Plankton Controls on Suspended Sediments Plankton Controls on Suspended Sediments and Water Clarity in Chesapeake Bayand Water Clarity in Chesapeake Bay

W. Michael Kemp W. Michael Kemp Walter R. Boynton Walter R. Boynton

University of Maryland University of Maryland Center for Environ. ScienceCenter for Environ. Science

Horn Point Laboratory Horn Point Laboratory Chesapeake Biological LabChesapeake Biological Lab

ObjectivesObjectives

••Investigate co-variations in water clarity, TSS and phyto-Investigate co-variations in water clarity, TSS and phyto- plankton chlorophyll-aplankton chlorophyll-a

••Relate water clarity to TSS and Chl-Relate water clarity to TSS and Chl-aa concentrations and concentrations and sinking ratessinking rates

••Relate Chl-a sinking to plankton production cyclesRelate Chl-a sinking to plankton production cycles

••Relate TSS sinking to plankton Chl-a sinking for mid BayRelate TSS sinking to plankton Chl-a sinking for mid Bay

••Test robustness of relationships among years and regionsTest robustness of relationships among years and regions

Conceptual Model of ProcessesConceptual Model of Processes

•Plankton pigments and inorganicPlankton pigments and inorganic particles contribute to attenuationparticles contribute to attenuation of PAR in water column of PAR in water column

•Concentrations of TSS & Chl-Concentrations of TSS & Chl-aa affect each other interactivelyaffect each other interactively

•Plankton affect PAR attenuationPlankton affect PAR attenuation directly (absorption) & indirectlydirectly (absorption) & indirectly (sinking rates)(sinking rates)

••TSS sinking is affected by algal TSS sinking is affected by algal excretion & flocculationexcretion & flocculation

••Initially, flocs sink slowly becauseInitially, flocs sink slowly because of low density of amorphous mixof low density of amorphous mix

••Eventually, flocs sink faster due toEventually, flocs sink faster due to increase density and size increase density and size

Stokes Law of SettlingStokes Law of Settling

Particle Settling VelocityParticle Settling Velocity

uu = [ = [∆∆ ·· gg ·· d d 22] (18] (18µµ))-1-1

∆∆ = density difference = density difference (particle - fluid) (particle - fluid) gg = gravitational acceleration = gravitational accelerationdd = diameter of particle = diameter of particleµµ = viscosity of fluid = viscosity of fluid

Thus, particle sinking rate increases withThus, particle sinking rate increases withparticle density and diameterparticle density and diameter

Hypothesized plankton control on mineral particle sinkingHypothesized plankton control on mineral particle sinking• Mucous excretion binds mineral particles into aggregatesMucous excretion binds mineral particles into aggregates• Initial low-density (slow sinking) aggregatesInitial low-density (slow sinking) aggregates• Eventually, large dense (fast sinking) aggregatesEventually, large dense (fast sinking) aggregates

Example Diatom-Clay AggregateExample Diatom-Clay Aggregate

SEM image (Hamm 2002)SEM image (Hamm 2002)

Monitoring Station MapMonitoring Station Map

Adapted from www.chesapeakebay.net

CB4.3c

CB2.2

CB3.3c

CB6.1

(Sed Traps)

•Plankton Chl-Plankton Chl-aa stocks and fluxes stocks and fluxes follow seasonal cyclesfollow seasonal cycles

•Ratio Flux/Stocks is greater inRatio Flux/Stocks is greater in summer than springsummer than spring

•Control by ecological processesControl by ecological processes

•TSS stocks & flux follow Chl-TSS stocks & flux follow Chl-aa seasonal cycles seasonal cycles

•Ratio Flux/Stocks is greater inRatio Flux/Stocks is greater in summer than springsummer than spring

•Clearly, TSS & plankton Chl-Clearly, TSS & plankton Chl-aa dynamics are linked dynamics are linked

Time-Course Chl-Time-Course Chl-aa & TSS Stocks and Fluxes & TSS Stocks and Fluxes

Springbloom

Maycrash

Summer peaks

Fallbloom

Total Solids & Chl-a Fluxes vs. StocksTotal Solids & Chl-a Fluxes vs. Stocks

•Plankton Chl-Plankton Chl-aa stocks and fluxes stocks and fluxes are significantly correlatedare significantly correlated

•Weak relation overall, but strongerWeak relation overall, but stronger by when grouped by seasonby when grouped by season

•Similar relationship among yearsSimilar relationship among years

•Total solids stocks and fluxesTotal solids stocks and fluxes are significantly correlatedare significantly correlated

•Weak relation overall, but strongerWeak relation overall, but stronger by when grouped by seasonby when grouped by season

•Slope of relationship slightly Slope of relationship slightly higher than for Chl-higher than for Chl-aa

Light Attenuation (Light Attenuation (KKdd) & Secchi Depth () & Secchi Depth (ZZSDSD))

•Fluxes of total solids & Chl-Fluxes of total solids & Chl-aa are strongly correlatedare strongly correlated

•Correlations significant only Correlations significant only if fall-winter data excludedif fall-winter data excluded

•Because TSS & Chl-Because TSS & Chl-aa sources sources differ, suggests same controls differ, suggests same controls

•““Non-algal” solids dominateNon-algal” solids dominate total mass of sinking particlestotal mass of sinking particles

•Inorganic, non-algal particlesInorganic, non-algal particles comprise 80% total masscomprise 80% total mass

•Non-algal fraction more variableNon-algal fraction more variable in summer in summer

Ratio Chl-Ratio Chl-aa (Total Solids) (Total Solids)-1-1 Variations Variations

•Ratio [µg Chl-Ratio [µg Chl-aa (mg TSS) (mg TSS)-1-1] varies] varies along salinity gradient but is along salinity gradient but is remarkably consistent overallremarkably consistent overall

•Peak ratios in mesohaline Peak ratios in mesohaline salinity zone (10-15) in summersalinity zone (10-15) in summer

•May imply that dynamics of TSSMay imply that dynamics of TSS and Chl-a are linked and Chl-a are linked

Light Attenuation & Total Suspended SolidsLight Attenuation & Total Suspended Solids

•Diffuse PAR attenuation (Diffuse PAR attenuation (KKdd) ) strongly correlated with TSSstrongly correlated with TSS

•Correlations significant only in Correlations significant only in oligohaline & upper mesohalineoligohaline & upper mesohaline

•Slope & correlation coefficientSlope & correlation coefficient decline from upper to lower Baydecline from upper to lower Bay

•TSS range declines from upperTSS range declines from upper to lower Bay to lower Bay

Light Attenuation & Plankton Chlorophyll-Light Attenuation & Plankton Chlorophyll-aa

•Diffuse PAR attenuation (Diffuse PAR attenuation (KKdd) ) weakly correlated with Chl-weakly correlated with Chl-aa

•Correlations significant only in Correlations significant only in lower mesohaline & polyhalinelower mesohaline & polyhaline

•Slope & correlation coefficientSlope & correlation coefficient increase from upper to lower Bayincrease from upper to lower Bay (note slope for CB6.1 is 0.016)(note slope for CB6.1 is 0.016)

•Pattern inverse of that for TSSPattern inverse of that for TSS

•Implies TSS masking of Chl-Implies TSS masking of Chl-aa effect on effect on KKdd

Concluding CommentsConcluding Comments

• • Seasonal and interannual patterns of plankton Chl-Seasonal and interannual patterns of plankton Chl-aa deposition deposition follows plankton production and grazing cycles follows plankton production and grazing cycles

• • Patterns of TSS deposition follow Chl-Patterns of TSS deposition follow Chl-aa deposition cycles deposition cycles

• • Chl-Chl-aa & TSS depositions are related to respective concentrations & TSS depositions are related to respective concentrations but relationships are weak and vary seasonallybut relationships are weak and vary seasonally

• • Chl-Chl-aa & TSS deposition rates are correlated significantly even & TSS deposition rates are correlated significantly even though non-algal particles comprise 80% of total sinking mass though non-algal particles comprise 80% of total sinking mass

• • PAR attenuation controlled by TSS and Chl-PAR attenuation controlled by TSS and Chl-aa, but algal effects , but algal effects masked in much of the Bay by high TSSmasked in much of the Bay by high TSS

• • Regional and interannual variations still need to be examinedRegional and interannual variations still need to be examined more closelymore closely

General Study DesignGeneral Study Design

A) A) Statistical Analysis of Monitoring VFX dataStatistical Analysis of Monitoring VFX data 1) Related water clarity, plankton, temp, sal and sedimentation. 1) Related water clarity, plankton, temp, sal and sedimentation. 2) Non-linear multivariate statistics (spatial, temporal aggreg.) 2) Non-linear multivariate statistics (spatial, temporal aggreg.)

B) B) Mesocosm ExperimentsMesocosm Experiments 1) Use existing facility (1 m1) Use existing facility (1 m33 tanks) tanks) 2) Manipulate nutrients, fine-grain particle density2) Manipulate nutrients, fine-grain particle density 3) Measure concentrations, sinking rates, water clarity3) Measure concentrations, sinking rates, water clarity

C) C) Incorporate Algorithms into Simulation ModelsIncorporate Algorithms into Simulation Models • • Dynamic, spatially aggregated scenariosDynamic, spatially aggregated scenarios • • Scenarios varying nutrient and sediment inputs Scenarios varying nutrient and sediment inputs • • Transfer tested algorithms to WES modelTransfer tested algorithms to WES model