUARY (highly stratified estuary) Large consistent river flow (Colombia or Mississippi Rivers)Key point: salt water is denser (heavier) then the fresh water which floats in the salt water.The wedge moves up or down the estuary as the tide rises or falls.
14YAQUINA SALT WEDGESummerWinterRiver flowTidal flow
15PARTIALLY MIXED ESTUARIES More tidal influence and less river flow More turbidity and more ocean/river water mixing Fine sediment settles out and is not washed out to sea as in estuaries with massive river flow, but is deposited in the estuary (estuary surface rises slowly=accretion)
16WELL MIXED ESTUARIESTidal flow is sufficient to remove virtually all the vertical salinity differences Tides dominate over the river flow
17DIFFERENCES BETWEEN EAST & WEST COAST ESTUARIES Rain in summerSnowFresh water in summerContinental climateWide continental shelfLarge temperature swingsSmaller salinity changesRain in winterNo snowFresh water in winterMarine climateNarrow continental shelfNarrower temperature swingsLarger salinity changes
18DIFFERENCES BETWEEN EAST & WEST COAST ESTUARIES Estuaries below Cape Cod very old (millions of years)Generally don’t smell the oceansGreater estuarine diversity with a lower proportion introduced speciesMost 5- 10,000 years oldSmell the ocean (because of the winds)Less diversity & more density with a greater proportion of introduced species
19Winds and current structure off coastal Oregon: Winter:Winds from the SouthDownwelling – shore-ward transport of surface waterPoleward-flowing Davidson CurrentUniform cross-shelf hydrographySpring Transition – sea level drops suddenlyApril 4 ± 25 daysSummer:Strong winds from the NorthCoastal upwelling – off-shore transportEquatorward alongshore transport (California current)Strong cross-shelf physical gradientsSlide modified from William Peterson42N356NewportWAORThis slide summarizes seasonal variation in the wind and current patterns off our coast.In Winter, winds are from the south, the Davidson Current flows pole-ward, and downwelling causes onshore transport of surface waterThen sometime around April 4, the Spring Transition occurs. This event is marked by a sudden reversal in the wind pattern and a sudden drop in sea level.In Summer, we get strong North winds which sets up equatorward flow and upwelling, andThere’s strong cross-shelf physical gradients– very difficult for larvae to make it back to shore – unless the winds relax and upwelling ceases for a while.
20YAQUINA BAY & ESTUARY FACTS Area = about 5 sq. miles (relatively small) Watershed = 256 sq. miles (relatively small), 95% of watershed is forest. Two rivers, Yaquina and Elk, contribute to the river flow equally. 70% of estuary water exchanged with each tidal cycle This is a WELL MIXED estuary in summer and a PARTIALLY MIXED estuary in the winter. Yaquina bay is closely coupled to the near shore ocean
21NUTRIENTS IN YAQUINA BAY WINTER nutrients primarily from riversSUMMER nutrients primarily from oceanNorth windsUpwellingNitrates, nitrites & 2 daysChlorophyll 6 daysSummer algae blooms are not pollution or eutrophication but a result of upwelling of ocean nutrients
22HOW TO TELL WHEN UPWELLING HAS OCCURRED? Sea foam will be on the beach.Water temperature in the bay will drop (thisis measured by the LOBO exhibit)Water temperature in the touch tanks may dropWater temperature is a surrogate for measuring Nitrates and Phosphate nutrients!
23LIFE IN THE ESTUARY Rocky shore is “2D” Estuary (or soft bottom) is “3D”After: Little, C. The Biology of Soft shores & Estuaries
24ORGANISMS ADAPTATION TO THEIR ENVIRONMENT Rocky “2D” Tide poolSoft “3D” EstuaryArmoredFirmly attachedLightly armoredLive in burrowsGood diggersAdapted for low oxygen conditions (anoxia)
25PHYSICAL DIFFERENCES BETWEEN BEACH & ESTUARY Sand (>63 microns)Water movement by wave energy (high energy)Salinity 35Sediment deposition coarser sand higher on shoreMud (<63 microns)Water movement by tidal flow (less energy)Salinity 40 = to 0Sediment deposition coarser mud more near channel
26Mud includes both silt and clay After: Little, C Mud includes both silt and clay After: Little, C. The Biology of Soft Shores & EstuariesFrom Little, C. The Biology of Soft Shores & Estuaries
27HYPOXIA The #1 problem for estuary infauna!!! Surface Oxygenated mud Hypoxic mudThis line moves up in summer and down inThe winter. WHY?
28BLACK MUD 1. Sulfates Desulphovibrio Hydrogen sulfide (H2S) (present in hypoxic mud) (sulfate-reducing bacteria) (clear & colorless, but foul smelling)H2S + Iron oxides Iron sulfide (black)(present in the mud)Iron sulfides Beggiatoa sp Elemental sulfur(from equation 2 ) (oxidizes) (white or yellow patches onthe surface of the mud flat)
29DEALING WITH LOW OXYGEN Hypoxia is a bigger problem in the mud than the sand. Why? Hypoxia is worsened by accumulated organic material. Why? Animals (and plants) in the estuary must be able to cope with low oxygen. How?
30COPING MECHANISMSThey can move (fish, shrimp, crabs, etc.) They can form a water current in their burrows (ghost shrimp, mud shrimp). They can trap oxygenated water from high tide in their shells (clams). They can reduce their respiratory rate (cockles). Some can absorb oxygen from the air if the mud dries out (some cockles). Some (Callianassa/Neotrypaea sp.) oxidize sulfides into thiosulfates (a much less toxic compound)
31SALINITY GRADIENTFrom Little, C. The Biology of Soft Shores & Estuaries