2007 South Florida Environmental Report Appendix 12-3 

Appendix 12-3: Report on Algae 

Blooms in Eastern Florida Bay and 

Southern Biscayne Bay 

NOTE: This document is provided through the permission of its authors 

as an appendix to the 2007 SFER – Volume I. It appears in its 

original format and content and has not been edited or reviewed by 

the SFER Production Team.

 App. 12-3-1 
_____________________________________________________________________________________________

* This report was originally published on July 28, 2006. Following peer review as part of the 2007 South Florida 

Environmental Report, minor changes were incorporated in this updated version. It should be noted that this version 

only incorporates some minor revisions and does not include an update of information collected after July 2006. 

Report on Algal Blooms in Eastern Florida Bay and Southern Biscayne Bay 

November 20, 2006* 

David Rudnick, Christopher Madden, Stephen Kelly, Robin Bennett, and Kevin Cunniff 

Coastal Ecosystems Division and Everglades Division 

South Florida Water Management District 

SUMMARY 

A highly unusual algal bloom has persisted in eastern Florida Bay and southern Biscayne Bay 

(Manatee Bay, Barnes Sound, and Card Sound) since at least November 2005. Similar algal 

blooms have been observed in central and western Florida Bay, but not in eastern Florida Bay. 

Chlorophyll a concentrations (an indicator of the amount of algae in the water column) peaked in 

the fall and early winter in 2005 and after decreasing in the spring, increased again in June and 

July 2006. These concentrations greatly exceeded values recorded during fifteen years of water 

quality monitoring in this region (SFWMD/FIU Coastal Water Quality Monitoring Program). A 

summary timeline of water quality changes in association with other events (U.S. Highway 1 

construction, hurricanes, canal discharges) is presented in Table 1. 

The algal bloom has been found to be mostly composed of cyanobacteria (blue-green algae), 

which are photosynthetic bacteria. The dominant species of blue-green algae in the eastern 

Florida Bay / southern Biscayne Bay bloom is also the typical dominant species in central 

Florida Bay blooms, which have been common since 1991. 

Causes of the bloom are not certain, but may be related to at least two factors: 1) disturbance 

associated road construction activity along U.S. Highway 1 between the Florida mainland and 

Key Largo (Eighteen Mile Stretch), and 2) hurricane impacts from August through October 2005 

(Katrina, Rita, Wilma). Highway construction has entailed the cutting and mulching of 

mangrove trees and soil tilling (mixing fresh mulch into the peat soil) and soil stabilization with 

injection of cement since May 2005. Hurricane disturbances included a large discharge of fresh 

water and phosphorus from the C-111 canal and the impact of high winds, waves, storm surge, 

and abrupt salinity change on plants, soils, sediments, and ground water. The proximity of the 

blooms to both sides of U.S. Highway 1 – an area where blooms have not been previously 

recorded – points to the likelihood that the unique disturbance of road construction is involved as 

a cause of the bloom. A summary of hypotheses regarding the cause of the blooms is presented 

in Table 2. 

Monitoring results indicate that the bloom was most likely initiated by a large increase in total 

phosphorus (TP) – a sharp peak in TP concentrations (to record high values) was measured in a 

small area (Manatee Bay) in late August immediately following Hurricane Katrina and also in 

the large region of eastern Florida Bay and southern Biscayne Bay in October. The highest P 

and chlorophyll a concentrations were in basins closest to the Eighteen Mile Stretch near Key 
 Florida Bay Algal Bloom Report – Page 2 

Largo. However, some lower, but elevated TP concentrations were also observed at the same 

time in areas remote from the road. The timing of the TP peak and subsequent bloom appears 

more associated with hurricane activity, with the regional TP peak occurring after Hurricane 

Rita. Despite major road construction activity during the late spring and through the summer, no 

blooms or unusually high TP was measured prior to Hurricane Katrina. Thus, while the spatial 

pattern of the bloom points toward the importance of road disturbance as a cause of the blooms, 

the timing of these blooms points toward hurricane disturbance as a cause. An interaction of 

these two factors (disturbance from road construction plus hurricanes) appears to be the likely 

cause of the blooms.

One component of the hurricane effects may have been associated with water management 

operations. A major runoff event occurred in late August 2005 in association with high rainfall 

from Hurricane Katrina. This resulted in a large loading of TP into Manatee Bay from the C-111 

Canal along with a lower quantity of TP loading into Florida Bay through the southeastern 

Everglades. After this runoff event, TP concentrations in Manatee Bay sharply increased and 

then returned to near pre-storm concentrations within one week. TP in Barnes Sound and all 

Florida Bay waters remained low for more than one month before peaking regionally in October. 

This one-month time lag, along with the absence of a concentration gradient away from Manatee 

Bay, indicates that the widespread October peak was unlikely to be caused by canal inputs. It is 

more likely that storm surge transported sediments, seagrasses, organic matter (perhaps including 

materials from the U.S. 1 worksite), and ground water nutrients. Furthermore, when the TP peak 

did occur, those areas with low salinity (associated with the most runoff) had lower TP than 

those areas with higher salinity. Similar discharges of water and TP into Manatee Bay in the 

1990s did not result in algal blooms similar to those observed between November 2005 and 

March 2006. 
 Florida Bay Algal Bloom Report – Page 3 

Table 1. Timeline of Florida Bay & Biscayne Bay algal bloom and potentially associated events. 

WATER QUALITY IN 

NORTHEAST FL BAY – S. BISC 

BAY REGION 

U.S. HIGHWAY 1 

ACTIVITIES 

TROPICAL 

STORM 

EVENTS 

C-111 CANAL 

DISCHARGE 

Apr 

2005 

No change from historic baseline (low 

chl a with median 0.4 ppb, and TP 

with median 6 ppb) 

Mangrove clearing 

begins near Jewfish 

Creek 

May No change 0.6 miles cleared N of 

Jewfish Creek 

June No change Clearing continues N 

and S of Lk Surprise

S197 open, 7,000 

ac-ft discharge 

July No change Clearing to Barnes; 

mixing of soil, 

mangrove mulch, 

and cement begins 

Aug After Katrina, rapid salinity drop, TP 

increase (84 ppb) in Manatee 

Clearing and soil 

mixing continues N 

(Barnes Sound area)

Hurricane 

Katrina (high 

rainfall, runoff, 

47 mph wind, 2 

ft surge) 

S197 opens 8/26 

(5 d; 27,000 acft; P load 0.8 

metric tons) 

Sept TP near baseline in region, chl a

increase in Manatee and Barnes (7 to 

16 ppb) 

Clearing and soil 

mixing continues N 

(Barnes Sound area)

Hurricane Rita 

(38 mph wind, 

2 ft surge) 

S197 open for 3 

periods (20 d; 

21,000 ac-ft) 

Oct High TP in region (60 to 100 ppb) 

before Wilma; chl a still low except 

Manatee and Barnes (6 ppb) 

Clearing and soil 

mixing continues N 

(Barnes Sound area)

Hurr. Wilma (66 

mph wind, 2 to 

3 ft surge) 

S197 opens for 

2 periods (10 d; 

2,000 ac-ft) 

Nov Regional chl a increase (bloom in 

Blackwater and Barnes to 15 ppb); 

TP decrease (slightly > baseline) 

Clearing to Manatee 

Bay marina; soil 

mixing continues N 

Dec Bloom continues – highest in Barnes 

(near 10 ppb) 

Soil mixing S of Lk 

Surprise 

Jan 

2006 

Bloom increases – mapping shows 

highest chl a near US1 and Key Largo 

(peak 20 ppb), high turbidity 

Mangroves cleared 

near Manatee Bay 

Feb Bloom continues – chl a decrease (< 12 

ppb in Blackwater, Barnes, Manatee) 

Soil mixing near 

Barnes Sound 

Mar Bloom continues – chl a decrease (3 to 

12 ppb in Blackwater, Barnes, 

Manatee) 

Soil mixing near 

Barnes Sound 

Apr Bloom continues - chl a less than 10 

ppb in Blackwater, Barnes, Manatee 

Soil mixing near 

Manatee Bay 

May 

Jun 

July 

Bloom decrease in early May (chl a < 

6 ppb); increase in June–July (> 12 

ppb in Blackwater, Barnes, Manatee) 

to be determined 
 Florida Bay Algal Bloom Report – Page 4 

Table 2. Hypotheses that may explain the cause of 2005-2006 algal blooms. 

HYPOTHESIS EVIDENCE SUPPORTING EVIDENCE REFUTING 

U.S. Highway 1 road 

construction 

• No similar algal bloom known to 

occur in the region prior to road 

construction 

• Bloom spatial pattern brackets 

highway (especially BlackwaterBarnes) 

• Bloom sustained at least 9 months 

after hurricane events, while 

construction continued 

• Mangrove mulch decomposition and 

soil disturbance likely to yield large 

nutrient release to adjacent waters 

• Five months of construction 

activity before start of bloom 

• Bloom started immediately after 

Hurricane Katrina and Rita

• Bloom spatial pattern within 

basins adjacent to road do not 

show increasing chlorophyll a

near road 

Hurricane Katrina 

related discharge and 

P load through S-197 

(C-111 Canal) 

• High P load event occurred and 

primary production known to be P 

limited 

• Bloom began in Manatee Bay and 

Barnes Sound immediately after 

pulse discharge and measured TP 

increase in Bay 

• Elevated TP observed in areas 

beyond (west of) influence of 

S-197 discharge 

• Regional TP peak occurred one 

month after TP decreased to near 

baseline in Manatee Bay 

• TP load associated with particles 

– bloom does not follow gradient 

from canal mouth; chlorophyll a

concentrations higher near Key 

Largo than mainland

• Similar blooms did not occur 

after similar C-111 releases and 

TP loads (even after late 1980s – 

early 1990s drought)

Hurricane wind, 

waves, surge eroded 

sediment & plants, 

stripped leaves, 

pulsed ground water 

nutrients 

• P increase after Katrina and Rita; 

regional bloom after Wilma 

• Spatial pattern of highest 

chlorophyll a appears parallel to Key 

Largo coastline, as could occur with 

line of storm deposits or ground 

water pulse 

• Regional TP increase occurred 

prior to storm with highest surge 

(Wilma) 

• No similar blooms after previous 

storms (e.g. Hurricane Georges) 

Hurricane 

disturbance: salinity 

drop & seagrass 

• Salinity drop near coast with Katrina 

rapid enough to kill plants 

• Salinity drop also occurred in 

areas with little TP increase and 

no bloom 

Combination of road 

and hurricane 

disturbance 

• Storm energy could move nutrients 

from road fill - turbidity barriers next 

to U.S. 1 removed prior to storms 

• Spatial pattern of bloom follows road 

for 9 months, while bloom initiation 

timing follows hurricanes 
 Florida Bay Algal Bloom Report – Page 5 

TECHNICAL FINDINGS 

Phytoplankton Bloom Description 

Eastern Florida Bay and southern Biscayne Bay (Barnes Sound, Manatee Bay, and Card Sound) 

(Figure 1) typically have low phytoplankton (microalgae in the water column) biomass and low 

productivity, in large part because of low phosphorus availability. The SFWMD/FIU Coastal 

Water Quality Monitoring program has documented water quality conditions since March 1991 

and found that chlorophyll-a concentrations, an indicator of phytoplankton biomass, are 

typically (have a median value) near 0.4 μg/l (equivalent to ppb) and rarely exceed 2 μg/L in 

eastern Florida Bay and southern Biscayne Bay. Total phosphorus (TP) concentrations are 

most commonly 0.006 mg/L (6 ppb) and rarely exceed 0.02 mg/L (20 ppb) in this region. In the 

fall of 2005, however, chlorophyll-a and TP concentrations greatly exceeded these values 

(Figures 2, 3), with the blooms reaching 8 μg/L chlorophyll-a and TP reaching near 0.1 mg/L 

(100 ppb), as measured in the SFWMD/FIU program, and up to 20 μg/L chlorophyll-a as 

measured at different sites and times by SFWMD staff and Miami-Dade DERM staff. 

Initiation of the bloom occurred in Manatee Bay and Barnes Sound in September 2005 

(Figure 4). For about one month following Hurricane Katrina, Miami-Dade DERM frequently 

sampled these basins to assess S-197 release effects. On September 14, chlorophyll-a increased 

to 16 μg/L in Barnes Sound and 7 μg/L in Manatee Bay. By October 5, chlorophyll-a decreased 

to between 2 and 6 μg/L in these basins (measured by DERM and FIU) and increased to 2 μg/L 

in Blackwater Sound. By November, the bloom had intensified, with concentrations near 

10 μg/L in waters adjacent to the U.S. Highway 1 near Key Largo (Figure 5). Furthermore, the 

area of the bloom expanded away from its center in Blackwater Sound, Barnes Sound, and 

Manatee Bay toward eastern Florida Bay and Card Sound (with decreasing chlorophyll-a

concentrations toward the east, west, and north). The bloom persisted in this region through 

February 2006, but decreased considerably in March (Figure 5). Recent results show a 

resurgence of the bloom in June and July 2006 (Figure 4). 

In January, April, May, and July 2006, SFWMD scientists analyzed the fine-scale spatial pattern 

of the bloom, using the Dataflow multi-parameter mapping system, which includes a chlorophyll 

fluorometer. The high-resolution map of chlorophyll-a distribution (Figures 6-9) derived from 

Dataflow transects (with a data point collected every 5 seconds from a moving boat) indicates 

two spatial trends. First, chlorophyll-a concentrations were higher in basins immediately east 

and west of U.S. Highway 1 than farther east (Card Sound) and west (into Florida Bay proper), 

confirming the general spatial pattern derived from the small set of fixed stations in the water 

quality monitoring network. After April, the bloom in eastern Florida Bay was largely limited to 

basins adjacent the Highway (Blackwater Sound, Little Blackwater Sound, Long Sound). 

Second, chlorophyll-a concentrations were higher toward Key Largo than toward the mainland 

during January, May, and July (April data were insufficient to detect this). Chlorophyll-a

concentrations were consistently greater than 20 μg/L in Lake Surprise. 
 Florida Bay Algal Bloom Report – Page 6 

Plankton samples were taken in January by SFWMD for analysis of the taxonomic composition 

of the bloom by scientists at FAU and the Florida Fish and Wildlife Research Institute (FWRI). 

Dr. Cindy Heil at FWRI found that the samples contained a mixture of taxa, dominated by very 

small organisms (<2 μm), which were mostly cyanobacteria (blue-green algae). Species were 

primarily in genus Synechocystis and Synechococcus (several species, including elongatus) and 

smaller unidentified cyanophyte species. Some smaller diatom species and flagellates were 

detected, but were rare. The dominance of cyanobacteria was confirmed by Dr. William Louda 

of FAU by pigment analysis, with 86% of samples containing nearly all cyanobacterial pigments 

that were similar to Synechococcous elongatus. 

SFWMD scientists also confirmed that the plankton composing the bloom were 

photosynthetically active. Changes in dissolved oxygen (DO) were measured in March 2006 to 

estimate productivity in a bloom area in Blackwater Sound (with about 12.5 μg/L) and in 

northeastern Florida Bay near Duck Key (with about 11.9 μg/L), and in a non-bloom area about 

one hundred meters beyond the edge of the bloom near Duck Key (with about 0.6 μg/L). 

Gross primary productivity in the bloom areas was high, with about 0.15 mg O2 L-1 h-1 (roughly 

0.5 g C m-2 d-1) in Blackwater Sound and northeastern Florida Bay, and near zero (about 0.01 mg 

O2 L-1 h-1) in the adjacent non-bloom area. Previous measurements of net primary production in 

this region have found rates similar to that measured in the non-bloom area in March. 

Hurricane disturbance and the bloom relationship with phosphorus and salinity 

Three hurricanes impacted south Florida from August through October 2005 – Katrina, Rita, and 

Wilma (Figure 10). Katrina was notable in south Florida for its high rainfall and runoff, 

resulting in a rapid decrease in salinity in south Florida estuaries, particularly close to the coast 

(Figure 11). Rainfall during Katrina also caused the opening of S-197 to lower stages in the 

C-111 Canal, yielding the discharge of canal water and associated materials (including TP) from 

the C-111 Canal into Manatee Bay in late August and early September (Figure 12). Wilma was 

notable for its strong winds and storm surge, which exceeded those of any 2005 hurricane in the 

Florida Bay region (Figure 13). 

A relationship between TP inputs from Katrina-related canal discharges and the algal bloom 

appears likely in Manatee Bay. One day after Hurricane Katrina, which passed through south 

Florida on August 26 with high rainfall, and the discharge of C-111 water through S-197, 

TP concentrations in Manatee Bay increased to 84 ppb (DERM data). By August 30, TP 

concentrations had dropped to about 12 ppb. By September 14, chlorophyll-a increased to 

7 μg /L in Manatee Bay and 16 μg /L in Barnes Sound, far above previously recorded values. 

With the exception of the late August peak in TP in Manatee Bay, TP concentrations remained 

low in the region until early October and chlorophyll-a concentrations in the region (other than 

in Manatee Bay and Barnes Sound) remained low until November (Figure 5). 

The spatial pattern of TP concentration in October 2005 (Figure 14) was similar to that of the 

phytoplankton bloom (Figure 5), with highest concentrations in Barnes Sound and Blackwater 

Sound and decreasing concentrations toward the east, west, and north. These TP concentrations 
 Florida Bay Algal Bloom Report – Page 7 

were far higher than previously measured in this region (Figures 2, 3), with concentrations as 

high as 60 ppb at Duck Key. Changes in TP spatial pattern through the fall and winter showed a 

rapid decrease in concentration throughout the region after October and a slight shift in the 

gradient, with more uniform concentrations in a north-south direction. Concentrations remained 

above historic values, with these elevated values bracketing U.S. Highway 1. An exception to 

this pattern occurred in January, when the center of the high TP concentration area was further 

west in Florida Bay. 

The temporal relationship of chlorophyll-a, TP, and salinity at three sites within the bloom area 

is shown in Figure 15. These figures clearly show that the TP peak in October 2005 preceded 

the sharp increase in chlorophyll-a at all stations and that chlorophyll-a remained low through 

the spring and summer months, a period during which considerable road construction occurred 

along U.S. Highway 1 between Blackwater Sound and Barnes Sound. The magnitude of the 

phytoplankton bloom at a given site in November 2005 was strongly correlated with TP 

concentrations at the site in October (Figure 16). This finding is consistent with the expectation 

that primary producers in this region are strongly limited by P availability. P concentrations 

dropped after the formation of the strong bloom, but chlorophyll and TP remained tightly 

correlated (Figure 16). 

Figure 15 also shows the drop in salinity associated with Hurricane Katrina in August 2005, 

which is most evident at the Barnes Sound site, occurred without a concurrent increase in TP. 

The TP peak occurred about one month after the freshwater pulse. Salinity and peak TP 

concentrations were not strongly correlated in October 2005 (Figure 17) and the slight positive 

slope of this relationship shows that TP was not higher in areas with lower salinity, which 

received more P inputs from the C-111 Canal and the Everglades than areas with higher salinity. 

Causes of Phytoplankton Blooms 

The results presented here are correlative and do not prove cause-and-effect relationships. 

However, these results do point toward the potential importance of U.S. Highway 1 construction 

and hurricane disturbance as factors stimulating the phytoplankton bloom. Inputs of TP from the 

C-111 Canal following Hurricane Katrina also may have contributed to the bloom. 

Highway construction. 

The spatial distribution of the bloom and extremely high TP concentrations corresponded with 

the vicinity of the highway, with elevated chlorophyll and TP on both sides of the highway 

(Figures 5-9, 14). Based on these spatial patterns and the chronology of bloom events 

(Figure 15), it appears that the proximate cause of the bloom was elevated TP. Highway 

construction potentially released P (along with other nutrients) via two mechanisms: 1) extensive 

cutting and mulching of mangrove trees along the Highway, and 2) soil disturbance, perhaps 

including the use of materials added to the soil to stabilize the roadway. The process of mixing 

fresh organic matter (mangrove mulch) into the peat soil likely resulted in a short-term release of 

porewater nutrients and a long-term release of decomposition products, including inorganic and 

organic nutrients. While turbidity barriers were employed during construction, this would not 

stop the loss of soluble decomposition products (leachates) from mulched organic matter, which 
 Florida Bay Algal Bloom Report – Page 8 

commonly constitutes about 30% of organic matter loss from mangrove leaves. Furthermore, 

these barriers were removed in preparation for hurricane onslaught and an unknown amount of 

material was lost from the site during Hurricanes Katrina, Rita, and Wilma. No major erosion 

was noted at the site (personal communications with John Palenchar [from FDOT] and Heather 

Carman [from SFWMD]). 

However, the timing of the TP peak and bloom are not consistent with the hypothesis that road 

construction alone caused the phytoplankton bloom. Mangrove clearing began in April 2005 and 

proceeded throughout the remainder of the spring and summer months (personal communication 

J. Palenchar). Soil stabilization, with extensive soil disturbance, began in June 2005. Based on 

observations of H. Carman, the rate of tree and soil disturbance appeared to be fairly even 

through these months. The absence of elevated P or chlorophyll from May through September 

indicates that nutrient inputs from the construction area were not sufficient to stimulate blooms. 

It should be noted that a study of mangrove leaf decomposition in northeastern Florida Bay 

(Davis et al. 2003) found initial P loss via leaching during the first three weeks of decomposition, 

but strong P retention over the next year. If mangrove mulch remained at the construction site, P 

retention would also be expected. 

Hurricane disturbance 

The timing of the P peak points toward the possibility that Hurricanes Katrina and Rita played a 

role in the incidence of elevated P and phytoplankton blooms. Hurricane Katrina impacted the 

area on August 26 with winds up to about 45 mph (recorded at the SFWMD weather station in 

Joe Bay) and Hurricane Rita impacted the area on September 20 with winds up to about 37 mph 

at this station (Figure 10). Hurricane Wilma impacted the area on October 24 with higher winds 

– 64 mph at Joe Bay. The direct effect of wind may have been secondary to that of fresh water 

runoff (especially during Katrina) and storm surge (especially during Wilma) (Figure 13). 

The October 2005 peak in TP was observed in samples collected on October 6, between 

Hurricanes Rita and Wilma. The high TP values cannot be attributed to suspended sediments or 

low DO at monitoring stations at the time of TP sampling; both turbidity and DO were near 

typical values at the time of sampling. However, sediments, porewater, ground water under the 

Florida Bay and Biscayne Bay and the Keys, and seagrass beds that were disturbed during the 

weeks between sampling times (September 6 to October 6) may have been sources of elevated P. 

It should be noted that although the highest TP values were found near U.S. Highway 1, lower 

peaks (that were nevertheless near or above record levels) occurred on October 6 throughout 

eastern Florida Bay and southern Biscayne Bay, even at sites such as Little Madeira Bay, which 

is more than 10 miles away from the highway. Rapid salinity changes during and after 

Hurricane Katrina (Figure 11) in coastal embayments such as Joe Bay and in coastal wetlands, 

including rapid salinity increases from storm surge and a rapid salinity drops from the 

subsequent runoff event, may have killed plants and resulted in a time-lagged nutrient release. 

An interactive effect of highway and hurricane disturbance? 

Despite the widespread disturbance of the region by hurricane events, perhaps indicated by 

elevated P throughout the eastern Florida Bay and southern Biscayne Bay, elevated 

chlorophyll-a levels in this region persisted (through July 2006) only in waters adjacent to 

U.S. Highway 1. This finding, combined with the timing of P and chlorophyll increases, 
 Florida Bay Algal Bloom Report – Page 9 

indicates that the bloom may have been caused by a combination of both Highway and hurricane 

disturbance. It is possible that soil and mangrove mulch and associated nutrients along the 

Highway were mobilized by storm surge and local runoff, concentrating nutrients in portions of 

basins and coves near the Highway. 

Fresh water discharge 

One major attribute of Hurricane Katrina in south Florida was high rainfall and fresh water 

runoff. This runoff not only affects salinity conditions in coastal waters, but also can be a 

mechanism for increased nutrient loading. In August 2005, approximately 0.8 metric tons of P 

was released into Manatee Bay from the C-111 Canal through structure S-197 in association with 

hurricane runoff (Fig. 12). The calculation of this relatively high P load (the highest monthly 

value at this site) in August 2005 was mostly attributable to a single TP grab sample (with a 

concentration of 116 ppb) at S-197 on August 27. Much of this P may have been associated with 

sediment particles; total suspended solids in the C-111 Canal at S-197 were extremely high (15 

mg/L) in the August 27 grab sample. 

The fate of P that entered Manatee Bay through S-197 is unknown. While TP concentrations in 

Manatee Bay were very high for two days following Hurricane Katrina, they were 12 ppb by 

September 1. It is likely that much of the P input to Manatee Bay during Katrina was associated 

with particles that settled to the bottom of the Bay and thus was not measured in water samples. 

It is highly unlikely that the regional peak in TP in October could be explained by the 

distribution of TP derived from the Katrina discharge. If this were the case, concentrations 

would most likely have had a gradient from being high at the source (near Manatee Bay) to being 

lower with distance from the source; this clearly was not the case, with higher concentrations 

toward Key Largo. The greater than one-month lag between Katrina and the regional TP peak in 

October also argues against the C-111 canal being the main source of this TP. 

It should be noted that seven pulse water and nutrient releases from C-111, similar to what 

occurred with Hurricane Katrina, also occurred between 1991 (when the SFWMD/FIU water 

quality monitoring program began) and 2000 (Figure 12). None of these earlier releases resulted 

in large phytoplankton blooms similar to those observed from November 2005 to March 2006. 

Phosphorus may also have been transported over the banks of the C-111 canal toward Florida 

Bay through the southeastern Everglades by storm runoff. While TP concentrations in the 

wetland south of the canal never rose above 18 ppb and almost all values remained below 8 ppb 

(SFWMD/FIU data), USGS has estimated that about 0.2 MT of TP was loaded into Long 

Sound from West Highway Creek during September 2005. While inputs were much higher 

from the C-111 canal, inputs from natural creeks along the northeast Florida Bay and southern 

Biscayne Bay coast may also have contributed to the bloom. Creek inputs, however, had a low 

TP concentration (< 6 ppb) and cannot explain much higher concentrations in the bay. 

This evidence, combined with the absence of a negative relationship between salinity and TP 

concentration (Figure 10) indicates that P associated with fresh water discharges during 

Hurricane Katrina was not a likely source for the P peak that was observed in the entire region 

(including Florida Bay), especially when the limited hydrodynamic connection of the Biscayne 

Bay and Florida Bay systems is considered. 
 Florida Bay Algal Bloom Report – Page 10 

Acknowledgements 

We thank the many scientists and managers who contributed information and ideas to the 

original draft of this report, as well as review and contributions to this revised draft. In 

particular, we thank Joe Boyer (Florida International University), Steve Blair (Miami-Dade 

DERM), Susan Markley (Miami-Dade DERM), Chris Kelble (NOAA-AOML), Mark 

Zucker (USGS), Jeff Woods (USGS), Cindy Heil (FFWCC-FWRI), Bill Louda (Florida 

Atlantic University), Doug Morrison (NPS - Everglades National Park), Sarah Bellmund 

(NPS – Biscayne Bay National Park), Teresa Coley (SFWMD), John Palenchar (FDOT), 

Jay Marshall (SFWMD), and Heather Carman (SFWMD). 

References 

Davis, S.E., C. Coronado-Molina, D.L. Childers, and J.W. Day. 2003. Temporally dependent C, 

N, and P dynamics associated with the decay of Rhizophora mangle L. leaf litter in oligotrophic 

mangrove wetlands of the southern Everglades. Aquatic Botany 75:199-215. 
 Florida Bay Algal Bloom Report – Page 11 
 Florida Bay Algal Bloom Report – Page 12 
 Florida Bay Algal Bloom Report – Page 13 
 Florida Bay Algal Bloom Report – Page 14 
 Florida Bay Algal Bloom Report – Page 15 
 Florida Bay Algal Bloom Report – Page 16 

Figure 6. High resolution map of chlorophyll fluorescence (preliminary estimate) in eastern 

Florida Bay and southern Biscayne Bay, January 24-26, 2006. Map from high density 

Dataflow boat tracks (black line) throughout the mapped region. 

 

January 2006 – Chlorophyll-a (μg /L) 

Provisional data (cmadden@sfwmd.gov) 
 Florida Bay Algal Bloom Report – Page 17 

Figure 7. High resolution map of chlorophyll fluorescence (preliminary estimate) in eastern 

Florida Bay and southern Biscayne Bay, April 11, 2006. Map from high-density 

Dataflow boat tracks (black line) throughout the mapped region, except for north of 

southern Barnes Sound and Blackwater Sound, where rough conditions prevented 

analysis. Strong easterly winds existed during this survey. 

 

April 2006 – Chlorophyll-a (μg /L) 

Provisional data (cmadden@sfwmd.gov) 
 Florida Bay Algal Bloom Report – Page 18 

Figure 8. High resolution map of chlorophyll fluorescence (preliminary estimate) in eastern 

Florida Bay and southern Biscayne Bay, May 25-26, 2006. Map from high-density 

Dataflow boat tracks (black line) throughout the mapped region. 

 

May 2006 – Chlorophyll-a (μg /L) 

Provisional data (cmadden@sfwmd.gov) 
 Florida Bay Algal Bloom Report – Page 19 

Figure 9. High resolution map of chlorophyll fluorescence (preliminary estimate) in eastern 

Florida Bay and southern Biscayne Bay, July 19-20, 2006. Map from high-density 

Dataflow boat tracks (black line) throughout the mapped region. 

 

July 2006 – Chlorophyll-a (μg /L) 

Provisional data (cmadden@sfwmd.gov) 
 Florida Bay Algal Bloom Report – Page 20 
 Florida Bay Algal Bloom Report – Page 21 
 Florida Bay Algal Bloom Report – Page 22 
 Florida Bay Algal Bloom Report – Page 23 
 Florida Bay Algal Bloom Report – Page 24 
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