Estuaries and Salt MarshesMARS 345015 October 2013EstuariesCanonical definition: “An estuary is a semi-enclosed body of water which has a free connection with the sea and within which sea water is measurably diluted with fresh water.” (Pritchard)Does this cover everything?No!• Lagoons – little fresh water, often seasonally hypersaline, “reverse estuaries”• Atolls – no river, may receive ground water, rain• Tidal Fresh Water – inland portion of an estuary• Bights and other continental shelf features –physical behavior may be similar to estuariesCommonalities• Shallow: benthic-pelagic coupling important• Strongly influenced by surrounding land mass• Strong physical (diurnal, seasonal) signals• Typically highly productive (but not always!)• Subsidized by terrestrial inputs of organic matter and (especially) nutrientsTypology and OriginCoastal plain estuaries:drowned river valleysChange in Sea LevelLowHighMean Depth 14 mTypology and Origin“drowned river valley”Bar-built estuariesNybakken and Bertness 2004Bolinas LagoonMean Depth0.5 mDynamic features: Long-shore sediment transport shapes and maintains the bar – no bar, no bayPamlico SoundMean Depth3.6 mGeorgia’s estuaries are a combination of bar-built and drowned river valleysTypology and Origin“drowned river valley”Tectonic estuaryMean Depth3.2 mSan Francisco BayTectonic Estuaries on San Andreas FaultTomales BayMean depth2.6 mTypology and Originhttp://www.prism.washington.edu/file/show/1716http://www.wfga.net/SJDF/faq.htmlFjords:Carved by glaciers, then flooded. Deep, steep-sided280 m1200 mMean Depth 137 mCirculation patternshaloclineMicrotidal(Chesapeake Bay, Pamlico Sound, atolls in the tropics)Tidal or well-mixed (Georgia, SF Bay, Bay of Fundy)Other important factors: “openness,” wind mixing, mean depth, sinuosity??Tides are Important!Minimal mixingStrong mixingCirculation can vary seasonallydepending on runoff patternsStream FlowStream FlowJan DecInterannual Variation in Runoff1993 (El Nino year)1992 and 1994WinterHigh runoff, lots of fresh water, cold temperaturesTempSalinityDensityTempSalinityDensityNo GradientLowerHigherLowerHigherLandOceanSpringRunoff decreasing, water warmingTempSalinityDensityColder WarmerLowerHigherLowerHigherLandOceanLate SummerNo runoff, warm temperatures, net evaporationTempSalinityDensityTempSalinityDensityColder WarmerLowerHigherNo GradientLandOceanCirculation can vary interannuallydepending on climate variationStream FlowStream FlowGreen – El Nino YearNormal yearsJan Dec20035OceanLandEl Nino YearsEstuaries are sensitive to climate change, fresh water diversionDroughtDistance InlandDistance InlandSalinity gradientAffects organism distributionsCirculation affects plankton, esp larval, retention, etc.Estuarine Food WebsSalinity Tolerance is important for estuarine organismsOrganism Distribution“Oligohaline”Species DiversityOligohaline – minimum diversity2-10 PSUOsmosisLow Salt High SaltProcess by which water passes through a semi-permeable membrane from low to high solute (salt) concentration.WaterEqualEqualOsmosisOsmoregulatorexternal salt conc.internal solute conc.No ChangeOsmoregulators3514140Why aren’t marine fish isotonic? Biochemistry evolved when sea was less salty?Osmosisexternal salt conc.internal solute conc.OsmoconformerOsmoconformer “trick”external salt conc.internal solute conc.Estuarine DependenceHigh Primary ProductionMenhadenShrimpCrabsOrganisms living in estuaries respond to complex gradients of environmental factors such as salinity, temperature, estuarine circulation patterns, and sediment characteristics.Take home messagesSalt Marshes – intertidal habitatVery few salt marshes –coastline too steepSalt marsh plantsCommon plants:Spartina – “Cordgrass,” “marsh hay”East coast dominantSalicornia – “Pickleweed,” “Ice cream cone plant”West coast dominantSalt marsh plantsCharacteristics:• Adaptations to handle salt (halophytes)Adaptations to handle saltCompatible solutes, sugar, DMSP, glycine betaine, serine, alanineSalt marsh plantsCharacteristics:• Adaptations to handle salt (halophytes)• Adaptations for anaerobic sedimentAdaptations for anaerobic sediment:Surface roots Capable of anaerobic metabolismAerenchyma tissue –transports oxygen into roots and sedimentZonationTallPoorly-drainedCompacted, Salty, AnoxicSulfidicWell-drainedBioturbated, PorousNutrient-richLower saltLower sulfideShortTallShortTallShortZonationSalt marsh food webFood chain varies with tideAnimals take turns – “shifts”Theories about salt marshes1. Detritus-based food web is dominant2. They support “Outwelling” – export of C to adjacent shelf watersWinter Die-backWhat happens to the biomass?Protein content increasesGRAZERS – more important in summerDetritivoreskcal m-2y-1Input as sunlight 600,000 Loss via photosynthesis 563,620Gross production 36,380 Producer respiration 28,175Net production 8,205 Bacterial respiration 3,890 1 consumer respiration 596 2 consumer respiration 48Total consumer respiration 4,534EXPORT 3,671 6.1% total input77% of gross production23% of gross production47% of net production7% of net production0.6% of net production55% of net production45% of net productionEnergy Budget for a Salt MarshCalculated from budget by differenceAvailable for exportOther functions of