inundation of the kissimmee river floodplain is dependent ... · july 27, 2013 •the photo to the...
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TheKissimmeeRiverFloodplainUnderLow-flowConditions
• InundationoftheKissimmeeRiverfloodplainisdependentonhigherlevelsofdischargefromwatercontrolstructurestothenorth.• Forexample,inthephototothelefttakenlastMay,flowfromthenorthwaslowandwascontainedwithintheriverchannel,leavingsandbarsexposedandthefloodplaindry.
StarvationSloughatlowflow(5/30/17) S65ADischarge:130cfs
**AwaterdepthmapforMay30isshownintheinset.Marooncolorsdenotedrierconditions;yellowdenoteswater justaboveground.
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TheKissimmeeRiverFloodplainUnderHigh-flowConditions
S65ADischarge:7200cfs
S65ADischarge:130cfs
StarvationSloughathighflow3daysafterIrma(9/13/17)
• Thedarkbandsofforestonbothsidesofthefloodplainmarktheouteredgesofthefloodplainwherefloodplainwetlandstransitionintouplandoakhammocks.• Ecologically,annualfloodpulsesaredesirable(althoughideallylessextremeeventsthanIrma!)andareessentialtomaintainfloodplainwetlandsinlow-gradientriverecosystems.
• AfteralargeraineventlikeH.Irma,flowfromthenorthmayneedtobeincreaseddramaticallytoprovidefloodcontrolintheKissimmeeChainofLakesupstream.Inthephotobelow,taken3daysafterIrma,waterhasovertoppedtheriver’sbanksandspreadoverthesurroundingfloodplain,inundatingthefloodplain.
**AwaterdepthmapforSeptember13isshownintheinset.Increasinglydarkbluesdenoteincreasinglydeepwater.
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StarvationSlough threedaysafterHurricane Irma(9/13/17)
FlowandDissolvedOxygen
S65ADischarge:7200cfs
S65ADischarge:130cfs
• ThisgraphofDOandflowin2017showsthetypicalnegativecorrelationseenintheKissimmeeRiverbetweendischargeatS65Aanddissolvedoxygen.
• RisingflowcausesDOtodeclineprimarilybecauseitcauseswaterdepthtorise,reducingtheamountofsunlightreachingphotosyntheticorganisms.
• Whendischargemustbeincreasedquicklyforfloodcontrol,theresultisoftendeepsagsinDO,especiallyinthewetseasonwhentemperaturesarehigh.
• Suchdeclinescanimpactfishpopulations.
• AnhypoxicconditioniswhenDOdeclinesto<2mg/L,whichcausesphysiologicalstressinmanyfish.
• Anoxicconditions(DO<1mg/L)canbelethaltosensitivespecieslikebassandothersunfish. 0
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DO(m
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Hypoxicoranoxic(DO<2mg/L)DO2mg/L(physiological stress)1mg/L(potentially lethal)S65Adischarge
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FishPopulationsandthe2017HypoxicEvents• Largemouthbass,bluegill,andothersunfishareverysensitivetolowDO(hypoxic)conditionsandmaybekilled.• Otherfishspecies,forexampleFloridagar,catfish,andmanyexoticfish,arerelativelytolerantoflowDO.• Thegraphtotherightshowstheresponsesinoursurveydataofintolerantspecies(primarilysunfish)andtolerantspecies.• Withthethree2017sampleswewereabletodocumentlikelyeffectsonpopulationsofbothsunfishasawhole(thisslide)andbassalone(nextslide).
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JuneDOCrash
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HurricaneIrma
BassResponsetothe2017HypoxicEvents• InFlorida,bassarephysiologicallystressedatDOlevelsbelow2mg/L,andmaydieenmasseatDOlevels lessthan1mg/L.
• TheKissimmee Riverpopulationoflargemouthbass(heresplitoutfromotherspecies)experiencedsubstantialsetbacksinthe2017wetseason,withasevereDOcrashandfishkillinJunefollowedbyanothercrashinSeptemberafterHurricaneIrma.
• Bass(especially larger,reproductive-sizedbass)arehighlysensitive tolowDO.Populationshavebeenimpactedforyearsbyhypoxicevents,resultinginlowabundanceofbassinrecentyearscomparedtodatacollectedfromasemi-restoredchannelin1988(inwhich~40BPUEofbasswererecorded).
• Ourhypothesisisthatthisdecline isduetoalmostannualhypoxicoranoxiceventssincerestorationofflowinthesechannels.
• Almostnobasswererecordedinthe2017summerandfallsurveys,andthatnonewerelargesuggests itwilltakeyearsforthepopulationtorecovereventopre-2017levels.
• Intermsofbiomass,sunfishpopulations includingbassareseverelydepressed.Thisislikelyduetorecurringhypoxicandanoxicevents.
• TheDistrictcontinuestoworktoreducetheseverityanddurationofKissimmee Riverhypoxiceventstotheextentpossible.
JuneDOCrash
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GoodBluegillRecruitmentDuringPost-IrmaFloodplainInundation
• Anencouragingnoteisthatnumbersofsmall,first-yearindividualsofanothersunfish,bluegill,wereveryhighinthepost-Irmasurvey,suggestingthatthisspecies,whichreproducesinthesummer,mayhavebenefittedfromrefugiaavailableonthefloodplainduringthelongperiodoffloodplaininundation
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MonocultureofinvasiveexoticWestIndianmarshgrass(Hymenachne amplexicaulis)inMacArthurImpoundmentbeforeIrma
July27,2013
• Thephotototheleftshowsamonocultureoftheinvasiveexotic,WestIndianmarshgrass, inMacArthurImpoundmentinthePhaseIrestorationarea.• ThisandotherinvasivegrasseshaveencroachedonmuchoftheKissimmeeRiverrestorationareafloodplain.
WestIndianmarshgrass(Hymenachne amplexicaulis)appears tohavebeenreduced/topkilled inMacArthur Impoundment Post-Irma;likelyduetoprolonged deepwaterandhigh floodplainvelocities.
• FieldstaffreportthatareasformerlydominatedbyexoticgrasseswereclearedoutbytheprolongeddeepwaterandhighflowduringHurricaneIrma(photolowerright),providingnewlyopensubstratefornativeplantrecruitmentandwadingbirdforaging.
PositiveEffectsontheFloodplain