## Characteristics of Accelerated Eutrop hication in the Lower St. Johns River Estuary and Recommended Ta rgets to Achiev e Water Quality Goals for the Fulfillment of TMDL and PLRG Objectives

John Hendrickson Edgar F. Lowe, Ph.D. Dean Dobberfuhl, Ph.D. Peter Sucsy, Ph.D.

Dean Campbell

Water Resources Department Technical Memorandum No. __, St. Johns River Water Management District, Palatka, FL.

August 8, 2003

### EXECUTIVE SUMMARY

To address water and biologica l quality im pairment of the lo wer St. Johns River (LS J R)

related to excessive alg a l growth and accel erated eutroph ication, the St. Johns River

Water Managem e nt District and the Florid a Departm e nt of Environm ental Protection

have join tly pursued the Federal Clea n W a te r ActPs Total Ma xim u m Daily Load (TMDL)

process (and analogous m a ndates under the F l orida Adm i nistrative Code Chapter 62-40

for the determ ination of Pollution Load Reduc tio n Goals (PLRG)) as a means to establish

enforceable and ach ievable lim its o n nutrien t p o llution. T h e plan to establish TMDLs

and PLRGs envisioned three large endeavor s (Hendrickson and Magley, 2002): 1) an

assessm ent of the external nut rient and organic carbon loads to the LSJR; 2) a series of

diagnostic studies and monitoring designed to be tter describe pattern s of algal comm unity

com position, algal productivity, nutrient util ization and sediment-water colum n
interactions; and 3) hydrodynam i c and water qu ality m odeling for integrating the results

of diagnostic work and linking external nut rient loads to eutrophi cation effects.

W ith respect to the inves tiga tions ide n tif ied abov e, the objectives of this r e port a r e to :
1) describe the spatial and tem poral patterns in algal biom ass, nutrient utilization and

lim itation, p l ankton community composition and water quality effects related to

eutrophication, in order to im prove the ge neral understanding of these processes,

and to calibrate and guide revisions, if necessar y, to the water quality modeling

endeavor; and

2) identif y the point on the continuu m of adverse water quality ef f ects, stemm i ng

from nutrient enrichm e nt and eutrophi cation, that represents significant

im pair m e nt, for the purpose of establishi ng targ ets for wate r quality m o deling of

nutrient load reduction scenarios.

St. Johns River Water M a nagem e nt Distr i ct 

### ii

### LSJR Freshwater Reach

The degree to which the lower St. Johns River manifests th e effects of nutrient pollution

is determ ined through a com p lex interplay of hydrodynam i c, m e teorol ogic and biological

processes. Because of the predom inant, ove rlap ping pattern s of river flow and spring ?

summer heat and solar energy, the LSJR exhib its a strong seasonality in algal blooms

, particula r ly within the f r e shwater rea c h. Thes e bloom s are more intense in dry years, due

to increased river resi dence tim e , which presents the algal comm unity the opportunity to

more fully exploit the nutrients supplie d by local point and nonpoint, upstream and

atm o spheric sources. Because nu trient load is inextricably linked to stream runoff and

river flow (nutrient load = concentration x fl ow), this leads to the irony that as total

annual nutrient load increases, m ean annual al gal biom ass decreases. During dry years,

when total nutrient exploitation is achieved, algal biom ass, m easured as chlorophyll a ,
can exceed 150 m g / m 3 

### in the riverKs freshwater reach.

Nitrogen us ually appea r s to be the f i rst lim itin g m acro-nutrien t to alga l growth in the

freshwater reach. (In actua lity, silica is a l most inva riab ly the f i r s t lim iting macronutrient, and the disappearance of bioavailab le silica sign als th e in itiation of the blue

green dom inated growth phase (Schelske and Aldridge, 1997).) Ho wever, due to the

presence of nitrogen-fixing bl u e g r een algae, growth inv a riably continues beyond the

point of nitrogen lim itation. This growth, supplem ented by N-fixati on, can result in an

appreciable am ount of internal nitrogen loa d, at tim es doubling the ex ternal load-supplied

concentration. At phosphorus concentrations presently observed in the freshwater LS JR,

phosphorus lim itation of the algal community is only achieved in dry, long residencetim e years. When the algal comm unity is phosphorus lim ited for an extended period, on

the order of several weeks, a precipitous bloom crash occurs. Extrem e low dissolved

oxygen levels are associated w ith these bloom crashes.

To quantify harmful effects of algal bloom s , plankton (m icroscopic plants and anim al s

that cons titu te the foundation of the riverKs aq uatic food chain) m onitoring data were

analyzed to determ ine potential disruptions in food web interactions during algal bloom

St. Johns River Water M a nagem e nt Distr i ct 

### iii

### events (Phlips and Cichra, 2002). These data dem onstrated that when algal bloom s

exceed ch lorophyll a concentrations of 40 m g / m 3 

### , the phytoplankton community

becom e s dom i nated by only a few blue-green alga l species, and the num bers of beneficial

zooplankton, representative of the 2 nd 

### trophic level, begin to decline. When bloom s in

excess of 40 m g / m 3 

### chlorophyll a pe rsis t f o r m o re tha t 40 da ys, sign if ica n t dec line s in th e

num b ers of copepod and cladoceran zooplan kton are ob served. In addition, when

chlorophyll a of am bient river sam p les exceed ed concen trations of 40 mg/ m 3 

### in nutrient

enrichm e nt incubations, the possibility of high concentrations of the algal toxin

m i crocystin increased dram a tically (Paerl et al. and Carm ichael, 2002). From these

observations, an algal biom ass target for the fr eshwat er LSJR was der i ved t h at speci fi ed

chlorophyll a concentrations not exceed 40 m g /m 3 

### for continuous durations longer than

40 days. Additional analysis of bloom duration O intens ity data estim ated a peak

chlorophyll a associated with a 40 day, above 40 mg/ m 3 

### bloom of 70 mg/m 3



### .

LSJR Predominantly Marine Reach

When the LSJRQs freshwater phytoplankton ar e exposed to salinities as low as 2 ppt,

transform a tions begin to occur in comm unity com position and physiological processes.

These transf orm a tions have im portant effects on the aggregate properties of the algae,

and are manifested in biom ass attained and rates of nutri en t utiliza tion and

rem i neralization. Becau se of this transfor m a tion, an entirely different algal comm unity

resides in th e predom inantly m a rine reach of the river. In the A tlantic Ocean near the

riverQs m out h, a comm unity dom inated by m a rine form s of the diatom division of algae

exists. In the m ildly salty portion of the ri ver, from the southern Duval C ounty line north

to the Fuller W a rren Bridge, a m i xed comm unity of salt-tolerant blue greens,

dinoflagellates and diatom s are pres ent (Phlips and Cichra, 2002).

In the narrow, 25-m ile, narrow stretch of ri ver connecting these zones, conditions of

water column turbulence and m i xing, reduced light, and rapi dly changing salinity are

unfavorable for either of thes e algal communities. W h en st eep, salinity-induced declines

in the algal community occur just ahead or in the upper po rtion of this narrowest and

deepest portion of the river (approx im ately fr om river m ile 20 to 10, located adjacen t to

St. Johns River Water M a nagem e nt Distr i ct 

### iv

### the downtown Jacksonville stretc h of the river), low concentr ations of dissolved oxygen

result that can lead to large fish kills, as was observed in July and August of 1999. The

im port of Atlantic, near-coastal bloom s duri ng reverse-flows m a y al so negatively affect

oxygen levels in this re ach, due to the changes in river ch annel dim e nsions that lead to

reduced pho tic zon e and su rface reaeration area.

Oxygen deficits in the m e sohaline reach of th e river appear to be larg ely influenced by

processes of the algal comm unity, and levels of algal biom ass, either im ported or

produced within this rea c h of the L S JR are s i g n if icantly, p o sitiv ely cor r ela t ed with the

general levels of oxygen defic it that occur in a given year. Inorganic nitrogen and

phosphorus concentrations in this reach alm o st always exist at levels in excess of what

could be co nsidered ind i cative of nutrient li m itation, and only approach lim iting levels in

the nea r coa s tal wa ters o f the Atlantic, thus large decrea ses in upstre a m and loca l nu trient

load m a y be necessary to lim it algal growth to accep table levels. Unlike th e bloom s

im ported to the freshwater LSJR, which can expand due to f a vorable conditions of light

and nutrient supply downstream of Palatka, th e salinity-transfor m ed algal comm unity in

the m a rine reach aris es from within this zone o r from the n ear-coastal Atlantic. Local

loads do not contribute to th e expansion of the im ported, freshwater algal comm unity,

which is usu a lly in d ecline due to s a linity stre ss. Because of this, lo cal nu trient loads can
be viewed as contributing to a dis tinctly different algal community.

The reduction of algal detr itus and live a l gal biom ass loading to prevent low oxygeninduced m o rta lity in th e f i sh community was established as the nutr i ent load r e d u ction

target for th e m a rineKinfluenced LSJ R . Because of concern regardi ng the appropriateness

and achievability of the State Standard of 5 m g / L daily aver age or 4 m g /L instantaneous

for a blackw a ter estu ary such as the lower St . Johns, the approach for evaluating potential

estuarine fish m o rtality describ e d in the recently publish e d EPA guidance, Ambient

Aquatic Life Water Quality Criter ia for Dissol ved Oxygen (Saltwater) : Cape Cod to Cape

Hattaras was instead u s ed to evaluate detr imental ep isod es of low dissolved ox ygen.
This approach utilizes establ ished low oxygen duration K intens ity tolerances of estuarine

fish, and allows for some excursions of oxyge n below the Florida S t ate Standards if they

St. Johns River Water M a nagem e nt Distr i ct 

### v

### are not severe enough to result in fish death. Applying th e approach detailed in the

guidance docum e nt for evaluating persistent

, chronic impairm ent in estuarin e fish

communities, 3 out of the 6 years of data co llected at Dam e s Point from 1996 through

2001 exhibited continuous low dissolved oxygen episodes severe enough to result in fish

community impairm e nt. Based on this result, it is believed th at this reach of the river can

benefit from reductions in loading of algal de tritus and nu trients tha t can lead to the

growth of marine alga l c o mm unities.

Acknowledg ements

Special reco gnition go es to the follo w ing rese archers that have pioneered the concepts on

which the analysis of eutrophication effects de scribed in this repor t, and the TMD L and

PLRG targets, have been based.

Drs. Claire Schelske and Rick Aldridge , who conducted som e of the earliest river

prim ary production experim e nts, and the first nutrient enrichm e nt assays to identify the

patterns of silica and nitr ogen lim itation in the LS JR.

Dr. Ed Phlips and Ms. Mary Cichra, who pe rform e d years of plankton m onitoring and

analys is to d e scrib e the cascade of algal comm unities assoc i ated with salinity and nutrient

regim e s, and did the first quan tification of river N-fixation.

Drs. Hans Paerl and M i chael Pieh ler, who fu rther inves tiga t ed and quantif ied the sp atia l

and tem poral patterns in blue green N-fi xation, specific blue green species growth

adaptations, and confirm e d the negative effects on high blue green biom ass on
zooplankton grazing.

Mr. John Burns and Dr. W a yne Cha r m i chael, who f i rst inve stiga t ed th e presence of blue

green algal toxins in the freshwater L S JR.

St. Johns River Water M a nagem e nt Distr i ct 

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### TABLE OF CONTENTS

EXECUTIVE SUMMARY

............................................................................................. ii

INTRODUCTION ............................................................................................................1
ALGAL BI OMASS PATTERNS AND WATE R QUALITY EFFECT S RELATED TO
EUTROPHI CATION ........................................................................................................6 Patterns of Nutrient Partitioning and Al gal Growth of the Freshwater LSJR ..............6

Algal Biomass Patterns .............................................................................................6

Phytoplankton Nutrien t Utilization Pa tterns and Community Com positio n ..........12

Frequency of Occurrence and Duration of Algal Biom ass .....................................23

Algal Bloo m Characteristics of the LSJR Marin e Reach .......................................29

Nutrient Lim itations to Marine Phytoplankton C o mm unity Growth .....................40

Patterns in Oxygen Deficits ....................................................................................55

IMPAIRMENT TARGE T S FOR IDENTI FYING TMDL AND PL RG NUTRIE N T
REDUCTIONS ...............................................................................................................66 LSJR Freshwater Targets: Phytopl ankton Community Composition Dynam i cs,
Zooplankton Interactions and Al gal T oxin Production Potential ...............................67

Freshwater LSJR Algal Biom ass Criteria ...................................................................68

Maintenance of Phytoplankton Diversity ...............................................................68

Facilitation of Upward Trophic Tr ansfer of Prim ary Production ...........................68

Algal Toxin Form ation Potential ............................................................................70

Algal Bloom Duration .............................................................................................73

Marine LSJR Dissolved Oxygen Criteria ...................................................................75

Dissolved O xygen Effec t s .......................................................................................75

Organism Acute Oxygen Levels .............................................................................76

Growth Effe cts ........................................................................................................77

Larval Recruitm ent .................................................................................................79

Application of the Criteria ......................................................................................79

Additional Considerations ......................................................................................81

Dinoflagellate Bloom Potential ...............................................................................82

RECOMME NDATIONS ................................................................................................84
LITERATURE CITED ...................................................................................................87

St. Johns River Water M a nagem e nt Distr i ct 

### vii

### List of Figures

Figure 1 The lower St. Johns River Basin .......................................................................2

Figure 2 The Predom inantly Freshw ater Reach...............................................................7

Figure 3 Spatial-tem poral pattern in Chlorophyll a , 1995 ...............................................8

Figure 4 Spatial-tem poral pattern in Chlorophyll a , 1996 ...............................................8

Figure 5 Spatial-tem poral pattern in Chlorophyll a , 1997 ...............................................9

Figure 6 Spatial-tem poral pattern in Chlorophyll a , 1998 ...............................................9

Figure 7 Spatial-tem poral pattern in Chlorophyll a , 1999 .............................................10

Figure 8 Annual TP load and Annual Chlorophyll-a ....................................................11

Figure 9 Patterns at Racy Point, 1995 ............................................................................13

Figure 10 P a tterns at Racy Point, 1996 ..........................................................................14

Figure 11 P a tterns at Racy Point, 1997 ..........................................................................15

Figure 12 P a tterns at Racy Point, 1998 ..........................................................................16

Figure 13 P a tterns at Racy Point, 1999 ..........................................................................17

Figure 14 P a tterns at Racy Point, 2000 ..........................................................................18

Figure 15 P a tterns at Racy Point, 2001 ..........................................................................19

Figure 16 P hytoplankton Bloom Stat us and Dissolved Oxygen Levels ........................22

Figure 17 P a rticulate N u trient Form s and Chlorophyll a Concentrations .....................24

Figure 18 Boundary Relationships.................................................................................25

Figure 19 F r equency Distributions ................................................................................26

Figure 20 Durations of Algal Bloom s ............................................................................28

Figure 21 Water Quality and Plankton Monitoring Stations .........................................30

Figure 22 Change in Phytopl ankton Community Richness ............................................32

Figure 23 Mean Num b er of Phytoplankton Species ......................................................32

Figure 24 T o tal Chlorophyll a Concentrations ..............................................................34

Figure 25 T o tal Algal Biovolum e ..................................................................................36

Figure 26 Calculated OrganicC arbon to Biovolum e Conversion ..................................39

Figure 27 S ilica Concentrati ons and Diatom Biovolum e ..............................................41

Figure 28 Mean Relative Abundan ce of Dinoflagellates Biovolum e ............................43

Figure 29 Cum u lative F r equency Dist ribution of Inorganic N and P ............................48

St. Johns River Water M a nagem e nt Distr i ct 

### viii

### Figure 30 T i m e Series Plots of Tota l Inorganic Nitrogen Concentrations ....................49

Figure 31 T i m e Series Plots of Orthophosphate C oncentrations ...................................51

Figure 32 T o tal Dissolved P at Fulton Point ..................................................................53

Figure 33 Historic Change in Dissolved Oxygen Levels...............................................56

Figure 34 Mean Daily Mid-depth Dissolved O xygen Concentrations .........................57

Figure 35 Mean Daily Dissolved O xygen .....................................................................60

Figure 36 L ongitudinal Dissolved O xygen Saturation Pattern ......................................62

Figure 37 Daily Mean Oxygen Saturation Deficit .........................................................63

Figure 38 Direction and Magnitude of Change in Chlorophyll a

................................. 63

Figure 39 Blue Green R e lative Abundance ...................................................................69

Figure 40 Mesozooplankton Re sponse to Algal Biom ass .............................................69

Figure 41 T o tal Chlorophyll a and C opepod / Cladoceran ............................................71

Figure 42 Annual Trend .................................................................................................71

Figure 43 Microcysti n Concentrations ...........................................................................72

Figure 44 Copedod and Cladocern Z ooplankton ...........................................................73

Figure 45 Bloom Maximum Chlorophyll a Concentration............................................74

Figure 46 T o tal Chlorophyll a at Racy Point .................................................................76

Figure 47 L ong term chronic e xposure threshold relationship ......................................80

St. Johns River Water M a nagem e nt Distr i ct 

### ix

### List of Tables

Table 1. Top Ten Spring-Summer Fr eshwater Phytoplankton Based
on Biovolum e at Racy Point from 1998 D 2001 ..............................................20

Table 2. Top Ten Marine Phytoplan kton Based on Biovolum e Observed at Fulton Point, 1998 D 2001 .............................................................................31

Table 3. Comparison of Relative Abundance of Major Phytoplankton Groups from th e Fresh and Marine Reaches of the LSJR ................................31

Table 4. Principle Dinof lagellat e Phytoplankton Observed During Episodes of Peak Dinoflagellate Biom ass ........................................................44

Table 5. Fish Species K now to be Present in the LSJR Estuary That are Represente d in Studies Upon W h ic h the EPA Estuarine Dissolved Oxygen Guidance is Based ..............................................................78

St. Johns River Water M a nagem e nt Distr i ct 

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### INTRODUCTION

The St. Johns River is one of the largest blackwa ter rivers of the southeast U.S. The river

is loca ted in northeas t Florid a and drains the northeast 1/5 th 

### o f the state, encom p assing a

9,562 square m ile drainage area. The river is slow m oving, and is esse ntially at sea level

for its final 120 m iles. The lower S t . Johns is the estuarine portion of the river, form e d at

the confluence of the middle St. Johns and the Ocklawaha River, and encom p assing a

2,750 square m ile area (Figure 1). W ithin this reach, the St. Johns River is sligh tly more

that 100 m iles long and has a water surface ar ea, includ ing tributary m o uths below h ead

of tide, of 85,000 acres.

The lower S t . Johns can be divided into thre e riverine salinity and lim nologic zones: a

f r esh tida l la custr i ne zon e which extends f r om the city of Palatk a north to approxim a tely

the m outh of Black Cre e k; a predom inantly oligohaline, lacustrine zone extending fro m

Black Cree k northwar d to the F u lle r W a rren Bridge (I-95) in Jacksonville; and a

m e so/polyhaline, riverine zone downstream to the m outh. The slow moving, lacustrine

nature of the river facili tates phytoplankton prim ary produ ction, and spring and summe r
algal bloom s in this nutrient-rich river often exhibit chlorophyll a con cen trations

exceeding 1 00 P g/L. Due to a long history of de velopment within the basin, and its

associa t ed water quality problem s, the LSJR was one of the StateZ s origin ally id e n tif ied

Surface W a t e r Im provem e nt and Managem e nt Act (SW I M; Chapter 37 3.451, F.S .) water

bodies for restoration, and has been identified as a high priority water body for the

establishm ent of TMDLs and PLRG s to lim it nutrient pollution.

Background

Accelerated eutroph ication due to n u trient en ri chm e nt of estuaries represents one of the

most signif i cant water quality p r oblem s f aced by near coastal w a ters world

- wide

(National R e search Council, 2000). Investigation in to the ef fects of nutrient enrichment

and elevated levels of algal biom a ss in the LSJR has, however, revealed noteworthy

departures from the eutrophication paradigm esta blished for other estuaries. The LSJR is,

St. Johns River Water M a nagem e nt Distr i ct

### Figure 1. The lower St. Johns River Basin.

St. Johns River Water M a nagem e nt Distr i ct 

### 2

### first, a blackwater river, with large a m ounts of allochthonous organic carbon and, at

tim es, substantial light lim itation to prim ar y production imparted by colored dissolved

organic m a tter. Also, the broa d, sh a llow zones that ex ist in the m e sohaline reach of most

river m outh estuaries, and where algal produc tion peaks, are, in the L S JR, due to its

peculiar m o rphology, lo cated in the upper, fr eshwater and oligohaline reaches. T h is

morphology also results in a very different shape in the zone of oxygen depletion, the

most often cited m a nifestati on of estuarine eutr ophication. Instead of the m e sohaline

zone vertical stratification typical of m o st eutrophic estu aries, the LSJR Cdead zoneD

exhibits a stronger longitudina l character, with strong vertic al m i xing and top to bottom

, long duration, sub-acute low oxygen levels.

Because of its bro a d, sh allow shape and low flow - long residence tim e co-occurrence
with spring and summer enhanced algal grow th, the LSJR can exhibit prodigious am ount

of seasonal algal productivity and biom ass. River flow, tide, and wind currents

continually advect, disperse and diffuse algae, nutrients an d salinity, with the resu lt that

the m a nifestations of nutrient loads freque ntly occur far from the source of entry.

Changes in nutrient status, sali nity, water co lumn ligh t ava i lability and water tem p eratur e
bring about changing environm ents that seld om favor one particul ar algal group, so a

success i on o f plankton comm unities is typ i ca lly observed through the spring and summ er
growth seasons. Environm ental stressors can at tim es be abrupt e nough to lead to m a ss
death in the algal community, lead in g to a sequence of water quality cha r acte r is tics w ith

im portant implications for nut rien t recycling, comm unity change, and water quality

effects.

Because of these interacting com p lexities, lin k i ng anthropogenic nutrient loading to algal

growth and its adverse wate r quality requires a com putational fram ework that accounts

for tem poral and three-dim e nsional spatial variation. For the LS JR TMDL and PLRG

assessm ent, the SJRWMD and FDEP have em ployed the services of the U.S. Ar m y
Corps Environm ental Research Developm ent Center to ada p t their tim e varying th reedim e nsional water quality m odel, CE-QUAL -ICM (Cerco and Cole, 1995), to the LSJR

estuary. To adapt and p a ram e teriz e this m ode l, or any m ode l so com p lex, it is necessary

St. Johns River Water M a nagem e nt Distr i ct 

### 3

### to have an understanding of th e phenom ena to be m odeled at two levels. F i rst, it is

necessary to have m easurem ents and analys is results that describe th e sub-pro c esses
leading to eutrophication at di screte levels for specific ci rcum stances, for the purpose of

model set-up and param e terization. Second, to learn from, and ultim a tely believe the

outcom e s of m odel scenarios, it is necessary to have at least a qua litative understanding

of how the interplay of various fa ctors will affect river water quality and biological

responses on a broad scale.

For a m odeling study of eutrophic ation effects to be succes sf ul, it is also neces sar y to

have identified the targets of ecosystem restoration, and how th ese relate to the variables

at the m o delers disposal. Preferably, the restoratio n targets are based upon an

understand ing of the en dem i c biolo g ical attribu t es and am plitud e of the system . For th is

reason, the targets developed herein rely on im proving plankton comm uni ty diversity and

enhancing upward transf er of prim ar y pr oduction to zooplankton and fish, and reducing

episodes of low dissolv ed oxygen th at m a y lead to m o rtality in fish communities. W ith

regard to th e res t ora tio n targe t s de scribed in this report, it m u st be kept in m i nd the

ecosystem context in wh ich thes e targets have been developed. From the point of earliest

record ed floristic h i sto r y, when W illiam Bartram paddled the LSJR shoreline in 1 776,

until 1 970, this was a sy stem with its biolog ical energy supp lied from stream and swamp

runoff and floating aquatic pl ants. Though the principle species dom inance shifted from

water lettuce ( Pis tia s t r a tioites ) in the late 1800Os with the introduction of water hyacinth

( Eichornia crassipies ), the ecosyste m is believe d to have re m a ined, at least structu r ally,

essentially the sam e until app r oximately 1940. W ith the advent of increased nu trient

loading and aquatic weed spraying from th e late 1940Os to Operation Clean Sweep in

1970 (a concerted aerial spraying effort with 2,4-D to Ueradi cateV water hyacinth),

autochthonous prim ary production has shif ted from dom i nance by m acrophytes, to

dom i nance by phytoplankton (Moody, 1970). The fra m ework for the LSJR TMDL

assum e s tha t it will rem a in a plankton-dom inated system

. This fram e w ork in m a ny ways

invalidate s the resto r ation approach that re lies on the retur n of the system toward its

natural, pre-colonial state.

St. Johns River Water M a nagem e nt Distr i ct 

### 4

### It is the objective of this report to present data and analysis that form s the foundation of

our understanding on the spatial, seasonal and inter-annual patt erns in nutrient

enrichm e nt effects in the LS JR. In addition, we describe , confirm and qua ntify plankton

community phenom ena of the LSJR for revision of existing coefficients, or addition of

algor ithm s to the CE-QUAL-ICM eutroph ication m odel. These inclu d e in particular:

blue green nitrogen fixation; carbon, n itrogen and phosphorus stoichiom e tric

relationships; algal bloom senescence; phy toplankton L zooplankt on interactions; and

algal group differentiation. In the analysis results, various data sets collected from

between 1994 through 2001 have been used. Although the intervals of data collection

m a y be inconsistent with the established TMDL and PL RG modeling tim e fra m e of 1995

through 1999, the findings are beneficial for distinguishing genera l relationships and

patterns in algal biom ass and nu trients th at are expected to be valid at all tim es. T i me

inte rvals ha ve varied pr im arily to allow f o r the incorpor atio n of relevant data tha t h a ve

been m a de available through the evolution of monitoring program s and com p letion of

specific s t ud ies.

St. Johns River Water M a nagem e nt Distr i ct 

### 5

### ALGAL BI OMASS PATTERNS AND WATE R QUALITY EFFECT S RELATED TO

EUTR OPHI CATION

Patterns of Nutrient Pa rtitioning a n d Algal Growth of the Freshwater LSJR

Algal Bioma ss Pattern s

The slow moving, lacustrine nature of the freshwater L S JR (Figure 2) facilitates

phytoplankton production, and spring and early su mm er rainfall deficits, which co-occur

with increased day length and wa ter tem p erature, lead to alg a l bloom s within this re a c h,

typically attaining peak chlorophyll a concentrations exceeding 100 m g / m 3 

### . Maximum

biom ass is reached betw een May an d August. From an annual tem poral perspective, the

pattern in productivity is som e what analogous to that observed in m o st Virginian and

Georgian province estuaries, in which nutrien t-rich runoff following la te winter sn owm e lt

or r a in f i lls the e s tua r y, and then th is wate r m a ss, slowed an d largely retained owing to

spring drought, is capable of high degree nut rient exploitation and high algal standing

stock.

Exam ination of the annual spatial a nd tem poral pattern in chlorophyll a concentration

(Figures 3 Z 7) reveals that bloom s generally arise sim u ltane ously throughout the river in

the spring. Only in 1998, a high flow year following a El N i no fall and winter in 1997-

98, did bloom s appear to have a strong longitudi nal transport character. In general, algal

biom ass is high departing Lake George, and exhi bits som e decline in stan ding sto c k a s it

traverses the narrower, riverine reach to Pala tka, then expands again to for m a second

peak between Federal P o int and Picolata (F igure 2). Due the long residence tim e and

trem endous productivity potential of the upstr eam Lake George, spring bloom s generally

exit the lake nitrogen and phosphorus lim ite d (Paerl et al, 2002). These bloom s are
capable of further expansion in the L S JR due to favorable photic zone to volum e ratios of

the broad river, and the fresh influx of nutri en ts f r om within-bas in so urces (Phlip s and

Cichra, 2000). From 1995 Z 1999, the m ean c oncentration of total phosphorus entering

the LSJR at Buffalo Bluff was 0.063 m g /L, wh ile m ean concentration for the sam e tim e

St. Johns River Water M a nagem e nt Distr i ct 

### 6

### Figure 2. The Predom inantly Freshw ater Reach of the Lower St. Johns River.

Shands Br.

Palatka

Lake George Watson Isl.

Racy Point

Federal Point Mouth o f

Black
Creek (downstrea m

boundary)

Buffalo Bluff

(upstrea m boundary)

St. Johns River Water M a nagem e nt Distr i ct 

### 7

### Figure 3. Spatial-Tem poral Pattern in Chlorophyll a in the Lower St. Johns River, 1995.
Data collec ted in a bi-weekly water quality m o nitoring program

, typically during the 2 nd



### and 4 th 

### weeks of each m o nth. X axis refers to m o nth and week of sam p ling, and Z axis to location, with m o st upstream st ation against the b ack wall. Som e values interpolated
when sam p ling done m o nthly.123456789101112131415161718192021222324 F u l t on Pt. Ta lle yra n d

Pi ney Pt. M andar i n H i ber ni a Pi c o l a ta W a ts on I s l

. Ra cy P t

. F eder al Pt. Pal a tk a L. Geor ge

0 20 40 60 80 100 120 140 160 C

h l o r o p h

y l l - a

, m

g / m 3

Bi -w eekl y I n terval 

### 1995

F u lton Pt.

T a lley r and
Piney Pt.

Mandar in

Hiber nia

Pic o lata

W a ts on Is l.

Rac y Pt.

F eder al Pt.

Palatk a

L. G eor ge



### Figure 4. Spatial-Tem poral Pattern in Chlorophyll a in the Lower St. Johns River, 1996.
Data collec ted in a bi-weekly water quality m o nitoring program

, typically during the 2 nd



### and 4 th 

### weeks of each month. X axis refers to m onth and week of sa m p ling, and Z axis to location, with m o st upstream station against the back wall. Som e values interpolated
when sam p ling done m o nthly.123456789101112131415161718192021222324 F u l t on Pt. Ta lle yra n d

Pi ney Pt. M andar i n H i ber ni a Shands Br

. W a ts on I s l

. Ra cy P t

. F eder al Pt. Pal a tk a L. Geor ge

-40 10 60 110 160

C

h l o r o p h

y l l - a

, m

g / m 3

Bi -w eekl y I n terval 

### 1996

Ful t on P t

. Ta lle y r a n d

Pin e y Pt.

M andari n

Hi berni a

S hands B r

. W a tso n Isl.

Rac y P t

. Federal P t

. Pa la tka

L. George

St. Johns River Water M a nagem e nt Distr i ct 

### 8

### Figure 5. Spatial-Tem poral Pattern in Chlorophyll a in the Lower St. Johns River, 1997.
Data collec ted in a bi-weekly water quality m o nitoring program

, typically during the 2 nd



### and 4 th 

### weeks of each month. X axis refers to m onth and week of sa m p ling, and Z axis to location, with m o st upstream station against the back wall. Som e values interpolated
when sam p ling done m o nthly.123456789101112131415161718192021222324 Ful t on Pt

. T a lle y r a n d Pi n e y Pt

. M a nda r i n Hi b e r n i a Sh a n d s Br

. W a ts o n Is l. Ra c y Pt

. Fe de r a l Pa l a t k a L. G e or g e

0 20 40 60 80 100 120 140 16 0 C h l o r o p h y l l - a , m g / m 3

B i

- w e e k ly In t e r v a l 

### 1997

F u l t on Pt.

Ta l l e y r a n d

Piney Pt.

Ma ndar in

Hi b e rni a

Sha nds B r

. W a ts on Is l.

Ra c y P t

. Fe d e ra l

Pal a tk a

L. Geor g e



### Figure 6. S p atial-Tem poral Pa tte rn in Chloroph yll a in the Lower St. Johns River, 1998. Data collected in a bi-weekly water quality m oni toring pr ogram , typically during the 2 nd



### and 4 th 

### week s of each m o nth. X axis refers to m o nth and week of sa m p ling, and Z axis to location, with m o st upstream station against the back wall. Som e values interpolated
when sam p ling done m o nthly.123456789101112131415161718192021222324 Ful t on T a lle y r a n d

Pi n e y Pt

. M andar i n Hi b e r n i a S hands W a ts o n Is l. R a cy P t

. Fe de r a l Pt

. Pa l a t k a L. G e or ge

0 20 40 60 80 100 120 140 160 C h l o r o p h y l l - a , m g / m 3

B i

- w eekl y I n t e r v al 

### 1998

Fu l t o n

T a lley r and

Piney Pt.

Mandar in

Hiber nia

Shands

W a ts on Is l.

Rac y Pt.

F eder al Pt.

Palatk a

L.G eor ge

St. Johns River Water M a nagem e nt Distr i ct 

### 9

### Figure 7. Spatial-Tem poral Pattern in Chlorophyll a in the Lower St. Johns River, 1999.
Data collec ted in a bi-weekly water quality m o nitoring program

, typically during the 2 nd



### and 4 th 

### weeks of each month. X axis refers to m onth and week of sa m p ling, and Z axis to location, with m o st upstream station against the back wall. Som e values interpolated
when sam p ling done m o nthly.123456789101112131415161718192021222324 Ful t on P t

. T a lle y r a n d

Pi n e y Pt

. M andar i n Hi b e r n i a S hands B r

. W a ts o n Is l Ra c y

Pt

. Fe d e r a l Pt

. Pa l a t k a L. G e or ge

0 20 40 60 80 100 120 140 160 C h l o r o p h y l l - a , m g / m 3

Bi

- w e ekl y I n t e rval 

### 1999

Ful t on P t

. T a lle y r a n d

Pi ney P t

. M andari n

H i berni a

Shands B r

. W a tso n Isl

Ra c y P t

. Federal P t

. Palat k a

L

. George



### period at Racy Point, approxim a tely 25 m iles downstream , was 0.087 m g /L, and increase
of 38%.

In m o st years, chlorophyll a falls d r am atically do wnstream of Shands Bridge, coinciding

with the g r a dual sa linity

- induced tra n sf orm a tion of the plankton community. This decline

is brought about by a com b ination of salinity stress, increased zooplankton grazing, and

finally, reduced hydraulic residence tim e . Sa linities can vary considerably, and upstream

inputs of brackish artesian spring water can also push total dissol ved solids concentration

to nearly 1 ppt during drought without m a rine influence. During the severe drought years

of 2000 and 2001, m a rine salinity was seen to encroach upstream as far as RKm 100, or

near Racy P o int.

In the 5-year m odeling tim e window for LSJ R TMDL/PLRG developm ent, springsummer algal biom ass was the lowest in the 1995 high-flow year an d greatest in the 1999

low-flow year. Prevailing river flow and its control over residenc e tim e within the

freshwater reach is the most im portant fact or controlling the inte r-ann ual variatio n in

St. Johns River Water M a nagem e nt Distr i ct 

### 10

### algal bloom intensity and durat ion. Mean residence tim e is around one month, although

flow regi m e s between 1995 and 2001 have seen water replacem ent o ccur in less than 10

days (March 1998), to condition s where wa ter was essentially static (August 1999).

River flow c ontrols phytoplankton biom ass, as it co-varies with a suite of factors that can

account for the potential of the algal community to optim ize bioavailable nutrient supply.

High flows typically occur in fall and winter, when cooler w a ter tem p eratures and shorter

irradiance duration reduces production, and higher terrestrial runoff im ports greater

am ounts of colored aquatic hum i c substances , thus increasing light attenuation. Higher

flow also shortens segment residence tim e, reducing the time for nutrient depletion and

phytoplank t on comm uni ty m a turatio n. Because nutrient load is linked to river resid e nce

tim e through discharge, the ir ony exists that as nutrient lo ad increases, m ean annual

chlorophyll a decreases (Figure 8).

Figure 8. Relationship between A nnual TP L o ad to the Freshwater LSJR and Mean Annual Chlorophyll-a C oncentration, 1995-99. S quare represents projected m ean annual chlorophy ll-a at a hypothetical ze ro terrestrial flow setting, a nd this point is included in the regression equation.



### R a cy P o i n t

, 1995- 9 9

y

= - 0

. 0648x + 73. 526

R 2 

### = 0. 8775

0 10 20 30 40 50 60 70 80

0 1 00 2 0 0 3 00 4 0 0 5 00 6 0 0 7 00 8 0 0 9 00

M e a n A nnua l TP Loa d, M T / y rMean Annual Chla,mg/m3

St. Johns River Water M a nagem e nt Distr i ct 

### 11

### Phytoplankton Nutrien t Utilization Patte rns and Community Com positio n

The effect of the interp lay of factors regul ating the creation and sequestration of carbon

and nutrients by phytoplankton can be seen in F i gures 9 ? 15. These annual tim e series

plots of chlorophyll a , total nitrogen, phosphorus cell quota (estim ated with particulate P

to algal C ratio) and inorganic nutrient concentrations for the Racy Point station (located

at the m i dpoint of th e freshwater reach ) de monstrate the contro l of river nu trient

concentrations by phytoplankton growth patterns. W ith the exception of 1997,

chlorophyll a can be seen to exhibit at least one pronounced peak during the year. The

absence of such a peak in 1997 is due to the effects of a spill of m i ne tail-water that

contributed a large , ex trem ely turbid and hum ic- s tain ed plu m e to the river in th e v i cinity

of Racy Point on about April 30 th 

### of tha t yea r . T h is even t d r am atically r e duced the p hotic

zone, and effectively curtailed the spring bl oom . The tim ing and num ber of bloom pe aks

is largely dependent upon river flow. Under a lo w to m oderate f l ow con d ition, the f i rst

bloom peak will occur in May; under extrem e l o w flows, ( a s occurred in 1999 ? 2001),

multiple blo o m peaks can be observed. Under higher flow conditions, the bloom peak

m a y be delayed until July.

Algal taxonom ic inform ation, available for years 1998 ? 2001 (Table 1) reveals the

community success i on pattern resp onsible fo r patterns in algal b i om ass and nutrient

partition i ng. Diatom species dom inate the phy toplankton as sem b ledge until the spr i n g or

summer bloom season. Common diatom ge nera seen at this time are Melo sira

, Merismoped i a , and Fr agilaria . When chlorophyll a surpasses concentration s of

approxim a tely 40 m g / m 3 

### , blue green species begin to dom i nate. The end of diatom

dom i nance occurs coincident with dissolved silica falling to very low levels, suggesting

silica lim itation as an importan t trigg e r f o r the onset of blue green dom inance (Schels k e
and Aldridge, 1997). T ypically, the non-N-fixing blue green Micro cystis will be p r es ent

in the com m unity as d i atom dom i nance e nds, but it is supplanted soon by the N-fixing

Anabaena when assim ilable inorganic nitrogen is depleted. This usually corresponds to

total inorganic N (NH 4 

### +NO X 

### ) concentration being less than 0.020 mg/L. Pronounced

spikes in river total N coincident with algal biom ass peaks support the phenom e na of

St. Johns River Water M a nagem e nt Distr i ct 

### 12Figure 9. Patterns in Chlorophylla, total nitrogen,calculated phosphorus cell quota and inorganic nutrients at Racy Point, 1995.0.000.010.020.030.040.050.060.070.080.090.1011/301/293/305/297/289/2611/25

Particulate P/Algal CEst. Cell P:C00.020.040.060.080.10.120.140.1611/301/293/305/297/289/2611/25

Concentration, mg/LPO4TINSiO2/100199502040608010012014016011/301/293/305/297/289/2611/25

Chlorophyll a , mg/m 3Chlorophyll-a00.511.522.533.511/301/293/305/297/289/2611/25

Total N , mg/LTotalNSt.Johns RiverWaterManagementDistrict13Figure 10. Patterns in Chlorophylla, total nitrogen, calculated phosphorus cell quotaand inorganic nutrients at Racy Point, 1996.199602040608010012014016011/271/263/265/257/249/2211/21

Chlorophyll a, mg/m 3Chlorophyll-a0.000.010.020.030.040.050.060.070.080.090.1011/271/263/265/257/249/2211/21

Particulate P/Algal CEst. Algal P/C00.020.040.060.080.10.120.140.1611/271/263/265/257/249/2211/21

Concentration, mg/LTINPO4Diss.SiO2/10000.511.522.533.511/271/263/265/257/249/2211/21

Concentrati on, mg/ LTotalNSt.Johns RiverWaterManagementDistrict14Figure 11. Patterns in Chlorophylla, total nitrogen, calculated phosphorus cell quotaand inorganic nutrients at Racy Point, 1997.199702040608010012014016012/11/303/315/307/299/2711/26

C h lor ophy ll a , m g /m 3Chlorophyll a00.020.040.060.080.10.120.140.1612/1 1/30 3/31 5/30 7/29 9/2711/26

Concentration, mg/LTINPO4Diss.SiO2/1000.000.010.020.030.040.050.060.070.080.090.1012/11/303/315/307/299/2711/26

Particulate P/Algal CEst. Algal P/C00.511.522.533.511/271/263/265/257/249/2211/21

Concentration, mg/LTotalNSt.Johns RiverWaterManagementDistrict15Figure 12. Patterns in Chlorophylla, total nitrogen, calculated phosphorus cell quotaand inorganic nutrients at Racy Point, 1998.0.000.010.020.030.040.050.060.070.080.090.1011/161/52/244/156/47/249/1211/112/21

Particulate P/Algal CEstimated Cell P:C02040608010012014016011/161/52/244/156/47/249/1211/112/21

Concentrati on, mg/ m 3Chlorophyll-a199800.511.522.533.511/161/52/244/156/47/249/1211/112/21

Concentrati on, mg/ LTotalN00.020.040.060.080.10.120.140.1611/161/52/244/156/47/249/1211/112/21

Nutrient, mg/LTINPO4Diss.SiO2/10St.Johns RiverWaterManagementDistrict16Figure 13. Patterns in Chlorophylla, total nitrogen, calculated phosphorus cell quotaand inorganic nutrients at Racy Point, 1999.02040608010012014016012/11/303/315/307/299/2711/26

Co n cen trati o n , mg / m 3Chlorophyll-a19990.000.010.020.030.040.050.060.070.080.090.1012/11/303/315/307/299/2711/26

Particulate P/A l gal CEstimated Cell P:C00.511.522.533.512/11/203/114/306/198/89/2711/16

Concentrati on, mg/ LTotalN00.020.040.060.080.10.120.140.1611/1112/312/194/105/307/199/710/2712/16

Concentration, mg/LTINPO4Diss.SiO2/10St.Johns RiverWaterManagementDistrict17Figure 14. Patterns in Chlorophylla, total nitrogen, calculated phosphorus cell quotaand inorganic nutrients at Racy Point, 2000.00.020.040.060.080.10.120.140.1612/11/303/305/297/289/2611/25

Concentration. mg/LTINPO4Diss.SiO2/100.000.010.020.030.040.050.060.070.080.090.1012/1 1/30 3/30 5/29 7/28 9/2611/25

Particulate P:Algal CEstimated Cell P:C200002040608010012014016012/11/303/305/297/289/2611/25

Concentrati on, mg/ m 3Chlorophyll-a00.511.522.533.512/11/303/305/297/289/2611/25

Concentrati on, mg/ LTotalNSt.Johns RiverWaterManagementDistrict18Figure 15. Patterns in Chlorophylla, total nitrogen, calculated phosphorus cell quotaand inorganic nutrients at Racy Point, 2001.00.020.040.060.080.10.120.140.1611/301/293/305/297/289/2611/25

C oncentration. mg/LPO4TINDiss. SiO2/100.000.010.020.030.040.050.060.070.080.090.1011/301/293/305/297/289/2611/25

Particulate P:Algal CEstimated CellP:C200102040608010012014016011/301/ 293/ 305/ 297/289/ 2611/25Chlorophylla00.511.522.533.511/301/293/305/297/289/2611/25

Concentration, mg/LTNSt.Johns RiverWaterManagementDistrict19Table 1. Top 5 most abundant phytoplanktonby biovolumeduring Spring-Summer sampling atRacy Point, 1998-2001. Values to theleft of scientific names are biovolume,Pm3* (mL x 1000)-1. Numbers in bold beloweach sampling event columnrepresent thepercent of total biovolumerepresented by the top 5 phytoplankton. Bottomrows are mean and standard error of the percent monthlytop 5 dominance.MarchAprilMayJuneJulyAugustSeptemberOctober4/2/19984/27/19985/26/19986/30/19988/3/19988/24/19989/22/199810/28/1998220Melosira124Fragilaria2086Unid.Chrysophyta745Lyngbya1817Oscillatoria3219Oscillatoria<2μm2326Oscillatoria<2μm1174Oscillatoria137Unid.Cryptophyta98Unid.Cryptophyta442Melosira616Anabaena1255Anabaena647Cylindrospermopsis756Microcystis273Unid. Centric Diat.53Fragilaria79Unid. Centric Diat.290Microcystis aerug.368Unid. Chrysophyta680Ocillatoria453Melosira464Unid. CentricDiat.215Microcystis41Unid. Centric Diat.71Melosira172Anabaena324Microcystis436Unid. Pennate Dait.432Microcystis340Ocillatoria211Microcystis33UnidChlorophyta66Unid.Chlorophyta161Lyngbya293Anabaena390Lyngbya340Ocillatoria316Microcystis155Thalassiosira73765.7105841.5395479.7409057.4869452.7838560.7711159.1384852.73/30/19994/29/19995/27/19996/29/19997/27/19998/26/19999/23/199910/26/19993057Oscillatoria<2μm3713Oscillatoria<2μm7389Oscillatoria<2μm572Oscillatoria<2μm923Cylindrospermopsis8651Oscillatoria<2μm6164Oscillatoria<2μm2811Oscillatoria<2μm376Anabaena3559Anabaena6747Cylindrospermopsis172Microcystis504Lyngbyacontorta5388Cylindrospermopsis480Ocillatoria1071Melosira(Aulac.)200Microcystis700Melosira(Aulac.)1474Anabaena153Meris.tenuissima502Microcystis1391Unid.CentricDiat.291Cylindrospermopsis560Microcystis158Aphanizomenon432Anabaena431Unid. Centric Diat.138Unid. Cryptophyta476Ocillatoria712Unid. Centric Diat.281Lyngbyacontorta444Lyngbyacontorta117Unid Centric Diat.391Anabaenacircinalis414Anabaenacircinalis89Unid.Chlorophyta275Lyngbya641Pennates154Unid.Pennate Dait.314Ocillatoria514276.01225071.82029481.1177363.4467757.32098180.0883183.5717772.53/28/20004/25/20005/23/20006/27/20007/25/20008/23/20009/27/200010/30/2000996Unid. Chrysophyta1711Unid. Chrysophyta9588Oscillatoria<2μm324Pennates1904Oscillatoria<2μm3436Oscillatoria<2μm1144Oscillatoria<2μm1279Oscillatoria<2μm158Unid. Centric Diat.1485Oscillatoria<2μm3750Anabaena304Melosira(Aulac.)494Melosira(Aulac.)1046Cryptophyta203Unid. Centric Diat.506Unid. Chrysophyta156Melosira(Aulac.)151Anabaena1926Cylindrospermopsis214Oscillatoria<2μm343Unid. Pennate Dait.730Unid. Chrysophyta165Unid. Cryptophyta480Unid. Centric Diat.129Unid. Centric Diat.95Unid. Centric Diat.986Unid. Pyrrhophyta190Unid. Pyrrhophyta302Melosira(Aulac.)529Aphanizomenon136Unid. Pyrrhophyta379Unid. Centric Diat.115Microcystis95Unid. Centric Diat.596Anabaenacircinalis190Unid. Centric Diat.289Unid. Pennate Dait.511Anabaena127Unid. Centric Diat.332Unid. Centric Diat.308051.6440280.32014583.6263146.4526263.31017161.5273464.9410672.53/29/20015/1/20015/30/20016/28/20017/23/20018/20/20019/25/200110/24/20012494Unid. Chrysophyta1175Oscillatoria<2μm6380Oscillatoria<2μm8218Oscillatoria<2μm2813Oscillatoria<2μm6704Oscillatoria<2μm1601Oscillatoria<2μm113Lyngbyacontorta174Anabaena823Unid.Chrysophyta1959Cylindrospermopsis2986Cylindrospermopsis548Lyngbyacontorta939Cylindrospermopsis272Fragil.construens73Unid.Cryptophyta163Oscillatoria<2μm260Anabaena486Ocillatoria464Unid. Centric Diat.475Unid. Centric Diat.412Melosira(Aulac.)136Lyngbyacontorta66Melosira(Aulac.)117Ankistrodesmus153Unid.CentricDiat.476Plagiotropis333Ocillatoria462Microcystis352Ocillatoria127Unid.Pyrrhophyta59Oscillatoria<2μm92Scened. quadricauda144Anabaenopsis402Plagiotropis285Unid. Pennate Dait.371Melosira(Aulac.)326Lyngbyacontorta101Rhizosolenia(Freshwater forms)50Frag. Construens439369.2391765.21240478.21519380.9649271.91007186.7286778.059360.965.664.780.662.061.372.271.464.610.316.72.314.48.313.111.39.7St.Johns RiverWaterManagementDistrict20

### algal N fixation. Phlips and Cichra (2001) identified nitrogen fi xation rates in the

freshwater LSJR during a year 2000 survey, and determ ined that this pathway is a

significant contributor to th e total segm ent nitrogen load , and the importance of Nfixation has been subsequently confirm e d in gr owth assays (Paerl et al, 2001). In 1998, a

single large bloom is seen to occur, with a coinci dent N concentratio n spike. In 1999,

2000 and 2001, double bloom s occur, but only in the 1999 bloom is there a nitrogen

concentration spike associated with the second bloom

.

If low river flow allows for sufficient tim e for phosphorus lim itation to occur, then a

dram atic collapse of the phytoplankton comm uni ty can be observed. Such bloom crashes

were observed in 1999 L 2001. These crashes occur 1) in the absence of freshwater

inflows that could possibly dilu te the bloom ; 2) before the su mm er solstice, and hen c e are
not attributable to day lengt h reduction senescence; and 3) despite falling num bers of

bloom -consum ing zooplankton. Substantial comm unity shifts can be seen with these

bloom crashes, with dom i nan ce by the N-fixing blue greens Anabaena or
Cylindrospermopsis giving way to diatom s or Microcystis . Extrem e phosphorus

lim itation in the comm unity, estim a ted in Figure s 13(c )

L 15 (c) by th e c o -occur r enc e of

low particulate P:algal C ratio (indicative of low internal phosphorus stores) and low PO 4 

### ,

seem s to be an im portant condition f o r the tr iggering of these bloom crashes. Minimum

P:algal C ratios during these tim e s were generally in the range of 0.010 - 0.015, a nd

values in this range were considered to represent th e m i ni m u m c e ll quota for the

predom inantly blue green algal comm unity pres ent at this tim e

.

Coincident with these precip itous declin es in algal stan ding stock are declines in

dissolved oxygen (Figure 16a-c) that sugg est algal respiration or organic m a tter

decom position, events that would be consistent with rapid bloom senescence. These low

dissolved oxygen levels, often belo w 3 m g /L for large areas o f river, are in a range th at is

detr im ental to the health of f

i sherie s in this rea c h. Possible f actors f o r this community

declin e include settling, bacter ial p r edation (per haps f acilita ted by a nutr ition a lly s t re ssed

phytoplankton comm unity), or physiological stress of extrem e nutrient lim itation.

St. Johns River Water M a nagem e nt Distr i ct 

### 21

### Figure 16. Relationship Between Phytoplan kton Bloom Status and Low Dissolved Oxygen Levels in the Freshwater LS JR.

a

. 1999

0 20 40 60 80 100 120 140 160

3 / 1 3 /3 1 5 /1 5 / 3 1 7 / 1 7 /3 1 8 /3 1 9 /3 0 1 0 / 3 1Chlorophyll a, mg/m3, or D.O.,mg/L x 10 Continuous DO x 10

Rac y P t. Chl

. a
Ambient Mo nitor i ng D.O

.



### b. 2000

0 20 40 60 80 100 120 140 160

2/29 3/30 4/30 5/30 6/30 7/30 8/30 9/29 10/30Chlorophyll a, mg/m3, orD.O., mg/L x 10 Racy Pt. Chlor ophyll a

Continuous D.O

. x 10

Ambient Monitor i ng D.O

.



### c. 2001

0 20 40 60 80 100 120 140 160

2/ 28 3/ 30 4/ 30 5/ 30 6/ 30 7/ 30 8/ 30 9/ 29 10/ 30Chlorophyll a, mg/m3, orD.O., mg/L x 10 Chlor ophyll a

Amb. Monit. DO x 10

Continuous D.O

. x 10

St. Johns River Water M a nagem e nt Distr i ct 

### 22

### Superior nutrient uptake capabilities of som e species under extrem e l y low m i neral

nutrient con centration s m a y also play a ro le in bloom crashes and re-em e rgence.

Because of the strong ph ytoplank t on contro l over the rive r=s nutri ent pa rtition i ng during

the peak algal growth seasons , p a r ticu l ate org a nic nu tr ien t s a r e co rre lated with a l gal

biom ass on sam p ling dates when low inorga nic nutrient concentrations are observed

(Figure 17). Particulate organic nutrient con cen trations for these d a tes also ag ree well

with the Redfield stoichiom e tric conversions to algal biomass. The greater am ount of

spread and slight cu rv ilin ear natu re of the chlorophyll a to particulate phosphorus

relationship suggests a fair am ount of elastic ity in growth requirem e nts for phosphorus,

and this would be expected if phosphorus upt ake occurred ahead of present growth needs

(luxury uptake).

Com p arison of particulate organi c carbon to corrected chlorophyll a suggests that a

conversion factor of 50 :1 carbon:chlorophyll a is generally appropriate for LSJR

freshwater phytoplankton communities (F igur e 18(a)). In calculations utilizing

biovolum e m easure m ents, perform e d when dist inguishing the algal carbon within algal

taxonom ic groupings, a conversion of 0.3*biovolum e, in μm 3 

### /m l, was used to con v ert to

algal carbon, in m g /L (Figure 18(b)).

Frequency of Occurrence and Duration of Algal Biomass

Chlorophyll a frequency distributions for the three st ations residing with in the LSJR fresh

reach (Federal Poin t, Racy Point and W a tson Island, at 110, 1 00 and 90 RKm ) are sho w n
in Figure 19 for all data and spring and summer data from 1995 through 2001. Because

algal bloom biom ass, m e asured as chlorophyll a , is skewed to ward higher concentrations,

the values are presented as th e natural log of chlorophyll conc entration to render the data

norm a lly distributed. Chlorophyll a tends to exceed 20 mg/ m 3 

### (benchm a rk associated

with fair trophic condition) 50 Y 75% of the time for all data and 68 - 88% of the time for

spring Y summer data. Chlorophyll a exceeds 40 m g / m 3 

### (benchm a rk associated with

St. Johns River Water M a nagem e nt Distr i ct 

### 23

### Figure 17. Relationship Between Particulate Nu trient Form s for Low Inorganic Nutrient

Sa m p ling Dates and C h lorophyll a Concentr ation, 1995-99. Low inorganic nutrient
concentrations considered to be LE 0.005 m g /L for PO4 and 0.02 m g /L for TIN. Solid lines indicate phytoplankton N and P for phyt oplankton C:N and C:P of 5.67:1 and 41:1, and a C:Chlorophyll a ratio of 50:1. Dashed line is m odel of Huber et al. (1982).

Phosphorus

0 20 40 60 80 100 120 140 160 180

0 0 .0 2 0 .0 4 0 .0 6 0 .0 8 0 .1 0

. 1 2 0

. 1 4

Part iculat e P hosphorus, m g /LCorr. Chlorophylla, mg/m3 Rac y Pt.

Palatk a

Pic olata



### Nitrogen

0 20 40 60 80 100 120 140 160 180

0 0

. 5 1 1

. 5 2 2

. 5

Particulate Organic N

, m g /LCorr. Chlorophylla, mg/m3 R a cy P t

. Palatk a

Pic o lata

St. Johns River Water M a nagem e nt Distr i ct 

### 24

### Figure 18. Boundary Relationships Between Pa rticulate O r ganic Carbon and (a) Total Chlorophyll a and (b) Algal Biovolum e for LSJ R Freshwater Sa m p ling Stations. Vertical red line in (a) identifies 50:1 C:chlorophyll-a. Vertical red line in (b) corresponds to 0.3

m i crog. C:1000 m i cro-m3 biovolum e. Da ta from Phlips and Cichra, 2001.

( a ) POC: Chlorophy ll-a

0 20 40 60 80 100 120 140 160

0 100 200 300 400 500

P O C : C h lor ophy ll a ra t i oTotal Chlorophylla,mg/m3



### (b) POC: A l gal Biov olume

0 5000 10000 15000 20000 25000 30000

0 0

. 002 0. 004 0. 006 0. 008 0. 01 0. 012

C : B i ov olum e R a tioBiovolume, micro-m3/ml x1000

St. Johns River Water M a nagem e nt Distr i ct 

### 25

### Figure 19. Frequency distributions of tota l and spring-summ er total (uncorrected) chlorophyll a for LSJR freshwater stations. Ln(20) = 3; Ln(40) = 3.7; Ln(60) = 4.09.

SprA ll

P

er

ce nt
R

an

a Ln T o t. Chl 5.4 5 .2 5 4 .8 4.6 4 .4 4.2 4 3.8 3 .6 3.4 3 .2 3 2 .8 2.6 2 .4 2.2 2 1.8 1 .6 1.4 1 .2 1 0 .8 0.6 10

9

8

7

6

5

4

3

2

1

0 Watson Isl. - RKm 90

A ll Data

Spr-Sum

P

er

ce nt
R

an

a Ln T o t. Chl 5.4 5 .2 5 4 .8 4.6 4 .4 4.2 4 3.8 3 .6 3.4 3 .2 3 2 .8 2.6 2 .4 2.2 2 1.8 1 .6 1.4 1 .2 1 0 .8 0.6 10

9

8

7

6

5

4

3

2

1

0 Rac y Pt - RK m 100

SprA ll

P

er

ce nt
R

an

a Ln T o t. Chl 5.4 5 .2 5 4 .8 4.6 4 .4 4.2 4 3.8 3 .6 3.4 3 .2 3 2 .8 2.6 2 .4 2.2 2 1.8 1 .6 1.4 1 .2 1 0 .8 0.6 10

9

8

7

6

5

4

3

2

1

0 Federal P t . - R K m 110

St. Johns River Water M a nagem e nt Distr i ct 

### 26

### poor trophic status) 18 / 29% of the tim e for all data and 33 / 49% of the tim e for spring

/ summer data.

The length of ti m e chlorophyll a exceeded 40 mg/m 3 

### for these stations was sorted in rank

order and again displayed as percent frequenc y distributions (Figure 20). To determ ine

the duration of above 40 m g / m 3 

### concentrations, the proporti on of tim e between sampling

dates in which concentrations went from be low to above or above to below was linearly

interpolated, and added to the duration for which concentration rem a ined above 40. The

50 th 

### percentile duration ranged from 24 to 29 days, while the 75 th 

### p e rcen tile du ration

ranged from 32 days at Federal point to 76 days at W a tson Island. For the 8 years of data

for which durations were calculated (1994 through 2001), bloom s exc e eding 40 mg/ m 3



### occurred 21 tim es at Racy Point, 18 tim es at Federal Point, and 16 tim es at Watson

Island.

In summ ary, nutrient control of phytoplankton biom ass produc tion within the freshwater

LSJR is seen to be in term ittent and seasonal, coincident with th e annual trend in

phytoplankton productivity, and m o derated by river flow. W a ters entering the freshwater

LSJR appear to be predom inantly phosphorus lim ited, but large a dditions of phosphorus

in th e ex ter n al load within th is rea c h appea r to of f s et this c ondition. O n ly in dry y e ars

does a con d ition of p hosphorus lim itation p r evail. W h en condition s of phosp horus

lim itation occur for extended intervals, the phytoplankton community appears to collapse,

and this event is associated with severely low levels of dissolved oxygen. W h ile nitrogen

appears to b e the p r im ary lim iting n u trient (when nutrients are lim iting), N-fixation by

blue green algae would appear to render P the p r inciple driv er of ultim ate phytoplan kton

biom ass. As such, particulate organic nitroge n is the better indicator of the am ount of

algal biom ass, but total phosphorus provides the better indicator of algal comm unity

expansion potential.

St. Johns River Water M a nagem e nt Distr i ct 

### 27

### Figure 20. Distribution of durations of algal bloom s gr eater than 40 m g / m 3 

### tota l chlorophyll a for LSJR freshwater stations.

B l oom D u r a tion D i s t r i bution

0 10 20 30 40 50 60 70 80 90 100

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 1 1 0 1 2 0



### B l oom dur a t ion, da y sPercent Rank



### R K m 100

R K m 110

RK m 9 0

St. Johns River Water M a nagem e nt Distr i ct 

### 28

### Algal Bloom Characteristics of the L S JR Marine Reach

The degree to which m a rine salinity encr oaches into the lower St. Johns River is

dependent prim arily upon river flow, and to a lesser extent on episodic, short term

changes in ocean elevation (Sucsy and Mo rris, 20 01). Under average river flow

conditions, the greatest upstream advance of marine waters typically occurs in May or

June (the peak of the spri ng dry season), to the area near the m outh of Black Creek

(Figure 21). For this reason, this point has b een used to distinguish the m a rine-influenced

(also referred to in this repor t as the oligo/m e sohaline reac h) lower St. Johns from its

predom inantly freshwater section. F e w, if a ny algal species of the freshwater LSJR are

capable of surviving the transition to the hi gher salinity environm ent of the oligohaline

and m e sohaline reach es. This results in a com p lete ch angeover in phytoplank t on
community species in m a rine reaches of the rive r (Table 2). Unlike the cyanobacterial

dom i nation of algal bio volum e of the freshw ater reach, th e oligo/m e sohaline re ach is

dom i nated by diatom s, with sm aller relative amounts of blue greens, and with som e what

greater numbers of dinoflagellates (T able 3).

The zone of salinity-driven phyt oplankton community transition appears to extend from 3

to 18 ppt (Figure 22). The zone of m a xi m u m communi ty transition, based upon the

fewest numbers of phytoplankton in common between sam e -day longitudinal sampling,

was found to occur between 18 to 25 ppt. (Figure 23). Because som e of the species of the

freshwater bloom s i m ported to the oligoha line and m e sohaline river are under salinity

stress and in decline, the paradox arises such that total algal biom ass appears to be lowest

where ex ternal nu trient loads are the greates t

. It is as sum e d that nu trient loads within this

reach hav e little effect o n perpetu a ting the al gal biom ass expansion of sp ecies that are in

decline through salinity stress, and are instead prim arily responsible for nourishing and

accelerating growth within the riv e r or in near o ffshore waters for prim arily salt-to l erant

or m a rine phytoplankton. For this reason, efforts in developing causal relationships

between nutrient loads and algal growth with in the oligohaline and m e sohaline reaches

have focused prim arily on the e ffects of thes e lo ads to m a rine bloom s. In the process of

quantifying accelerated algal growth effects and judging load reduction p e rform a nce, the

St. Johns River Water M a nagem e nt Distr i ct 

### 29

### Figure 21. Water Quality and P l ankton Monito ring S t ations of the Oligo/Mesohaline
Reach of the LSJR.

Mouth of
Black Creek

(Upstream boundary) 

### D octors Lak e D ames P

oin t

A costa
Brid ge Fulton

P

oin t Talle y ran d

P ine y Poin t

P

lummer s Cove

M andarin Poin t

St. Johns River Water M a nagem e nt Distr i ct 

### 30

### Table 2. T op 10 Most Predom inant Phyt oplankton Species based on Biovolum e in

Sa m p ling from the LSJ R Stations at Fulton Po int (Mar ine) and Racy Point (Fre sh). Data
from Phlips and Cichra, (2001).

Rank Racy Point (Freshw ater) Fulton Point (Marine)

1 Oscilla toria <2μm diam eter Bellerochea

2 Cylindrospermopsis spp. Rhizosolenia

3 Anabaena spp

. Centric Diatom s < 25m

4 Microcystis incerta Centric Diatom s >> 100m

5 Melosira (Aulacoseira) Guinardia flaccida

6 Ocilla toria (other d i am eters) Coscinodiscus

7 Lyngbya contorta Skeletonema

8 Centric Diatom s < 25m Leptocylindrus

9 Raphidiopsis Division Cryptophyta

10 Pennate Diatom s > 25m <

50m Gymnodinium spp.

Table 3. Mean Percent Com position of Algal Functional Groups for LSJR Ol igoMesohaline Stations During Predom inantly Fresh (Total Chloride < 1,500 m g /L) and
Predom inantly Marine (T. Chloride > 1,500 mg/L) Spring and Summer (April X Septem ber) Sa m p ling Events.

C y a n o b a c t e r i a G r e e n s D iatom s Cryptophytes D i n o f l a g e l l a t e s O t h e r F r e s h 3 1

. 1 2

. 9 5 7

. 5 3

. 6 4

. 3 0

. 7

M a r i n e 1 1

. 6 1

. 1 7 7

. 2 3

. 8 5

. 9 0

. 3

St. Johns River Water M a nagem e nt Distr i ct 

### 31

### Figure 22. Change in Phytoplan kton Community Richness from Freshwater to Marine
Stations in the LSJR.



## R e la t i v e S p e c ie s R i c h n e s s x S a lin it y

0 10 20 30 40 50 60 70 80 90 10 0

6. 00 6. 50 7. 00 7

. 5 0 8

. 0 0 8

. 5 0 9

. 0 0 9. 50 1 0

. 0 0 1 0. 50



### L n ( S al i n i t y x 1000)Relative Spp. Richness, %



### 2001

1999 4 t o 16 p p t



### Figure 23. Mean Number of Phytoplankt on Species within the T op 10 based on
Biovolum e, at a Given S t ation, Present in the N e xt Downstream Station as a Function of
the Mean S a linity Between the Two Stati ons. Data are for 1999 and 2001 (Phlips and Cichra, 2001).

P h y t op l a nk t o n C o m m u ni t y C o nt i n u i t y

0 1 2 3 4 5 6 7

123 4567

S a l i ni t y R a ng eSpecies inCommon BetweenStations

I:\\e s d a t a \ l s j \ U F

- P l a n k t o n I D \P h y t o

- T a x a \ S a lin i t y

St. Johns River Water M a nagem e nt Distr i ct 

### 32

### condition of a predominantly m a r i ne bloom was assum e d to apply when chloride

concentrations were greater than 1,500 m g /L (roughly equivalent to 2.7 psu), consistent

with the def i nition of Cpr e dom inantly m a rineD wa ter in the F.A.C. 62-302.

Plankton and water quality data from five ambient m o nitoring stations have been

exam ined extensiv ely to describe the pattern s of algal gro w th within this r e ach. These

stations, shown in Figure 21, are Mandarin Po int, Piney Point, Talleyrand, Fulton Point

and Plumm e rs Cove (a short te rm monitoring station). W ith the exception of Plummers ,

all sta tion s are loca ted at the rive rP s m i d-channel. There is som e indication th at this

center channel approach to plankton m onito ring m a y lead to an under-reporting of the

am ount of algal biom ass with in th is reach. Observation a l and anecdotal inform ation

indica tes th at alga l blo o m s m o re frequently reach nuisance le vels in near shore areas

. The possibility of high er alg a l b i o m ass near shore, due to f actors s u ch as positive

buoyancy com p ensation, salinity-induced aggr egation and subsequent wind-stacking of

Microcystis (Sellner et al., 1988), dense growth of filam e ntous green alga on SAV

(Magley W unpublished data), or longer near -shore water entrainm ent (Dobberfuhl, pers.

comm.) are plausib l e. In a dem onstration of th e potential fo r near sh ore or cove locations

to exhibit higher algal biom ass levels than ch annel stations, paired, sam e -day sam p le data

from two near-by stations at Mandarin Po in t, one in the channel an d the othe r in

Plummers Cove, were com p ared from the tim e period from Dece mber 1996 through

October 1999. The in-cove station was foun d to have a significantly higher m ean
chlorophyll a concentration (two-tailed paired t-te st, p=0.05), with an average increase of

3.2 m g / m 3 

### . The in-cove station exceeded the channel station by m o re than 10 m g / m 3 

### on
3 of the 34 paired even ts, while the channe l station never exceeded the cove statio n by

more than 6 mg/ m 3 

### . Thus there is reason to sus p ect that alg a l biom ass, as es tim ated b y
centerline sampling stations, m a y underest im ate the area-weighted condition.

Annual patterns of chlorophyll a and algal biovolum e for the years from 1998 through

2001 are shown in Figures 24 and 25 for the f our river channel stations. Both of these

algal biom ass indicators are show n, as neither appears to b e a superio r m easure in this

St. Johns River Water M a nagem e nt Distr i ct 

### 33

### Figure 24 . Total Chlorophyll a Co ncentr ation s f o r Oligo/M e sohaline Stations in the LSJR, 1998 C 2001.

(a ) 1 9 9 8

0 10 20 30 40 50 60 70

1/ 1 1 / 3 1 3 / 3 4 / 2 5 / 3 6/ 2 7 / 3 8 / 2 9 / 2 10 / 2 11 / 2 1 2 / 2 1 / 2Total Chlorophyll-a, mg/m3 Fu lt o n P t

. Ta l l e y r a n d

Pi n e y P o i n t

M a nd ar i n P t

.



### ( b ) 1999

0 10 20 30 40 50 60 70

1 / 1 1 /3 1 3 / 3 4 / 2 5 / 3 6 / 2 7 /3 8 / 2 9 /2 1 0 /2 1 1 / 2 1 2 /2 1 / 2Total Chlorophyll-a, mg/m3 Fu l t o n
Ta l l e y r a n d

Pi n e y P t

. M a nd ar i n

St. Johns River Water M a nagem e nt Distr i ct 

### 34

### Figure 24 (cont.). Total Chlorophyll a Concentrations for Oligo/Mesohaline Stations in the LSJR, 1998 E 2001.

( c ) 2000

0 10 20 30 40 50 60 70

1/ 1 1 / 3 1 3 / 2 4/ 1 5 / 2 6/ 1 7 / 2 8/ 1 9 / 1 1 0 / 1 11 / 1 1 2 / 1Total Chlorophyll-a, mg/m3 Fu l t o n

Ta l l e y r a n d

Pi n e y Pt

. M a nd ar i n



### ( d ) 2001

0 10 20 30 40 50 60 70

1 / 1 1 / 3 1 3 /3 4 / 2 5 /3 6 / 2 7 /3 8 / 2 9 /2 1 0 / 2 1 1 /2 1 2 / 2 1 / 2Total Chlorophyll-a, mg/m3 Fu l t o n

Ta l l e y r a n d

Pi n e y P t

. M a nd ar i n

St. Johns River Water M a nagem e nt Distr i ct 

### 35

### Figure 25. T o tal Algal Biovolum e for Oligo/ Mesohaline S t ations in the L S JR, 1998 C 2001. From Phlips and Cichra, 2000.



### (a ) 1 9 9 8

0 20 00 40 00 60 00 80 00 10 00 0 12 00 0

1/ 1 1 / 3 1 3 / 3 4/ 2 5 / 3 6/ 2 7 / 3 8/ 2 9 / 2 1 0 / 2 11 / 2 1 2 / 2 1/ 2Total Biovolume, micro-m3/ml*1000 Fu lt o n P t

. Ta l l e y r a n d

Pi n e y P o i n t

M a nd ar i n P t

.



### ( b ) 1999

0 20 00 40 00 60 00 80 00 10 00 0 12 00 0

1 / 1 1 /3 1 3 / 3 4 / 2 5 /3 6 / 2 7 / 3 8 / 2 9 /2 1 0 / 2 1 1 /2 1 2 /2 1 / 2Total Biovolume, micro-m3/ml*1000 Fu lt o n

Ta l l e y r a n d

Pi n e y P t

. M a nd ar i n

St. Johns River Water M a nagem e nt Distr i ct 

### 36

### Figure 25 (cont.). Total Algal Biovolum e for Oligo/Mesohaline Stations in the LSJR,

1998 F 2001. From Phlips and Cichra, 2000.



### ( c ) 2000

0 20 00 40 00 60 00 80 00 10 00 0 12 00 0

1 / 1 1 / 3 1 3 / 2 4 / 1 5 /2 6 / 1 7 /2 8 / 1 9 / 1 1 0 /1 1 1 /1 1 2 /1Total Biovolume, micro-m3/ml*1000 Fu lt o n
Ta l l e y r a n d

Pi n e y P t

. M a nd ar i n



### ( d ) 2001

0 20 00 40 00 60 00 80 00 10 00 0 12 00 0

1/ 1 1 / 3 1 3 / 3 4/ 2 5 / 3 6 / 2 7 / 3 8/ 2 9 / 2 1 0 / 2 1 1 / 2 12 / 2 1/ 2Total Biovolume, micro-m3/ml*1000 Fu l t o n

Ta l l e y r a n d

Pi n e y P t

. M a nd ari n

St. Johns River Water M a nagem e nt Distr i ct 

### 37

### river reach. W h ile chlorophyll a should be a better indicator of produ ctiv ity po te ntia l,

because it is a less d o m i nant photosynthe tic pigm ent in the m a rine phytoplankton

community, it m a y not provide as reliable an indicator of algal biom ass. Biovolume

m easure m ents m i ght be expected to provide a better indication of biom a ss here, but can

be difficult due to the high am ount of tripton and possibility for em pty diatom frustules

appearing to be live cells. Both m easur es consistently predict the high biom ass
associated with the import of the fres hwater bloom in August of 1998, but do not

correlate well otherwise. Unlike the freshwater L S JR, where chlorophyll a concentration

was found t o be a reliable indicator of al gal biom ass, and linear regressions between

particulate organic carbon and chlorophyll a , and between algal biovolum e and

chlorophyll a , produced high R 2 

### valu es, sim ilar com p arisons in this reach were poor The

boundary relationships between POC and the P O C:chlorophyll a ratio and between POC

and the POC:tota l biov olum e ratio (Figure 26a and b) sugges ts th e presence of a much

larger am ount of non-algal POC for m a rine samp les. This is not a surprising result for

the low s a linity reg i on of a riv e r estua r y su ch as the LSJR, as the delivery of

allochthonous and autochthonous organic m a tter, and the possible flocculation of

dissolved organic m a tter, likely contribu te greatly to the POC pool. Boundary

relationships can be discerned, however, and when the lower bounds of these scatter plots

are com p ared to the freshwater algal carbon to chlorophyll a and biovolum e, conversions

developed for LSJR freshwater algal comm uni ties do not appear to be inconsistent for

m a rine communities, an d therefore have been u s ed when conversions to algal carbo n are
required.

W ith the ex ception of the peak bio volum e observed in 1998 at th e Mandarin and Piney

Pt. Stations, all summ er sa m p ling events in th is rea c h were c h arac ter i zed by

predom inantly m a rine conditions and were assum e d representa tive of estuarine

phytoplankton communi ties. For low-flow year s, peak biovolum e m eas urem ents tended

to range between 2,000,000 to 4,000,000 P m 3 

### / m l, with large bloom s of over 9,000,000

P m 3 

### / m l occurring at Mandarin Point in July 2000 and Fulton Point in June 2001. In

recen t work on the Ind i an River Lag oon, Phlips et al. (2003) identified a biovolum e level

St. Johns River Water M a nagem e nt Distr i ct 

### 38

### Figure 26. Calculated organic carbon to bi ovolum e conversion for predom inantly m a rine
bloom s of t h e Lower St. Johns River. Based on 186 m easurem ents fr om August 1998 through Novem b er 2001. Red line indicate carbon to biom ass relationships based on freshwater phytoplankton in the L S JR. Dashed pink line of (a) repr esents calculated
reduction in carbon to biom ass ratio correspond ing to the proportional loss from silica in
diatom s.



### ( a ) M a r i ne P O C : B i ov ol um e R a t i o

0 20 00 40 00 60 00 80 00 10 00 0 12 00 0

0 0

. 0 01 0

. 00 2 0

. 0 03 0

. 00 4

P O C : B i ov ol um eTotal Biovolume, microm3/mlx1000 O b s e r v e d D a ta

F r

es hw at e r C : B i o v R a t i o

S i l i c a -A dj us t e d R a t i o



### ( b ) M a r i ne C a r bon: C h l o r ophy l l

- a

0 5 10 15 20 25 30 35 40 45 50

0 1 0 0 20 0 3 00 40 0 5 0 0 6 0 0 7 00 80 0



### P O C : C h lor o phy ll- aChlorophyll-a, mg/m3

O b s e r v e d D a ta

5 0 :1 C : C h l o r o p h y l l

- a

St. Johns River Water M a nagem e nt Distr i ct 

### 39

### of 1,000,000 P m 3 

### / m l (roughly equivalent 6 μg/L chlorophyll a ) as indicative of a marine

bloom condition.

Peak chloro phyll a concentrations range d between 10 and 40 mg/ m 3 

### . W i t h the exception

of the very high value at Ma ndarin in July 2000, biovolum e te nded to be slightly higher

at downstream stations Talleyrand and Fulto n Point. W h en sam p ling ev ents were
perform e d for both high and low tides in th e sam e day at Fulton Point, it was observed

that higher chlorophyll and algal biovolum e tended to occur on high tide sam p ling,

despite low e r nutrient concentr ations. High tide collections at this location, due to its

close proxim ity to the riverNs m outh, are assume d to be largely repres entative of the near

coastal plankton community. Due to less vert ical m i xing and greater transparency , th e

near co astal area at the St. Johns mout h m a y support co nditions m o re favorab le for

growth, as has been observed for the near co astal area offshore of Georgia (Yoder et al.,

1993), and thus river nutrients can be e xploited by m a rine phytoplankton.

While increases in spring-summ er biom ass appear to be less pronounced than that

observed for the freshwater reach, the rela tive m a gnitudes of biom ass increas e are only

m a rginally less. Mean oligo/m e sohaline April V Septem be r chlorophyll a from 1997

through 2001 was 11.4 mg/ m 3 

### , a 75% increase over the Oc tober V March m ean of 6.5

mg/ m 3 

### . In com p arison, freshwater m ean Apr il V Septem ber chlorophyll a m ean of 34.4

mg/ m 3 

### represents a 95% increase over the Oc tober V March concentration of 17.6 m g / m 3



### .

Nutrient L i mitations to Marine Phytoplankton C o mmunity Growth

The am ount of bioavailable silica may be a ke y regulator in the diatom bloom expansion

potential within th e LSJ R m a rine reach. Lo w silica conc en trations co -occur with peak

diatom biomass (Figure 27). The occurrence of low concentrations of essential inorganic

nutrients, in the range of reported half saturati on constant concentra tions, can be a us eful

indicator of potential nutrient lim itation. This technique is more difficult to apply with

confidence in this instance due to the m e t hod detection lim it for silica analyses being

over 10 times greater than the commonly reporte d half saturation concentration range of

St. Johns River Water M a nagem e nt Distr i ct 

### 40

### Figure 27. Relationship between silica concentr ations and diatom biovolum e. Data from 1997 throug h 2001 for predom inantly m a rine co ndition (>2. 7 ppt) sam p les.



### R e la t i o n s h i p B e tw e e n D i s s o l v e d S ilic a C o n c e n t r a t io n a n d

D i a t om B i ov ol um e

0 20 00 40 00 60 00 80 00 10 00 0 12 00 0

0 1 2 3 4 5 D i s s

o lv e d S i, mg /LDiatomBiovolume, micro-m3/1000

6



### R e l a t i ons hi p B e t w

. M ont hl y M e a n D i a t om B i ov ol um e a nd

P e r c en t o f D i sso l ved S i A n al yses B e l o w t h e M D L

0 10 20 30 40 50 60 70 80 90 10 0

0 2 0 0 40 0 6 00 8 0 0 1 00 0 1 20 0 1 40 0 1 6 0 0 1 8 0 0 2 0 0 0

M e a n M ont hl y D i a t om B i ov ol um e , m i c r o- m 3 / 1 0 0 0Percent Diss. Si Below MDL

St. Johns River Water M a nagem e nt Distr i ct 

### 41

### 20 - 100 μg/L (EPA, 1990; Chapra, 1997). In th e data set used here, @best estim atedD

concentratio ns below th e MDL, rather th an censored values, ar e reported, and peak

diatom biovolum es appear to be asso ciated w ith low, even po tentially limiting, disso lved

silica conce n tra tions. However, due to the lo w conf idence attr ibuted to these be lowMDL values, the derivation of a quantitativ e relationship has not been attempted.

Prevailing low silica concentration s appears to be a natural characteristic in m a ny of

FloridaRs su rface waters , presum ably due to wa tershed parent m a terial predom inated by

sands resistant to weathering, and the general absence of lattice clays that are rich in

bioavailable silica. In the LSJR m a rine reach, the upper bounda ry of the silica to diatom

biovolum e relationship suggests that diatom biom ass within the river m a y bec o m e

genera lly lim ited by silica in th e ran g e of 3 to 4 m illion μm 3 

### /m l (Figure 27).

Low bioavailable silica m a y play an i m portant role in shaping phytoplankton

communities when other m acro-nut rien ts, primarily N and P, ar e in suf f icient supply to

prom ote silica lim itatio n. The b a r chart of Figure 28 shows the relationship between

dinoflagellate relative abundan ce and the potential severity of silica lim itation, based

upon dissolved silica concentration. W h ile th e confidence intervals in F i gure 28 overlap

f o r the two lowest conc entra tion cla sses, th e removal of one sam p le ev ent that occurred

during the El Nino year (1998) early summ er results in sign ificant difference betw een
these two groups at a level of p = 0.10. This suggests that when silica concentration is

very low and possibly lim iting to diatom growth, other algal species, prim a r ily

dinoflagellates, are ab le to take adv a ntage of excess bioav a ilable N and P and reduced

com p etition to increase their abun dance. Turner (2002), in a recent article on the

influence of nutrient ratios in shaping plankton food webs, cites 10 nutrient m a nipulation

studies perf orm e d in mesocosm s in estuarin e environm ents that strongly support the

concept of f

l agellate gr owth being positiv el y a dvantaged b y incre a ses in nitrogen and

phosphorus relative to silica. Turner (2002) sugge sts a ratio of bioavail able Si:N of <1

repres ents a sensitive p i vot po int a t which d i a t om species tend to de cline re lativ e to

flagellate sp ecies.

St. Johns River Water M a nagem e nt Distr i ct 

### 42

### Figure 28. Mean relative abundance of dinoflagellates biovolu m e within silica
concentratio n classes. Error bars encom p ass 90% confidence interval.



### D i nof l a ge l l a t e R e l a t i v e A bunda nc e w i t h i n S ilic a
C o n c en t r at i o n C l asses

0. 0 2. 0 4. 0 6. 0 8. 0 10. 0 12. 0 14. 0 16. 0 18. 0

0 - 0. 25 0. 25 - 0. 5 0

. 5 - 1. 0 > 1. 0

S i C o n c e n t r at i o n C l assMean Relative Abundance

St. Johns River Water M a nagem e nt Distr i ct 

### 43Table 4. Dinoflagellate Species Occurringin the Oligo/Mesohaline LSJRfor Bloomswith DinoflagellateBiovolume > 300,000μm3/ml.Dinoflagellate Species Composition for Bloomswith Biovolume >= 300. Mean Relativeabundance = 37%.BiovolumeGenus/SpeciesBiovolumeGenus/SpeciesBiovolumeGenus/SpeciesFultonPt. Surface3/31/1998FultonPt. Bottom3/31/1998Mandarin Pt.9/22/19986208Unidentified armored dinoflagellates > 25m4656Unidentified armored dinoflagellates > 25m17480Gymnodinium< 30m6829Unidentified armored dinoflagellates < 25m7152Ceratium hircus284778Division Pyrrhophyta armored < 25m421Katodinium2894Gymnodinium < 30m2659Prorocentrum471393Gymnodinium12042Prorocentrum maximum6912Prorocentrum1564Dinophysis caudata41791Prorocentrum maximum1263OxyphysisPlummersCove5/27/1999FultonPt.Surface8/31/1999FultonPt.Bottom8/31/199915278Unidentified armored dinoflagellates > 25m278098Unidentified armored dinoflagellates > 25m128010Unidentified armored dinoflagellates > 25m4223Unidentified armored dinoflagellates > 25m3016Ceratium2171Gymnodinium< 30m17480Gymnodinium< 30m724Gymnodinium< 30m2490Gyrodinium386937Prorocentrum minimum2171Gymnodinium< 30m3446Gyrodinium31426Gymnodinium323Gyrodinium minimum5041Gymnodinium3090Gyrodinium micans7340Gyrodinium micans4785Gyrodinium1607Gyrodinium1564Dinophysis caudata6027Gonyaulax3013GonyaulaxSt.Johns RiverWaterManagementDistrict44Table 4. (cont.)BiovolumeGenus/SpeciesBiovolumeGenus/SpeciesBiovolumeGenus/SpeciesFultonPt. Surface9/29/1999FultonPt.Bottom9/29/19995174Unidentified armored dinoflagellates > 25m21812Unidentified armored dinoflagellates > 25m3576Ceratium hircus10729Ceratium hircus2521Gymnodinium<30m276076Gymnodinium<30m2490Gyrodinium2490Gyrodinium803Prorocentrum5022Prorocentrum micans3013Gonyaulax6026Prorocentrum3127Dinophysis caudata1482?421Oxyphysis5091?Mandarin Pt.6/27/2000FultonPt.6/27/2000Mandarin Pt.7/25/2000442989Unidentified armored dinoflagellates > 25m406896Unidentified armored dinoflagellates > 25m24770Unidentified armoreddinoflagellates > 25m52439Gymnodinium< 30m64305Gymnodinium<30m219812Gymnodinium<30m28320Katodinium22608Gymnodinium161Prorocentrum minimumTalleyrand Surface11/2/2000Talleyrand Bottom11/2/2000FultonPt.6/26/20016871Unidentified armored dinoflagellates > 25m436141Unidentified armored dinoflagellates > 25m848496Unidentified armoreddinoflagellates > 25m1672Gymnodinium<30m5532Gymnodinium<30m3713?161Prorocentrum minimum5238Gymnodinium7548Ceratium tripos1066Katodinium2605Gymnodinium<30m5179?94Prorocentrum micans2300GonyaulaxSt.Johns RiverWaterManagementDistrict45

### The principle dinoflagellate sp ecies or genera that are seen to occur at tim e of high

dinoflagellate biom ass are summ arized in Ta ble 4. Am ong these dinoflagellates are a

num b er of species with know n toxin production capability, thus, the reduction in the

abundance of dinoflagellates pr esents itself as a potential ly im portant restoration

objective for nutrient m a nagem e nt in the LSJR . Doctors Lake, located near Mandarin

Point along the riverGs western shore, pr ov id es an ex trem e exam pl e of how flowrestricted coves and e m baym ents, under pred o m inantly oligo- to m e sohaline cond itions

(a condition under which, it is im portant to note, the lake has been fed m a inly be river

waters), can m a nifest conditions of nutrient enrichm e nt into serious bloom s of potentially

toxic dinoflagellate species. Doctors Lake is heavily used f o r r ecreational purposes, is

surrounded by dense residential developm ent, a nd is extensively fished for shri mp and

crab. In the 18 sam p ling events perform e d within the lake betw een 1997 and 2001 in

which predom inantly m a rine conditions pr evailed, 7 of these had dinoflagellate

biovolum es in excess of 300,000 μm 3 

### / m l, and 5 events exhibited dinoflagellate

biovolum es in excess of 1,000,000 μm 3 

### / m l. In 2 of these 5 events, a species of

Gymnodinium was the dom i nant phytoplankton, and the dom i nant dinof lagella te in one

more. In one of the 5 events, Prorocentrum minimum was the dom inant phytoplankton,

with a biovolum e alone of over 1,500,000 μm 3 

### /m l.

The presence and patterns in bioavailable N and P can be an i m portant indicator of

potential nutrient lim itation in the phytopl ankton community. High concentrations of

bioavailable nutrients, in excess of the requi rem e nts for algal growth, can indicate that

large nutrient reductions m a y be necessary in order to bri ng nutrients into the growthlim iting range. High c oncentrations also pose the risk of large, detrim ental blooms

should the proper set of hydro dynam i c and m e teorological con d itions prevail.

Bioavailable nutrients are ge nerally more abundant in the oligo/m e sohaline reach of the

river, owing to the proxim ity of urba n area ex ter n al load and the rem i ner a liz ation of algal

nutrients f r o m the salin ity-st ressed freshwater community.

Hydrodynam i c and river m o rphologic factors relevant to algal biom ass accrual are

dram atically different in the o ligo / m e soha line reach when com p ared to the ups tream,

St. Johns River Water M a nagem e nt Distr i ct 

### 46

### freshwater zone. Increased channel depth, pa rticu l ar ly in the m e sohaline reach, dec r e a ses
the proportion of river volum e within the ph otic zone, and acts to lower per area

production rates. In ad dition, tidal exchange within the dredged riv e r m outh is very

large, resu lting in water volum e exchange rates from Piney Point onward of less than 10

days (Sucsy, pers. comm.). Thus, despite the large influx of external load N and P, and

abundant within-river nutrient concentrations , hydrodynam i c exchange can offset rates of

bloom expa nsion. Hydrodynam i c mixing m a y al so m ove bloom s out of the photic zone,

contributing to dissolved oxygen depression a nd worsening the negative water quality

im pacts when bloom s do occur.

Cum u lative frequency distribu tio ns of tota l inorgan i c nitrog en an d soluble reactive

phosphorus for sam p ling perform e d under m a rine conditions within the oligohaline and

m e sohaline reach are sh own in Figu re 29, and fro m these it can be seen that low or near

lim iting concentrations are seldom observed. For sam p ling perform e d be tween 1998 and

2001, inorganic nitrogen concentrations were onl y seen at potentially lim iting levels in

14% of the 188 sa m p le collections, and ort hophosphate only at 3.5%. Figures 30 and 31

present time series data for inorganic nutrients (tot al inorganic N (TIN) and

orthophosphate (PO 4 

### )) for the m o st downstream plankt on and water quality m onitoring

station at F u lton Point, to dem onstrate thes e patterns in potential N and P com p e tition.

For the Fulton Point stati on in 1997 and 1998, TIN is for the most part above

concentratio ns believed to be lim itin g to growth. In th e dry years of 199 9 and 2000, the

potential for nitrogen lim itati on appears greater, in partic ular for incom i ng (high) tide

sam p les. In years when high and low tide sample data are availab l e, high tide ev ents

exhibit low e r concentrations of TIN. This is believed to be due to dilution by low

concentratio n oceanic waters, as well as gr e a ter com p etition for nu trients in th e near

coastal zon e at the riv e rs m outh, where algal bio m ass is of ten grea ter. A sim ilar pa tte rn
occurs for orthophosphate (Figure 31); howev er, concentrations of dissolved total

phosphorus (Figure 32) are h i gh at this s t ation, s o the po ssib i lity of phosp horus lim itation

in the phytoplankton is seem s less likely. Ve rity et al. (1992) al so observed lim iting

concentratio ns of inorganic nitrogen, relati ve to silica and orthophosp h ate, in South

Atlantic Big h t near coastal wate rs.

St. Johns River Water M a nagem e nt Distr i ct 

### 47

### Figure 29. Cum u lative frequency distribution of inorganic N and P for the LSJR near Piney Point, 1998 D 2001.



### (a) Total Inorganic N

0 10 20 30 40 50 60 70 80 90 100

0 1 2 3 4 5 6 7

Ln(TIN, mg/m 3 )Percent Frequency

Doctor s Lake

F u lton Pt.

T a lleyr and
Piney Pt.

Mandar in Pt. 20 mg/m 3



### ( b ) Soluble R eact ive P

0 10 20 30 40 50 60 70 80 90 100

0 1 234 5 6

Ln(TIN, mg/m 3 )Percent Frequency

Doctor s Lake

F u lton Pt.

T a lleyr and Piney Pt.

Mandar in Pt. 5 mg/m 3

St. Johns River Water M a nagem e nt Distr i ct 

### 48

### Figure 30. Tim e series plots of total inorgani c nitrogen concentration for the LSJR near Fulton Point, 1997 @ 2000. Total inorganic nitr ogen calculated as the sum of total NH 4 

### +
NO X 

### . Evol ution in m o nitoring program s results in changin g levels of vertical and tidal
distinction in sam p ling data from year to year. Pink dashed line corresponds to 0.02 mg/L, a concentration at which nitrogen is a ssum e d to be potentially lim iting to growth.



### a. 1997

0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6

1/ 1 1 / 3 1 3 / 2 4/ 2 5 / 2 6 / 2 7 / 2 8/ 1 9 / 1 1 0 / 1 11 / 1 1 2 / 1TIN, mg/L To p



### b

. 1998

0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6

1/ 31 3/ 2 4 / 1 5 / 2 6 / 1 7/ 2 8 / 1 8 / 3 1 10 / 1 1 0 / 3 1 1 2/ 1 1 2 / 3 1 1/ 30TIN, mg/L To p - H i g h

To p - L o w

St. Johns River Water M a nagem e nt Distr i ct 

### 49

### Figure 30 (cont.). Tim e series plots of total i norganic nitrogen concen tra tion f o r the LSJR near Fulton Point, 1997 B 2000. Total inorganic nitrogen calculated as the sum of total

NH 4 

### + NO X 

### . Evolution in m onitoring program s resu lts in changing levels of vertical and
tidal distinction in sam p ling data from year to year.



### c. 1999

0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6

1 / 1 1 /3 1 3 /2 4 / 2 5 /2 6 / 2 7 /2 8 / 1 9 /1 1 0 /1 1 1 /1 1 2 /1 1 2 / 3 1TIN, mg/L B o t t om - Hi gh

B o t t om - Lo w

Mi d - H i g h

Mi d - L o w

To p - H i g h

To p - L o w



### d

. 2000

0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6

1 2 / 3 1 1 / 3 0 2 /2 9 3 /3 1 4 /3 0 5 /3 1 6 / 3 0 7 / 3 0 8 / 3 0 9 /2 9 1 0 / 3 0 1 1 /2 9TIN, mg/L B o t t om - Hi gh

B o t t om - Lo w

Mi d - H i g h

Mi d - L o w

To p - H i g h

To p - L o w

St. Johns River Water M a nagem e nt Distr i ct 

### 50

### Figure 31. Tim e series plots of orthophosphate concentration for the L S JR near F u lton Point, 1997 ? 2000. Evolution in monitoring pr ogram s results in changing levels of
vertical and tid al d i s tin ction in sa mpling data f

r om year to y ear. Pink dash ed lin e corresponds to 0.005 mg/L, a concentration at which phosphorus is assum e d to be potentially lim iting to growth.



### a. 1997

0 0. 02 0. 04 0. 06 0. 08

0. 1

1/ 1 1 / 3 1 3 / 2 4 / 2 5 / 2 6 / 2 7 / 2 8/ 1 9 / 1 10 / 1 11 / 1 1 2 / 1Orthophosphate, mg/L To p



### b

. 1998

0 0.02 0.04 0.06 0.08

0.1

1/ 31 3/ 2 4 / 1 5/2 6 / 1 7/2 8 /1 8/31 10/ 1 10/ 31 12/1 12/31 1/30Orthophosphate, mg/L To p - H i g h

To p - L o w

St. Johns River Water M a nagem e nt Distr i ct 

### 51

### Figure 31 (cont.). Tim e series plots of ort hophosphate concentration f o r the LSJR near Fulton Point, 1997 A 2000. Evolution in m onito ring programs results in changing levels
of

vertica l and tida l distinc tion in sam p li ng data from yea r to year. Pink dashed line corresponds to 0.005 mg/L, a concentration at which phosphorus is assum e d to be potentially lim iting to growth.



### c. 1999

0 0. 02 0. 04 0. 06 0. 08

0. 1

1 / 1 1 / 3 1 3 / 2 4 / 2 5 /2 6 / 2 7 / 2 8 / 1 9 /1 1 0 /1 1 1 /1 1 2 / 1 1 2 /3 1Orthophosphate, mg/L B o t t om - Hi gh

B o t t om - Lo w

Mi d - H i g h

Mi d - L o w

To p - H i g h

To p - L o w



### d

. 2000

0 0. 02 0. 04 0. 06 0. 08

0. 1

1 2 /3 1 1 /3 0 2 /2 9 3 / 3 1 4 / 3 0 5 / 3 1 6 / 3 0 7 / 3 0 8 /3 0 9 /2 9 1 0 / 3 0 1 1 /2 9Orthophosphate, mg/L B o t t om - Hi gh

B o t t om - Lo w

Mi d - H i g h

Mi d - L o w

To p - H i g h

To p - L o w

St. Johns River Water M a nagem e nt Distr i ct 

### 52

### Figure 32. T o tal dissolved P at Fulton Point, 1997 9 2001.



## a. 1997

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16

12/31/ 96 3/ 2/97 5/ 2/97 7/2/ 97 9/1/ 97 11/1/ 97Total Dissolved P, mg/L To p



## b. 1998

0 0. 02 0. 04 0. 06 0. 08

0. 1 0. 12 0. 14 0. 16

2/ 4/ 98 3/ 26/ 98 5/ 15/ 98 7/ 4/ 98 8/ 23/ 98 10/ 12/ 98 12/ 1/ 98 1/ 20/ 99Total DissolvedP, mg/L T op - H i gh

T op - Low

St. Johns River Water M a nagem e nt Distr i ct 

### 53

### Figure 32 (cont.). Total dissolved P at Fulton Point, 1997 < 2001.



## c. 1999

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16

12/31/ 98 3/1/ 99 4/ 30/99 6/ 29/99 8/28/ 99 10/ 27/99 12/ 26/99Total Dissolved P, mg/L B o t t om - Hi gh

B o t t om - Lo w

Mi d - H i g h

Mi d - L o w

To p - H i g h

To p - L o w



## d. 2000

0 0.02 0.04 0.06 0.08

0.1 0.12 0.14 0.16

12/26/ 99 2/ 25/00 4/26/ 00 6/26/ 00 8/ 26/00 10/26/ 00Total DissolvedP, mg/L B o t t om - Hi gh

B o t t om - Lo w

Mi d - H i g h

Mi d - L o w

To p - H i g h

To p - L o w

St. Johns River Water M a nagem e nt Distr i ct 

### 54

### Patterns in Oxygen Deficits

Persistent, low concentrations of dissolved oxygen in the m e so/polyhaline reach of the

LSJR are a well documented but poorly unders tood phenomena. First studied intensively

in the 1950Es, these occurrences were attribut ed to the discharge of untreated dom e s tic

sewage and industrial waste (Pyatt, 1964). Des p ite large improvem e nt s in point source

treatm ent, the occu rren ce and severity of these episodes has rem a ined unchanged over

tim e (Figure 32). Intensifi cation of m onitoring of di ssolved oxygen since 1996, the

com p rehensive exam ination of external load sources, and the current level of

understanding of the m a nifestat ions of nutrient loading and estuarine eutrophication have

now helped to clarify our unders tanding of these events.

To better describe the short-term fluctua tion in dissolved oxygen associated with tide

stage, diurnal photosynthesis patterns and inte rmittent reverse flows, the U.S. Geological

Survey established a series of continuous, autom a ted dissolved oxygen stations in the

fresh and m a rine reaches of the LSJR (s ee m a ps Figures 2 and 21). Stations are

instrum e nted with tem p erature, salinity a nd dissolved oxygen sensors and configured to

collect at tw o to th ree v e rtical positions at hou rly intervals. The daily av erage d i ssolved

oxygen data from the monitoring stations at Da m e s Point and the Acosta Bridge are

shown in Figure 33. From the annual tim e series plots of Figur e 33, annual m i nimum

dissolved oxygen concentrations can be seen to occur be tween July and September,

coincident with the annual m a xi mum te m p eratures and m i ni m u m oxygen saturation

concentrations.

Lower levels of dissolved oxyge n are consistently seen at the Dam e s Point station. For

the 21⁄2-year record at Da m e s Point fr om early 1996 through Septem ber 1999, oxygen

concentratio ns were b e lo w 5 m g /L 15 percen t of the tim e at the su rface and 35 percent of

the tim e in the near-bottom water (F igure 35). Over the sam e ti m e period, the gauge at

Acosta Bridge exhibited below 5 m g /L oxygen concentrations only 1⁄2 percent of the tim e
at the surface and 4 percent of the tim e in near-bottom water. Extrem e low dissolved

oxygen levels (< 2 m g /L) occur rarely, with th e 1 percentile daily m ean concentration f o r

St. Johns River Water M a nagem e nt Distr i ct 

### 55

### Figure 33. Com p arison with hi storic (1961-65) m easure m ents shows no change in m ean monthly dissolved oxygen levels



## LSJR at Jacksonv i l le

2 3 4 5 6 7 8 9 10

F eb. Apr

. Jun. Aug

. Oct. D e c.Mean Monthly D.O., mg/L 

### M a i n St., 19 61- 65

Ac osta Br

., 1996- 01

D a m e s Pt., 1996- 01

St. Johns River Water M a nagem e nt Distr i ct 

### 56

### Figure 34. Mean daily dissolved oxygen con centrations measured at USGS autom a ted monitoring stations at Acosta Bridge a nd Da mes Point, Mid-depth, 1996 through 2001. Lines with sym bols are the obs erved data. Finer, solid un -symboled lines are the oxygen
concentrations for based on m ean daily m i d-de pth salinity and tem p erature. Horizontal red line corresponds to the water quality s t andard of 5 m g /L daily m ean of F.A.C. 62-302.



## (a) 1996

2 3 4 5 6 7 8 9 10 11

1/ 1/ 1996 3/ 1/ 1996 4/ 30/ 1996 6/ 29/ 1996 8/ 28/ 1996 10/ 27/ 1996 12/ 26/ 1996mg/L



### Da me s Pt.

Aco s ta Br

.



## (b) 1997

2 3 4 5 6 7 8 9 10 11

12/ 31/ 1996 3/ 1/ 1997 4/ 30/ 1997 6/ 29/ 1997 8/ 28/ 1997 10/ 27/ 1997 12/ 26/ 1997mg/L

Dam e s Pt Meas ur ed.

Ac os ta Br . Meas ur ed

St. Johns River Water M a nagem e nt Distr i ct 

### 57

### Figure 34 (cont.). Mean daily m i d-depth di ssolved oxygen concentrations m easured at

USGS autom a ted m onitoring stations at Acosta Bridge and Da m e s Point, 1996-2001.



## (c) 1998

2 3 4 5 6 7 8 9 10 11 12

12/ 31/ 1997 3/ 1/ 1998 4/ 30/ 1998 6/ 29/ 1998 8/ 28/ 1998 10/ 27/ 1998 12/ 26/ 1998mg/L



### Dam e s Pt.

Acosta Br.



### (d ) 1999

2 4 6 8 10 12 14

12/ 31/ 1998 3/ 1/ 1999 4/ 30/ 1 999 6 / 29/ 1999 8/ 28/ 1999 10/ 27/ 1999 12/ 26/ 1 999mg/L



### Dam e s Pt.

Aco s ta Br

.

St. Johns River Water M a nagem e nt Distr i ct 

### 58

### Figure 34 (cont.). Mean daily m i d-depth di ssolved oxygen concentrations m easured at

USGS autom a ted m onitoring stations at Acosta Bridge and Da m e s Point, 1996-2001.



### ( e ) 2000

2 3 4 5 6 7 8 9 10 11 12

1 2 / 3 1 / 1 9 9 9 2/ 29 / 2 00 0 4 / 2 9/ 20 00 6 / 2 8 / 2 0 0 0 8 / 2 7 / 20 00 1 0 / 2 6 / 2 0 0 0 1 2 / 2 5 / 20 00Dissolved Oxygen, mg/L



### Da m e s P t

. A

c o s ta B r

.



### (f

) 2 0 0 1

2 3 4 5 6 7 8 9 10 11 12

1 2 / 3 0/ 20 00 2/ 28 / 2 00 1 4 / 2 9 / 2 0 0 1 6 / 2 8 / 2 0 0 1 8 / 2 7 / 20 01 1 0 / 2 6/ 20 01 1 2 / 2 5 / 2 0 0 1Dissolved Oxygen, mg/L



### Da m e s P t

. A

c o s ta B r

.

St. Johns River Water M a nagem e nt Distr i ct 

### 59

### Figure 35. Cum u lative frequency distributions of m ean daily dissolved oxygen for USGS

autom a ted stations at Acosta Br. and Da m e s Point.

A c os ta D a ily D i s s o lv e d Ox y g e n Fr e que nc y D i s t r i bution

0 10 20 30 40 50 60 70 80 90 100

2 3 4 5 6 7 8 9 1 0 1 1 1 2



### C onc e n tr a t ion, m g /L D .O.Cumulative Frequency 

## Surface

Middle

Bottom

Dam es P t

. Dai l y Di ssol v ed Oxygen Frequency Di stri buti o n

0 10 20 30 40 50 60 70 80 90 100

234 5678 9 1 0



### Concentrati on, m g / L D. O.Cumulative Frequency 

## Surface
Middle
Bottom

St. Johns River Water M a nagem e nt Distr i ct 

### 60

### Da m e s Point being 3.8 mg/L. Vertical oxygen stratification is not strongly exhibited,

with the m ean difference between s u rface a nd m i d sensors, and between m i d and bottom

sensors at Dam e s Point being 0.34 mg/L a nd 0.30 m g /L, and at Acosta being 0.26 mg/L

and 0.17 m g /L. The longitudinal pattern in dissolved oxygen concentration is stronger

than the vertical (Figure 35(a)), and tends to exhibit an oxygen m i nim u m zone between

river m ile 15 (10 m iles upstream of the m outh) and river m i le 20.

Exam ination of oxygen saturation defici t (oxygen saturation deficit = saturation

concentration P observed concentration) allows for the comparison of oxygen dem a nd

without the effect of salinity and tem p erat ure. The difference between oxygen saturation

deficit at Acosta Bridge and D a m e s Poin t is significant, but exam ination of the

distribution of saturation deficit (F igure 36) reveals that the difference is due to the

tendency for lower values (i.e., greater inst an ces of near saturation or even supersatura tion ) to occur at th e Acosta Bridge site. The intensity of severe satu ration def i c i t is

sim ilar for both locations, i ndicating that the lower oxygen levels at Da m e s Point are

largely due to greater salinity.

The am ount of algal biom ass present, and the rate of expansion or contraction in the

phytoplankton community, is significantly co rrelated to the general level of oxygen

saturation deficit. The degree of this c ontrol is de m onstrated in Figure 37, which

com p ares the rate of change in chlorophyll a between sampling da te s to the ox ygen

deficit observed for these events. E xpansion in the algal co mmunity can be seen to be

significantly, negatively correlated with the oxygen saturation deficit existing on a given

sam p ling day, while contraction in the com m unity is a ssocia t ed w ith incre a se s in

saturation deficit. The per unit change in oxygen saturation deficit for a given am ount of

chlorophyll a change between consecutive sam p ling ev ents is not significantly different

between Acosta Bridge and Dam e s Point (i.e ., slopes and intercep ts not significantly

different). Large, posi tive changes in chlorophyll a are not typically s e en at the Dam e s

Point station

, and this is consistent with the lack of condition s of oxygen super-s aturation

m easured at this location. The intercep t of this relationship, 1.54 m g /L oxygen

St. Johns River Water M a nagem e nt Distr i ct 

### 61

### Figure 36. Longitudinal diss olved oxygen saturation pattern in the Meso/Polyhaline
LSJR. Data are from Summer 1997 am bient m o nitoring program s

.



### (a ) Ox y g e n C o n c e n tr a t io n

4. 5

5 5. 5

6 6. 5

7 7. 5

0 5 1 0 1 5 20 25 30 35



### R i v e r M ileMean Dissolved Oxygen,mg/L



### (b ) P e rc e n t S a t u ra ti o n

70 75 80 85 90 95 10 0

0 5 10 1 5 2 0 25 30 3 5



### R i v e r M ileMean Oxygen % Saturation

St. Johns River Water M a nagem e nt Distr i ct 

### 62

### Figure 37. Distribution of daily mean oxygen saturation deficit for Acosta Bridge and

Dam e s Point in th e LSJR near Jacks onville.

Ox y g e n Sa tura tion Defic i t = Sa tura tion - Obs e r v e d

0 10 20 30 40 50 60 70 80 90 100

- 2

- 1 0 1234

S a tu rati o n Defi ci t, m g / L% of Time Greater Da m e s Po i n t

Ac o s ta Br.



### Figure 38. Relationship between the Directi on and Magnitude of Change in Chlorophyll

a and the S a m p ling Da y Oxygen Saturation Defi cit at Dames Point and Acosta Bridge. Chlorophyll a change rate dete rm ined as the dif f e rence between sampling dates / tim e inte rval f o r

water m a sses of equal salin ity. W a ter m a ss equal salin ity chlo roph yll a concentration determ ined by interpolation be twe e n bracke tin g salin ities. Regression line
determ ined for com p lete data set; individual regression lines not si gnif i cantly different.

Determ inations m a de for June M Septem ber sampling dates from 1996 through 2000, with the exception of 1999, when Oct ober and early Nove m b er data were included to include an event of significant oxygen supersaturation.

St. Johns River Water M a nagem e nt Distr i ct 

### 63 -2 -1 .5

-1 -0 .5 0 0.5

1 1.5

2 2.5

3 3.5

-2 -1 0 1 2 3

Da ily Ra te of Chlor ophy ll a Change, mg/m 3 /daySampling Day Oxygen SaturationDeficit, mg/L Ac o s t a B r

. Dames Po in t

O 2 S a tu rati o n Def. = -0. 97*(Ch l -a Change Rate) + 1. 54 S a tu rati o n Defi ci t

Su

p ersaturati o n

### saturation deficit, is interesti ng and suggests that the St. Johns River in this reach tends to

m a intain a background level of respiration in excess of production.

The overall relationship of Figure 37 suggests that over two thirds (R 2 

### = 0.68) of the

variation in oxygen saturation deficit can be accounted f o r by chan ges in the algal

community. The short-term changes in oxygen saturation deficit were also com p ared to

the occurrence of rainfall and s t ormwater run o ff events. W h ile on som e occasions,

oxygen saturation deficit does appear to incr ease in days f o llowing storm events, this

effect is not consistent, and c ould not be distinguished from other cyclic factors (such as

tide reversals) or secondary effects on the phytoplankton co mmunity (such as tem porary
turbidity or color increases that m i ght re duce the photosynthesis/re spiration ratio).

The prevailing salinity regim e in the narro w, Jacksonville reach of the LSJR (the 25 th 

### and

75 th 

### percentile values of da ily m ean salinity at Da m e s Poi n t from May 1996 through

Septem ber 2001 were 20.3 and 27.6 psu), and th e longitudinal trend in phytoplankton

community com positio n changes (as shown in Figures 22 (a) and (b); m a ximu m
community com positio n change occurr ing between 18 and 25 psu) leads to the

conclus i on that this re ach of the river is f r e quently the location of rela tiv ely sharp

transitions in the algal comm unity. Expected with the decline of out-flowing, fresh and

oligohaline phytoplankton communities, or in flowing m a rine comm unities, would be

increased algal resp iration, senescence, a nd decom position, leading to increases in

oxygen deficit. In add ition, th e narrower and m o re turbulent chann e l in this reach

trans l ates to a reduction of the cross-secti onal area of photic zone and an overwhelm ing

of light-enhancing vertical m i gr atio n adapta tion s in the a l g a e. I t shou ld the r ef ore be

expected tha t as alga l biom ass incre a ses, ra tes o f algal community decline will inc r ease,
as will associated oxyg en defic its in this river zo ne.

In summ ary, salt- t ole r ant and marine alg a l comm unities pr esent f r om the r i verXs

oligohaline front to the m outh appear capable of exploiti ng nutrient loads, at tim e s
leading to a dverse wate r quality co nditions . As has been commonly docum ented for

other eutrop hic estua r ie s , augm ented algal growth in the LSJR ultim ately m a nif e sts in

St. Johns River Water M a nagem e nt Distr i ct 

### 64

### lowered dissolved oxygen, and levels below the st ate standard of 5 m g /L daily average or

4 m g /L instantaneous value are commonly obser ved during summ er and early fall. The

degree of nutrient exploitation and eutrophicat ion-related water quality problem s appears
dependent on a com p lex m i x of factors: river flow, stability of salinity regim e , gradients

in the phytoplankton comm unity due to sa linity stress, hydrodynamics and channel

morphology. Due to th is m i x of factors, b l oom s within th is reach are neither as regu lar

nor predictable as seen for the freshwater river. The near-coastal region outside the

mouth of the river, pres um ab ly due to m o re favorable ligh t and hydrody nam i c conditions,

exhibits m o re com p lete utiliza tion of rive r nutrient loads by al gae, and frequently

supports higher biom ass than is seen in th e m e so-polyhaline river. These off-shore

bloom s m a y at tim e s be im ported into the rive r and contribute to water quality problem s

. In addition to instigating oxygen deficits, th ere is som e suggestion that the supply of

nitrogen and phosphorus in excess of bioavaila ble silica concentrati on m a y lead to the

increase in relative abundance of problem a tic dinoflagellate species in the phytoplankton

community.

St. Johns River Water M a nagem e nt Distr i ct 

### 65

### IMPAIRMENT TARGE T S FOR IDENTI FYING TMDL AND PL RG NUTRIE N T

REDUCTIONS

Background

Som e m easure of the three m o st c o mm only identif ied water qua lity ef f ects of estu arine

eutrophicationFnuisance levels of algal biom ass, reduced dissolved oxygen and reduced

transparency Fwere recomm ended in the orig inal Plan d o cum e nt as the respo n se

variab les in estab lish i ng nutr i ent T M DLs and PLRGs for the LSJR. T h ese TMDL and

PLRG targets were originally established consis tent with standards or thresholds set forth

in Chapter 62-302, F.A.C. , the Florida State water quality standards, and Chapter 62-303,

F.A.C ., the TMDL listing cr ite ria f

o r im paired su rface waters. In th e process of data

analysis and investigation to describe nutri ent enrichm e nt effects and to quantify these

relationships through water quality modeling, th ese targets have undergone refinem e nt in

order to m o r e closely address th e m o st problem atic aspects of eu trophication in the LS JR.

Relevant questions driving the refinem e nt of targets were:

1) Is the dissolved oxygen State standard sufficiently protective, or conversely,

unrealistically protective, for biota en dem i c to the LSJR?

2) Is the m a i n tenance of transparency, based upon ope n water changes in

com p ensation depth, relevant to S AV health and re-colonization?

3) Does a m ean annual chlorophyll a target sufficiently address acute effects of

extrem es in algal b i om ass chara c te ris tic of episod ic, in tense b l oom s ?

Because of the weak linkage betw een open water phy toplankton light attenu ation (the

concept of which is more closely em bodied i n the transparency standard as stated in

F.A.C. 62-302) and the m o re realistic case of ep iphytic algal attenu ation for littoral

subm erged grasses, it was fe lt that th e transp arency criteria could n o t be sufficiently

justif ied f o r protec tion o f SAV in the LSJR. Investig ation s rela ting nutr i ent enr i chment

ef

f ects to SAV health, and the inte r action s between natura l f actors of lig ht, color, salinity

and substrate are ongoing and can be used to revise the LSJR nutrient TMDL in

subsequent iterations if warrant ed. In light of the great am ount of research in support of

St. Johns River Water M a nagem e nt Distr i ct 

### 66

### oxygen criteria, and the recent work accom p lished in com p iling and refin i ng th is research

in EPA:s A m bient Aqua tic L ife Wa ter Quality C r iter i a for D i ssolv ed Oxy g en ( Saltwater) :
Cape Cod t o Cape Hat t eras , (U.S. EPA, 2000) it was felt that the effort necessary to

modify this guidance approach f o r the LSJR was not warranted. Theref ore,

m e thodologies provided in this guidance ha ve been relied upon for establishing algal

biom ass targets for the predom inantly m a rine reach of the river. These m e thods apply a

less restrictive criteria for m a intenance of aquatic life based on dissolved oxygen than the

current Florida State Standard, and is arguabl y more realistic given the natural stressors

to oxygen level in a southern temperate bl ackwater river estuary. And finally, as

experim e ntal evidence suggests that the greate st level of harm from algal bloom s oc curs

from extrem e bloom events, the chlorophyll a targ ets for the LSJR were redefine d to

em phasize the reduction of high concen tration, long duration events.

LSJR Freshwater Targe t s: Phytop lankton Community Composition Dy namics, Zooplankton Interactions and Algal Toxin Production Potential

Freshwater LSJR TMDL and PLRG targets o n which to base nutri en t load redu c tions

have been founded prim arily on the goal of enhancing plankton ecology. This approach

was taken b ecause 1 ) th e LSJR is largely a plan kton based s y stem , with the m a jority of

its autochthonous carbon produced thr ough phytoplankton prim ary production; 2)

diversity in plankton asse m b ledges, and the enhancem ent of energy tran sfer from

phytoplankton to zooplankton was assum e d to translate to greater abundance and

divers ity in the f i sh comm unity; and 3) a large data base com pose d of 5 years of

phytoplankton and zooplankton monitoring data exists for the LSJR, representing the

most powerful biological evaluation tool ava ilable. For the freshwater river, th re e

elem ents of plankton ecology were assessed:

1) Are there levels of algal biom ass at wh ich diversity in the plankton community is

significantly reduced, i.e., the point of m onospecific bloom form ation?

2) What m a xi mum levels of algal bi om ass, or what phytoplankton community

com position, is associated with the greatest levels of zooplankton abundance and

diversity, and, presum ably, the greatest upward transf er of planktonic prim ary
production to higher tr ophic levels?

St. Johns River Water M a nagem e nt Distr i ct 

### 67

### 3) What levels of algal biom ass m i ni m i ze the potential for the expansion of

detr im ental algal species or the production of algal toxins?

Freshwater LSJR Algal Biomass Criteria

Maintenance of Phytoplankton Diversity

The m a intenance of organism diversity is a fundam e ntal goal of bi ological restoration.

Diversity in biological syst em s promotes stability; conve rsely, ecosystem s with narrow

species diversity are prone to large perturbations in co mm unities (W etzel, 2001). The

loss of phytoplankton diversity, and the dom i na nce of cyanobacteria during the spring

and summ er growth seasons is one of the m o st conspicuous aspects of freshwater bloom s
of the LSJR. As total phytoplankton co mmunity biom ass (expressed as chlorophyll a )

increases, the fraction of the to tal comm unity biom ass com posed of blue-greens

(determ i ned from biovolum e estim a tes) incr eases (Figure 38). Blue green relative

com position is variable and often low for chlorophyll a concentrations to about 40

mg/ m 3 

### . Aft e r this point, blue green biom ass represents the m a jo rity of phytoplankton

community com position. At chlorophyll a concentration above 60 m g /m 3 

### , blue green

rela tive abu ndance is co nsisten tly between 80 to 90 percent.

Facilitation of Upward Trophic Transfer of Primary Production

The Chesapeake Bay Water Quality Criteria Guidance Manual (CBP 2002) outlines an

approach to the developm ent of chl o rophyll a criteria for the purpose of enhancing the

upward transfer of phytoplankton carbon to th e zooplankton comm unity. The conceptual

model utilized in the C h esapeake Bay Guid ance relating m e sozooplankton response to

increases in algal b i om ass is depicted in Figure 39. This model is based on a number of

investigations that have de m onstrated the decline of various m e sozooplankton species in

blue-green algal bloom s, believed due princi pally to the presence of noxious com pounds

in certain cyanobacteria (Paerl et al., 2001; DeMott and Moxter, 1991; Fulton, 1988).

At low to moderate phytoplankton densities, zooplankton populations respond favorably

St. Johns River Water M a nagem e nt Distr i ct 

### 68

### Figure 39. Relationship between blue green relative abundance based on biovolum e and chlorophyll a for LSJR Freshwater Stations, N ov. 1997 C O c t. 2001. P i colata represented by the W a tson Island monitoring station in 2000 and 2001 due to high salinity conditions at Shands Bridge. Data from Phlips and Cichra, 2002.

B l ue- G reen R e lat i v e A b undance

0 20 40 60 80 100

0 4 0 8 0 120 160

C h lorophy ll- a, m g /m 3% Blue-green Composition

Rac y Poi n t

Pal a t k a

Pi c o l a t a

I :\\es data\l s j \ U F = P l a n k ton I D \ D a ta\Z oo- P h y t o_C om p.x l s


### Figure 40. Conceptual model relating m e soz ooplankton response to increases in algal
biom ass. In average (A) and best (E) wate r quality conditions, zooplankton increase with increasing algal food. Zooplankt on increase ceases at some algal biom ass (B), at which point increases in algae resu lt in lower zooplan kton due to the predom inance of harmful or unpalatable species and f eeding interference (C1 and C2). Reprinted from the Chesapeake Bay Chlorophyll a Criteria Guidance Manual (CBP 2002).

St. Johns River Water M a nagem e nt Distr i ct 

### 69

### and increase with increase in algal biom ass associated with increase in f ood supply. At

som e point, however, the increase in toxi c or otherw ise unpalatable taxa in the

phytoplankton community, and an increase in feeding effort due to the density of

unfavorable species, leads to a lev e ling off and perhaps even decline in the desirable

zooplankton. The point of the departure from the linear increase in zooplankton >

phytoplankton biom ass represents the m a xi m u m tolerable algal biom ass.

Plankton monitoring data (Nov. 1996 through Oct. 2001) were exam ined to determ ine i f

a relationship sim ilar to that described a bove existed for the freshwater LSJR. The

zooplankton > algal biom ass relationship is shown in Figure 40. Desirable zooplankton

in these graphs are estim ated by summi ng the organism counts for copepods and

cladocerns only. Rotifers ar e excluded, as th ey are belie v ed to b e feeding on s m all

detrital particles and bacteria, and are not as im portant a group of zooplankton in

supporting the upward transfer of phytoplankt on carbon to the fish community. Although

a good deal of spread exists in this graph in zooplankton abundance at low to m oderate

chlorophyll a concentration, it is possi ble to discern a pattern th at m a tches the conceptual

model forwarded by the Chesapeake Bay guidan ce. This graph suggests that the linear

increase in zooplankton abundan ce with increasi ng chlorophyll a concentration begins to

decline somewhere between chlorophyll a concentrations of 40 to 60 m g / m 3 

### . The

adverse response of zooplankton numbers to high levels of al gal biom ass can be seen in

Figure 41 for the specific case of th e severe alg a l bloom s th at occurred at Racy Po int in

1999. At this station, zooplankton number s increase initially as chlorophyll

concentration increases, but then decline as chlorophyll c ontinues to increase. This

pattern is repeated for th e yearTs second bloom , which peaks in late August.

Algal Toxin Formation Potential

Paerl and Carm ichael (2002) examined levels of the algal toxins m i crocystin, anatoxin, and cylindrosperm opsin in nutrient enrichm e nt assays perfor m ed on LSJR sa m p les
collected from October 2000 thr ough August 2001. All toxins were detected during the

sam p ling, with m i crocystin present in ev ery assay. Microcystin was found to be

St. Johns River Water M a nagem e nt Distr i ct 

### 70

### Figure 41. Relationship between total chlorophyll a and the sum of copepod and
cladoceran abundance for LSJR freshwater stati ons at Palatka, Racy Point, Lake George and Shands Bridge/W atson Island. Data from Nov. 1996 through Oct. 2001. Green curve drawn through visual interpolation. Data from Phlips and Cichra, 2002.

L S JR F r esh

y = - 0

. 0619x 2 + 11. 347x - 41. 958

R 2 = 0. 5348

0 100 200 300 400 500 600 700 800 900 1000

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0

T o t a l C h lorophy ll- a, m g /m 3Copepods + Cladocerns, #/ml 

### Racy Pt. Pal a tka Shands, W a tson L. Geor g e

Figure 42. Annual tren d in chlorophyll a , total rotifer abundance, and the Copepods +
Cladoceran abundance f o r the Racy Point St ation in the Freshwater LSJR, 1999. Data
from Phlips and Cichra, 2002.



### 1999

0 20 40 60 80 100 120 140 160

12/ 31/ 1998 3/ 1/ 1999 4/ 30/ 1999 6/ 29/ 1999 8/ 28/ 1999 10/ 27/ 1999 12/ 26/ 1999Chlorophyll a, mg/m3or Zooplankton, #/ml Chl o rophyl l a

R o tife r s /1 0 0

Copeds

. + Cl ads

. / 1 0

I :\\esdata\l s j \ U F

- P l ankt onI D \ VOLU M E _AN A LY SI S2.xl s

St. Johns River Water M a nagem e nt Distr i ct 

### 71

### Figure 43. Microcystin con centrations determ ined in nutrie nt addition assays perf orme d
on freshwater Lower St. Johns River am bient water sam p les. From Paerl and
Charm i chael, 2002.

J u l 2000 y = 1. 4729x - 3. 879

R 2 = 0. 5836

Oc t 2000 y = 0. 0598x + 0. 1293

R 2 = 0. 5193

Feb 2001 y = 4. 9168x - 38. 112

R 2 = 0. 9053 A p r 2001 y = 3. 2444x - 26. 315

R 2 = 0. 7892

J u l 2001 y = 0. 5338x + 106. 14

R 2 = 0. 0983

A ug 2001 y = 2. 2215x + 261. 23

R 2 = 0. 2186

Oc t 2001 y = -0. 0272x + 5. 1031

R 2 = 0. 0124

0 100 200 300 400 500 600 700 800

0 2 0 4 0 6 0 8 0 100 120 140 160 180

Chlorophy ll a , mg/m 3Microcystin, nanog/L J u l 2000

Oc t 2000

Feb-01

A p r-01

Ju l

- 0 1

A ug-01

Oc t

- 01

I:\\e s d a t a \ l s j \ U F

- P l a n k to n

- ID \a l g a l

- t o x .x l s



### positiv ely correlated to chlorophyll a in all assays, and the relationships are show n in

Figure 42. Generally, m i crocystin le vels rem a ined low for chlorophyll a concentrations

below 40 μg/L. Above this level, m i crocystin levels were found to be variable, but on

occasion reached very high lev e ls, near th e World Health Organization s t andard for

drinking water of 1 μg/L . The LSJR is not a drinking water source, and relevance of this

standard for the protection of aquatic life has not been quantified. Extrem ely high

concentrations of m i croc ystin have, none the le ss, been m easured in the St. Johns and its

tributary m ouths. During one bloom respons e sam p ling in DoctorTs Lake, m i crocystin

concentrations were determ in ed at concentrations rangi ng from 157 to 211 μg/L (Green

Water Lab, 2002). The result of these assay ex perim e nts suggests that at concentrations

of chlorophyll a that ex ceed 40 μg/L, the poten tial for the appearance of m i crocystin in

am bient water increas es greatly.

St. Johns River Water M a nagem e nt Distr i ct 

### 72

### Algal Bloom Duration

Plankton m onitoring data and alga l toxin assays indicate that blue green algal bloom s of

the LSJR fr eshwater reach exhibit d e trim enta l effects when bloom biomass, m e asured as

chlorophyll a , exceeds 40 m g / m 3 

### . To exam ine the effect of bloom duration on desirable

zooplankton, the num bers of copepods and cl adocerans in sam p les collected during

bloom s were com p ared to the durati on of the bl oom in excess of 40 mg/ m 3 

### chlorophyll a
(Figure 43). For bloom s in excess of 40 m g /m 3 

### chlorophyll a that exceed 40 days,

num b ers of copepods and cladocerans are no ticeably reduced. Between 20 to 45 percent

of bloom s within the fres hwater reach exceed ed this duration (Fi gure 20). The m a xi mum

concentratio n that is achieved with in a bloom is signif i c a n tly cor r ela t e d to the bloom

duration (F igure 44). B a sed on the linear reg r ess i ons r e la tin g bloom duration to intensity,

m a xi m u m concentrations achieved by a bloom of 40 days range between 50 to 74 mg/m 3



### chlorophyll a , with a m e an of 67.5 mg/m 3



### .

Using the Racy Point station, it is possibl e to synthesize a distribution of chlorophyll a
that hypo thetically would m eet the conditions for the m a intenance of ph ytoplank t on and

zooplankton diversity. T h is was done by proporti onally scaling the stat istical distribution

Figure 44. Num b ers of Copedod and Cladocer n zooplankton in sa mples collected in algal blooms of greater than 40 m g / m 3 

### as a func tion of the duration of the bloom

.

Zooplankt on A bundance vs. D u r a t i on of C h lorophy ll a > 40 m g / m 3

0 100 200 300 400 500 600 700 800

0 2 0 4 0 6 0 8 0 100 120 140 160 180 200

Du r a ti o n , Day sCopepods + Cladocerns, #/ml 

### Racy Point

L. G eor g e O u t l et

Palat k a

St. Johns River Water M a nagem e nt Distr i ct 

### 73

### Figure 45. Bloom m a ximum chlorophyll a concentration as a function of bloom duration
for freshwater sam p ling stations of the LSJR, 1994-2001.

Bl o o m M a x i m u m Ch l o r o p h yl l a x Du r a t i o n > 4 0

y = 0. 8362x + 40.602

R

2 = 0.568 y = 0.4491x + 38. 809

R

2 = 0.7712 y = 0.5991x + 47. 769

R

2 = 0.4174 0. 0 20. 0 40. 0 60. 0 80. 0 100. 0 120. 0 140. 0 160. 0 180. 0

0. 0 20.0 40.0 60.0 80. 0 100.0 120.0

D u r a t i o n > 40 m g / m 3

, d aysBloom Max Chlorophyll a, mg/m3 

### R acy P t

. Fe de r a l P t

. W

a t s on Is l.



### of the existing data (shown in Figure 45 by th e dark navy blue line; the natural log of

chlorophyll a is used to norm a lize the distribution) to for m a new, distribution (Figure 45

light blue line) for which: a) the 1 percen tile o ccurrence w a s the sam e as the observed

data (reflecting the assump tion that m i nim u m chlorophyll a values w ould rem a in the

sam e if nutrient load were reduced); b) th e population variance was reduced such that the

synthetic, new distribution has a 99 th 

### percen tile o ccurrence ( p = 0.01 for a one tailed test)

equivalent to a chlorophyll a of 74 mg/ m 3 

### . This synthesized di stribution has a m ean of

20.1 m g / m 3 

### , a variance of 0.56 m g /m 3 

### , and a 10.6 percent occurr ence rate for chlorophyll

a concentrations greater than 40 mg/m 3 

### . The synthesized di stribution thus suggests

fairly good agreem ent between a not to be exce eded level of 10% for bloom s in excess of

40 m g / m 3 

### , a nd the m ean concentration of 20 m g /m 3 

### of the recently pro m ulgated T M DL

listing ru le o f F.A.C . 62- 303.

St. Johns River Water M a nagem e nt Distr i ct 

### 74

### Marine LSJR Dissolved Oxygen Criteria

Dissolved O xygen Effects

As dem onst r ated in the previous section out lin in g eutroph ica tion ef f ects, low dissolv ed

oxygen excursions (persistent episodes below the State criteria of 5 m g /L) occur in both

the freshwater and oligo/m e sohaline reach es of the LSJR. These episodes occu r

coincid e nt with high s u mm ertim e tem p eratures , and app e ar to be ass o ciated with th e
decline or crash of significant algal bloom s. The im prove ment of the dissolved oxygen

regim e for the river and estuary was one of th e origin ally stated ob jec t ives of the T M DL

and PLRG plan for th e riv e r, and the S t at e standard of 5 m g /L (instantaneous for

freshwater reaches, and as a daily averag e for predom inantly m a rin e reach es) was

identified as the target on which to base nutrient reduction scenar io m o deling. Even at

the tim e of the propos ition of this target, however, cons iderab le un certainty ex isted

regarding its appropriateness and achievab ility. Low dissolved oxygen episodes have

long been known to occur in southeast U.S. estuaries (Schroeder and W i se m a n, 1988),

and naturally low dissolved oxygen concentr atio ns are a co mmonly accepted featu r e of

blackwater river system s. For these reasons, e ffort ha s be en dire cted to ward refin i n g an

oxygen reg i m e that is based upon the levels necessary for the protection of nativ e
estuarine fish and invertebrate species.

As an alternative to the fixed standard of 5 m g / L , the procedure described in the recently

published U

. S. Environm ental Protection Agency Guidance, Ambient A quatic L ife Water

Quality Criteria for Dis s olved Oxyg en ( Saltwater) : Cape Cod to Cape Hattaras , (U.S.

EPA, 2000) has been used to define the di ssolved oxygen target on which reductions of

algal biom a ss, achieved through nutrient load reduction, can be based. The Guidance is

built upon the established tolera nces of fish and invertebra tes present in the estuarine

environm ent to low oxygen episod es. In its approach, the Guidance establishes an

absolute m i nim u m oxygen level for the protec tion of m o st estuarine sp ecies agains t low

concentratio ns that resu lt in acute organism mortality, and establishes above this level a

sub-le thal ra nge that resu lts in reductions in growth and recruitm ent, and with this,

St. Johns River Water M a nagem e nt Distr i ct 

### 75

### Figure 46. Observed and synthesized distributions for total chlorophyll a at Racy Poin t in the freshwater LSJR. Observed data based on sam p ling from 1994 through 2001; n =

191.

Rac y Pt - RKm 100

0 10 20 30 40 50 60 70 80 90 100

1. 2 1

. 4 1. 6 1

. 8 2 2

. 2 2. 4 2

. 6 2. 8 3 3. 2 3

. 4 3. 6 3

. 8 4 4

. 2 4. 4 4

. 6 4. 8 5 5. 2



### Ln ( C hl o r ophy l l a , m g /m 3 

### )Percent Rank



### presum ably fish health and survival probabilit y. Fish community ef f ects within th is subletha l range are ba sed up on the inten s ity and duration of hypoxic events. The Guidance

also offers approaches for assessin g eff ects of two common types of low dissolved

oxygen common to eutrophic estuaries: persiste nt, low dissolved oxygen associated with

late season algal bloom decline; and diurnal patterns of low oxygen associated with high

algal standing stock photosynthesis and respir ation cycles or tidal transport of low

oxygen water m a sses. In the LSJR, the m o st comm on and severe low oxygen episodes

within th e o ligo/m e sohaline reach are pers isten t events associated with late season algal

community declin e, and the Guidance procedure for assessing these typ e s of events has

been used to define oxygen targets.

Organism Acute Oxygen Levels

The data set used in the Guidance to develop criteria m i nim u m concentration (CMC) was

assim ilated from previous studies that exam in ed species o r g e nus-specific survival u nder

continuous low dissolved oxygen exposures. Th ese studies covered 12 invertebrate and

St. Johns River Water M a nagem e nt Distr i ct 

### 76

### 11 fish estu arine species, m o stly at juvenile life stages. Of these 23 species, 12 are

known to inhabit estuarine waters of north east Florida, based upon sa mpling perform e d

by The Florida Marine Research In stitu te (FM R I, 2002), Coas ta Shelf Associates (CSA

Inc., 1993) and W h itney Marine L a b (Table 4). From the FMRI non-gam e fisheries

monitoring data (FMRI, 2002) a trend is evident between the num b ers of individuals of a

given species present, and the low oxygen LC50 value of the Guidance , in that a s an
individual species low dissolved oxygen tolera nce decreases, its abundance declines in

the northeast Florida sampling reg i on. A num ber of factors cou l d account for this,

including species natura l ranges, sa m p ling m e thodol ogy, m i gration patterns or

com p etitive interaction s , though the possib i lity that thes e s p ecies are excluded du e to

prevailing low dissolved oxygen, either as a natural occurrence or through accelerated

eutrophication, should be considered as a potential contributing factor.

Following the procedure established in th e developm ent of toxics criteria, the Guidance

adjusts the CMC upward to es tim ate an LC5 concentration, using th e m ean LC5/ LC50

ratio for all studies, applied to th e most sen s itive species m ean acu te value (SMAV). In

the stud ies c o m p iled in the Guidance , pipe fish ( Syngnathus fuscus ), exh i bited the hig h est

SMAC, at an LC50 concentration of 1.63 m g /L. Pipe fish has been reported in northeast

Florida region in all sampling studies, albeit at low num b ers. Because of the num b er of

species p r es ent in North Florida in c o mm on with those lis te d in the Guidance , inclu d ing

the pre s ence of the m o st sensitive sp e c ies (pipe f i sh), the Guidance CMC value is viewed

as protectiv e for the LS JR. The Guidance CMC, determ ined as the product of the m e a n
LC5/LC50 ratio (1.38) and the m o st sensitiv e species LC50 (1.63 m g /L), is 2.3 m g /L.

Growth Effe cts

To develop a m easure of sub-acute e ffects due to low dissolved oxygen, the Guidance

relied upon previous studies that exam ined reductions in fish gr owth, usually during

larval or juvenile life stages, due to lo w dissolved oxygen concentration. Growth is

usually m o re sensitive than survival to low dissolved concentrations, though the

St. Johns River Water M a nagem e nt Distr i ct 

### 77Table 4

. S a lt wa t e r Ani m a l s Up on W h ic h Lo w Di ssol ved Ox ygen To ler a nc es of t h e EP A Salt wa t e r Di ss olved Oxygen Cri t e r i a

Ar e B a s e d T h a t Hav e B e en R e p o rt ed i n No r t h e a s t F l o r i d a

. S p eci es o c c u rr en ce d a t a f r o m F M RI (2 0 0 2 ) , C o as t a l

S h elf Associates, and f r om the Whi t ney La bo r a tory we b si te (ht t p: // www.whi t n e y.ufl.e d u/s p e c ies/avail a bl .h tm )

.

Sp ec ie s Co mmo n N a me FMRI W h itne y L a b CSA

, In c.

Pa laemonetes vul gari s m a r s h grass shrim p fr eq

Pa laemonetes p ugi o d a ggerblade gra s s shrim p f r e q
C

a l l i n e c tes sap idus b l ue cr ab 861 fr eq

Eu ry p anopeus depressu s f l a t

m u d cr ab x

Ri th ropa nopeus har ris i i Har r is mud cr ab x
C

r a sso str e a v i rg ini c a ea s t er n oys ter fr eq

L e ios t omu s x ant hur us s pot 433 3 f r e q f r e q

Pr ion o tu s t r i bul us b i ghea d s e a r ob in ge n u s

Br e v oort ia t y ra nnus At lanti c m e nh a d en 788 fr eq

Pa ral ichthys dentat us s u m m er floun de r 9 r a r e g e n u s Syngn ath us fus c us pi p e f i sh 1 r a r e g e n us

Mor one sa x a t i l i s s t riped ba s s fr eq



### Guidance notes several exceptions in which studies repo rt g r eater ra tes of mortality than

growth reduction. In general, inverteb rates exhibit low acute dissolved oxygen

concentrations, but a large ra nge in growth reduction. Fi sh, on the other hand, exhibit

higher acute concentrations but a relatively narrow range in growth reduction, and it is

not unusual for fish species to exhibit consid erable overlap in oxyge n levels that cause

mortality and growth reduction. Based upon a sm aller number of studies that reported

sim ilar redu ctions in rep r oductive su ccess at low dissolved o xygen levels, the Guidance

concluded that oxygen levels that are protective of growth e ffects would also likely be

protective of reproductiv e success.

Of the 11 species for which growth effects data were found, 5 have been reported in

FMRI, CSA, Inc. or W h itney Lab sampling, or are otherwise know to occur here at the

species level: summ er flounder ( Paralichthys dentatus ), sheepshead m i nnow
( Cyprinodon variegates ), striped bass (Morone saxa tilis), marsh grass shrimp

(Palaem onetes vulgaris), northern quahog ( Mercenaria mercenaria ). Silve r side

( Menidia ) and spider crab ( Libinia ) are also reported to occur here at the genus level.

The reported no observed effects concentratio ns (NOEC; c oncentrations above which

St. Johns River Water M a nagem e nt Distr i ct 

### 78

### reduction in growth was not observed in studies ) for these species range from 2.5 to 7.23

mg/L, with a species m e an of 4.63 mg/L. Based upon these ranges and the species m e an
value, it appears that the final chronic va lue (FCV) at which low dissolved oxygen is not

expected to effect growth of 4.8 m g /L as suggested by the Guidance is appropriate for

northeast Florida.

Larval Recr uitment

To estim ate the effects of hypoxic conditions at concentrations between 2.3 and 4.8

mg/L, the Guidance applies a larval recruitm ent m odel to estim a te the num ber of

individu als that are Jrecr uitedK from early life s t ages to juv e nile stage. This m odel is

based upon larval developm ent tim e, larval seas on, attrition rate and patterns of vertical

distribution. The larval recru itm ent model can be adapted with regionally specific data if

available. No attem p t has been m a de to pa ram e terize th e larv al rec r uitm ent m odel f o r the

LSJR, and the m odel for m ulation as provided in the G u idance has been used for

evaluating the organism effects due to low dissolved oxygen. Nine genra had sufficient

data to param e terize the m odel as developed in the Guidance . Six of these, Menidia,

Scianops

, P a laemonetes

, Eurypanopeus

, Libinia and Morone , are known to be present in

northeast Florida.

Application of the Criteria

The m a xi mum acute v a lue, g r owth effects th reshold and larval recruitm ent m odel are

com b ined into one relationship r e la ting the in tensity and duration of a given continuous,

low dissolved oxygen event. This approach is graphically depicted in Figure 46. Above

4.8 m g /L, estuarine organism s are assum e d to suffer no chronic effect from hypoxia

(defined as dissolved oxygen below satura tion concentration; for exam ple, oxygen

satura tion c oncentr ation at 30 o 

### C and 15 ppt chlorinity = 6.5 m g /L). Oxygen levels below

2.3 m g /L are expected to have acute lethal e ffects to at least som e organism s. Between

these two values, the deg r ee of m o rtality in the p opulation is proportional to the du ratio n
of exposure. A given interval of low dissolv ed oxygen is considered to be a JdoseK of

St. Johns River Water M a nagem e nt Distr i ct 

### 79

### potentially low dissolved oxygen, and is expresse d as the fraction of the total duration of

the in terval at th at concentra tion needed to cau se m o rtality in a t leas t 5% of the most

sensitive sp ecies of the fish community. Fo r exam ple, the im pair m e nt index calculated

duration of exposure to dissolved oxygen at 3 mg/L is 5.57 days. A one-day duration of

3 m g /L dissolved oxygen is cons idered to be 1/5.57 or 18% of a lethal dose. Individual

doses of continuous exposure that sum up to gr eater than 1 are considered to represent a

lethal dose.

Following the approach, 3 out of the 6 years of data co lle cte d at the Da m e s Point station

exhibited at least one, long excursion of continuous low oxygen that exceed ed the

im pair m e nt threshold. Durations of these even ts ranged from 4 to 7 we eks. Calculated

im pair m e nt scores for Dam e s Point we re 1.74, 3.57, and 1.14 fo r 1997, 1999 and 2001.

In 1999, a large fish kill of m a ny thousands of adult shad and m e nhaden occurred in this

Figure 47. Graphical representation of th e long term chronic exposure threshold relationship defined in the Ambient Aquatic Life Water Q uality Criteria For Dissolved Oxygen (Saltwater) : Cape Cod to Cape Hatteras (2000).



### Dissolv ed Oxy g en Supression - Duration: Continuous

Ev ent s

0 1 2 3 4 5 6

0 200 400 600 800 1000 1200



### HoursMinimum Tolerable D.O. Chroni c P r otecti on V a l u e = 4. 8 m g / L

S u rvi val Level = 2. 3 m g / L Assessm ent Range

I :\\e s d a t a \ l s j \ W E S W QM o d \ C a l i b r a ti o n
D a ta \M a r i n e C to C H L A

. x l s

St. Johns River Water M a nagem e nt Distr i ct 

### 80

### reach of th e river, ass o ciated with this lo w D.O. event. No low D.O. events were

m easured at the Acosta Bridge station be tween 1996 and 2001 that qualify for chronic

im pair m e nt under the EPA guidance approac h, with the greatest score being 0.73,

recorded in 1998.

Additional Considerations

The m e thodology descried in the E P A estu arine dissolved oxygen guidance addresses

only acute and chronic (growth) direct eff ects from low diss olved oxygen. Because of

predator-prey inte ractions, the tim ing of reproductive ac tivities, additional stressor effects

under conditions of nutrient enrichm e nt and eutrophicat ion, direct effects m a y be

m itigated or enhanced. Breitbu r g (2002), in h e r rev i ew o f hypoxia effects, addresses

m a ny of the perm utations of tr ophic alterations that m a y poten tially occur as a result of

low oxygen-induced m o rtality in v a rious segmen ts of the coastal fi sh population. An

im portant as pect of low dissolv ed e v ents in th e LSJR is th at they tend to be ve rtically

uniform and extending for significant length. Such slugs of low dissolved oxygen water

of

f e r little r e f uge f o r motile f i sh, an d can ef f ectively trap lar g e num bers of anim als when

low oxygen-favoring hydrodynam i c factors and f eedi ng or m i gratory patterns intersect.

While the approach used is expected to be appropriate for other regions outside the

Virginian Province es tua r ies, th e Guidance does note that anim als m a y have adapted to

lower oxygen levels in regions of higher tem p er atures or with naturally high dem a nds for

dissolved oxygen. In particular, it m a y be appropri ate at som e point to develop

regiona lly s p ecif i c data f

o r revisin g the larva l recru itm ent model on which cum u lative,

sub-lethal effects are b a s e d. At the p r esent tim e, however, in lieu of spec if ic recru itm ent

studies for northeas t Florida, the G u idance approach represents a m eans to judge the

im pact of low dissolved oxygen events, that is supported in a num b er of independent

studies on species that are pres ent in large num bers in the lo wer St. Johns River, and is

less a r bitra r y than the a pplica tion of a strict 5 m g /L standard.

St. Johns River Water M a nagem e nt Distr i ct 

### 81

### Dinoflage lla te Bloom Potential

Nutrien t an d organic matter enrich m e nt leadi ng to the stimulation of growth of m a rine

dinof lagellate algal spe c ies rep r es e n ts a poten tia lly detrim ental ef f e ct attribu t ab le to

estuarine eutrophication. Seve ral toxic dinoflagella te species have been identified in

regular plankton m onitoring, including Karenia brevis (red tide) an d Prorocentrum

minimum , and dinoflagellate infections have b een postulated as a possible factor in

ulcerative disease syndrom e th at plagued the LS JR during much of the early 1990Es. A

monitoring program conducted in the m i d-1990Es, with the objective of determ ining the

presence of Pfies t eria Ilike species, discovered a previ ously unidentified dinoflagellate,

subsequently nam e d Cryptoperidineopsis brodii , present in LSJR mesohaline reach

sedim e nts.

The tendency for dinoflagellate populations to increase in relative abundance under

conditions o f increas ing potential d i atom silica lim itation leads to the po s s ibility that high

levels of nitrogen and phosphorus enrichm e nt, in excess of that balanced by bioavailable

silica, m a y contribute to dinofla gellate bloom s. In a recent review on the effects of the

changes in nutrient ratios on estuarine pla nkton food webs, Turner (2002) cites num erous

studies that dem onstrate the cause for conc ern that N and P increases m a y increas e the

potential for harm ful dinoflagellate bloom s. Dinof lagella te lif e cyc l es and surv ival

strategies are extrem ely com p lex, however, and occurrence of high populations in the

LSJR is poorly correlated with nutrient concentr ation or diatom biom ass. For this reason,

the lim itatio n of dinof lagellate blo o m s exists as a qualita tive ta rget in LSJR TMDL

developm ent. The reduction of dinoflagell ate bloom potential as a water qu ality

resto r ation goal is not without p r ecedent. In recen t work investig atin g the relatio nship

between nutrient enrichm e nt effects on nuisanc e algal growth in the Indian River Lagoon,

the occurrence of potentially toxic dinoflagella te bloom s is iden tif ied as a signif i cant

water quality im pairm e nt (Phlips et al. (2003) ). And in recently proposed algal biom as s
criteria for Chesapeake Bay (CBP, 2000), the in crease in the incidence of the potentially

St. Johns River Water M a nagem e nt Distr i ct 

### 82

### toxic dinoflagellate Prorocentrum minimum at detrim ental biom ass levels is u s ed to

support the m a intenance of chlorophyll a levels below 25 mg/m 3



### .

St. Johns River Water M a nagem e nt Distr i ct 

### 83

### RECOMME NDATIONS

Water Quality Model Enhancements

Based upon the exam ination of existing wa ter qua lity data an d the results of

investigations on algal community com positi on and nutrient utilization patterns, the

following findings should be integrated into the m odeling of eutrophication of the LSJR

f o r the dete rm ination of nutrien t po llution ass i m ilative cap acity (TMDLs) and nutrien t

pollution reductions (PLRGs).

1) Blue green nitrogen fixa tion provides a significant cont ribution to the riverOs total

nitrog en bu dget, and must be inc l uded in th e water qua lity m odelin g f o r the

TMDL and PLRG. Nitrogen fixation rate s appear to be variable, based upon the

adequacy of external phosphorus availability. Anabaena appears to be the m o st

prom inent N-fixer when external phosphorus supply is high, and

Cylindrospermopsis the m o st abundant when P supply is low.

Cylindrospermopsis , based upon assay work under in creasing levels of salinity

(Paerl et al, 2002), showed the lowest leve ls of salinity tolerance, with effects

evident at salinity below 2 ppt. Thus , m odel algorithm s should begin to reduce

blue green N-fixation at these low salinit ies. In addition, m o re field studies

should be perform e d to determ ine the para m e ters of growth, N-fixation, nutrient

lim itation, toxicity and potential food web effects of these two im portant bloom

for m ing species.

2) Com p arison of model stoichiom e try to m easured data de m onstrates good

agreem ent to stand a rd Redfield ratios. A curvilinea r rela tionsh i p between

particulate P and algal C tends to s upport the choice of Droop kinetics (Droop,

1973) in the LSJR application of C E -QUAL-ICM for m ode ling the uptake and

sequestration of phosphorus. Com p arison of chlorophyll a to particulate organic

carbon supports the choice of a carbon:chlorophyll a ratio of 50:1. A m i ni m u m
phosphorus cell quota of between 0.02 to 0.01 P:C is suggested by monitoring

St. Johns River Water M a nagem e nt Distr i ct 

### 84

### data collected, based upon sam p l e s with high algal carbon and low PO 4



### concentration.

3) Zooplankton abundance clearly exhibi ts declines associated with high

concentrations of blue green algal biom ass. To m i m i c this e f f ect in wate r quality

modeling, algal predation rates should be reduced at high levels of blue green

algal carbon.

4) Extended periods of phosphorus lim itation in freshwater blue green algal bloom s

appears to r e sult in pr ec ipitous b l oo m crashes. The CE-QUAL-ICM model has

no m echanism to trigger such a bloo m collaps e. Because these crashes seem to be

associated with som e extended period of very low extern al orthophosphate

concentration, the recomm endation for m ode ling is to trigge r rapid senes c ence in

freshwater blue green bloom s when phos phorus cell quota reaches som e very low

level.

5) The transition from the oligohaline, low-salinity tole rant, diatom , dinoflagellate

and blue green-dom inated community to the m a rine diatom community is

believed to be an im portant aspect of m e sohaline reach low dissolved oxygen

levels. In o r der to capture this in the water quality m odel, the 3 av ailable alga l

groups should be re-aligned to represen t the f o llowing: a prim arily freshwater

community dom i nated by blue greens and represented by blue green settling,

uptake and growth coefficients ; a m ildly sa lt tolerant community, with senescence

triggered by salinities in the 18 R 25 ppt range, and dom inated by freshwater

diatom s; and a m a rine community, with a programm e d fr eshwater in toleran c e,

dom i nated by m a rine diatom s.
6) Original intentions in modeling were to use the 1997 as a calibration year.

However, due to th e la r g e RGC Mine spill th at left m u ch of the freshwater reach

opaque during the peak of the spring al gal bloom season, it is recomm ended to

shift calibration to the y ears 1998 and 1999. These two years also offer largely

contrasting settings of flow and nut rient lim itation, which should im prove
calibration range.

St. Johns River Water M a nagem e nt Distr i ct 

### 85

### Water Quality Targets to be Atta ined Through Nutrient Reductions

W ithin the freshwater reach of the LSJR, regular, in tens e spring an d summer algal

bloom s were found to reduce the num b ers of be neficial zooplankton, lead to intense,

rapid collapses in dissolved oxygen, and pres ent potential harm through the form ation of

cyanotoxin s

. To m itigate thes e im pa cts, b l oom s in excess of chlorophy ll a concentration

of 40 m g / m 3 

### should not be present for greater than 10% of the tim e . As a secondary

thresho l d, maxim u m algal biom ass should not ex ceed 70 m g /m 3 

### at any tim e

.

The attainment of a m o re favorable dissolved oxygen regim e is the goal of the nutrient

reductions in the oligohaline and m e sohaline reaches of the LSJR. Biodegrading organic

m a tter in th is reach, which appears to be dom inated by algal organic m a tter, should not

exceed that which would trigg e r a continuous , persisten t chronic level of low oxygen,

based on th e approa ch outlin ed in the U.S. EPA guidance, Ambient A quatic L ife Water

Quality Criteria fo r Dis s olved Oxyg en ( Saltwater) : Cape Cod to Cape Hattaras (U .S.

EPA, 2000). A number of potentially overlapping factors, such as the intensity off-shore,

near-coastal bloom s i m ported to the river through reverse tides, ups tream algal detrital

load, and the location of the polyhaline transition all app ear to play a role in the seve r i ty

of low oxygen even ts. Because of these in tr icacies, it is suggested that m odelin g of

nutrient load reductions not be directed to the achievem ent of an algal biom ass level, but

rathe r to th e ach ievem e nt of th e p e rsis ten t , ch ronic low d i ssolved ox ygen im pair m e nt

index described in the E P A guidance.

St. Johns River Water M a nagem e nt Distr i ct 

### 86

### LITERATURE CITED

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, on coastal fishes and fis h eries. Es tu aries 25:4b (767-781).

CBP, 2002. Chesapeake Bay W a te r Quality Criteria: Chapter 5 Chlorophyll a Criteria. Chesapeake Bay Program W e bsite. http://www.chesapeakebay.net/pubs/wa terqualitycriteria /12022002/Chapter5.pdf

Cerco, C.F. and T. Cole. Three dimensi onal Eutrophication Model of Chesapeake B a y. J. of Environmental Eng . 119:1006-1025.

Cerco, C.F., M.R. Noel and D.H. Tillm a n. 2 003. A practical application of Droop kinetics. Manuscript in review.

C h a p r a , S

. C

. 1 9 9 7

. S u r f a c e W a ter Quality Modeling . McGraw Hill, New York, NY.

CSA, Inc. 1993. Fish Assem b lages Inhabiting an Oligohaline Segm ent of the Lower St. Johns River, Florida. St. Johns River W a te r Managem e nt District Special Publication SJ93-SP11. 75 pp.

DeMott, W

. R. and F. Moxter. 1991. Foragi ng on cyanobacteria by copepods: Responses
to chem ical defenses and resource abundance. Ecology 72(5): 1820-1834.

Droop, M. 1973. Som e thoughts on nutri ent lim itation in algae. J. Phyco logy 9:264-272.

FMRI, 2002. Fisheries Independent Monito ring Program 2001 Annual Data Summ ary Report. Flo r ida Ma rin e Research In stitu te, St. P e tersbu rg, Florida.

Fulton, III, R.S. 1988. Grazing on filam e nt ous algae by herbivorous zooplankton.
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Huber, W

. C., P.L. Brezonik, J.P. H eaney, R. E. Dickinson, S.D. Preston, D.S. Dweornik
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Nutrien t P o llution . National Academy Pr ess, Washington D.C.

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### Paerl, H.W

. , M.F. Piehler, W

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A.W a ggener. 2002. Phytoplankton and zoopla nkton in the St. JohnDs River System : Factors affecting community structure and fu nction. Year 2 Final Report to St. Johns
River W a ter Managem e nt District under Contract No. SD154RA.

Paerl. H.W

. , R.S. Fulton, III, Miosander, P. H, a nd J. Dyble. 2001. Har m ful Freshwater Algal Bloom s , with and Em phasis on Cyanobacteria. The S c ientific Wo rld 1: 76-113.

Phlips, E.J. and M. Cichra. 2002. Spatial and Tem poral Patterns in the Plankton Community of the Lower St. Johns River. Final Report to the St. Johns River Water Managem e nt District, C ontract No. 97W 165.

Phlips , E.J., S. Badylak and T. Grosskopf. 2003. Nutrient lim itation of phytoplankton
communities in the Ind i an River L a goon. Fi n a l report to the St. Joh n s River W a ter Managem e nt District. 45 pp.

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Schroeder, W.W. and W.J.W i se m a n, Jr. 1988. The Mobile Bay Estuary: S t ratification, oxygen depletion and jubilees. p. 42-52. In B.Kjerfve (ed.) Hydrodynam i cs of Est u aries
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Sellner, K.G., R.V. Lacouture and C.R. Parrish . 1988. Effects of increasing salinity on a cyanobacteria bloom in the Potom ac Ri ver. J. Plankton Res. 10(1): 49-61.

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Turner, R.E. 2002. Element ratios and aquati c food webs. Estuaries 25(4b): 694 e 703.

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### Verity, P.G., J.A. Yode r, S.S. Bishop, J.R. Ne lson, D.B. Craven, J.O. Blanton, C.Y.
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.

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, R

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St. Johns River Water M a nagem e nt Distr i ct 

### 89