TheKissimmeeRiverFloodplainUnderLow-flowConditions

• InundationoftheKissimmeeRiverfloodplainisdependentonhigherlevelsofdischargefromwatercontrolstructurestothenorth.• Forexample,inthephototothelefttakenlastMay,flowfromthenorthwaslowandwascontainedwithintheriverchannel,leavingsandbarsexposedandthefloodplaindry.

StarvationSloughatlowflow(5/30/17) S65ADischarge:130cfs

**AwaterdepthmapforMay30isshownintheinset.Marooncolorsdenotedrierconditions;yellowdenoteswater justaboveground.

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.

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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Hypoxicoranoxic(DO<2mg/L)DO2mg/L(physiological stress)1mg/L(potentially lethal)S65Adischarge

FishPopulationsandthe2017HypoxicEvents• Largemouthbass,bluegill,andothersunfishareverysensitivetolowDO(hypoxic)conditionsandmaybekilled.• Otherfishspecies,forexampleFloridagar,catfish,andmanyexoticfish,arerelativelytolerantoflowDO.• Thegraphtotherightshowstheresponsesinoursurveydataofintolerantspecies(primarilysunfish)andtolerantspecies.• Withthethree2017sampleswewereabletodocumentlikelyeffectsonpopulationsofbothsunfishasawhole(thisslide)andbassalone(nextslide).

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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

GoodBluegillRecruitmentDuringPost-IrmaFloodplainInundation

• Anencouragingnoteisthatnumbersofsmall,first-yearindividualsofanothersunfish,bluegill,wereveryhighinthepost-Irmasurvey,suggestingthatthisspecies,whichreproducesinthesummer,mayhavebenefittedfromrefugiaavailableonthefloodplainduringthelongperiodoffloodplaininundation

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